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1994-08-25
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Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
With Multi-Satellite Tracking
(Enhanced Version for 386/486 Computers)
(C) Copyright David H. Ransom, Jr., 1989-1994
All rights reserved.
Version 9435A
August 25, 1994
David H. Ransom, Jr.
7130 Avenida Altisima
Rancho Palos Verdes, California, 90275 USA
CompuServe: 75240,176
Bulletin Board System
---------------------
RPV ASTRONOMY BBS
(310) 541-7299 @ 2400-14400 Baud
Program STSORBIT PLUS Satellite Orbit Simulation Page ii
TABLE OF CONTENTS
INTRODUCTION ......................................................1
HARDWARE AND SOFTWARE REQUIREMENTS ................................6
PROGRAM DESCRIPTION ...............................................7
STSORBIT PLUS FILES ...............................................9
STSPLUS MAP PROJECTIONS AND DATABASES .............................12
PROGRAM SETUP AND USAGE NOTES .....................................14
DOS 5.0 CONFIG.SYS Setup ........................................14
Using a RAM Disk ................................................15
Copying Files for STSORBIT PLUS .................................16
Slow Computers and 80x87 Math Coprocessor Chips .................17
Starting Program STSORBIT PLUS and Command Line Options .........20
Predicting Visible Satellite Passes .............................22
Predicting Satellite Passes with STSPLUS ......................23
Predicting Satellite Passes with TRAKSTAR .....................25
Printing Graphics Screens .......................................27
Known STSPLUS Problems and Bugs .................................28
Satellite Name Cross-Reference using STSPLUS.XRF ..................31
Preparing 2-Line Elements using VEC2TLE by Ken Ernandes ...........32
PROGRAM OPERATION .................................................34
STSORBIT PLUS SATELLITE TRACKING FEATURES .........................36
Orthographic Projection Maps ....................................36
Rectangular Projection World Maps ...............................37
Rectangular Projection Quadrant Maps ............................37
Rectangular Projection Zoom Maps ................................38
Location Maps with Isocontours ..................................39
Tracking Station Maps with Isocontours ..........................39
Location and Features Labels ....................................40
Big Clock Options ...............................................42
Satellite Motion Maps ...........................................42
Satellite Position and Orbit Projections ........................43
Satellite Visibility ............................................44
User's Circle of Visibility .....................................44
Spacecraft Circle of Visibility .................................45
SUN and Solar Features ..........................................46
TDRS and Real Time Satellite Features ...........................48
Ground Tracking Stations and .TRK Files..........................50
Event Timers and Audible Alarms .................................52
Pausing the Ground Track Display (F6 Key) .......................55
Switching between MET and T+Epoch ...............................56
Using FAST Time (F4 Key) ........................................56
On-line Help (F1 Key) ...........................................57
Satellite Communications and Amateur Radio ........................58
STSPLUS Doppler Shift Mode ......................................59
Satellite Phase (Mean Anomaly) ..................................61
Satellite Communications Technique and Cautions .................62
Preparing File STSPLUS.FRQ for Amateur Radio Use ................64
ACTIVE KEYS DURING GROUND TRACK DISPLAY ...........................68
STSORBIT PLUS MAIN MENU ...........................................72
F1 Convert Keplerian Data to 2-Line Format .....................73
Program STSORBIT PLUS Satellite Orbit Simulation Page ii
Example Data Input and Output ...............................75
Received Keplerian Orbital Data Form ........................77
F2 Read/Update NASA/NORAD 2-Line Elements ......................78
Select/Update Preset Frequency Selections ...................78
Update Current TDRS and Real Time Satellites ................78
Read NASA/NORAD 2-Line Elements from a File .................80
F3 Data Output and Pass Prediction Selections ..................84
Setting up Position and State Vector Data Output ............86
Setting up Tabular Pass Predictions .........................89
Data Mode 1: Azimuth/Elevation Data Format ..................94
Data Mode 2: Latitude/Longitude Data Format .................95
Data Mode 3: Topocentric RA/DEC Data Format .................96
Data Mode 4: Ascending Node X-Y-Z State Vector ..............97
Data Mode 5: X-Y-Z Cartesian State Vector, 2 Data Lines .....99
Data Mode 6: X-Y-Z Cartesian State Vector, Comma Delim ......101
Data Mode 7: X-Y-Z Cartesian State Vector, Labeled Data .....103
Data Mode 8: Doppler Shift Predictions ......................105
Data Mode 9: Pass Predictions ...............................106
F4 Calculate Satellite Positions with TRAKSTAR .................108
F5 Set Launch Time and Date ....................................108
Using File STSPLUS.LTD for Launch Date & Time ...............109
F6 Set/Read/Save TDRS and Real Time Satellites .................110
F1 Display/Modify Satellite Assignments ....................110
F2 Save SCF Satellite Configuration File ...................114
F3 Read SCF Satellite Configuration File ...................115
F4 Select New PRIMARY Satellite ............................115
F5 Select New TARGET Satellite .............................116
F6 Clear Static and Real Time Satellites ...................117
F7 Set FILENAMES and PATHS .....................................117
F8 Set Program TIME and DATE....................................118
F1 Restore System Date and Time ............................120
F2 Set DOS System Clock ....................................120
F3 Set Simulated Date and Time using Calendar Method .......121
F4 Set Simulated Date and Time using MET ...................121
F9 Display Current RIGHTIME Corrections ....................122
F10 Set UTC OFFSET and DAYLIGHT Flag ........................123
F9 DOS Shell ...................................................124
F10 Set STSORBIT PLUS Program Options and Features ..............124
ENTER Resume Mission ...........................................125
ESC Quit STSORBIT PLUS and Save Current Mission ..............125
PROGRAM OPTIONS AND FEATURES MENU .................................126
F1 Program STSORBIT PLUS Information ...........................126
F2 Set New Local Coordinates ...................................126
F1/F2 Search CITYFILE for location ..........................127
F3/F4 Enter New Coordinates for Location ....................128
F5 Clear (disable) Secondary Location ......................129
F3 Set Display Features (see separate section below) ...........129
F4 Set Satellite Coordinates ...................................130
F5 Show Ascending & Descending Node Data .......................130
F6 Set Map Projection and Size .................................131
F7 Enable/Disable EVENT TIMERS .................................131
F8 Enable/Disable Audible ALARMS ...............................131
F9 Set User-Definable Map Colors ...............................132
F10 Enable/Disable Printer Logging ..............................133
SET DISPLAY FEATURES ..............................................134
Program STSORBIT PLUS Satellite Orbit Simulation Page iii
F1 Display LOCAL Circles of Visibility .........................134
F2 Display TDRS and Real Time Satellites .......................134
F3 Display Additional Map Grid Lines ...........................135
F4 Display Tracking Stations ...................................135
F5 Display Ground Track: DOTS/LINE .............................135
F6 Display Spacecraft Circle of Visibility .....................136
F7 Display South Atlantic Anomaly Zone .........................136
F8 Display Terminator, Sun and Spacecraft Lighting .............136
F9 Display Map Locations and Features ..........................137
F10 Display Lakes and Rivers ....................................137
STSORBIT PLUS's Orbital Model .....................................138
Accurate Time and the Personal Computer ...........................140
Methods for Setting DOS Time ....................................141
Maintaining Accurate DOS Time ...................................142
Programs TIMESET and RIGHTIME ...................................144
Program PRECISION TIME ..........................................148
Computer Bulletin Board Systems ...................................150
STSORBIT PLUS Revision History ....................................152
Program STSORBIT PLUS Satellite Orbit Simulation Page 1
INTRODUCTION
------------
Program STSORBIT PLUS is an enhanced version of STSORBIT, my original
orbital tracking and display program. As a general rule, a 386 or better
(IBM compatible) computer is required. A math coprocessor chip is STRONGLY
RECOMMENDED and will dramatically improve performance; the math coprocessor
chip is REQUIRED for acceptable performance when using the orthographic
projection. (Some users have reported acceptable performance using a
286/287 system but some operations are quite slow. Other users report
"usable" performance on an XT-class machine with a math coprocessor
(8088/8087) but the performance is marginal at best.) See the section
HARDWARE REQUIREMENTS for additional information and discussion. The
program is intended for use during Space Shuttle missions and for general
satellite tracking using NASA/NORAD 2-Line Orbital Elements. One primary
satellite and up to 32 additional "static" or "real time" satellites may be
simultaneously tracked in real time on most computers. Both orthographic
and rectangular map projections are available, displaying the Earth as a
globe or the more traditional "flat map". Tabular line-of-sight satellite
pass predictions may be made from within STSORBIT PLUS and passes of
interest may be easily displayed.
STSORBIT PLUS is very accurate when used with current (and accurate)
2-line elements. The program has been qualified by the USAF and meets the
requirement of placing a satellite within 0.5 km over a 24-hour time span
from the epoch time of the 2-line elements. It is used daily at the USAF
Central Computer Complex at Cape Canaveral, by the DOD C-Band Radar Network
at their worldwide radar sites, and at half a dozen NASA and aerosapce
control centers around the country. The program is made available to schools
through the NASA Spacelink BBS and the NASA Teacher Resource Centers.
Numerous schools and amateur radio enthusiasts have made contact with the
space shuttle via SAREX amateur radio while using STSORBIT PLUS.
STSORBIT PLUS is copyrighted software; you are hereby granted a non-
exclusive license for non-commercial or educational use only. Agencies of
the U.S. Government are also hereby granted a non-exclusive license for
internal use. Use STSORBIT PLUS if you like it, discard it if you don't.
There are no warranties of any kind. If you wish to use STSORBIT PLUS
commercially, write for license information. The only request I make of
users is that they take the time to complete and return the confidential
questionnaire in file README. The questionnaire gives users a chance to
offer comments and suggestions, and lets me know that people use and
appreciate STSORBIT PLUS. Registration of STSORBIT PLUS is inexpensive and
optional -- but will be appreciated and will encourage me to continue
supporting and enhancing the program. Additional higher detail map database
files are available to registered users by mail.
Program STSORBIT PLUS (which I will usually refer to as STSPLUS from
here on) is intended to display the position and ground track of an
orbiting satellite on a selection of maps ranging from a full map of the
world to zoom maps showing considerable detail. The program has special
features implemented at the request of NASA astronauts and others for use
during a NASA Space Shuttle mission. With the appropriate 2-line elements,
STSPLUS displays the position and ground track of a variety of satellites
such as the Space Shuttle, the Hubble Space Telescope, the Gamma Ray
Observatory, or the Russian MIR Space Station. Accurate TDRS coverage,
including times for acquisition and loss of signal, is calculated for
satellites which use that satellite network for communications. Special
Program STSORBIT PLUS Satellite Orbit Simulation Page 2
Location and Tracking Station displays show concentric isocontours, circles
of equal satellite altitude; these special maps can be especially valuable
for visual or amateur radio sightings.
**********************
* IMPORTANT NOTICE *
**********************
After almost four years, I have discontinued support for the
simple orbital model first used in my original STSORBIT program.
The accuracy of that model is marginal at best and timely 2-line
orbital elements for space shuttle missions and other satellites
are now widely available. If you wish to use the simple orbital
model, use STSORBIT or a version of STSORBIT PLUS prior to 9240.
Users who wish to convert space shuttle or satellite state
vectors to 2-line format should see the section "Preparing 2-Line
Elements using VEC2TLE" for a description of a program by Kenneth
Ernandes written specifically for this purpose. VEC2TLE has been
validated during several space shuttle missions and is highly
recommended.
The initial premise for STSORBIT was to attempt to duplicate the wall
map in NASA's Mission Control Center in Houston, Texas. Before I started
this project, I had seen several other programs which tracked satellites
but each fell short of my map and display objectives for one reason or
another. I therefore set out to do the job myself. STSORBIT and now
STSORBIT PLUS have been the result. Since then other programs have appeared
which produce similar information, most notably Paul Traufler's excellent
TRAKSAT (which was inspired by STSORBIT). It may be, of course, that others
will judge this effort lacking for some tasks, but no one program can do
everything. One problem is that of screen size and resolution: the wall map
at Mission Control Center is some twenty feet wide with an impressive pixel
resolution, very different from the typical personal computer monitor. The
NASA wall map shows essentially the entire globe in a cylindrical
projection; STSORBIT also used a cylindrical projection and restricted the
vertical display to latitudes from +85 degrees to -85 degrees in order to
achieve reasonable proportions and vertical resolution while at the same
time showing recognizable land features. STSORBIT PLUS now presents the
Earth as a globe using an orthographic projection with zoom while still
retaining the original cylindrical (rectangular) projection. STSPLUS adds
many additional features and improved accuracy over the original STSORBIT.
Initially, and as a consequence of a lack of accurate orbital data for
Space Shuttle missions while they were in progress, I did not try to be
especially precise with respect to the orbital mathematics. Additionally,
mathematical complexity had to be held to a reasonable minimum if older
computers not equipped with a math coprocessor were to be able to maintain
the presentation in real time. My somewhat casual attitude toward
mathematical precision changed with the launch of the Hubble Space
Telescope (HST) and the regular availability of US Space Command 2-Line
Elements via modem from TS Kelso's Celestial BBS. Until HST, I had been
content to manually adjust the orbital data occasionally during the course
of a typical five day mission and live with the errors inherent in my
Program STSORBIT PLUS Satellite Orbit Simulation Page 3
original simple orbital model. The accuracy of that model degrades rapidly
after five or ten orbits and, although it could be adjusted from time to
time during a mission, more accurate data are now readily available prior
to a launch and during a mission. The NASA SpaceLink BBS in Huntsville,
Alabama began posting 2-line orbital elements for the Space Shuttle in
early 1991 due in part to my persistent and continuing requests; Bill
Anderson, Jeff Ehmen, and Flint Wild, sysops of the SpaceLink BBS, are
continually upgrading the services available.
Beginning in mid-1990, therefore, STSORBIT was extensively modified to
read orbital data from these USSPACECOM 2-line elements and thereby
maintain significantly improved accuracy over long periods of time. As an
incidental benefit, the ground tracks of other satellites (such as the
Russian space station MIR) could also be displayed. At present, the orbital
model (SGP4) used with 2-line elements is accurate only for low Earth
orbits. Deep space orbits, defined as orbits having an orbital period
greater than or equal to 225 minutes, require a more complex orbital model
(SDP4) which takes into account solar and lunar perturbations for best
accuracy. STSPLUS calculates data and displays a ground track for deep
space objects but the accuracy of these data has not been validated; it is
believed to be "reasonably" accurate. I plan to add the SDP4 orbital model
to STSPLUS in a future release when time permits.
At about the same time, STSORBIT also found its way to the NASA
Johnson Space Center in Houston, Texas. Quite a few individuals from JSC
sent me comments and suggestions for further improving the program, among
them Ron Parise of the STS-35/ASTRO-1 crew. Ron suggested that I make
modifications to allow the display of Mission Elapsed Time (MET) for
shuttle missions while using the USSPACECOM 2-line elements. This would allow
both the higher accuracy of the USSPACECOM 2-line orbital data and permit
following the mission timeline using MET. Since launch time and date are
not included in the 2-line elements but are required to compute MET, these
data must be entered independently. Another suggestion from Ron and others
was to include the Sun, solar terminator (calculated at Mean Sea Level),
and spacecraft lighting conditions to determine if the spacecraft is
visible.
Not satisfied with the somewhat rough map used with STSORBIT (a
digitized EGA world map), I upgraded the maps to use a modified version of
the World Data Base II. This had the desired effect, to the point where
rivers and other landmarks could easily be recognized on the monitor and on
downlinked orbiter television. As a side effect, however, the processor
overhead increased dramatically -- some slower computers not equipped with
a math coprocessor were unable to keep up. I therefore essentially "froze"
the original STSORBIT program (except for minor updates) and created this
new program, STSORBIT PLUS, intended for the faster, more capable
processors. Since mid-1991, STSPLUS has also spread throughout the various
NASA Centers and around the world.
In addition to NASA and individual users all over the world, STSPLUS
and STSORBIT are also being used in an educational setting. As many as 1100
high schools participated in the Inspire Project, a VLF propagation test
flown on STS-45 and for which STSPLUS was one of the recommended tools. At
a middle school in Kansas, the program is projected in the school
auditorium from time to time during a mission to show the children
graphically what is happening and to give them a sense of "real time"
participation in our space program. At an Air Force training facility,
STSORBIT is one of many tools used to prepare Air Force officers for their
duties in the Air Force Space Command. The program was widely distributed
Program STSORBIT PLUS Satellite Orbit Simulation Page 4
at a recent National Association of Science Teachers convention and by
radio amateurs at regional "ham fests". It is also available to educators
through the NASA Teacher Resource Centers and the NASA Spacelink BBS.
In perhaps its most prestigious installtion, STSPLUS is the software
used by the NASA/JPL Multimission Computer Control Center in Pasadena,
California, to display the ground track of Earth-orbiting satellites. The
Canadian Space Agency used STSPLUS as part of their briefing government
officials during the STS-52 mission in October, 1992. Intelsat used STSPLUS
operationally in May of 1992 at their Launch Control Center in Washington,
DC, and at five tracking stations around the world during the exciting STS-
49 mission, the maiden flight of Endeavour and the rescue/reboost of the
INTELSAT-VI satellite. Intelsat was kind enough to send me a letter saying
that STSORBIT PLUS was "critical to mission success"! Numerous other
official and semi-official installations use STSPLUS as the primary
satellite tracking software or to supplement other software.
A brief biographical note: I am a retired physicist and engineer who
spent all of his professional life in the world of electronics, data
communications and, more recently, computers. As a young man I was actively
involved in the early American space program including projects such as
Ranger, Mariner, Mercury, Gemini, and Apollo. Exciting times indeed! I
spent considerable time at the Jet Propulsion Laboragory in the early
1960's as a contractor on Ranger and Mariner; my respect and admiration for
JPL and its people has, if possible, increased over the intervening
decades. My interest in space has continued to this day. The desire to
"keep in touch" with our Space Shuttle missions was one of the incentives
in the development of this software. I continue to be astonished that a
relatively inexpensive personal computer is sufficient to perform
calculations that pushed the limits of our best mainframe computers only a
decade or so ago. If STSORBIT PLUS also serves to help spark the interest
of young people in science and technology or can be a learning tool at any
level, I will have more than achieved my goals.
No discussion of satellite tracking would be complete without thanks
to Major T. S. Kelso, USAF, who almost single handedly brought satellite
tracking within the reach of "ordinary folks". TS's Celestial BBS has been
providing unclassified 2-line orbital elements direct from US Space Command
(formerly NORAD, the North American Air Defense Command) at Cheyenne
Mountain, Colorado, since 1986 or so. For many years, Celestial BBS was the
only electronic source for orbital elements in the world. The Celestial BBS
may be reached at (513) 427-0674 and is located near Dayton, Ohio. TS has
also written a variety of satellite tracking software and his most recent
program, TRAKSTAR, may be used directly from within STSPLUS to generate
tabular data on upcoming satellite passes.
Special thanks to Paul Traufler for his friendship and encouragement.
Our regular telephone conversations have generated many a new idea and the
synergism has been beneficial to us both. Our two programs, STSORBIT and
TRAKSAT, have engaged us in a friendly rivalry which has, I think, improved
both programs many fold. I may have provided the initial spur to Paul to
write TRAKSAT (in order to improve on my "sloppy orbital math", as Paul
described it) but TRAKSAT has in turn kept my nose to the grindstone and is
recognized by many as the standard against which other satellite tracking
programs are judged. The emphasis of the two programs is slightly
different, with STSORBIT concentrating on the graphical display and TRAKSAT
on high precision analytical and predictive techniques. I highly recommend
Program STSORBIT PLUS Satellite Orbit Simulation Page 5
TRAKSAT for the serious satellite tracker. My thanks as well for Paul's
help in upgrading STSORBIT to use the USSPACECOM 2-Line Elements and other
technical assistance.
Thanks also to Rob Matson and Joel Runes. Rob for offering comments
and code to help me implement several of STSPLUS's more exotic features;
Rob coined the phrase "isocontours" to describe the circle of equal
satellite altitude around a location and his fine SKYMAP program generates
high accuracy printed star maps with or without satellite tracks. And Joel
for keeping us all up to date with current elements for space shuttle
missions and his patience in testing innumerable beta versions of STSPLUS,
thereby helping to track down some of the more subtle bugs.
Finally, my thanks to all those individuals who have taken the time to
write or leave a message on my BBS with comments and suggestions. While I
haven't implemented every suggestion, many are now included and the
feedback is most welcome.
For individuals interested in our space program and who have access
to a modem, I recommend NASA's SpaceLink Bulletin Board System in
Huntsville, Alabama, (205) 895-0028, available twenty four hours per day,
300 to 2400 baud. NASA SpaceLink, located at the NASA Marshall Space Flight
Center and with 8 lines, provides a wealth of information on NASA and its
projects. 2-line orbital elements for a Space Shuttle mission are usually
available while the mission is in progress. In addition to educational
materials and software (including my programs STSORBIT PLUS, STSORBIT and
JPLCLOCK), general information on NASA programs and plans, news releases,
and images from prior spacecraft missions such as Voyager, SpaceLink also
devotes a complete section to current news and information on the Space
Shuttle. I particularly appreciate the STS Mission Press Kit, posted about
two weeks before each mission, which provides a great deal of information
on the upcoming mission, payload and crew as well as broadcast schedules on
NASA Select Television, Satellite F2-R, Transponder 13. Mission status
reports are generated daily during the course of a mission. I regularly
call SpaceLink and post files of interest on my own RPV ASTRONOMY BBS.
For current Space Shuttle orbital information (if a mission is in
progress), 2-line elements for more than 1,000 satellites, and the most
recent versions of STSORBIT PLUS, STSORBIT, TRAKSTAR, TRAKSAT, and SKYMAP,
call RPV ASTRONOMY BBS (see title page for telephone number and data rates
available). The main system has well over 1,500 more or less regular users
and is often busy, so please be patient. If you wish to receive STSORBIT
PLUS (or any of my other programs) on disk, see file README for
information.
David H. Ransom, Jr.
7130 Avenida Altisima
Rancho Palos Verdes, CA 90275
Program STSORBIT PLUS Satellite Orbit Simulation Page 6
HARDWARE AND SOFTWARE REQUIREMENTS
----------------------------------
A 386SX-class computer running at 20MHz and equipped with a 387 math
coprocessor chip is the minimum system used for all program testing and
development. While other systems may give acceptable performance, this
minimum configuration assures that most features will execute as described
and in real time. Performance with 386DX/387 and 486DX or higher systems
will be considerably superior to 386SX systems. Note that NO TESTING is
performed on systems not equipped with a math coprocessor chip. The
following minimum hardware is recommended:
386 or higher IBM-compatible computer
387/487 math coprocessor chip (if not included in main processor)
VGA color display
Hard disk with up to 3MB available
RAM disk with at least 500K space
The 387 (and 487 for 486SX processors) math coprocessor chip is
STRONGLY RECOMMENDED and is REQUIRED for acceptable performance. The
calculations relating to orbital mechanics are very complex and STSPLUS
will use the coprocessor if one is equipped; performance is improved by
about an order of magnitude. Other "fast" processor and coprocessor
combinations may yield acceptable performance. Math coprocessor chips are
now reasonably inexpensive and the performance improvement is impressive
and well worth the modest cost. As an example, my vintage Zenith laptop,
equipped with an 80C88 processor and an 8087 math coprocessor, is just able
to keep up in real time (rectangular modes ONLY!) when running at a clock
speed of 8 MHz but the map drawing times are very slow. However, an 8 MHz
286 computer without a math coprocessor does NOT provide reasonable
performance; map drawing times are painfully slow.
STSPLUS is intended to be used with an EGA or VGA video adapter and a
color monitor; with these systems, the display is in color. Because of its
improved vertical resolution, the VGA is recommended over the EGA. A
monochrome display with shades of gray may also be used with the program
(with the "/M" command line option). Because of hardware limitations, CGA
and HGC systems can only present graphics in monochrome; although those
display adapters are supported to some degree in current versions of
STSPLUS, that support may NOT continue in future versions. The original
STSORBIT will continue to support CGA and HGC monitors.
A hard disk is required for performance reasons and for storage of the
program, map databases and orbital elements files. A RAM disk with
sufficient space to hold the various data files is also recommended for
improved performace and to reduce wear and tear on the hard disk during
periods of extended use.
Although the program may execute properly on other software operating
systems, STSPLUS has been designed and tested using standard configurations
of Microsoft DOS 3.3 and 5.0. No optional Terminate and Stay Resident
programs (TSR's) or "shell" programs have been tested except for Tom
Becker's RIGHTIME. Third party memory management programs and Digital
Research DRDOS may experience problems although some users report that the
latest release of DRDOS 6.0 works correctly.
Program STSORBIT PLUS Satellite Orbit Simulation Page 7
PROGRAM DESCRIPTION
-------------------
A typical Space Shuttle orbit is nearly, but almost never exactly,
circular with an altitude of approximately 160 nautical miles to a maximum
of approximately 300 nautical miles and an inclination of about 28 degrees
through about 57 degrees. Occasional missions, especially military
missions, fly at higher altitudes and/or inclinations and often use more
elliptical orbits. Prior to 1990, little of this information was known to
very good accuracy by the casual listener. Initially, therefore, the
interested would-be mission observer may have only the time and date of
launch and intended orbital altitude and inclination to initialize a
tracking program. Given the geographical coordinates of the Kennedy Space
Center and assuming a circular orbit, the data is sufficient to calculate
at least a rough idea of the Shuttle's position for the first several
orbits. After that, additional information was required if the position was
going to be very close. This was the method used in my original STSORBIT
program when 2-line orbital elements were not available.
Estimated 2-line elements are usually available prior to a space
shuttle launch and I usually post "adjusted" 2-line elements within two
hours of a launch. "Real" 2-line elements from NASA or US Space Command are
usually available 8 to 12 hours after launch. 2-line elements yield a more
accurate position over longer time periods (provided no orbital maneuvers
are performed). Using 2-line elements for any satellite is quite simple; no
adjustment of orbital parameters is necessary. An abbreviated version of
the 2-line element file available at the time of this release of STSPLUS is
included in the distribution files; this abbreviated file contains
approximately 150 satellites while the "full" file as posted on my BBS
typically has more than 700 satellites. The data for each satellite is
referenced to a specific date and time, the "Epoch" of the data. As a
general rule, orbital calculations will be relatively accurate for 10 to 20
days after the Epoch date; the lower the orbit, the greater the effect of
factors such as atmospheric drag and the less accurate the calculations
will be as time passes.
STSPLUS displays a portion of the Earth using either an orthographic
porjection (the Earth seen as a globe) or cylindrical projection (similar
to the Mercator projection commonly used). The maps show most of the
Earth's land boundaries and continental areas. Major oceans, seas, and
rivers are easily recognizable. Considerable detail is shown at higher zoom
factors. Automatic map generation ensures that the satellite is always
displayed. The display shows the selected satellite as a small symbol or
icon, the projected orbital ground track for the next three hours and the
the past one and a half hours, and many other features including circles of
visibility, TDRS coverage, and the solar terminator.
Data is displayed which gives the current ground track position of the
satellite, known as the "sub-satellite point", antenna or viewing angles,
spacecraft lighting, TDRS communications coverage (when applicable), and a
variety of other information. A selection of map modes and display features
allow users to configure the program to meet their requirements.
STSPLUS has been validated by the USAF and is approved for use on the
Eastern and Western Ranges. It is sufficiently accurate (given current and
accurate 2-line orbital elements, of course!) that the program is being
used operationally by NASA, USAF, and Intelsat. Among the current users
are:
Program STSORBIT PLUS Satellite Orbit Simulation Page 8
NASA/JPL Multimission Computer Control Center, Pasadena, CA
NASA/Lewis User Operations Facility, Cleveland, OH
Rockwell Mission Control & Support, Downey, CA
Aerojet Emergency Control Center, Sacramento, CA
USAF Central Computer Complex, Cape Canaveral, FL
DOD C-Band Radar Network, worldwide radar sites
In addition to these official or semi-official users, thousands of amateur
radio operators and "just plain folks" all over the world use STSPLUS to
track the space shuttle and other satellites.
Program STSORBIT PLUS Satellite Orbit Simulation Page 9
STSORBIT PLUS FILES
-------------------
STSORBIT PLUS is normally distributed via bulletin board systems in
archived form using the ZIP format by PKWare. Note that all files (except
map databases) for STSORBIT PLUS are called "STSPLUS" in order to conform
to DOS filename requirements and to avoid confusion with the similarly
named files for the original STSORBIT. The following files are usually
included (files marked with "*" are available separately):
STSPLUS.EXE Main STSPLUS Program (required)
STSPLUS.DOC Documentation (not required)
STSPLUS.FRQ Preset Frequencies (optional)
STSPLUS.ICO Icon for WINDOWS 3.x (optional)
STSPLUS.KEY STSPLUS Active Keys (optional)
STSPLUS.LOC Map Locations & Features (optional)
STSPLUS.LTD Satellite Launch Dates (optional)
STSPLUS.SCF Satellite Config File (optional)
STSPLUS.TRK NASA Tracking Stations (optional)
STSPLUS.CTY City Coordinates (optional)
STSPLUS.XRF Sat Name Cross Reference (optional)
STSPLUS.INI Initialization data (see below)
EARTH4.MCX Level 4 Map Index (required)
EARTH4.MCP Level 4 Rect Map Data (required)
EARTH4.XYZ Level 4 Ortho Map Data (required)
EARTH3.MCX Level 3 Map Index (optional) *
EARTH3.MCP Level 3 Rect Map Data (optional) *
EARTH3.XYZ Level 3 Ortho Map Data (optional) *
EARTH2.MCX Level 2 Map Index (optional) *
EARTH2.MCP Level 2 Rect Map Data (optional) *
EARTH2.XYZ Level 2 Ortho Map Data (optional) *
EARTH1.MCX Level 1 Map Index (optional) *
EARTH1.MCP Level 1 Rect Map Data (optional) *
EARTH1.XYZ Level 1 Ortho Map Data (optional) *
MSHERC.COM Hercules driver (required for HGC)
TLEnnn.TXT 2-Line Elements (required)
NASA.TRK NASA Tracking Stations (not required)
CIS.TRK Russian Tracking Stations(not required)
INTELSAT.TRK INTELSAT Tracking Stns (not required)
SPACENTR.TRK Other Tracking Stations (not required)
STSLNDG.TRK Orbiter Landing Sites (not required)
README STSPLUS Registration and Questionnaire
SETUP.DOC Quick Setup Instructions
SOP9311.ICO Alternate STSPLUS Icon (not required)
Files noted as "(required)" must be in the current default directory (or in
a specified directory in some cases) for program operation. Files noted as
"(optional)" are not required when STSPLUS is operated but provide
Program STSORBIT PLUS Satellite Orbit Simulation Page 10
additional features or information if present. In order to minimize the
disk space required, all.EXE files been compressed with PKWare's PKLITE
Professional; these files require additional time to begin execution since
they are decompressed "on the fly" at load time.
*** IMPORTANT NOTE ***
File STSPLUS.INI contains initialization data from previous runs
of the program. If file STSPLUS.INI is not present it will be
created. Note that if STSPLUS.INI was written by a version prior
to 9332, all data will be ignored and the program must be
initialized as if being run for the first time.
STSPLUS can use map databases with different degrees of map detail.
Level 4, required for operation, contains the minimum detail and Level 1
contains the maximum detail. As noted in the list above, three files are
used for each level of map detail: MCX files contain an index of the map
data; MCP files contain map coordinates for rectangular projection; and
XYZ files contain map coordinates for orthographic projection. STSPLUS
checks for the levels that are present and uses the level appropriate for
the zoom factor in effect or, if that level is not present, the maximum
level that is present. Level 1 is checked first, then Level 2, etc. Level 4
files MUST be present or an error message is displayed and the program
aborts.
*** IMPORTANT NOTE ***
STSPLUS assumes that if a particular level of map database is
found, ALL lower levels of map database are present. Missing
levels of map database will cause a program error.
File STSPLUS.FRQ contains a list of preset frequencies for amateur
radio satellites and is not required except when STSPLUS is operated in the
Doppler Shift Mode. See the section "Satellite Communications and Amateur
Radio" for additional information.
File STSPLUS.KEY is a quick reference list of the keys that are
active while the map is displayed and includes a brief description of the
function of each key. It has been extracted from this documentation.
File STSPLUS.LTD contains the launch date and time for selected
satellites. The file may be updated when new satellite launch date and
time data is entered via the program.
Files with filetype .TRK are tracking station locations or other
locations of interest which may be plotted on the map. These files may be
created or edited with a standard ASCII editor. If you wish to use a
different TRK file, use Function Key F7 from the Main Menu to select
the desired file.
File STSPLUS.SCF is a sample multiple satellite configuration file
which may be used to display multiple TDRS and real time satellites. Up to
16 additional satellites may be tracked using this feature.
File STSPLUS.XRF is a satellite name cross-reference file (NORAD
Number to Satellite Name) which may be used to substitute a preferred name
for that found in a TLE file. STSPLUS.XRF must be in the same directory as
the main program. See the section Satellite Cross-Reference for additional
Program STSORBIT PLUS Satellite Orbit Simulation Page 11
information.
File TLEnnn.TXT (where "nnn" will be a number such as "153") is a set
of USSPACECOM 2-line elements as of the date of the file. Note that the 2-
line elements should only be used for ten to twenty days after the epoch
date for each satellite if reasonable accuracy is to be maintained. Current
orbital elements are regularly posted on my bulletin board system and
elsewhere. Other files with 2-line elements are also available; they
typically have names like GSFCnnn.TXT or N2L-nnn.TXT for general
satellites, and STSmmNnn.TXT for Space Shuttle missions. Space Shuttle
orbital elements are usually posted at least daily during missions; because
of orbital maneuvers, Space Shuttle elements more than 24 hours old may
yield inaccurate positions.
File STSPLUS.LOC contains geographic coordinates and labels for
selected locations and major oceans and seas. These labels may optionally
be displayed on the maps. The file may be edited with a standard ASCII
editor to add or delete locations and features. See the section "Location
and Features Labels" for additional information.
Other files, such as 2-line elements for an upcoming Space Shuttle
mission or a mission in progress, may be included from time to time. Files
with 2-line orbital elements normally have filetype ".TXT" or ".TLE". Some
common satellite name abbreviations are:
STS Space Shuttle missions
HST Hubble Space Telescope
GRO Compton Gamma Ray Observatory
UARS Upper Atmosphere Research Satellite
TOPEX Topex/Poseidon Earth Resources Satellite
ROSAT Roentgen Satellite Observatory
MIR Russian Space Station
There are many other satellites for which data is available. US Space
Command (formerly NORAD) currently tracks some 7000+ objects, of which data
for more than 700 is usually included in the full TLEnnn.TXT files posted
on my bulletin board system.
Program STSORBIT PLUS Satellite Orbit Simulation Page 12
STSPLUS MAP PROJECTIONS AND DATABASES
-------------------------------------
Cartographers and navigators have long wrestled with the problem of
map projections, the process of transferring location information from a
sphere to a flat surface or map. The U.S. Geological Survey publishes "An
Album of Map Projections", Professional Paper 1453, that contains some 90
basic projections in over 130 different modifications and aspects. Each
projection or modification was developed to serve some specific need or to
optimize certain parameters. The primary concern with any map projection is
distortion. For STSPLUS, this means the accuracy with which the selected
portion of the Earth's surface is displayed. Naturally, the viewer desires
accuracy in area, shape, and distance; unfortunately, you can't have all
three simultaneously with a single map projection.
The cylindrical or rectangular projection, used here and with the
original STSORBIT program, is a good compromise where drawing speed is to
be minimized. The map coordinate data translate exactly to screen pixels
with a minimum of computer processing. However, this projection is unable
to diplay the polar regions well; the distortion increases non-linearly as
the latitude increases. I have chosen to limit the latitude to plus and
minus 85 degrees to avoid some of the severe problems which occur very near
the poles. As the magnification is increased, the distortion inherent in
this projection is reduced for the area shown but different latitudes are
displayed at different scales for a given magnification. A satellite
appears to move more rapidly in high latitudes than at mid or equatorial
latitudes.
The orthographic projection views the world as a sphere and thus only
a single hemisphere can be seen at any given time. However, since the map
center may be placed at any desired point, the "hemisphere" may include a
pole. The projection is calculated as if the viewer were at a great
distance from the Earth and therefore can see a complete hemisphere. This
makes the projection ideal for viewing high inclination satellite orbits.
Perspective is not included in the projection calculations for simplicity.
The orthographic projection has the advantage that ANY area of the Earth
may be viewed, including the poles, and the scale remains the same for any
given magnification and is independent of the area viewed. At the center of
the map, circles of visibility appear as true circles; however, area
distortion increases toward the edge of the screen and is especially
noticeable when the full hemisphere is displayed.
The map databases used for STSPLUS are an adaptation of the Micro
World Database II ("WDB"), generously placed in the public domain by Peter
Pospeschil and Antonio Riveria, and were produced in about 1986. The
original data were from the U. S. Central Intelligence Agency (CIA) as
distributed by the National Technical Information Service (NTIS). There are
several known errors in the database: one island in the South Pacific is
missing its northwestern portion, and several islands near the North Pole
are classified as "lakes" instead of "islands" and are therefore rendered
in the wrong map color. There are also numerous gaps in coastlines which
make color fill very difficult over the range of magnifications used here.
The original map data are identified by "level of detail" with Level 1
having the greatest detail and Level 5 having the least detail. I have
elected to use Levels 1 through 4 for STSPLUS; Level 5 is so coarse as to
be almost useless. I have also written several utility programs to extract
the map coordinate data from the original WDB files by level of detail and
to build an index file for each level to speed access to the data. For the
Program STSORBIT PLUS Satellite Orbit Simulation Page 13
orthographic projection, the data are also converted from latitude and
longitude to geocentric Cartesian coordinates to minimize subsequent
processing time. Although the resulting map database files are
substantially smaller than the original data files, they are still quite
large for the higher levels of detail; for example, the Level 1 files
require approximately 1.5MB.
STSPLUS attempts to select the map database files appropriate to a
given magnification and map projection. If the selected level is not
present, the program tries the next lower level until the selection process
reaches Level 4, the lowest level of detail. The Level 4 map database files
are required for operation of the program and are included in the standard
program distribution. The Level 3 map database files are included with
program registration and are available separately on my BBS. The Level 2
and Level 1 map database files are available separately to registered
users. See file README for registration information.
Because of the size of the map database files, and because certain
third party memory managers have had problems with the dynamic memory
allocation (as implemented by Microsoft BASIC) used in STSPLUS prior to
Version 9240, map data are ALWAYS read directly from disk. This means that
map drawing times, even for the rectangular projection, are somewhat slower
than with previous versions of STSPLUS. It also means that the program uses
the disk files every time the map is redrawn. Users who plan on running
STSPLUS for long periods of time may wish to place the map database files
on a RAM disk to minimize wear and tear on their disk drive. Use Function
Keys F7+F3 from the Main Menu to set up the correct map database path.
The structure of the map database files is the same for all levels of
detail and the index file (filetype .MCX) is the same size in each case.
STSPLUS cannot distinguish between levels except by file names. Thus, if
you are using a high speed computer such as a 486DX, you may rename the
files to force STSPLUS to use a higher level of detail for a given zoom
or magnification factor. All three files (.MCX, .MCP, and .XYZ) for a
particular level must be kept together with the same filename or chaos will
result! Naturally, drawing times will be increased as the price of the
improved detail.
Program STSORBIT PLUS Satellite Orbit Simulation Page 14
PROGRAM SETUP AND USAGE NOTES
-----------------------------
The following notes may prove helpful in setting up STSPLUS to operate
most efficiently on your system or to provide hints in ways that some of
the system and program features may be used to advantage.
DOS 5.0 CONFIG.SYS Setup
------------------------
Users with DOS 5.0, especially those who take advantage of the high
memory management capabilities and those who use add-on memory managers,
should include the following line in their CONFIG.SYS file:
STACKS=9,256
This command causes DOS to allocate more memory for the internal stacks
used by DOS and some applications programs. DOS 5.0 seems more sensitive to
the amount of allocated stack space than were prior DOS versions and
programs which executed with no problems on DOS 3.3 may fail on DOS 5.0. A
common symptom of insufficient internal stack space is that STSPLUS
"freezes" the computer and a reboot is required. Other unpredictable errors
can also result from stack errors. "9,256" creates 9 stacks of 256 bytes
each; the "256" may be replaced by "384" or "512", and the "9" may be
replaced by "15" if the basic STACKS command improves but does not cure the
problems. See your DOS manual for additional information.
The use of memory managers such as EMM386, QEMM386, and 386MAX with
386 and 486 systems will cause the processor to operate in the Virtual 8086
Mode, a "feature" which is not well documented by Microsoft. Users should
be aware that this may cause considerable additional processor overhead,
especially with graphics. For example, my 486DX/33 typically draws the
orthographic map in almost half the time when a memory manager is NOT
present but the improvement is less significant with a 386SX/20:
Pentium 90 Drawing Time WITHOUT EMM386: 1.05 seconds
Pentium 90 Drawing Time WITH EMM386: 2.80 seconds
486DX/33 Drawing Time WITHOUT 386MAX: 3.68 seconds
486DX/33 Drawing Time WITH 386MAX: 6.70 seconds
386SX/20 Drawing Time WITHOUT QEMM386: 17.91 seconds
386SX/20 Drawing Time WITH QEMM386: 21.97 seconds
Times will vary as a function of the satellite position and other program
features. As the example times above illustrate, the time saving is
proportionally higher with a faster computer. Note, however, that a memory
manager may be required for the use of extended or expanded memory and for
certain applications. The use of different configuration files, selected by
a batch file or other methods, can optimize performance for various
applications. DOS 6.2 and higher includes a multiple boot configuration
facility. Another method is to boot the computer from a floppy disk
(suitably formatted and configured) when the "simple" CONFIG.SYS is to be
used.
You can still use HIMEM.SYS and load DOS in high memory when EMM386 or
another memory manager is not used by just including the following lines in
Program STSORBIT PLUS Satellite Orbit Simulation Page 15
CONFIG.SYS:
DEVICE=C:\DOS\HIMEM.SYS
DOS=HIGH
Change the "C:\DOS\" portion of the first line to correspond to the actual
drive and directory where HIMEM.SYS is located in your system.
Using a RAM Disk
----------------
A RAM disk is a simulated disk drive, created in the extended memory
of your computer. Under most circumstances, it is much faster to read and
write data to a RAM disk than to an ordinary disk drive. Remember that all
data on a RAM disk is lost when the computer is shut down or power is lost.
However, disk caching such as that provided by the Microsoft SMARTDRV
driver or, better yet, hardware caching if it is included in your system,
can perform as well as or even better than a RAM disk. The hardware and
software caching I use on one of my 486DX laptops is sufficiently large
that even with Level 2 Map Database files, no disk reads are performed as
the map is being redrawn. Performance of disk caching varies as a function
of both hardware and software, so testing may be required to determine the
optimum configuration for a given computer.
Because of program memory requirements, a RAM disk should be used only
if your computer is equipped with expanded or extended memory. Using a RAM
disk in conventional memory (the memory up to 640K) will use memory that
STSPLUS (as well as most other programs) may need to operate correctly. The
actual size RAM disk you can provide will depend upon how much memory is
equipped in your computer and what memory may be required for other uses.
The following line may be added to your CONFIG.SYS file and will
create a 3000Kb RAM disk using the RAMDRIVE software provided with
Microsoft DOS 5.0:
DEVICE=G:\WINDOWS\RAMDRIVE.SYS 3000 /E
where the file "RAMDRIVE.SYS" is located in "G:\WINDOWS\" in this example.
The "3000" specifies the size of the RAM disk in Kb, and the "/E" instructs
the program to use EXTENDED memory. See your DOS manual for additional
information.
Many of the files used by STSPLUS are read only once when the program
is first started. Little gain in performance will be achieved by putting
these files on a RAM disk. The map database files (EARTH*.MCP and
EARTH*.XYZ) are read each time the map is drawn. If you frequently change
satellites, moving the 2-line elements file(s) to a RAM disk may also
improve performance. Users with fast hard drives and/or effective disk
caching software will probably notice little or no difference in
performance when using a RAM disk; however, if the program is being run for
extended periods of time, using a RAM disk will eliminate hard disk use
(and wear and tear) during program operation.
All map database files MUST be in the MAP DATABASE path displayed when
F7 is pressed from the Main Menu. The size of the RAM disk must be large
enough to contain all map database files used for normal operation. Once
the maximum map database level has been chosen, ALL lower level map
database files must also be present in the directory. For the lower zoom
Program STSORBIT PLUS Satellite Orbit Simulation Page 16
factors, Levels 3 and 4 are sufficient; even when using the higher zoom
factors, most users will be satisfied with Levels 2, 3, and 4. Map database
file sizes are shown in the following table:
EARTH1.MCP 613800 08-20-92 6:44a
EARTH1.MCX 11914 08-20-92 6:44a
EARTH1.XYZ 920700 08-20-92 6:44a
3 files 1546414 bytes
EARTH2.MCP 373948 08-06-92 1:32a
EARTH2.MCX 11914 08-06-92 1:33a
EARTH2.XYZ 560922 08-06-92 1:32a
3 files 946784 bytes
EARTH3.MCP 88144 08-06-92 1:04a
EARTH3.MCX 11914 08-06-92 1:04a
EARTH3.XYZ 132216 08-06-92 1:04a
3 files 232274 bytes
EARTH4.MCP 44804 08-06-92 1:07a
EARTH4.MCX 11914 08-06-92 1:07a
EARTH4.XYZ 67206 08-06-92 1:07a
3 files 123924 bytes
I use a batch file called "S.BAT", located in the same directory as
STSPLUS.EXE, which takes care of copying the map database files to my RAM
disk (drive J: in the example below) the first time the batch file is run
and then starts STSPLUS:
@echo off
if exist j:\earth4.mcp goto Run
copy /b \sop\earth4.* j:
copy /b \sop\earth3.* j:
copy /b \sop\earth2.* j:
:Run
stsplus /r %1
The files copied to the RAM disk in the example require somewhat less than
1.5Mb. The line which begins "if exist ..." tests to see if the files have
already been copied to the RAM disk and jumps to the label ":Run" if so.
The "%1" allows me to enter an additional command line option (such as
"/M" or "/EGA" for testing. Depending upon where the map database files are
located, the drive and/or path will have to be changed in the lines which
copy the files. I also set the various paths and filenames in STSPLUS using
F7 from the Main Menu to those required for use with the RAM disk.
Copying Files for STSORBIT PLUS
-------------------------------
STSPLUS is intended to be used on systems with a hard disk. If all
files are present, up to 3MB may be required. While it is possible to
operate the program from a high density floppy disk (with some files
omitted), map drawing times are painfully and unacceptably slow.
I recommend that a separate directory called STSPLUS be created for
Program STSORBIT PLUS Satellite Orbit Simulation Page 17
all of the required and optional files. If you received STSPLUS on disk
with unpacked files, simply copy all files from the floppy disk(s) to your
hard disk using the command:
COPY /B A:*.* C:\STSPLUS
where the floppy drive is assumed to be A:, the hard disk is assumed to be
C:, and the subdirectory STSPLUS already exists. Use the commands
C:
CD \
MD STSPLUS
to create the subdirectory STSPLUS if it does not already exist.
If you received the program in compressed, self-extracting .EXE format
(with a filename like SOP9435A.EXE and/or SOP9435B.EXE), create the STSPLUS
directory as above then log into the STSPLUS directory and unpack the files
with the commands:
C:
CD \STSPLUS
A:SOP9435A
and repeat the last command for each .EXE file received, changing the
command to reflect the correct filename.
If you received the program in compressed format (.ZIP), copy the .ZIP
file(s) to the STSPLUS directory and then enter the command:
PKUNZIP <filename>
where <filename> is the name of the .ZIP file to unpack. After all files
have been unpacked, you may delete the .ZIP files (but keep a backup copy
just in case!). You MUST use PKUNZIP Version 2.04G or later to successfully
unpack .ZIP files received from my BBS or from NASA SpaceLink BBS!
********************
* IMPORTANT NOTE *
********************
If you are upgrading from a prior version of STSPLUS and
experience problems, delete the file STSPLUS.INI to force the
program to recreate its initialization parameters! This will
resolve most path and filename problems. Use Function Keys F7 and
F10+F3 from the Main Menu to set all program paths, filenames,
and options.
Slow Computers and 80x87 Math Coprocessor Chips
-----------------------------------------------
STSPLUS has been designed for 80386/80387 or better computers equipped
with an EGA or VGA color display. While the program can be executed on some
older 8088/8087 (XT-class) or 80286/80287 (AT-class) computers, performance
is seriously degraded. But it would seem that warnings and suggestions can
NEVER convince people that their old clunker is past its prime or that the
Program STSORBIT PLUS Satellite Orbit Simulation Page 18
calculations required for orbital mechanics and graphics are very complex
and tax even a powerful computer. The best mainframe computers we had a
decade or more ago had trouble doing what I now take for granted on a
486DX personal computer!
Not all personal computers are created equal. Further, the 80x87 math
coprocessor chip can do many of the calculations ten or twenty times faster
than the main processor. For 80386 computers, this makes a tremendous
difference AND for a very modest cost, often well under $100. Some users
report problems with coprocessor chips manufactured by IIT and ULSI; while
the problems may be related to the computer rather than the coprocessor
chip, I recommend avoiding coprocessor chips by those manufacturers.
Finally, I really don't want to hear from users how slow this program runs
on older machines; I recommend the original STSORBIT if you want the best
performance from any computer not equipped with a math coprocessor chip.
Having said that, I DO occasionally run STSPLUS on my old 8MHz 8088/8087
LCD laptop with most features enabled.
STSPLUS always runs as fast as the processor will permit and, since
most features are available for all computer configurations, it is the
responsibility of the user to select program features and options
consistent with the desired performance. For example, the solar terminator
requires considerable time to perform the required calculations and to
update the display and, if this feature is not required, performace will be
enhanced if it is disabled.
As features have been added to STSPLUS, it has become increasingly
difficult for very slow computers or computers not equipped with a math
coprocessor to perform the necessary calculations in a reasonable time.
STSPLUS tests to determine whether or not a math coprocessor chip is
present and will use it if so. The following table illustrates the
difference the processor and a math coprocessor chip make:
Processor Speed Coprocessor Time (secs)
---------------------------------------------
Pentium 90 MHz YES 2.5
486DX 33 MHz YES 6.2
386DX 20 MHz YES 12.8
386SX 20 MHZ YES 16.8
386SX 20 MHz NO 66.0
286 8 MHz YES 30.0
286 12 MHz NO 86.6
8088 8 MHz YES 65.0
8088 8 MHz NO 426.4
All systems used MS-DOS in the "typical" configuration for the machine
under test; a memory manager was present in 386 and higher systems. The
tests were performed with STSPLUS by measuring the time required from the
Main Menu until the satellite appeared on the world map display using the
rectangular map projection. (Not all tests were performed with the same
version of STSPLUS!) All data were resident in memory (no disk operations
required). All tests were made using the same display options (most were
enabled). Slightly better performance can be achieved from the slower
computers if some options, such as Sun terminator, are disabled. Clearly,
the 8088 without the math coprocessor chip is not acceptable, and NONE of
the computers without the math coprocessor chip performs very well.
When STSPLUS begins, it checks to determine the type of processor and
math coprocessor. The Title Screen displays the processor type, coprocessor
Program STSORBIT PLUS Satellite Orbit Simulation Page 19
type (if present, otherwise "(not installed)") and display type. Since
STSPLUS cannot distinguish between 486DX and Pentium processors, it
displays "486DX+" for those processors. If no math coprocessor chip is
detected, the following caution message is displayed. Press ENTER (or any
key) to continue.
** CAUTION **
STSORBIT PLUS has detected NO MATH COPROCESSOR CHIP!
CPU Type = 80386DX or 80386SX
NDP Type = (not installed)
STSPLUS requires a Math Coprocessor Chip for acceptable performance.
Calculation and map drawing times will be VERY SLOW. There is no
remedy except to add a Math Coprocessor Chip to your computer.
Users without a coprocessor should consider using
STSORBIT
which is my original, simplified tracking program.
If, in spite of everything, you insist on using STSPLUS on your old
clunker, here are a few cautions and reminders.
1. Especially at startup and when drawing the maps, long time delays can
be expected with no math coprocessor -- on the order of minutes in
some cases. Status messages are presented on the screen during some
(but not all) of these delays. Note also that STSPLUS.EXE is
compressed to save disk space and is decompressed at load time; this
may cause a noticeable delay on some systems.
2. Avoid using the orthographic projection with slow computers; the map
drawing times are much longer than the rectangular projections. Also
avoid high zoom factors since it is possible that the satellite may
move during the drawing process to the point where as soon as the
display is completed, it's time to redraw the map again. This process
will repeat endlessly and a reboot may be required. Restart the
program without the "/R" command line option and use F10+F6 from the
Main Menu to select WORLD or QUAD maps.
3. If you have a monochrome monitor, experiment with the "/M" command
line option to force monochrome operation. On some monochrome systems
the program may otherwise fail with or without an error message. On
other monochrome systems, certain colors may not be visible when
simulated using shades of gray.
4. The original CGA Color Graphics Adapter, even when equipped with a
color monitor, can display reasonable graphics (640x320) ONLY in
monochrome. Your color CGA monitor buys you nothing for graphics that
are quite inferior to the EGA and VGA. Support for CGA and Hercules
monitors may be discontinued for future versions of STSPLUS.
Program STSORBIT PLUS Satellite Orbit Simulation Page 20
Starting Program STSORBIT PLUS and Command Line Options
-------------------------------------------------------
STSPLUS uses file STSPLUS.INI to save various information required for
operation. Since the format of that file may change from time to time,
STSPLUS ignores the file unless it was written by a recent program version.
If the file does not exist, STSPLUS will automatically create it.
To start program STSPLUS, use a batch file similar to "S.BAT" in the
preceeding section or enter one of the following commands:
STSPLUS Automatic monitor, CGA/HGC/EGA/VGA
STSPLUS /EGA Force EGA (or lower) monitor
STSPLUS /CLK Use 43 or 60 lines for graphics display of
data and large clock characters. NOTE: This
feature available with EGA and VGA displays
ONLY! It is ignored for CGA/HGC monitors.
STSPLUS /CGA Force CGA monitor
STSPLUS /M Force monochrome operation, EGA/VGA
STSPLUS /R Resume last mission automatically
STSPLUS /R/SS Force "screen saver" mode
Only one display option (/EGA or /CGA) may be used. Other options may
be combined and entered in any order. For example, using the following
command will resume the prior mission and force EGA mode:
STSPLUS /R/EGA
If you are using a Hercules Graphics Card, run the program MSHERC
prior to running STSPLUS. This Microsoft program works with compiled BASIC
programs to enable use of the Hercules Graphics Card. Orthographic
projections are NOT supported for Hercules Graphics Cards. One user
reported that setting the HGC to FULL and selecting Page Zero (using
software supplied with the HGC) was sufficient for proper operation. At
least one HGC "clone" user reported that STSPLUS could not be run under any
circumstances.
If you have already run STSPLUS and simply wish to resume the prior
mission, use the /R (resume) command line option:
STSPLUS /R
STSPLUS will sense the monitor type, enable color for EGA and VGA systems,
then proceed directly to plotting the mission. The data from the last run,
as saved in file STSPLUS.INI, is used to initialize the program. Once
started in this manner, pressing the ENTER key after the map is displayed
will return to the Main Menu.
The special command line option "/R/SS", used after you have already
run STSPLUS, forces the "screen saver" mode:
Program STSORBIT PLUS Satellite Orbit Simulation Page 21
STSPLUS /R/SS
In this mode, available only with EGA and VGA monitors, the program
displays the orthographic globe with ground track and other selected
display features but NO DATA. Using the orthographic globe, the screen
changes frequently EXCEPT that the satellite icon remains always centered
on the map and the circle outlining the globe is always drawn (which may
eventually cause phosphor burns in those areas). To return to DOS, press
ENTER or ESC.
Several additional command line options are available to control
certain map display features. These may be included in addition to the
command line options above.
+L Include Location and Feature Labels
-L Exculde Location and Feature Labels
+R Include Rivers and Lakes
-R Exclude Rivers and Lakes
+T Include Tracking Stations
-T Exclude Tracking Stations
+V Include Local Circle of Visibility
-V Exclude Local Circle of Visibility
These command line options are useful in the "screen saver" mode, with
batch files, and for operations when no operator is present. When a feature
is enabled or disabled with these command line options, the new status of
the feature is saved for subsequent uses. For example, the following
command line could be used in "screen saver" mode for a "minimum" display:
STSPLUS /R/SS-L-R-V
and normal use would be invoked with:
STSPLUS /R+L+R+V
The following sequence of operations is recommended when STSPLUS is run for
the first time:
1. Make sure all required STSPLUS files are in subdirectory \STSPLUS (or
whatever you named it). In addition to the program files, check that
2-line elements are also available; the file TLEnnn.TXT (where "nnn"
is a number like "440" is usually supplied with STSPLUS) and similar
files are available via BBS or the Internet.
2. STSPLUS will first request that the user enter the time offset from
Universal Coordinated Time ("UTC") and whether or not Daylight Savings
Time is in effect. Enter the appropriate responses. Examples are shown
on the screen.
3. After a short delay, the Main Menu will be displayed. Press Function
Key F7 and set all paths and filenames. If all files have been copied
to the subdirectory from which the program was executed, the default
values shown should be correct. Press ENTER to return to the Main Menu
when all changes have been completed.
Program STSORBIT PLUS Satellite Orbit Simulation Page 22
4. Press Function Key F10 followed by Function Key F2 to set your local
coordinates. STSPLUS defaults to Palos Verdes, CA, near Los Angeles
and some program functions require your coordinates for accuracy.
Press Function Key F1 to set the primary location and follow the
instructions. If your location is not included in STSPLUS file of city
names (STSPLUS.CTY), select a large nearby city. If you know your
local coordinates, you may enter them manually using Function Key F3
and append them to file STSPLUS.CTY. When your local coordinates have
been set, press ENTER twice to return to the Main Menu.
5. Press Function Key F2 to select the primary satellite you wish to
track with STSPLUS. You will be asked to select a filename (the
available files whose filetype is ".TXT" or ".TLE" are displayed and
may be selected using the arrow keys). Type the filename or press
ENTER after selecting a filename. You will then be asked to select a
satellite by name or NORAD number. If you do not know a specific
satellite name, enter "HST" for the Hubble Space Telescope. (Caution:
some TLE files also include "HST Array"; press the SPACE BAR to
continue searching for HST.) The data for the satellite is displayed;
press ENTER to accept the data. STSPLUS will immediately begin drawing
the map.
6. While the map is displayed you may press ENTER to return to the Main
Menu. Press ESC at the Main Menu to return to the DOS prompt.
7. STSPLUS is a complex program. Only the most basic and essential
features have been covered in this brief startup list. Please take
time to read the manual with your favorite editor or print the text as
reference material.
Predicting Visible Satellite Passes
-----------------------------------
One of the most popular uses for a satellite tracking program is to
show when a satellite of interest will be visible from a specified
location. Using STSPLUS, my wife and I have spotted four different Space
Shuttle missions, the Hubble Space Telescope, the Russian MIR Space
Station, and many others with the naked eye. The trick, of course, is
knowing when and where to look for the satellite.
During normal operation, STSPLUS displays two timers in the form of
countdown clocks (Minutes:Seconds), "AOS" and "LOS", for the user's
location (as well as for a number of other events). AOS, Acquisition of
Signal, is the time remaining until the satellite is next within the circle
of visibility. LOS, Loss of Signal, is the time remaining until the
satellite next passes outside the circle of visibility. STSPLUS looks ahead
four hours (240 minutes) from the time the map is drawn to determine the
next AOS and LOS event; the clocks are blank if the time is greater than
240 minutes. A quick inspection of these clocks can therefore determine if
a potentially visible pass is upcoming within four hours.
Using its internal pass prediction feature, STSPLUS can look ahead
in 48 hour blocks and list the passes when the selected satellite will
be within the local circle of visibility (line of sight, no lighting
constraints applied).
For more extensive tabular data on upcoming visible passes, external
Program STSORBIT PLUS Satellite Orbit Simulation Page 23
software must be used. There are a number of satellite tracking programs,
most notably Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR, which can
generate tabular data for a given satellite or group of satellites listing
when the satellite(s) will be visible subject to various visibility
constraints.
Predicting Satellite Passes with STSPLUS
----------------------------------------
STSPLUS has a pass prediction capability (using F3 from the Main Menu)
in addition to its graphics capabilities to make Line-of-Sight pass
predictions for the current satellite quick and easy. Once a satellite has
been selected (with F2 from the Main Menu), pressing F3 from the Main Menu,
and selecting Data Format 9 (Pass Predictions ) will quickly produce a
listing of the Line-of-Sight passes for that satellite over the next 48
hour period. See the section "Pass Predictions and Data Output" for
additional information. Here are some comments and suggestions for
satellite viewing and tracking with STSPLUS.
1. The pass predictions are listed in blocks of 48 hours beginning with
the current real or simulated time, and are given an arbitrary pass
number from 1 to 99. The data include the "AOS" or Acquisition of
Signal when the satellite rises above the local horizon, "MAX
VISIBILITY" or the time at which the satellite reaches the highest
altitude above the local horizon, "LOS" or Loss of Signal when the
satellite sets below the local horizon, and "Duration" or the total
time the satellite is above the local horizon. Note that "local
horizon" means the true horizon rather than local terrain. For either
visual or electronic tracking, the altitude above the local horizon
when the satellite may actually be tracked is usually at least five
degrees even under optimum conditions.
CAUTION: Users with slow computers, especially those without a math
coprocessor, will find that pass predictions may require considerable
time -- up to tens of minutes using a slow 286 without a 287!
2. Be sure to use current orbital elements for the satellite. My RPV
Astronomy BBS always has current 2-line orbital elements for some 650+
satellites and these data are also available from other electronic
sources. For Low Earth Orbit satellites like the Space Shuttle or MIR,
orbital elements should be no more than about ten days old; for higher
orbit satellites, orbital elements remain accurate for longer periods,
up to about 30 days. Satellite maneuvers can radically change the
orbital elements. Pass predictions can be no more accurate than the
orbital elements used!
3. Examine the "Alt" (maximum altitude) given under the "MAX VISIBILITY"
columns for each pass and select a suitable pass. As a general rule,
the higher the maximum altitude, the better the visibility. If you
wish to see a particular pass as a ground track display, enter the
pass number and STSPLUS will set simulated time to about 30 seconds
prior to the time of maximum visibility and prepare the display. Press
"L" while the ground track is displayed to use the Location Map
centered on your location with the "bulls-eye" concentric circles of
Program STSORBIT PLUS Satellite Orbit Simulation Page 24
equal altitude. You may stop/pause the display by pressing Function
Key F6, then move the satellite forward or backward in time using the
"+" and "-" keys and adjust the time step (1, 10, or 60 seconds) with
Function Key F4. Press ENTER to resume normal (simulated time)
operation.
4. STSPLUS lists Line-of-Sight passes, those passes where the satellite
rises above the local true horizon, and all dates and times are given
in Coordinated Universal Time (UTC). Remember that under most
circumstances a "visible pass" means that the satellite is in full
sunlight and the viewer is in darkness. Although there are exceptions
in unusual situations, this generally restricts the times for visible
passes to the several hours prior to dawn and the several hours after
sunset. (Note, however, that "visible" to a ham radio operator or
radar tracking station simply means above the horizon!) In most cases,
the Space Shuttle and satellites such as MIR Space Station and Hubble
Space Telescope are visible with the naked eye given favorable
lighting and weather conditions. Satellites in higher altitude orbits
will be visible sooner before dawn and longer after sunset. Satellites
in very high orbits, no matter how large the satellite, are seldom
visible without high power binoculars or a telescope.
5. The geometry of the pass and the attitude and geometry of the
spacecraft are also important. The relative angles between the Sun,
the satellite, and the viewer determine how light is reflected from
the surfaces of the spacecraft to you, the viewer. A spacecraft
passing between you and the Sun may not reflect much light to you and
may therefore not be visible even at higher altitudes. On the other
hand, a spacecraft nearer the horizon but on the other side of you
from the Sun may appear brilliantly lighted. The kinds of surfaces on
the spacecraft are important too; solar panels and flat surfaces can
reflect enough light to appear the most brilliant objects in the sky
while larger but rounded spacecraft may seem all but invisible.
6. Given otherwise good conditions and favorable weather, the single most
important factor is spacecraft apparent altitude ("Alt") during a
pass. This is the spacecraft's apparent elevation above your local
horizion. Depending upon local conditions, an altitude of at least 5
to 10 degrees will generally be necessary before a spacecraft can be
seen even under the best lighting conditions. In the Los Angeles area,
at least 20 or 30 degrees is a better number to use because of smog,
haze and light polution (except when looking out over the Pacific
Ocean).
7. After altitude, the azimuth ("Azm") is the number which describes the
direction from the viewer to the spacecraft at any moment. This is
given in the sense NESW, North to East to South to West, in degrees.
For a good pass after sunset, for example, an azimuth ranging from 60
to 150 degrees would indicate a pass moving generally from the
Northeast to the Southeast, ideal lighting conditions with the Sun in
the West.
8. Remember that STSPLUS automatically sets SIMULATED TIME when using the
pass prediction feature to display passes. If simulated time is
already in effect, pass predictions start from the current simulated
Program STSORBIT PLUS Satellite Orbit Simulation Page 25
time and a new simulated time is automatically set for a selected
pass. Once set, simulated time remains in effect until changed by
selecting another pass or until reset with F8 from the Main Menu. To
return to "real time", press F8+F1 from the Main Menu. The Main Menu
displays the current time with the time mode in effect labeled as
"Current Time" or "Simulated Time".
Predicting Satellite Passes with TRAKSTAR
-----------------------------------------
In order to generate detailed tabular predictions for satellite
passes, an external program is required. I recommend two programs for this
purpose: Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR. Each programs is
copyrighted by the respective author and is readily available. They are
both fine programs and set a standard against which other satellite
tracking programs are measured for performance and accuracy.
I have selected TRAKSTAR as the default external program used with
STSPLUS for two reasons: first, the program quickly produces very accurate
tabular data without graphics; and second, TRAKSTAR requires minimum memory
and is easily configured for seamless operation with STSPLUS.
TRAKSAT is a very large program with many features, and most computers
will not have sufficient memory to execute TRAKSAT when STSPLUS "shells" to
DOS. In order to run TRAKSAT, users must first exit STSPLUS (press "ESC"
from the Main Menu).
For additional information on these programs, contact the authors:
TRAKSTAR: Dr. T. S. Kelso
2340 Raider Drive
Fairborn, OH 45324-2001 USA
BBS: Celestial BBS
(513) 427-0674
300/1200/2400/4800/9600 baud
TRAKSAT: Paul Traufler
111 Emerald Drive
Harvest, AL 35749 USA
BBS: RPV Astronomy BBS
(310) 541-7299
2400/9600/14400 baud
As a courtesy to the author, I suggest enclosing a stamped, self-addressed
envelope if you write and request a reply. The current version of each
program is always posted on the indicated BBS and messages may be left
there for the author.
There is no "standard" filetype used for 2-line elements files;
typical filetypes in regular use are ".TXT", ".TLE", ".N2L", and ".ELE";
some files also include comment lines, multi-line commentary, or additional
data, some or all of which must be removed prior to use with most satellite
tracking programs. As released by Dr. Kelso, TRAKSTAR expects a filetype of
".TLE" and cannot accept any other filetype without being re-compiled.
STSPLUS defaults to both filetype ".TXT" and ".TLE". TRAKSAT defaults to
filetype ".TXT" only. However, 2-line elements files, even on Dr. Kelso's
Program STSORBIT PLUS Satellite Orbit Simulation Page 26
Celestial BBS, may use either ".TLE" or ".TXT", depending upon the file.
For the past four or five years, Paul Traufler and I have been jointly
releasing file TLEnnn.TXT (usually as file TLEnnn.ZIP, where "nnn" is a
number like "143"). Until February, 1993, the file was named NASAnnn.TXT.
This file is a sorted concantenation of files TLE.TXT and GROUP000.TLE from
Celestial BBS and currently includes 2-line elements for some 700+
satellites.
STSPLUS solves the filetype problem with TRAKSTAR by dynamically
creating a file called STSPLUS.TLE which contains the 2-line elements for
the currently selected satellite. Since STSPLUS can select 2-line elements
from a file of any size, calling TRAKSTAR through STSPLUS also circumvents
a minor problem in the current version of TRAKSTAR which limits the number
of satellites in a 2-line elements file to 250 element sets. As a
convenience, STSPLUS also dynamically creates the files STSPLUS.OBS (which
contains the name, coordinates, and elevation of the current user location)
and TRAKSTAR.CFG (which contains the drive and path information for
TRAKSTAR).
An accurate elevation (above mean sea level) for the user location is
required for accurate calculations in any satellite tracking program,
including STSPLUS, TRAKSTAR, and TRAKSAT. Note that the elevations of most
locations in file STSPLUS.CTY are not readily available and have been set
to zero. The elevation is the last parameter on each line in file
STSPLUS.CTY and is given in integer meters; 1 meter equals 3.28083 feet.
STSPLUS is coded to operate with TRAKSTAR Version 2.15. It may or may
not operate correctly with other versions. To set up program TRAKSTAR
either for independent use or for use with STSPLUS, follow the following
steps:
1. Copy the TRAKSTAR files to your hard disk. Unpack the files if they
are contained in an archive file such as TRAKSTR2.ZIP. I recommend
using a separate directory called "TRAKSTAR". The complete TRAKSTAR
package includes documentation, Pascal source, example and test files,
and the program itself. The following two files are required for
operation with STSPLUS:
TRAKSTAR.EXE Main Program
TRAKSTAR.HDR Header File
Additional files are required for independent operation. Read the
TRAKSTAR documentation for details.
2. Run STSPLUS and enter the drive and path information for TRAKSTAR by
pressing F7+F5 (Set FILENAMES and PATHS) from the Main Menu. STSPLUS
will automatically default to its own drive and directory if you omit
this step.
3. Select the desired 2-line elements file and satellite by pressing F2
from the Main Menu.
4. When the map is on the screen and you have verified that the correct
satellite is being tracked, press ENTER to return to the Main Menu.
5. Now press F4 from the Main Menu to run TRAKSTAR. You should
immediately see TRAKSTAR's opening screen and the first selection.
Make the various selections by using the up and down arrow keys to
Program STSORBIT PLUS Satellite Orbit Simulation Page 27
move between selections and press ENTER when you have the correct
selection. Don't forget to press SPACE to select the satellite!
*************
* CAUTION *
*************
TRAKSTAR Version 2.15 uses the DOS clock to determine the default
start and stop times for its calculations. Not mentioned in the
TRAKSTAR documentation, however, is the fact that TRAKSTAR assumes
that the computer is set to Coordinated Universal Time (UTC). Be sure
to take that difference, including the date, into account when
entering start and stop times!
6. TRAKSTAR will now make its calculations and write the results to a
file. The file is written in the TRAKSTAR directory and will overwrite
an existing file of the same name. The time required will be a
function of the time span and time interval requested as well as the
calculation speed of your computer. Read the TRAKSTAR documentation
carefully so that you will recognize the name of the file that
TRAKSTAR writes. For example, requesting visible passes for the Hubble
Space Telescope (NORAD #20830) will result in a filename of "VOB20830"
and a filetype which is the last three digits of the element set
number (such as ".866").
7. As soon as TRAKSTAR finishes, you will return to STSPLUS's Main Menu
and may continue normal operations.
8. To examine the tabular data produced by TRAKSTAR, you must either
"shell to DOS" using F9 from the Main Menu or exit STSPLUS by pressing
ESC at the Main Menu. Use an ASCII editor to view the file or send it
to your printer for hard copy.
If STSPLUS cannot find TRAKSTAR.EXE (or TRAKSTAR.BAT, see below) in the
selected directory, an error message will be displayed. Press ENTER to
return to the Main Menu.
An alternative method is to create a file TRAKSTAR.BAT in which you
place all commands required to run TRAKSTAR or the satellite tracking
program of your choice. STSPLUS.TLE and TRAKSTAR.CFG will still be written
to the selected directory but they need not be used. This method is only
recommended for individuals who understand the use and operation of DOS
batch files.
Printing Graphics Screens
-------------------------
Many users have requested that I add a "print" function to STSPLUS.
Given the number and variety of printers available for use with these
systems and the fact that I only have a couple of printers I can use for
testing, this is not practical within STSPLUS. However, DOS includes the
GRAPHICS command which may be used with many computers to enable printing
of graphics images. Check your DOS and printer manuals for details. As an
example, I use the following command on systems equipped with a Hewlett-
Packard LaserJet II or III:
Program STSORBIT PLUS Satellite Orbit Simulation Page 28
GRAPHICS LASERJETII
There are also quite a number of screen capture and print screen
programs, both commercial and shareware, which can perform this task. Note,
however, that all these programs are TSR's (Terminate and Stay Resident)
and some could interfere with STSPLUS's operation.
Some print screen programs, inculding DOS's built-in GRAPHICS command,
do not render colors very well. Certain colors may not be visible on the
printed copy at all. For such programs, use the "/M" command line option to
force monochrome operation when you wish to print graphics images from the
screen.
Known STSPLUS Problems and Bugs
-------------------------------
STSPLUS is being used on thousands of computers around the world
without any significant problems. However, like almost any computer program
and in spite of my best efforts, there are several known problems or "bugs"
with STSPLUS. Some are the result of slow computers, others are in the
program itself. Hopefully, some or all of these problems, those I can
reproduce at least, will be repaired in due course. Some problems are
caused by other software interfering with the program's operation. Still
other problems are the result of incompatible "IBM-compatible" computers
for which there is no remedy.
One "problem" which I occasionally still hear about is that a user's
CGA color monitor only displays STSPLUS in monochrome. THIS IS NOT A BUG!
CGA systems display "high resolution" 640 x 200 graphics in monochrome
ONLY. Compared to the EGA or VGA, that resolution is barely acceptable. The
color graphics mode for the CGA is 320 x 200 which is inadequate for
STSPLUS. Because of the poor performance of the CGA display, some program
features are NOT available. Support for the CGA and HGC display may be
discontinued completely in the future.
1. STSORBIT PLUS has been run extensively on systems using Microsoft DOS
3.3 through 6.2 and there are no known problems with those operating
systems EXCEPT the STACKS problem with DOS 5.0 (see the section
Program Setup and Usage Notes above). Because of the many bugs
reported, I do NOT recommend use of DOS 4.xx under any circumstances;
upgrade ASAP to DOS 6.2! Many users report good performance using IBM
OS/2, Version 2.1; earlier versions of OS/2 are NOT recommended. Users
report memory allocation problems with some early versions of Digital
Research DRDOS 6.0 and certain third party memory allocation programs.
A typical symptom of this kind of problem is that when you attempt to
return to DOS, you receive an error message or the computer freezes.
2. Some math coprocessor chips fail to execute STSPLUS and similar
programs correctly. In at least two reported cases, early 387SX math
coprocessor chips from IIT generated random errors; when notified of
the problem, ITT replaced the suspect chips and the problems
disappeared. Reports indicate that USLI 387SX chips do not operate
correctly with STSPLUS or TRAKSAT; Intel or Cyrix 387SX chips have
always cured the problems. No problems have been reported for Intel or
Cyrix chips.
Program STSORBIT PLUS Satellite Orbit Simulation Page 29
3. Note that not all computers (especially older CGA systems) will
display the extended graphics characters used for the large clock
characters (selected with F2 when the map is displayed). The symptom
of this problem is that the lower left portion of the data block is
mostly blank after pressing F2. If you have this problem and your
computer is running DOS 3.x or higher, enter the command "GRAFTABL"
at the DOS prompt before running STSPLUS or include the line
"GRAFTABL" in your AUTOEXEC.BAT file; this sets the "code page" to
enable the computer to display the extended graphics characters. [The
program GRAFTABL.COM is usually included as part of DOS.]
4. Some users report problems with certain Terminate and Stay Resident
(TSR) programs for which the only remedy is to remove the offending
TSR. This usually requires a "trial and error" approach to pinpoint
the TSR causing the problem. The best method is to remove ALL such
programs from your AUTOEXEC.BAT file, including "DOSSHELL", to make
sure the program will work with your computer in the simplest possible
configuration. Similarly, delete all special memory and device drivers
from your CONFIG.SYS file. For DOS 5.0 and higher, include the line
"STACKS=9,256" to your CONFIG.SYS file. In some cases it may be
necessary to increase the number "256" to "384" or "512". One user
reported a problem on an IBM PS/2 when a mouse driver was used (but I
regularly execute STSPLUS with my mouse active!).
5. LCD VGA displays, such as are found on newer laptops, have 480 fixed
scan line positions (unlike the variable scan modes available with CRT
displays). This means that the EGA emulation used in the STSPLUS
Motion Maps may use only 350 of the available 480 scan lines and the
image will be compressed vertically. An alternate solution to EGA
emulation is to repeat (double) some scan lines; this can result in
peculiar display artifacts such as double-thick horizontal lines at
certain screen locations. The solution to this dilemma varies by
laptop manufacturer.
6. Even with CRT monitors, all VGA adapter cards are not equal -- just in
case any of you had some illusions left. In at least one case, the
aspect ratio of the CRT display is incorrect when the display is
operated in the EGA simulation mode. The vertical scale is compressed
by about 20% as compared to either a true EGA display or other
(correct) VGA adapter cards. So far as I know, there is no remedy.
Some early VGA cards (the 449 card from Zenith is an example) are not
always recognized as VGA; the card may not be register-compatible with
the IBM standard and is recognized only as EGA instead.
7. There appears to be a subtle problem when changing to or from Daylight
Savings Time (which recently happened and "announced" the bug). The
display appears to get caught in a loop, endlessly redrawing the
screen or shows the wrong time and/or time zone. To avoid the problem,
change the Daylight Flag then EXIT THE PROGRAM AND RESTART.
8. Several users have reported "bugs" with the local Circle of Visibility
and the ZOE (Zone of Exclusion) when displaying satellites with
relatively high eccentricity. This is NOT a bug, rather it's a problem
with the orbit. STSPLUS determines the local coverage and ZOE based
Program STSORBIT PLUS Satellite Orbit Simulation Page 30
upon the satellite altitude at the instant the map is drawn and these
map features are updated only when the map is redrawn. For a satellite
with a high eccentricity (such as RS-10, NORAD #18129, a popular
amateur radio satellite), the diameter of the local Circle of
Visibility can change considerably over relatively short time periods
especially when the satellite is near perigee. Likewise, TDRS coverage
will be continuous near apogee and hence no ZOE. When the map is
redrawn nearer perigee, coverage will not be continuous and a ZOE will
be shown. To minimize this effect, press ENTER twice as the satellite
approaches a point or time of interest; this will cause the map to be
redrawn with current data. As an aside, the TDRS system is NOT used
with such satellites!
9. The map database used with STSPLUS originated with the CIA quite some
years ago (early 1980's). Certain islands in Northern Canada are shown
instead as lakes, and several islands in the South Pacific are
misdrawn or are missing entirely; Fiji and Western Samoa are examples
respectively. Most very small islands were intentionally omitted. I
have a more recent version of the map database but the current files
are large and distribution is so widespread that changing the database
presents major problems. For the present, I plan to continue with the
current database files, errors notwithstanding.
10. Finally, as noted elsewhere, all computers are NOT equal. There are a
few (usually older) computers which will not execute STSPLUS under any
circumstances. Tandy is the most common offender followed by Leading
Edge. Some models from these and other manufacturers have BIOS
problems or errors which prevent programs compiled with the Microsoft
BASIC compilers from operating (sometimes only in graphics modes).
There is no remedy. Other computers, Ergo for example, exhibit
"strange" behavior in some graphics and text modes. There may be an
update or workaround available for these problems; check with the
computer manufacturer.
Program STSORBIT PLUS Satellite Orbit Simulation Page 31
Satellite Name Cross-Reference using STSPLUS.XRF
------------------------------------------------
STSPLUS can perform satellite name cross-references using file
STSPLUS.XRF. Each time TLEs are read and accepted, STSPLUS checks for the
cross-reference file and, if the file is present in the current directory,
checks for the NORAD Number of the satellite and a cross-reference name. If
found, the new name is substituted for that in the TLE file. The XRF file
is standard ASCII and may be created and/or edited with a standard ASCII
editor. Word processor users must use the "non-document" mode. Each entry
consists of a SPACE, the five-digit NORAD Number, a SPACE, and then the
satellite name. A sample file:
22920 HST Solar Array
22076 Topex/Poseidon
21225 Gamma Ray Observ
20638 Rosat Observatory
20580 Hubble Telescope
16609 MIR Space Station
NOTE: The leading space shown above is required for file compatibility with
XRF files used with my program ORBITEL (but is optional for STSPLUS). The
NORAD Number MUST be 5 digits; pad with leading zeroes if necessary.
Only one entry is read per satellite; the search stops with the first
match of NORAD Numbers. There is no limit on the number of entries, but
larger files with many entries may introduce a slight delay as the file is
read. If the satellite name is longer than 19 characters, only the first 19
characters of the name will be used because of space restrictions on the
display. Since the name substitution is unconditional, care should be taken
to enter the correct NORAD Number for the named satellite; if in doubt, use
F2 from the Main Menu to request orbital data by the NORAD Number (enter
"#nnnnn" for the satellite name) to inspect the data and to verify that it
is the correct satellite.
This feature may be used to substitute a preferred name for that given
in a TLE file (which may not always be consistent from source to source) or
to specify the name of a payload piggy-backed on another satellite (as is
frequently the case with amateur radio transponders). In the example above,
"Hubble Telescope" is substituted for "HST", the satellite name usually
present in TLE files for NORAD Number 20580. A number of XRF files are
posted on my RPV Astronomy BBS; such files must be renamed STSPLUS.XRF
before use with STSPLUS.
Program STSORBIT PLUS Satellite Orbit Simulation Page 32
Preparing 2-Line Elements using VEC2TLE by Ken Ernandes
-------------------------------------------------------
Especially for Space Shuttle missions, Earth-Centered Inertial ("ECI")
cartesian state vectors may be the only orbital information available in
near real time. Such a state vector, consisting of position and velocity
data at a specified time, is sufficient to determine the instantaneous
orbit of a satellite. NASA and other agencies may provide state vectors
referenced to the mean equator and equinox of the Besselian year 1950
("M50", "Mean of 1950", or "B1950") with units of measure in feet and feet
per second. Data may also be available for the true equator and equinox of
date (such as the state vectors generated by STSPLUS), the mean equator and
equinox of the Julian year 2000 ("J2000"), or in the time-independent
Earth-Fixed Greenwich ("EFG") coordinate systems. Kilometers or nautical
miles or variations may also be used as the units of measure.
However, STSPLUS and most other satellite tracking programs require
orbital data in the "2-Line Elements" or "TLE" format and state vectors
must be converted to that format before the data may be used. The 2-Line
format originated as 2-Card Elements back in the days of IBM punched cards
at NORAD (North American Aerospace Defense Command, now US Space Command),
and has become the de facto standard format for orbital data used with
satellite tracking software.
Mr. Kenneth J. Ernandes has written program VEC2TLE, Vector to Two
Line Elements, specifically to convert state vectors to the 2-line format.
VEC2TLE is copyrighted software distributed as shareware, and registration
is required prior to regular use. Mr. Ernandes has extensive experience in
orbital mechanics with US Space Command and in industry, and has used his
expertise to create a precision conversion program. For additional
information and registration details, write:
Mr. Kenneth J. Ernandes
16 Freshman Lane
Stony Brook, NY 11790-2712
CompuServe: 70511,3107
Internet: 70511.3107@cis.com
When writing Mr. Ernandes for information, I suggest including a stamped
self-addressed envelope as a courtesy. The current version of VEC2TLE is
usually posted on the RPV ASTRONNOMY BBS and on the CompuServe Astronomy
and Space Forum.
Note that although 2-line elements can be generated using only the
data in an ECI state vector and these elements will yield an accurate
position at the specified time, the "epoch" of the data, additional data
(in particular, Drag and B-Star parameters) are required to generate 2-line
elements which propagate accurately over time. Certain additional
parameters, such as element set number and orbit number, do NOT affect the
accuracy of the propagated position; these data may be obtained from other
sources or default values may be used. US Space Command assigns a Catalog
Number, often referred to as the "NORAD Number", some time after launch;
pre-launch elements for Space Shuttle missions may have a temporary Catalog
Number (corresponding to the mission number) until the actual Catalog
Number is assigned. The International Designation is assigned by COSPAS at
the time a launch is registered by the launching country and may be blank.
Element set ("ElSet") numbers are assigned arbitrarily by the originating
Program STSORBIT PLUS Satellite Orbit Simulation Page 33
individual or agency and have no effect on the orbital data. Orbit (or
revolution or "REV") numbers are incremented on each revolution at the
ascending node, the point at which a orbit crosses the equator heading
North. Note that US Space Command does not usually use the same reference
for orbit numbers as does NASA; NASA defines the first partial orbit as
"Rev 1" whereas US Space Command may call that "Rev 0" or some other
arbitrary number. At least for Space Shuttle missions, it is common
practice to adjust USSPACECOM orbit numbers to conform to the NASA
convention.
VEC2TLE accepts all data required to form a complete 2-line orbital
element set, either as manually entered data or from a properly formatted
vector input file, performs limited error checking on these data, then
displays and writes the generated 2-line elements file. VEC2TLE supports
STSPLUS Data Mode 5 through 7 state vector formats. The program also
supports a variety of coordinate systems, units of measure, and time
formats as well as offering many other useful features.
Care must be taken when using VEC2TLE that the proper units of measure
(kilometers, feet, or nautical miles), coordinate system (ECI or EFG), and
epoch (True of Date, Mean of 1950, etc.) are used. See the VEC2TLE
documentation for additional information on the available options. STSPLUS
generates ECI X-Y-Z state vectors for the true equator and equinox of date
and may use any of three units of measure. NASA, on the other hand, usually
generates their state vectors for the mean equinox and equator of 1950
("M50") and uses feet and feet/second units of measure. Obviously, using
the wrong units of measure or coordinate system will yield invalid results!
VEC2TLE has been extensively validated and tested in conjunction with
STSPLUS using NASA ECI state vectors (provided courtesy Willie Musty,
Mission Support, Rockwell International, Downey, CA) heginning with Space
Shuttle missions STS-56 and STS-55 in early 1993. The resulting 2-line
elements yielded orbiter positions which corresponded exactly with those
shown live on NASA Select TV, and the 2-line elements were in close
agreement with 2-line elements subsequently released by US Space Command
for a comparable epoch. In fact, during mission STS-56, Rockwell used 2-
line elements at their Mission Control Center which I generated using
VEC2TLE when USSPACECOM and NASA 2-line elements were not forthcoming in a
timely manner.
In addition to simply converting state vectors to 2-line elements,
the primary purpose of the program, VEC2TLE may be used in conjunction with
STSPLUS or other sources of state vectors to model orbit adjust burns and
similar maneuvers. STSPLUS is used to generate a state vector at the
midpoint of the burn, the appropriate delta velocities (obtained
independently) are added to the state vector quantities Xdot, Ydot, and
Zdot, then new, post-burn 2-line elements are generated with VEC2TLE. More
complex maneuvers may also be calculated or modeled although these more
complicated exercises are not recommended for the novice. VEC2TLE may also
be used to precess a set of 2-line elements to the next Ascending Node,
required by some software.
My thanks to Ken Ernandes for writing VEC2TLE, for making it available
to the satellite tracking community, and for his assistance in validating
the precision state vector output data from STSPLUS. Thanks also to Willie
Musty (for providing state vectors) and to Joel Runes (for validation and
testing). As with any complex program, considerable effort has been
expended in writing, testing, and documenting the program. If you use
VEC2TLE, please register your copy so as to encourage Ken and others to
continue writing such useful software.
Program STSORBIT PLUS Satellite Orbit Simulation Page 34
PROGRAM OPERATION
-----------------
STSPLUS automatically checks for the presence of a VGA or EGA and will
execute in color if one is found UNLESS the /M command line option is used
to force monochrome operation. However, if you wish to operate STSPLUS in
the EGA mode when you have a VGA monitor, you must use the /EGA option. In
cases where a monochrome monitor is connected to an adapter which simulates
color with gray scale, the /M command line option may be omitted but the
various portions of the display may or may not be visible. STSPLUS depends
upon the Microsoft BASIC Compiler to determine whether or not a particular
monitor type is available. Some video adapter boards which claim to be VGA
are not recognized as such by BASIC and therefore cannot be used in the
higher resolution VGA display mode. Similarly, "clone" Hercules Graphics
Cards do not always perform correctly.
The /M option is not required for HGC and CGA graphics operation,
since those adapters always render their "high resolution" graphics in
monochrome. Although color CGA systems do have a 3-color mode, the limited
number of colors and coarse resolution of 320x200 is not suitable for
STSPLUS. Naturally, the appearance of the program is enhanced by the use of
color. The vertical resolution is also adjusted depending upon the type of
adapter which has been detected. Microsoft does not support SVGA adapter
cards, unfortunately. Once STSPLUS has started, the display type may not be
changed without exiting the program at the Main Menu with the ESC key, then
restarting the program with the desired command line options.
The program checks for the presence of a math coprocessor and will use
it if found. Since the calculations required to determine orbital data are
very complex, the use of a math coprocessor will improve the speed of
operation by a very substantial amount.
STSPLUS selects the icon or symbol used to graphically represent the
satellite based upon the satellite name. Names which start with the letters
"STS" will use an icon resembling a plan view of the space shuttle and all
other missions will use an icon resembling the Hubble Space Telescope.
STSPLUS reads the map coordinates from the appropriate map database
files. These coordinates are converted to screen coordinates for the type
of monitor detected, the current projection method, and the current
magnification or zoom factor.
Once the initial "housekeeping" chores have been performed, the Title
Screen is displayed for 15 seconds for normal program operation or for 3
seconds if the /R command line option has been used. The Main Menu,
described in a subsequent section, is then displayed. Press ENTER to
proceed to the Main Menu immediately.
Program STSORBIT PLUS Satellite Orbit Simulation Page 35
Press ENTER to ACCEPT this city as your PRIMARY location, OR
Press ESC or SPACE to cancel this data:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:32 PDT 02:01:32 UTC
Current date: 26 JUL 1994 27 JUL 1994
Last Mission = Mir
2-Line Elements File = C:\STSPLUS\TLE431.TXT
CPU Type = 80486DX+ or 80486SX
NDP Type = 80486DX+ or 80487SX
Display = VGA Color
(C) Copyright David H. Ransom, Jr., 1989-1994
All rights reserved.
The Title Screen displays the program version, current time and date,
last mission, and 2-line elements path and filename. It also displays the
type of Central Processing Unit (CPU) and Numeric Data Processor (NDP, or
math coprocessor), and the type of display. The program detects 8088,
80286, 80386, and 80486 processors and the associated math coprocessor; if
the math coprocessor is not present or fails a simple test, it will show as
"(not installed)". The program detects CGA, HGC, EGA and VGA display
systems; unless the "/M" command line option is used to force monochrome
operation, EGA and VGA systems will always indicate "Color".
STSPLUS is now "aware" of program RighTime by Tom Becker. If RighTime
is active, the current version number will be displayed; if RighTime is not
active or is not detected, no message will be displayed. STSPLUS is
configured to use RighTime Version 2.5+; performance with prior versions
may be unpredictable and audible alarms should NOT be enabled in that case.
See the section "Accurate Time and the Personal Computer" for a further
discussion of RighTime and other aspects of maintaining accurate DOS time.
Program STSORBIT PLUS Satellite Orbit Simulation Page 36
STSORBIT PLUS SATELLITE TRACKING FEATURES
-----------------------------------------
The principal objective of STSPLUS is to graphically display the
position of the space shuttle or satellite relative to a map of the world
or some relevant portion of the world along with relevant time and
numerical data. Two map projections and six different map displays are
available: Orthographic, World, Quadrant, Zoom, Location, Tracking Station,
and Satellite Motion. Varying magnifications or zoom factors are available
in most map modes. Each is discussed below.
In addition to the map itself, a number of other items of interest are
displayed. Some features are available only with higher resolution displays
(EGA and VGA) in order to avoid cluttering the display screen. Other
features may be enabled or disabled according to the user's preference. The
sections which follow the map types discuss these various features.
Orthographic Projection Maps
----------------------------
The orthographic projection views the Earth as a sphere as if from a
great distance (perspective is not included) and is the latest addition to
the map projections available in STSPLUS. This projection has the advantage
that the map may be centered at any point on the Earth and may include a
pole, especially helpful for high inclination satellite orbits. Unlike the
world map shown with rectangular projection, only one hemisphere can be
seen at a given time and therefore automatic map redrawing is always
enabled. Because of the more complex calculations required to generate a
map, users with slower computers may find that drawing times in the
orthographic modes are unacceptably long. (A math coprocessor will improve
map drawing times by almost a factor of ten!)
Orbital ground tracks, especially for high inclination orbits, and the
solar terminator are more readily understood using this projection. The
orthographic projection displays circles of visibility as true circles near
the center of the map.
The default magnification for orthographic maps is 100% which displays
the entire globe as a hemisphere. Using the PgUp and PgDn keys, the
magnification may be selected from 100% to 4000% (2000% if Level 1 maps are
not present). Each time the map is drawn, the center of the map is selected
so that the satellite will remain on the map for the longest time
practical. When high magnification factors are selected and the computer is
not equipped with a math coprocessor, it is possible that the map drawing
time will exceed the time the satellite is in view; this will cause the map
to be immediately redrawn. The current map database file and map drawing
time are shown near the bottom of the data block (e.g. "EARTH4 10.91").
Because only one hemisphere is shown (or a portion of a hemisphere
when magnification factors greater than 100% are used), automatic map
generation is ALWAYS enabled in orthographic modes. In addition, even if
the satellite never leaves the current map (as is the case with
geosynchronous satellites), the map will be redrawn every 2.5 hours. Users
without a math coprocessor may find that map drawing times in orthographic
modes are painfully slow. The only remedy is to purchase a new, more
powerful computer or to add a math coprocessor chip; this will improve
performance by about a factor of ten and the math coprocessor chips are now
relatively inexpensive, often under $100.
Program STSORBIT PLUS Satellite Orbit Simulation Page 37
The orthographic version of the Satellite Motion Map, enabled with the
"M" key when the map is displayed on the screen (EGA and VGA systems ONLY)
centers the satellite on the map and "moves" the map beneath the satellite
using EGA graphics. The next map is started in offscreen memory as soon as
a map is completed and displayed, then that map is displayed when completed
and the process is repeated. Especially for slower computers, this map mode
may be preferred since a map is always on the screen regardless of the
drawing time required.
As a footnote, the orthographic version of the Satellite Motion Map
can duplicate many of the views presented on NASA Select TV during a
mission. NASA frequently uses the equivalent of MAG=150 or MAG=200 for
their display. STSPLUS, however, can display far greater map detail than
can the NASA program, especially when the Level 3 and Level 2 map database
files are present.
Rectangular Projection World Maps
---------------------------------
The STSPLUS rectangular projection (similar to Mercator projection)
ground track display defaults to a map of the world centered on the Prime
Meridian (0 degrees) and extending from approximately +85 degrees North
latitude to -85 degrees South latitude using a linear cylindrical
projection. Omitting the two 5 degree bands at the poles permits better
detail in the mid latitudes where all space shuttle orbits and many other
satellite orbits are concentrated and avoids the extreme distortion
inherent in the rectangular projection near the poles. Ground track details
very near the poles are therefore sacrificed for a better display in the
main portion of typical orbits. The vertical resolution of the display is
automatically adjusted for the type of display system in use from 200 lines
(CGA) to 480 lines (VGA). Two World Maps are available: one centered on the
Prime Meridian at Greenwich, England (0 degrees longitude); and, one
centered on the International Date Line (180 degrees longitude).
All screen maps drawn by STSPLUS use a vector database derived from
the Micro World Database II. The full map of the world as used here
can include up to approximately 470,000 sets of vector coordinates
describing the world's coastlines, islands, lakes, and major rivers when
used with the highest detail (Level 1) map database.
Pressing the "W" or "0" key will switch the display to the World map.
If automatic map generation is enabled, STSPLUS will select the map which
most nearly centers the satellite on the map. If automatic map generation
is disabled, pressing "W" or "0" will toggle between the two maps. When
automatic map generation is enabled, the letter "A" appears in the upper
right of the screen.
Rectangular Projection Quadrant Maps
------------------------------------
The original STSORBIT program used a digitized pixel map of the world
derived from an EGA display. As a consequence of the EGA source, boundaries
were sometimes discontinuous on VGA displays and the display on a CGA was
sometimes difficult to read. STSPLUS uses a vector map drawing method which
automatically adjusts to the display type and the scale of the map. The full
world map (above) is quite similar in appearance to the original display.
Program STSORBIT PLUS Satellite Orbit Simulation Page 38
However, some geographic details are still difficult to distinguish,
even on a VGA display. STSPLUS includes twelve quadrant maps, each overing
1/4 of the Earth's surface and using rectangular projection. These are
numbered 1 to 12 and are centered on the world map roughly according to the
following illustrations:
0 180
+---------------------------+ +---------------------------+
| | | | | |
| 1 4 7 | | 7 10 1 |
| | | | | |
| | | | | |
| | | | | |
| 2 5 8 | | 8 11 2 |
| | | | | |
| | | | | |
| | | | | |
| 3 6 9 | | 9 12 3 |
| | | | | |
+---------------------------+ +---------------------------+
The center vertical quadrants in the left illustration, 4 through 6, are
centered on the Prime Meridian at zero degrees longitude (Greenwich,
England). The center vertical quadrants in the right illustration, 10
through 12, are centered on the International Date Line at 180/-180
degrees. The center horizontal quadrants, 2, 5, 8, and 11, are centered on
the Equator.
Each individual quadrant map may be selected by pressing the
corresponding number key, "1" through "9"; use keys "!", "@", and "#" to
select quadrants 10, 11, and 12 respectively. Pressing any of these keys
for individual quadrant maps will disable automatic map generation if it is
enabled (indicated by the letter "A" at the upper right of the screen).
Pressing "Q" will allow STSPLUS to select the quadrant most appropriate for
the satellite's current position.
Rectangular Projection Zoom Maps
--------------------------------
Although I was pleased with the enhanced maps using the Quadrant Mode,
the map data base files contain far more information than can be
effectively displayed in that mode. The next obvious step was to add the
ZOOM feature, maps which yielded greater detail and which spanned as little
as 30 degrees across the screen, six times better than the 180 degree
quadrant maps. This approaches the practical limit for the map database
files. Because of the smaller area covered, a different approach was used
for map selection. There would simply be too many different possibilities
for manual selection so a fully automatic Zoom Mode was implemented which
calculates the optimum map center point based upon the current position of
the satellite.
Press the "Z" key to enable Zoom Mode. The initial map width is 75
degrees; use PgUp to widen the map width (up to 180 degrees) or PgDn to
narrow the map width (down to 30 degrees. The Home key will always select
75 degrees width and the End key will return to the prior field of view.
The width of the map is shown at the upper left of the map display. Press
Program STSORBIT PLUS Satellite Orbit Simulation Page 39
the TAB key to enable or disable automatic map generation (the map will
always be redrawn). When automatic map generation is enabled, the letter
"A" appears in the upper right corner of the screen next to the map width
or field of view. Zoom field of view selections are 30, 45, 60, 75, 90,
120, and 180 degrees.
Location Maps with Isocontours
------------------------------
By popular request, especially from the amateur radio community, I
have added the Location Map with Isocontours. (Isocontours is a term coined
by Rob Matson for his SkyMap program and for which he generously supplied
sample code which I adapted for STSPLUS.) Press the "L" key when the map
display is present to select this display. The map will be drawn with the
current magnification/zoom factor and centered on the user's location. The
usual circle of visibility will be drawn and within that "circle" are seven
isocontours representing viewing angles of 10 through 70 degrees in ten
degree increments (five degree increments at maximum magnification
factors). The projection, orthographic or rectangular, used for the
Location Map is the projection in use when the "L" key is pressed. The
balance of the Location Map includes the usual features.
If you have entered a second location (using F10+F2 from the Main
Menu), pressing the "L" key when the Location Map is already displayed will
toggle between your primary location and the second location. The data
related to your location (Location, Altitude, Azimuth, etc.) is calculated
with respect to the indicated location. If no second location has been
entered, pressing the "L" key while the Location Map is displayed will have
no effect.
The principal advantage of the Location Map is, of course, the
isocontours -- lines of equal viewing altitude (line of sight not taking
into account any refraction near the horizon) from the user's own location.
The user can immediately tell by inspection whether current or upcoming
passes will be "good" and what approximate maximum satellite viewing
altitude can be expected. Amateur radio buffs who need to know if a pass
will appear above some altitude threshold, say 20 degrees, now have that
information available visually.
Since this map mode uses the ZOOM map algorithms, the usual zoom map
features (PgUp, PgDn, Home, End) are active.
Tracking Station Maps with Isocontours
--------------------------------------
The Tracking Station Maps with Isocontours are similar to the Location
Maps except that they use the current TRACKING STATION file locations
rather than the user's location(s). This feature was implemented at the
request of folks working on the STS-49 Intelsat Reboost Mission. STSPLUS
was used operationally by INTELSAT during this mission at their Launch
Control Center near Washington, DC, and at their five ground tracking
stations around the world. I subsequently received a letter thanking me for
the use of the program and saying that it was "critical to mission
success".
Pressing the "T" key will select this map mode. STSPLUS calculates
which of the available tracking stations is nearest to the current
Program STSORBIT PLUS Satellite Orbit Simulation Page 40
satellite position and centers that tracking station on the screen. This is
calculated by determining the angular difference between the sub-satellite
point and each tracking station. However, this means that depending upon
the Zoom factor in effect, the satellite may or may not be visible on the
screen. For example, if the sub-satellite point is in South America and the
only tracking station in the Western Hemisphere is in the United States,
the satellite cannot be seen at narrower fields of view.
The "tracking stations" may be any locations the user chooses and
includes in the current TRACKING STATION file. Several different tracking
station files accompany the normal STSPLUS distribution as described in the
section "NASA Ground Tracking Stations" below. Use Function Key F7 from the
Main Menu to select the desired file. STSPLUS contains an internal list of
NASA tracking stations which will be used if the current tracking station
file cannot be found.
Maps in this mode are displayed using current map projection. Since
this map mode uses the ZOOM map algorithms, the usual zoom map features
(PgUp, PgDn, Home, End) may be used to adjust the field of view (zoom or
magnification).
Location and Features Labels
----------------------------
Beginning with Version 9240, STSPLUS can add labels for locations and
features to all maps. Enable or disable location and features labels using
Function Keys F10+F3+F9 from the Main Menu. By default, STSPLUS expects the
geographic location and features data to be in file STSPLUS.LOC. If you
have created your own .LOC file or the file is not in the current
directory, use F7 from the Main Menu to specify an alternate file and/or
path. The supplied file includes 350+ locations (cities) and features
(oceans and seas), their coordinates, and certain information required by
the program. The file is standard ASCII "comma-delimited" data. The
following is a typical data line in the file:
"London",-.1167,51.5,7,100
---+-- ---+-- --+- + -+-
| | | | |
| | | | +--- Minimum magnification to display
| | | |
| | | +------ Color to display label (1 to 15)
| | |
| | +--------- Latitude in degrees
| |
| +--------------- Longitude in degrees
|
+----------------------- Location or feature name
The label will be displayed if the current magnification is equal to or
greater than the minimum magnification value specified for that label. All
label names are converted to upper case for display; avoid the use of
punctuation other than the period ("."), dash ("-"), or comma (",").
The minimum magnification factors in file STSPLUS.LOC have been
carefully selected so that the display is not too "cluttered" at a given
magnification and so that location or feature names near to each other do
not usually overlap each other. Some care is required when adding new
Program STSORBIT PLUS Satellite Orbit Simulation Page 41
locations to avoid this problem! If you wish to add your own locations
and/or features, use the supplied STSPLUS.LOC file as a guide and template
for your changes. Use a standard ASCII editor; word processor users must
use the "non-document" mode.
Magnifications are calculated automatically and ranges from 50% to
4000%, depending upon the map mode in effect. In orthographic map mode the
magnification factor is displayed as "MAG". In rectangular map modes, the
displayed ZOOM factor is the approximate field of view and may be converted
to magnification according to the following table:
ZOOM MAG
-----------
360 50 World maps
180 100 Quadrant and Zoom maps
120 150 )
90 200 )
75 240 ) Zoom maps
60 300 )
45 400 )
30 600 )
The "color" is a number from 1 to 15 according to the following table:
Black = 0 Gray = 8
Blue = 1 LtBlue = 9
Green = 2 LtGreen = 10
Cyan = 3 LtCyan = 11
Red = 4 LtRed = 12
Magenta = 5 LtMagenta = 13
Brown = 6 Yellow = 14
White = 7 LtWhite = 15
The color Black is ignored and is only shown for completeness. If the color
is a NEGATIVE number, the small circle marking the location of the city or
feature will NOT be displayed and the label will be displayed centered on
the coordinates specified. Thus, if the a mountain range, lake, or river is
to be labeled, you may wish to set the color negative.
The latitude and longitude are expressed in degrees and decimal
fractions of a degree; West longitudes and South latitudes must be
negative. Note that many atlases show a number such as "24.45" which is
actually 24 degrees and 45 minutes (NOT 24.45 degrees!) and should be
entered as "24.75" (24 + 45/60). When using multi-line feature labels (see
file STSPLUS.LOC for examples), labels should be spaced approximately one
degree apart in latitude for display at a magnification of 100%, less for
higher magnifications. All labels are automatically centered with respect
to longitude.
IMPORTANT NOTE: The program performs no error checking on the contents of
the location and features file. Avoid the use of punctuation other than the
period or comma. Be sure to use a simple ASCII editor or use your word
processor in the "Non-Document" mode when editing or creating a location
and features file. Illegal characters will be replaced by a SPACE. Very
strange results can appear if the wrong data are present or the wrong
number of items is in a data line!
Program STSORBIT PLUS Satellite Orbit Simulation Page 42
Big Clock Options
-----------------
In rectangular map projections, STSPLUS defaults to a standard display
with a text block shown on the lower five lines of the display; three
different times are shown at the lower left of this display: Launch/Epoch
date and time, UTC date and time, and local date and time. Pressing
Function Key F2 while the map is displayed switches between this default
mode and three Big Clock modes: UTC date and time, local date and time, and
MET/T+Epoch. Because of display space limitations, big clock options are
NOT available in orthographic projections.
For EGA and VGA users, an additional command line option, "/CLK", is
available which changes the number of lines per screen to 43 and 60 lines
respectively for rectangular projections. The big clocks are then placed
below the standard data instead of replacing a portion of the regular data
area.
In orthographic modes, VGA monitors ONLY, F2 will display the time at
the bottom of the data block at the right of the screen. Note that for all
magnification factors above 100%, the time is shortened to hours and
minutes because of display space limitations.
Satellite Motion Maps
---------------------
It is sometimes instructive and interesting to see the ground track
from the satellite point of view. The Satellite Motion Map, available
ONLY with EGA and VGA displays, centers the satellite in the display and
draws the map accordingly. Unlike all other map displays, this mode takes
advantage of the dual-page capability of the EGA display and the VGA
display (operating in EGA emulation mode); the current map is always
displayed and the new map is drawn "off screen" and updated as frequently
as the capability of the processor will permit. For VGA users, the vertical
map resolution in this mode is reduced from 400 lines to 280 lines
(rectangular projections) and from 480 lines to 350 lines (orthographic
projection).
Users with slow computers may prefer this display because, once the
map has been drawn the first time (however long that may take), a complete
map is always displayed. This is especially true at higher zoom or
magnification factors where the map is redrawn more frequently.
The Satellite Motion Map is enabled by pressing the "M" key when the
map is displayed. The Motion Map will be displayed using the same
projection as is presently in effect, rectangular (automatically switches
to zoom) or orthographic. When switching to this map mode, the message
Switching to EGA Dual-Page Mode ...
is displayed on the screen while the initial map is being drawn offscreen.
Thereafter, the map is drawn off-screen and will require the "usual" time
during which the screen will be unchanged. (My 386DX systems update every
10 seconds but my 286 systems can only manage every 20 or 30 seconds -- and
they all have math coprocessors!) The following keys are active when the
Satellite Motion Map is displayed:
Program STSORBIT PLUS Satellite Orbit Simulation Page 43
Home Zoom=75 (rect) or Mag=100 (ortho)
End Return to last zoom/mag
PgDn Decrease field of view (zoom in)
PgUp Increase field of view (zoom out)
M Return to normal map mode (rect or ortho)
ENTER Return to Main Menu
Satellite Position and Orbit Projections
----------------------------------------
The focus of the display, and the reason for program STSPLUS, is to
show the position of the spacecraft or satellite. For the space shuttle
(and provided the mission name begins with the letters "STS"), a symbol has
been chosen which resembles that spacecraft. For all other satellites, a
symbol has been chosen which resembles the Hubble Space Telescope. In
either case, the symbol is shown in the following colors (EGA and VGA
displays only):
Satellite is sunlit Bright White
Satellite is in penumbra Yellow
Satellite in refracted sunlight Red
Satellite is in umbra Dim White
In addition, an asterisk ("*") is shown to the right of "Orbit #" when the
satellite is sunlit or in penumbra; this will assist users of monochrome
monitors where colors cannot be distinguished. For better visibility, the
satellite symbol will normally "blink" on CGA monitors; the symbol may be
made to blink on any system if desired by pressing the letter "B" while the
ground track is displayed. Note however that for very slow computers, the
blink may appear erratic if most of the time is spent performing
calculations.
Just seeing the spacecraft or satellite on the map display yields
information as to its present position. However, for satellite viewing and
planning purposes, STSPLUS calculates the predicted ground track for
approximately three hours in the future and the past ground track for
approximately one and a half hours in the past. The ground track may be
selected to display as a series of light green dots (future track) or light
red dots (past track), as a solid light green line, or as a solid light
green line with yellow dots(future track) and light red dots (past track).
The dots are plotted at one minute intervals. To select the desired ground
track display, press Function Key F10 and then press Function Key F5 until
the desired mode is displayed; the available selections are: OFF, DOTS,
LINE, and BOTH.
Note that for satellites in high Earth orbits, the ground track may
appear as a solid line if the dots are very close together. Unlike prior
versions of STSPLUS, the ground track is NOT updated (except to re-color
dots for past track). With automatic map generation off, the map will be
automatically redrawn every 2.5 hours.
Program STSORBIT PLUS Satellite Orbit Simulation Page 44
Satellite Visibility
--------------------
Satellite visibility, or the ability to see a satellite with the naked
eye (or binoculars for the truly dedicated), attracts the novice and expert
alike. It can be a great thrill to point out the Space Shuttle or MIR Space
Station to a child or a friend as it streaks across the sky where and when
predicted. Unfortunately, predicting that visibility is more complicated
than "simple" orbital mechanics and trigonometry; spacecraft altitude,
position, physical geometry, reflectivity, and attitude with respect to
both the viewer and the Sun, as well as local atmospheric clarity not to
mention weather, all contribute to whether or not a satellite may actually
be seen. Some of these factors are beyond the capabilities of a program
like STSPLUS. All that can be done is to indicate when conditions are such
that the satellite MIGHT be sighted visually. STSPLUS estimates viewer
visibility by calculating that:
a) The satellite is at least partially lighted by the Sun;
b) The Sun is 1.7 degrees or more below the viewer's horizon so that
the viewer is in at least partial darkness; and,
c) The satellite is within the viewer's local circle of visibility
and is four degrees or more above the horizon.
If all these conditions are met, STSPLUS displays the word "VIS" in the
data block next to the orbit inclination. To these calculations must be
added the uncertainties described above. In my experience, the best
satellite sightings have usually occured when I am between the satellite
and the Sun, enabling flat surfaces such as solar panels to reflect the
sunlight back to me.
Although STSPLUS makes the visibility calculations for any satellite,
as a general rule only satellites in low Earth orbit, say under 1000 km
(600 miles) altitude, are likely to be seen with the naked eye. Binoculars
can extend that range somewhat. Satellites in very high or geosynchronous
orbits can be seen only with precision optical or radar equipment. Last but
not least, current 2-line elements must be used for reliable predictions.
**********
* NOTE *
**********
SATELLITE VISIBILITY IS ONLY ACTIVE WHEN THE SOLAR
FEATURES ARE ENABLED WITH F10+F3+F8.
User's Circle of Visibility
---------------------------
Centered around the user's geographic location, and marked with a
small circle on EGA and VGA systems, is a magenta circle of the approximate
line of sight visibility for the mission in progress. For rectangular
projections, the "circle" appears on the display as a circle near the
Equator and as a distorted circle at higher latitudes. In near-polar
regions, the circle takes on a very strange shape. The shape is entirely an
Program STSORBIT PLUS Satellite Orbit Simulation Page 45
artifact of the map projection; when displayed using the orthographic
projection, it appear as a true circle near the center of the map. The
radius of this circle of visibility is calculated for each satellite based
upon its altitude at the instant the map is first drawn as well as the
user's elevation above mean sea level and corresponds to "line of sight"
visibility for that satellite. When a second location has been selected
using F10+F2, a second circle of visibility will also be drawn for that
location.
When audible alarms are enabled (F10+F8 from the Main Menu), tones
sound 2 minutes before the satellite enters the circle of visibility and
again 30 seconds before the satellite leaves the circle of visibility. Both
the primary and secondary locations are monitored, with slightly different
tones for each. And "up-down" sequence of tones is used prior to entry into
the circles and a series of tones prior to leaving the circles.
When a satellite is within the circle, direct visual, radio or radar
communications with the satellite should be practical. Actual visibility,
of course, depends upon more than simply whether or not the satellite is
above the viewer's horizon. Most important is the sun to satellite to
viewer geometry; the satellite must be in sunlight and the viewer in
darkness for reasonable visibility. Almost as important is the size and
geometry of the satellite itself; a large, bright-metal satellite with huge
solar arrays reflects far more sunlight than a small dark satellite. In
addition to the satellites themselves, many booster rockets and other
"spare parts" are orbiting the Earth. Since they are not attitude
stabilized, booster rockets often are tumbling and may therefore appear
to flash on and off as they pass over.
For the Space Shuttle as well as most other satellites with near
circular orbits, the circle of visibility calculations are reasonably
accurate; however, the position of the sun and the effect of atmospheric
refraction are not taken into account, only whether or not the satellite is
in line of sight view from the observing location. For highly eliptical
orbits, however, the accuracy is substantially degraded since the radius of
the circle of visibility changes dramatically depending upon whether the
satellite is nearer apogee or perigee at the time the calculation is made,
and the period of the orbit. In the course of a single orbit, the altitude
of such a satellite may change by thousands of miles. Satellite "DE 1",
usually included in the TLEnnn.TXT 2-line elements file, is in a highly
elliptical orbit with long period and illustrates the problem.
Spacecraft Circle of Visibility
-------------------------------
The spacecraft circle of visibility is calculated dynamically using
the same alrorithm as for the user's circle of visibility. Like the user's
circle, the spacecraft circle may appear on rectangular projections as an
odd shape because of the scaling factors used by the map projection. The
difference is that the spacecraft circle moves with the spacecraft and
illustrates the approximate area visible from the spacecraft at any given
moment. The circle is updated every ten seconds (or as frequently as the
processor will permit). Comparisons using a VGA display system during the
STS-35/ASTRO-1 mission in December, 1990 confirmed that the circle shown is
quite close to that shown by one of the special graphics displays
occasionally seen on NASA Select Television as well as the actual horizon
view seen from the payload bay television cameras.
Program STSORBIT PLUS Satellite Orbit Simulation Page 46
SUN and Solar Features
----------------------
Many types of observations, especially Earth observations, often
require that the target or terrain be in sunlight. The performance of solar
panels and certain other instruments on a spacecraft is dependent upon
whether or not the Sun is in view. Also, it is usually impossible to
visually see a spacecraft which is not in sunlight. The solar terminator is
a series of yellow points on the display which represent the line at which
the center of the Sun is at an observer's horizon for Mean Sea Level.
Although a quick glance at the clock should suffice to determine which side
of the terminator line is in sunlight and which in darkness, EGA and VGA
systems also display the Sun as a small yellow circle.
The terminator as displayed by STSPLUS is sometimes confused with a
line denoting sunrise and sunset. Two factors make the terminator only an
approximation: first, the terminator is based upon the center of the Sun,
while actual sunrise and sunset are calculated using the upper limb of the
Sun; and second, the terminator is calculated for Mean Sea Level rather
than a specific local elevation. These two factors combined can result in a
difference of up to ten minutes when the times are compared against
published values or those calculated by my program ASTROCLK, sunrise being
earlier and sunset being later.
The Sun and solar features are enabled and disabled using F10+F3+F8
from the Main Menu. Since these features -- especially the terminator --
require some calculation and drawing time, users with slower computers may
wish to disable these features for faster screen updates. The following
features are included:
Sun: A yellow circle is plotted at the sub-solar point, the
geographic coordinates directly beneath the current position
of the Sun. The position of the Sun is recalculated every 10
seconds and the display is updated every 60 seconds. (Not
shown on CGA and HGC displays.)
Terminator: A dotted yellow line is plotted for the solar terminator,
that point on the Earth at which the center of the Sun is at
the horizon. The terminator is partially updated every 10
seconds and is fully updated every 60 seconds.The terminator
is shown for Mean Sea Level and does NOT take into account
the non-spherical shape of the Earth.
Lighting: The current spacecraft lighting is shown using color for the
satellite icon, and in the data block (to the right of
"Orbit #:") and displayed using the following symbols and
colors:
* Bright White Full sunlight
+ Yellow Partial sunlight (penumbra)
- Light Red Refracted sunlight
White Full shadow (umbra), no symbol
Note that Yellow and Light Red will display as Bright White
or shades of gray on monochrome monitors.
Program STSORBIT PLUS Satellite Orbit Simulation Page 47
Solar lighting conditions are updated every second or as
rapidly as the speed of the processor will permit. In order
to minimize calculation delays during ground track plotting,
the event times for orbital sunrise and sunset are
approximated. The dynamic lighting calculations, used to
plot the color of the spacecraft icon, are more precise.
Typical errors due to the simplified algorithm, are on the
order of 10 seconds.
SUN Timer: When Event Timers are enabled, the orbital sunrise (AOS) and
sunset (LOS) times are shown. A blank AOS or LOS timer
indicates the event will not occur within the next four
hours. An asterisk ("*") to the left of "SUN" indicates
sunlight is on the satellite:
AOS LOS
*SUN 73:20 37:40
In this example, the satellite is in sunlight. Orbital
sunset will occur in 37:40 and the next orbital sunrise will
occur in 73:20.
Program STSORBIT PLUS Satellite Orbit Simulation Page 48
TDRS and Real Time Satellite Features
-------------------------------------
TDRS and Real Time Satellite features are available only on EGA and
VGA monitors. These features permit up to thirty two additional satellites
to be tracked in real time. Satellites to be tracked are designated by the
user as "static" (geosynchronous or geostationary) and "real time"
(satellites whose sub-satellite point changes substantially with time).
Static satellites are only plotted when the map is redrawn; real time
satellites are updated every second with 386/387 or better computers, every
ten seconds for older computers, or as often as the processor can complete
the required calculations. When using X10 or X60, the update occurs at the
display rate (10 or 60 seconds).
When TDRS and Real Time Satellite coverage is enabled (F10+F3+F2), all
active TDRS satellites (Tracking and Data Relay Satellites), used for most
communications to and from the Space Shuttle, the Hubble Space Telescope,
and other active spacecraft, are shown as a dot inside a small circle near
the Equator (provided they have been included in the current TDRS and Real
Time Satellite configuration). Use F6 from the Main Menu to display and/or
modify that configuration. See the text section on Function Key F6 for a
complete description of Static and Real Time satellites.
As of August, 1993, there are five TDRS satellites in geosynchronous
orbit. The primary satellites consist of TDRS East ("TDRS 3") at
approximately 41 degrees West longitude and the TDRS West Cluster
consisting of two satellites, TDRS West ("TDRS 4") and TDRS Spare ("TDRS
1") at approximately 174 and 170 degrees West longitude respectively. The
TDRS Spare satellite has partially failed but is used occasionally as a
backup; this satellite is also low on propellant and is allowed to drift
considerably with an inclination of about 7 degrees. "TDRS 2" has also
partially failed and is currently parked at approximately 62 degrees West
longitude and is presently dedicated to downlinking data from GRO, the
Gamma Ray Observatory, whose tape recorders have failed. "TDRS 5" is the
most recent satellite launched, is fully operational, and is parked at
about 138 degrees West longitude as an on-orbit spare. Users should check
the current positions of the TDRS satellites since they are periodically
moved or reassigned.
Each TDRS location provides communications coverage for almost half
of the Earth for low Earth orbits and essentially full time coverage for
higher orbits. However, since the NASA Ground Terminals are located at
White Sands, New Mexico, the coverage has been slightly overlaped to
provide good ground communications at White Sands. This, in turn, means
that there is a narrow band, known by NASA as the Zone of Exclusion (marked
"ZOE" on the screen), off the East coast of Africa which is not covered by
either primary TDRS for low Earth orbits. Two red "circles" on the display
show the limits of coverage for each primary TDRS satellite. Each circle,
whose shape may be quite distorted when using rectangular projection,
encloses an area where the TDRS satellite is out of range of the primary
satellite being tracked and is centered on the opposite side of the Earth
from the TDRS satellite's position.
While the ground track is being calculated, STSPLUS also calculates
the times for acquisition of signal (AOS) and loss of signal (LOS). When
TDRS coverage is enabled, these times are displayed for TDRS East and TDRS
West. The method used for the calculation of the TDRS coverage is usually
accurate to about 10 seconds (assuming accurate 2-line elements for the
satellite and for the TDRS). However, spacecraft attitude can cause loss of
Program STSORBIT PLUS Satellite Orbit Simulation Page 49
TDRS communications at unexpected times. When Event Timers are enabled,
STSPLUS calculates AOS and LOS for four hours (240 minutes) from the time
the map is drawn. If a time is beyond that limit (or if the condition does
not occur), the time is left blank.
Each time is presented in the form of a countdown clock, minutes and
seconds, until the next occurence of the condition:
*TDRE AOS/LOS 72:42 50:42 (for rectangular projections)
*TDRW AOS/LOS 45:42 22:42
AOS LOS
*TDRE: 72:42 50:42 (for orthographic projections)
*TDRW: 45:42 22:42
An asterisk ("*") is shown to the left of the satellite name if AOS is in
effect. For rectangular projections, these data are displayed in the lower
right portion of the map. For EGA and VGA users, however, the data may be
displayed in the lower section of the data block by pressing F2 while the
map is displayed until MET/T+E is displayed. For orthographic projections,
the data are part of the standard data block at the right of the screen.
The clocks for each TDRS are color coded to indicate the current
status: GREEN when the satellite is in communication, and RED when the
satellite is out of range of the TDRS. Two minutes prior to a change in
status, the appropriate clock color changes to YELLOW. Users with
monochrome monitors must observe the presence or absence of the asterisk to
determine the status.
STSPLUS can sound an audible alarm (three beeps) 30 seconds prior to
TDRS AOS or LOS. Use F10+F8 to enable or disable the audible alarms.
Most satellites which utilize the TDRS system for communications are
in low Earth orbits (generally below 1500 km). However, other satellites
may also use the TDRS system for regular or backup communications. The
NAVSTAR Global Positioning Satellites (GPS), with orbital altitudes of
about 11,000 nautical miles (20,000 kilometers), are an example. For such
high orbits, the coverage by each TDRS satellite is nearly continuous.
As noted above, there are currently five TDRS satellites in orbit as
of mid 1993, TDRS 1 through TDRS 5. (These numbers are those currently used
by US Space Command in their 2-line elements. NASA sometimes uses different
numbers corresponding to the original launch letters as shown in the
following chart. TDRS "B", which should have become "TDRS 2", was lost in
the Challenger accident.) As of July, 1993, the TDRS assignments are:
TDRS# * NORAD# Long Description
-----------------------------------------------------------------
TDRS 1 (A) 13969 -170W TDRS West Spare, used occasionally
TDRS 2 (C) 19548 -62W Dedicated to Gamma Ray Observatory
TDRS 3 (D) 19883 -41W TDRS East (STSPLUS default)
TDRS 4 (E) 21639 -174W TDRS West (STSPLUS default)
TDRS 5 (F) 22314 -138W On-orbit spare
* Original NASA letter designation at launch
STSPLUS will use TDRS 3 and TDRS 4 by default and approximate positions as
of July, 1993 are automatically saved in file STSPLUS.INI. Note that some
2-line element files (including TLEnnn.TXT) often refer to the TDRS
satellites using numbers 1 through 5 or letters A through D or E. Use the
Program STSORBIT PLUS Satellite Orbit Simulation Page 50
NORAD numbers to be certain that you display the correct satellite.
TDRS satellites do change position and/or assignment periodically for
one reason or another. Users who wish the most accurate TDRS positions and
AOS/LOS data should periodically update the default positions by using the
automatic update feature with F2 from the Main Menu to read and update the
2-line elements.
Ground Tracking Stations and .TRK files
---------------------------------------
NASA maintains a number of ground tracking stations around the world.
Some of these tracking stations are essential for the ascent or landing
phases of a space shuttle flight; others are used for in-flight
communications. File STSPLUS.TRK contains the information for these ground
tracking stations. Other files with filetype .TRK contain the information
for other launch and/or tracking stations.
Each ground tracking station is shown as a small symbol surrounded by
a brown or light yellow "circle of visibility" which gives the approximate
area of antenna coverage and shows how small a proportion of each orbit can
be monitored without the TDRS system. When for some reason the TDRS system
is down (as has occurred during infrequent computer failures at White
Sands, New Mexico, the TDRS Ground Station), these ground tracking stations
become the only means of communication with the Space Shuttle. (Another
unexpected method was demonstrated during a 1992 space shuttle mission when
the SAREX, Shuttle Amateur Radio EXperiment, was used during a complete
loss of normal communications!) Because of budget constraints, many of
these ground tracking stations may be (or have already been) shut down.
Some, such as MIL and BDA (see list below) will be retained because they
are required for the ascent phase of a space shuttle mission. Others, such
as HAW, CTS and GWM, are operated jointly with, or independently by, the
U.S. Air Force. NASA is not always consistent as to the abbreviations used
for these tracking stations; on NASA Select TV, Gwan, Hawaii, and
Vandenbert are usually shown as GTS, HTS, and VTS respectively.
When using rectangular map projections, the shape of the antenna range
"circle of visibility" varies as a function of the latitude and is an
artifact of the map projection; when projected on a sphere, as is the case
with orthographic projection, they are true circles. In order to avoid
cluttering the display with countless meaningless lines, tracking station
circles of visibility are shown only if that circle has an angular diameter
of 90 degrees or less.
The following table lists the internal ground tracking stations as of
early 1989 which are shown along with their abbreviations and approximate
map coordinates (longitude, latitude):
MIL -81,28 Merritt Island, FL
BDA -64,32 Bermuda
DKR -17,14 Dakar, Senegal
ACN -14,-8 Ascension Island
MAD -5,41 Madrid, Spain
IOS 56,-5 Indian Ocean
HAW -156,20 Hawaii
GWM 143.33,14 Guam
VAN -120.57,34.73 Vandenberg, CA
YAR 115,-29 Yarragadee, Australia
Program STSORBIT PLUS Satellite Orbit Simulation Page 51
CAN 149,-36 Canberra, Australia
GDS -116.88,35.93 Goldstone, CA
CTS -105,38 Colorado Springs, CO
AGO -71,-34 Santiago, Chile
NGT -106,33 White Sands, NM
STSPLUS first checks for the presence of file STSPLUS.TRK for its
ground tracking station information. This is the default TRACKING STATION
filename used if no other selection has been made using F7 from the Main
Menu. If that file is present, its data is used instead of the internal
data above. The supplied STSPLUS.TRK has the following format:
"Maui, Hawaii",-156.7,20.9,0,"HAW"
"Vandenberg, CA",-120.5667,34.7333,112,"VAN"
"White Sands, NM",-106,33,0,"NGT"
"Colorado Springs, CO",-105,38,0,"CTS"
"Merritt Island, FL",-81,28,0,"MIL"
"Santiago, Chile",-71,-34,0,"AGO"
"Bermuda",-64,32,0,"BDA"
"Dakar, Senegal",-17,14,0,"DKR"
"Ascension Island",-14,-8,0,"ACN"
"Madrid, Spain",-5,41,0,"MAD"
"Indian Ocean Stn",56,-5,0,"IOS"
"Yarragadee, Australia",115,-29,0,"YAR"
"Guam",143.3333,14,0,"GWM"
"Canberra, Australia",149,-36,0,"CAN"
These files are ASCII and may be prepared or edited with any standard
ASCII editor; if using a word processor, select the "non-document" mode.
Five items are required for each location; the longitude and latatude are
expressed in degrees and fraction of a degree, elevations above Mean Sea
Level are expressed in meters, and names or abbreviations are included in
double quotation marks. The following example illustrates the .TRK file
format:
"Merritt Island, FL",-81.0,28.0,0,"MIL"
--------+----------- --+-- --+- + --+--
| | | | |
| | | | +--- 3-Letter Abbreviation
| | | +------- Elevation (meters)
| | +---------- Latitude (degrees)
| +---------------- Longitude (degrees)
+------------------------------- Location Name
For those interested in the Russian space program, a list of Russian
ground tracking stations is provided in file CIS.TRK (data courtesy
Ellwood Marshall). With the breakup of the Soviet Union, some of these
installations may no longer be active or the name may have changed.
"Tyuratam Cosmodrome",63.3392,45.9235,0,"TYR"
"Kaliningrad Cntrl Ctr",37.816,55.916,0,"KAL"
"Plesetsk Cosmodrome",40.7,62.75,0,"PLS"
"Petropavlovsk Russia",158.933,53.216,0,"PTR"
"Tbilisi Georgia",44.75,41.66,0,"TBL"
"Ulan Ude Russia",107.683,51.983,0,"ULN"
Program STSORBIT PLUS Satellite Orbit Simulation Page 52
"Ussuriysk Russia",132.15,43.8,0,"USS"
"Yevpatoria Ukraine",33.3666,45.2166,0,"YEV"
Other nations also have facilities for satellite launches. As of early
1993, file SPACENTR.TRK includes the following locations:
"Alcantara LC Brazil",-44.3999,-2.3999,0,"ALC"
"Esrange,Kiruna Sweden",21.067,67.883,0,"ESR"
"Jiuquan Space LC China",100.033,40.83,0,"JIU"
"Kagoshima Center Japan",131.083,31.25,0,"KAG"
"Kourou Space Ctr Fr.Gu",-52.7669,5.23,0,"KOU"
"San Marco Platform",40.2,-2.9329,0,"SMP"
"Sriharikota Ctr India",80.25,13.78,0,"SRI"
"Tanegashima SC Japan",130.967,30.4,0,"TAN"
"Xichang Space LC China",102.217,27.967,0,"XUC"
The first mission of Endeavour, STS-49, was in May, 1992. This
dramatic and exciting mission captured the INTELSAT VI (F3) satellite,
stranded in a useless orbit by its booster rocket failure since January,
1990, and attached a new booster rocket which placed the satellite in its
proper orbit. STSPLUS was used operationally during the mission by
Intelsat, another "first" for the program. Intelsat used its own ground
tracking stations for communications with INTELSAT VI (F3); the ground
stations which participated in the mission are listed in file INTELSAT.TRK
(information courtesy Dee Smith):
"Paumalu, Hawaii",-158.0342,21.6711,157.86,"PAU"
"Tangua, Brazil",-42.7845,-22.7442,35.38,"TAN"
"Jatiluhur, Indonesia",107,-6.5213,161.49,"JAT"
"Perth, Australia",115.25,-31.8,0,"PER"
"Gandoul, Senegal",-17.4745,14.43,0,"GAN"
These TRK files are standard ASCII files and may be edited with any
editor; word processor users be sure to use the ASCII or non-document mode.
The files use a standard comma-delimited format as shown; positions are
given in longitude (degrees) and latitude (degrees), rounded to the nearest
degree. A maximum of 25 ground stations is permitted. The use of TRK files
is not restricted to tracking stations, of course. So long as the correct
data format is observed, any desired location may be included in the
tracking station file up to the maximum of 25 locations.
Event Timers and Audible Alarms
-------------------------------
STSPLUS is often operated for long periods of time with minimum
operator attention or intervention. Users may perform other tasks while the
satellite display is active and while awaiting some subsequent event of
interest. Event timers are displayed for the selected events if they will
occur within approximately four hours of the time that the map is drawn; if
an event will not occur within that time, the event is blank. Audible
alarms serve to alert the user to upcoming selected events. The event
timers are enabled with F10+F7 from the Main Menu. Audible alarms are
enabled with F10+F8 from the Main Menu and require also that the event
timers be enabled. All events are termed "AOS" (Acquisition of Signal or
Program STSORBIT PLUS Satellite Orbit Simulation Page 53
Source) or "LOS" (Loss of Signal or Source) and are generally calculated
for line of sight conditions.
Each phenomena which may be timed has an associated AOS and LOS timer
which displays the hours and minutes ("HHH:MM") remaining until the next
event if that event will occur within the next four hours (240 minutes),
one hour past the last time for which the ground track is plotted. The
current status of the signal or source is indicated by the color of the
timer digits and the presence or absence of an asterisk ("*") to the left
of the event name: GREEN indicates signal or source acquisition, and RED
indicates signal or source loss. Two minutes prior to an event, the timer
for that event will change from the signal status color (GREEN or RED) to
YELLOW to visually alert the user. Users with monochrome monitors will be
unable to distinguish these color changes, of course, but can determine the
current signal status using the asterisk indicator.
All calculations for upcoming events are made each time the ground
track is drawn on the display and will affect the time required to prepare
the display, especially on slower computers. In order to minimize these
calculation delays, the event calculations for orbital sunrise and sunset
use a simplified algorithm which does not take into account the non-
spherical shape of the earth (unlike the dynamically calculated spacecraft
lighting features which are more accurate). Orbital sunrise and sunset are
the times that the spacecraft transitions between refracted sunlight
(sunlight refracted through the Earth's atmosphere) to partial sunlight
(illumination from only a portion of the solar disk); this corresponds to
the transitions between RED and YELLOW color on the satellite icon and
illumination symbols respectively. The errors resulting from the simplified
algorithm are usually less than plus or minus 10 seconds; because of the
more oblique angles and geometry involved, higher errors are usually
associated with higher inclination orbits.
When no secondary location is selected, the headings "AOS" and "LOS"
will appear in orthographic modes; the headings do not appear in
rectangular modes or in orthographic modes when a secondary location is
selected in order to make room for the additional line of data. Typical
Event Timers are shown in the following examples.
For orthographic projections:
*STN 95:15 6:21 AOS now in effect
AOS will next occur in 95:15
LOS will occur in 6:21
STN 23:47 45:18 LOS now in effect
AOS will occur in 23:47
LOS will next occur in 45:18
and similarly for rectangular projections:
*TDRW AOS/LOS 85:14 33:43 AOS now in effect
AOS will next occur in 85:14
LOS will occur in 33:43
TDRW AOS/LOS 14:21 57:32 LOS now in effect
AOS will occur in 14:21
LOS will next occur in 57:32
Program STSORBIT PLUS Satellite Orbit Simulation Page 54
except the primary location AOS/LOS, which is unlabeled in rectangular
projections and appears at the upper right of the data block (immediately
to the right of MET/T+E):
* 89:39 1:27 AOS now in effect
AOS will next occur in 89:39
LOS will occur in 1:27
70:15 76:38 LOS now in effect
AOS will occur in 70:15
LOS will next occur in 76:38
The following events may be timed and will cause an audible alarm if
audible alarms are enabled and the appropriate events are enabled:
Local Visibility For the primary location ("STN" or "STN1"): three
sets of up/down tones two minutes prior to AOS and
five tones thirty seconds prior to LOS. For the
secondary location ("STN2" if enabled): two sets
of up/down tones two minutes prior to AOS and four
tones thirty seconds prior to LOS. Refers to the
times the satellite enters or leaves the local
circle of visibility.
TDRS Acquisition ("TDRE" or "TDRW" if enabled) Three short tones
thirty seconds prior to AOS or LOS. Refers to the
times the satellite acquires or loses the ability
to communicate with either of the programmed
Tracking and Data Relay Satellites.
Orbital Sunrise/set ("SUN" if enabled) Two tones thirty seconds prior
to approximate orbital sunrise or sunset. Refers
to actual line of sight solar contact; refracted
sunlight is not included.
The characteristics of the audible tones have been selected to allow the
user to uniquely identify the AOS or LOS event that is about to happen.
STSPLUS is now "aware" of program RighTime by Tom Becker and its use
is recommended for accurate timekeeping. Audible alarms in prior versions
would perform unpredictably when RighTime was active because they use the
hardware clock's timer functions (which RighTime also uses). STSPLUS now
detects RighTime and temporarily disables RighTime while an audible alarm
is being generated and then re-enables RighTime after the alarm has
completed, restoring precise timekeeping. With RighTime active, alarms are
generated in foreground, which may cause a slight delay in screen updating.
*************
* CAUTION *
*************
STSPLUS expects RighTime Version 2.5+; performance with prior
versions of RighTime may yield unpredictable results. If using a
prior version of RighTime, do NOT enable audible alarms!
Program STSORBIT PLUS Satellite Orbit Simulation Page 55
If RighTime is not present or is not detected, the audible alarms are
generated in background as in prior versions. This usually causes the loss
of several clock ticks in the DOS software clock for each audible alarm.
Although the time loss per audible alarm is very small, the cumulative
error may become significant over extended time periods.
Pausing the Ground Track Display
--------------------------------
Pressing F6 will cause the ground track display to "freeze" at the
current time. This is called PAUSE mode. This permits closer examination of
the data and/or display at any given time and to "move" the display forward
and backward in time. Note that the pause takes effect AFTER the next
second tick on the system clock; thus, if you wish to pause at 01:00 (one
minute exactly on one of the clocks), press F5 when the display reads
00:59.
After pressing F6, the following message will appear near the lower
right of the screen:
PAUSE...Press ENTER
This reminds the user that PAUSE is in effect and to press ENTER to
resume normal operation. When normal operation is resumed, the time
continues from its present value, as if you had set SIMULATED TIME using
F8+F3 or F8+F4 from the Main Menu. To return to REAL TIME, use F8+F1 from
the Main Menu.
While PAUSE is in effect, the "+" and "-" keys may be used to advance
or retard the current time by the amount of the current time step. You may
also use the "=" key instead of the "+" key to avoid pressing the SHIFT
key. The only other key active in PAUSE mode is F4, which may be used
to adjust the "time step" by pressing the key until the desired time
multiplier is displayed at the upper right of the screen. Time multipliers
of "X1" (no message displayed), "X10", and "X60" are selected in
succession. The default time step is 1 second.
Note that the automatic map generation feature is also used in PAUSE
mode; automatic map generation may be enabled or disabled in the
rectangular projections (use the TAB key) and is ALWAYS enabled in
orthographic projections. Thus, when the satellite is moved near the edge
of the display, the map may be redrawn if the appropriate point is reached.
If you wish to synchronize the time used by STSPLUS to some other
source (such as the slightly delayed orthographic displays presented from
time to time on NASA Select TV), you may also use PAUSE mode for this
purpose. Simply pause the display, use the "+" or "-" keys to adjust the
time slightly ahead of the time to which you wish to synchronize. Then
press ENTER when the times agree. Time can only be synchronized in this
manner to plus or minus one second. If you need higher precision, set
SIMULATED TIME using F8+F3 or F8+F4 from the Main Menu.
Program STSORBIT PLUS Satellite Orbit Simulation Page 56
Switching between MET and T+Epoch
---------------------------------
STSPLUS by default displays the time elapsed since the epoch date of
the elements in the upper right portion of the data block unless the launch
date and time are included in file STSPLUS.LTD, in which case Mission
Elapsed Time (MET) is the default. This marked on the display as "T+Epoch"
or "T+E" and "MET" respectively. While T+Epoch is not of particular value
for satellite viewing purposes, it does indicate the relative age of the
orbital data. As a general rule, especially for lower Earth orbits, the
effects of orbit decay make position predictions less accurate as time
passes. Data which are more than 10 or 20 days old may produce less
accurate positions.
For a space shuttle mission, however, all mission events are scheduled
against the mission timeline and are reckoned in Mission Elapsed Time
(MET), the time elapsed since launch. It is therefore useful to be able to
display MET during the course of a mission or to review the flight post-
mission. Unfortunately, the standard NASA/NORAD 2-line element format does
not include the launch time and launch date and therefore this information
must be secured independently and manually entered into STSPLUS. Once
entered, STSPLUS saves the information in file STPLUS.LTD.
Once the ground track map is displayed, the F5 command may be used to
switch the display between Time Since Epoch ("T+Epoch" or "T+E") and
Mission Elapsed Time ("MET").
The F5 command checks that you have already entered the launch time
and launch date or that it has been read from file STSPLUS.LTD. If no
launch time and date are present, the command will have no effect. Press
ENTER to return to the Main Menu and press F5 to enter launch time and
launch date.
Using FAST Time
---------------
Press F4 while the map is displayed to use FAST time. FAST TIME is a
variation of SIMULATED TIME which automatically advances the time displayed
by 10 or 60 seconds, as indicated at the upper left of the screen. Press F4
again to change the time step; when "(X10)" or "(X60)" is NOT displayed,
the time step is one second. The actual time increment is a function of the
computer's speed. For fast computers, the time increment will usually be 10
or 60 seconds but may vary by a second occasionally; for slower computers,
the time increment may be somewhat longer. FAST time is disabled when PAUSE
mode is in effect and for the Satellite Motion Map.
FAST time may be used to advance the display to a future time and for
demonstration purposes. Once the desired time has been reached, simply
press F4 until no time step is displayed at the upper left of the screen
and time will advance normally. Note that FAST time sets the program to
SIMULATED TIME; to restore "real time", press F8+F1 from the Main Menu. The
Main Menu also indicates when SIMULATED TIME is in effect: the words
"Current Time" will appear at the left of the times at the top of the
screen when real time (the time your DOS clock is using) is in effect; the
words "Simulated Time" appear when a simulated time is in effect.
Program STSORBIT PLUS Satellite Orbit Simulation Page 57
On-line Help
------------
An on-line Help Screen is available during the ground track display
to remind the user of the available functions and which keys to press to
trigger those functions. When the ground track display is active, press
Function Key F1 to display the Help Screen in the lower portion of the
display. The following help screen will appear in rectangular modes:
F1=Resume Data F6=Pause (+,-) TAB=Auto Maps On/Off L=Location Maps
F2=Select Clocks F7=Circle of Vis W=World Maps T=Tracking Maps
F3=Printer Log Q=Quadrant Maps M=Motion Map
F4=Time Step F9=Units (nm/km) Z=Zoom Maps: O=Orthographic
F5=MET/T+Epoch F10=Sat Coordinates Home,PgUp,PgDn STSPLUS Ver 9435
The help screen in orthographic modes is similar but in a vertical format
at the right side of the screen.
The ground track display will continue to be updated in real time
while the help screen is displayed. If only the graphical display of the
ground track is of interest, the help screen may be kept on the display
continuously. Press Function Key F1 again to return to the normal data
display in the lower portion of the screen. Note that the Help Screen is
disabled when the Motion Map is displayed.
Program STSORBIT PLUS Satellite Orbit Simulation Page 58
Satellite Communications and Amateur Radio
------------------------------------------
By now, everyone is familiar with communications satellites. They
provide almost instant communications, particularly television, around the
globe from their assigned geostationary "parking slots" some 22,300 miles
above the surface of the Earth. The concept of the geostationary
communications satellite was originated by the science fiction writer
Arthur C, Clarke some thirty-odd years ago. Novel and revolutionary at the
time, they have become an accepted part of global communications, all but
taken for granted by the millions of people who see the images they
transmit over vast distances. Glossing over some of the "minor
technological details" that make these miracles possible, the
communications satellite is relatively easy to use. Because of its
geostationary orbit (which matches its orbital velocity with the Earth's
rate of rotation), it appears to remain at the same point in the sky. Once
properly located, ground terminals may be more or less permanently aimed
and that's that. Reliable communications are routine except during the
semi-annual Sun blockage periods when the Sun, satellite, and ground
terminal are in a direct line with each other and the Sun's powerful
radiation overwhelms the signals from the satellite.
However, geostationary communications satellites are but one example
of the uses for satellite communications. Except for a relatively few
passive satellites, each satellite has on board radio transmitters and
receivers so that its ground control centers may send commands and receive
data; these commands and data provide for the operational control and
orbital position and stability of the satellite. Unlike the geostationary
communications satellites, these satellites are in orbits which cause them
to appear to move rapidly across the sky when viewed from the ground. The
typical effective ground speed of the space shuttle, for example, is some
17,500 miles per hour; other satellites in higher orbits move more slowly.
Viewed from afar, both the ground station and the satellite are moving
rapidly, sometimes toward each other and sometimes away, as a result of the
rotation of the Earth and orbital direction/velocity respectively.
Since the typical satellite's receiver(s) and transmitter(s) are
usually set for fixed frequencies, these high relative velocities cause a
problem on the ground known as Doppler Shift. Almost everyone has heard a
train whistle as it speeds past; the whistle's pitch is high when first
heard, then drops steadily as the train passes. The "true" pitch of the
whistle is heard when the train is opposite the listener. While the train
is approaching the pitch is shifted to a higher frequency, and as the train
recedes the pitch is shifted to a lower frequency. For satellite
communications, this effect is increased by the much higher relative
velocities involved and it is usually necessary to adjust the transmit and
receive frequencies on the ground to compensate for the shift.
Stated simply, the ground station must adjust its transmitting
frequency such that the shifted frequency as received by the satellite is
the exact frequency for which the satellite receiver is set. Similarly, the
ground station must adjust its receiver frequency to the shifted frequency
at which the satellite's signal will be received. Like the train whistle,
the ground station's transmit and receive frequencies are constantly
changing as the satellite approaches and then departs from the ground
station. As a general rule, no two satellite passes over a ground station
have exactly the same geometry and therefore these frequency shift
adjustments must be calculated dynamically for each pass. In the special
Program STSORBIT PLUS Satellite Orbit Simulation Page 59
case of Frequency Modulation (FM) transmissions using a receiver with
Automatic Frequency Control (AFC) and a sufficiently wide receiver AFC
bandwidth, no adjustments may be necessary.
Given a satellite's orbital paramaters and the appropriate computer
software, these data can be calculated in advance of an upcoming pass as
well as in real time. Most of the required data are already calculated in
satellite tracking software such as STSPLUS. Ken Ernandes, N2WWD, offered
his expertise and amateur radio equipment to assist in the implementation
and test of Doppler Shift calculations in STSPLUS. The necessary changes
and additions to the software were implemented in mid-March 1994 and Ken
made a preliminary test using Radio Sputnik 10 (RS-10, a piggybacked
transponder on the Russian COSMOS 1861 satellite, NORAD #18129). To our
considerable surprise and delight, the very first test was a complete
success; although the satellite only reached a maximum of 7 degrees above
the ground station's horizon, the transponder signal was heard (rather weak
and noisy) on the predicted frequency. Although we both were confident in
our mathematical solution to the Doppler shift problem, it is seldom that
such calculations turn out to be correct on the first try! Testing and
validation continue.
STSPLUS Doppler Shift Mode
--------------------------
STSPLUS' Doppler Shift Mode of operation may be used for real time
communications with any satellite, not just amateur radio transponders, for
which orbital data ("2-line elements" or "TLE") are available. For each
satellite, the user prepares a preset frequency list in file STSPLUS.FRQ
which includes the satellite's NORAD Number, the transmit (XMIT) and
receive (RECV) center frequencies, and a special code which is used to
select NORMAL or INVERTED satellite transmitter transponders (see below).
For satellites with fixed transmit and receive frequencies, that is
all that is required; for satellites which receive and transmit over a band
of frequencies, such as the passbands of the typical amateur radio repeater
transponder, the receive and transmit frequencies may be quickly "tuned" in
tandem by fine increments of 100 Hz or coarse increments of 1 KHz over the
entire passband.
For those who may be interested, the solution of the Doppler shift
computations required that the ground station position vector and the
satellite position and velocity vectors be calculated using standard
transformation algorithms (and the SGP4 Orbital Model for determining the
satellite data), then converted to Earth-Fixed Greenwich ("EFG")
coordinates, a geocentric intertial coordinate system using the WGS-72
Geodetic Model. From these data the relative velocity and frequency shift
ratios are next calculated. These ratios are then applied to the preset
transmit and receive center frequencies to yield the shifted frequencies,
all of which are then displayed to the user. Provided the computer is
equipped with a math coprocessor chip, all data are updated each second.
The following is an example of the frequency data displayed as a satellite
(RS-10 in the example) approaches the ground station:
UpLink: 145.8900 Uplink frequency received by satellite
XMIT: 145.8880 TRANSMIT frequency at ground station
DnLink: 29.3900 Downlink frequency xmitted by satellite
RECV: 29.3904 RECEIVE frequency at ground station
Program STSORBIT PLUS Satellite Orbit Simulation Page 60
The shifted transmit frequency (XMIT) and receive frequency (RECV) are
also color coded to indicate the signal status:
RED The satellite is below the receiver horizon; communications
are normally not possible.
YELLOW The satellite is from zero to five degrees above the
receiver horizon; transmissons MAY be possible.
GREEN The satellite is five degrees or more above the receiver
horizon; transmissions should be practical if the receiver
horizon is clear in the direction of the satellite.
The altitude (or elevation) of the satellite above the receiver
horizon is usually a good indicator of communications capability. However,
transmitter power, receiver sensitivity, antenna structure and orientation,
and atmospheric conditions all play a role in making reliable full duplex
communications practical. For example, the large antennas used by the DOD
C-Band Radar Network, used to track the orbiter and other satellites during
ascent and critical maneuvers, typically acquire signal lock when the
satellite is between 3 and 4 degrees above the local horizon. A low power
amateur radio rig may require that the satellite be from 5 to 8 degrees
above the local horizon for reliable communications. To illustrate the role
atmospheric conditions may play, the space-based geostationary TDRS
(Tracking and Data Relay Satellite) typically acquires signal lock with a
target satellite at or near Earth limb (what passes for the "horizon" at
the satellite). In addition to the frequency data, the ground station
("STN") times for Acquisition of Signal ("AOS") and Loss of Signal ("LOS"),
calculated for the true ground station horizon, are displayed so that the
user may quickly determine how soon a pass will begin or how much time
remains in a current pass.
For ground station to satellite communications, operation is
straightforward. The user simply adjusts his transmit ("XMIT") and receive
("RECV") frequencies to those shown by STSPLUS as the satellite passes his
location. Since the frequencies required at the satellite are known and do
not change, there are no "fine tuning" adjustments required.
Compared to a satellite with fixed receive and transmit frequencies,
the typical amateur radio satellite transponder (also referred to as a
"crossband repeater") presents a slightly more complex situation. The
transponder receives signals across a passband of frequencies (20 to 80 KHz
are typical bandwidths), then retransmits the received signals across a
passband of the same width but centered at a different frequency. The
center frequency of the receive and transmit passbands are known in advance
but may change from time to time depending upon the transponder mode (CW,
voice, digital packet, etc.). The transmit side of the transponder may also
operate in either NORMAL or INVERTED mode. That is, for NORMAL mode the
transmitted signal is the same frequency above or below the center
frequency as is the received signal; for INVERTED mode, the transmitted
signal is the same frequency above (below) the transmit center frequency as
the received signal is below (above) the receive center frequency.
STSPLUS addresses this situation in two ways. First, once the user has
received a signal of interest, he uses the PgUp, PgDn, UP, and DOWN keys to
"fine tune" the downlink frequency shown by STSPLUS ("RECV") until it
matches the actual received frequency. PgUp and PgDn perform "coarse
tuning" in increments of 1 KHz, and UP and DOWN perform "fine tuning" in
Program STSORBIT PLUS Satellite Orbit Simulation Page 61
increments of 100 Hz. The response is quite rapid and the fine tuning may
usually be performed in no more than several seconds. STSPLUS then makes
the necessary calculations to show the required uplink frequency ("XMIT")
to permit full duplex communications. The second part of the problem is the
transponder mode; STSPLUS selects NORMAL or INVERTED transponder mode based
upon the mode parameter supplied by the user in file STSPLUS.FRQ: 1 =
NORMAL, -1 = INVERTED.
Satellite Phase (Mean Anomaly)
------------------------------
Some amateur satellite transponders (an example is AO-13) change their
mode of operation based upon a parameter called "phase". Data is published
by AmSat and/or others for these transponders giving the mode of operation
for specific ranges of Phase. Phase is the Mean Anomaly, one of the six
parameters of orbital data, normalized to the range from 0 to 255. Phase =
0 (Mean Anomaly = 0 degrees) corresponds to perigee, the point at which the
satellite's orbit makes its closest approach to the center of the Earth
(NOT the surface!); Phase = 128 (Mean Anomaly = 180 degrees) corresponds to
apogee, the point in the orbit at which the satellite is most distant from
the center of the Earth.
When the Doppler Shift Mode is enabled in orthographic projection (by
pressing F8 while the map is displayed), the Phase is displayed PROVIDED
that the Eccentricity is greater than or equal to 0.005:
Phase: 123.9
When the conditions for the display of Phase data are met, it replaces the
orbital period data ("Per'd") in the Doppler Shift Mode; if not, the
orbital period data will be displayed. Technically, Phase is defined as an
integer in the range 0 to 255. However, in order to give the user some
advance warning when the Phase will step from one number to the next,
STSPLUS also displays the first decimal digit. Phase is NOT displayed in
rectangular projections due to insufficient display space.
TECHNICAL NOTES REGARDING PHASE:
1. The Mean Anomaly is dynamically calculated by the SGP4 algorithm
within STSPLUS. This value (in radians) is divided by (2 * PI) and the
result multiplied by 256 to obtain Phase. The Phase is then displayed
as a number ranging from 0.0 to 255.9. The technical definition of
Phase is as an integer ranging from 0 to 255 (so as to fit in a single
8-bit byte of computer data).
2. Phase is calculated based upon geocentric (center of the Earth) data
rather than geodetic (surface of the Earth taking into account the
shape of the Earth) data. What may appear as an apogee or perigee
based upon "Elv", the distance above Mean Sea Level, may NOT be the
actual apogee or perigee when calculated using geocentric data.
Because of the shape of the Earth, these distances may vary up to 21
kilometers from the Equator to a pole.
3. Mean Anomaly (and therefore Phase) is undefined for a perfectly
circular orbit; there is no perigee or apogee in this situation. In
addition, some uncertainties are also introduced by gravitational
Program STSORBIT PLUS Satellite Orbit Simulation Page 62
variations which can make accurate dynamic determination of apogee or
perigee difficult for low Earth orbits. These variations and
inaccuracies become significant for orbits with an Eccentricity of
0.005 or less, a situation which is typical for most low Earth orbits.
For this and other reasons, amateur satellites in low Earth orbits do
not use Phase to determine operating modes.
4. The following conditions are required for the Phase data to be
displayed:
a) The orthographic projection has been selected by pressing "O"
while the map is displayed.
b) The Doppler Shift Mode has been selected using F8 while the map
is displayed.
c) The Eccentricity of the satellite's orbit is 0.005 or greater.
If any of these three conditions is not satisfied, the orbital period
data ("Per'd") will be displayed.
Satellite Communications Technique and Cautions
-----------------------------------------------
Once full duplex communications have been established, remaining "in
lock" throughout a pass requires that both parties continually adjust their
transmit and receive frequencies to the values displayed by STSPLUS to the
extent practical and consistent with the bandwith capabilities of their
receivers. Although this may seem a bit daunting at first, the actual rate
of change of the frequencies is sufficiently slow that it can easily be
managed by the relative novice with a little practice.
Equally important in the relatively new area of communications with or
via manned and unmanned satellites is that all participants recognize that
the available bandwidth and communications opportunities are a "scarce
resource" that must be used with care and shared. This is in keeping with
long standing amateur radio tradition. The problem can be particularly
difficult with the manned spacecraft, MIR and the Space Shuttle. Careful
attention to doppler shift can be of considerable help in completing the
call by using the correct frequency or frequencies.
********************
* IMPORTANT NOTE *
********************
Experience with communications via amateur ratio satellites such as
RS-10 has shown that careful test and calibration of the receiver and
transmitter are essential to successful communications. For example, an
error or bias of 2 or 3 KHz on the receiver frequency can make the
difference between a successful call and a failure. If the receiver or
transmitter has a consistent bias, it may be possible to temporarily adjust
the values of the center frequencies to compensate for the problem but the
best solution, of course, is to have the equipment calibrated and operating
correctly.
Equally important, the computer clock must be accurately set. Radio
time signals such as those broadcast by the National Institute of Standards
Program STSORBIT PLUS Satellite Orbit Simulation Page 63
and Technology (NIST) on WWV are sufficiently accurate for this purpose.
The program TIMESET by Peter Petrakis is highly recommended to
automatically set the computer clock via the telephone time services of
NIST or the U.S. Naval Observatory (USNO).
Finally, the frequencies calculated by STSPLUS are no more accurate
than the orbital data used. For the typical amateur radio satellite, the
orbital data should be no more than a week old for reasonable results. If
the satellite is performing orbital maneuvers (as MIR does from time to
time), only the most current elements will yield satisfactory results.
Sources such as Internet, Celestial BBS, NASA Spacelink BBS, NASA GSFC
RBBS, and my own RPV Astronomy BBS offer up-to-date 2-line elements for all
or most of the common amateur radio satellites. See the section "Computer
Bulletin Board Systems" near the end of this document for current BBS
telephone numbers and related information. Since the amateur radio
transponders are often "piggybacked" on a primary satellite, the name of
the satellite used by these sources may be different from the amateur radio
designation. Use the example file STSPLUS.FRQ to check for the NORAD
numbers of common amateur radio satellites and use the NORAD number rather
than a satellite name or designation when searching for TLEs.
Program STSORBIT PLUS Satellite Orbit Simulation Page 64
Preparing File STSPLUS.FRQ for Amateur Radio Use
------------------------------------------------
File STSPLUS.FRQ contains the parameters required for STSPLUS to
operate in the Doppler Shift Mode. Each entry (line) in the file includes
the satellite NORAD Number, UPLINK and DOWNLINK center freqencies, and the
transponder mode, specified in in that order, separated by commas and
without any leading or trailing spaces. The following format is used for
each entry:
00000,100,100,1 (Default values if sat not included)
18129,145.8900,29.3900,1 (Parameters for NORAD #18129)
--+-- ----+--- ---+--- +
| | | |
| | | +-- Transponder Mode: 1 = NORMAL
| | | -1 = INVERTED
| | |
| | +------- DownLink Center Frequency (MHz)
| |
| +--------------- UpLink Center Frequency (MHz)
|
+----------------------- Satellite NORAD Number
The first sample line shows the "00000" entry which determines the default
values if the satellite is NOT included in file STSPLUS.FRQ. This should be
the FIRST LINE in file STSPLUS.FRQ. The second line gives real parameters
for a specific satellite; the frequencies shown select the Mode A voice
passband for Radio Sputnik 10 (RS-10, piggybacked on COSMOS 1861, NORAD
#18129). Preset frequencies may range from 1.0000 MHz to 99000.0000 MHz.
Neither the uplink nor downlink frequency should exceed approximately
99000.0000 MHz to avoid an overflow condition on the display. Although the
center frequencies are shown above in MHz, any desired units may be used
since STSPLUS simply calculates a ratio and displays the results with four
digits to the right of the decimal point.
File STSPLUS.FRQ may be created or edited with any ASCII editor; word
processor users, use the "non-document" mode. Note that only minimum error
checking is performed and the user must observe the required format exactly
for each line in the file. Up to ten entries may be included for a given
satellite (using the same NORAD Number) in order of preference. If more
than one entry is present for the current satellite, the user is presented
with a list and asked to make a choice.
Ken Ernandes, N2WWD, in conjunction with his tests of STSPLUS' Doppler
Shift Mode, has prepared a preliminary STSPLUS.FRQ file with the current
(as of March, 1994) center frequencies of fourteen amateur radio
satellites. Note that several satellites have more than one entry,
corresponding to different modes of operation:
00000,100,100,1 (Default values)
14129,435.1025,145.9025,-1 (AO-10)
16609,145.5500,145.5500,1 (MIR)
18129,145.8850,29.3800,1 (RS-10)
18129,21.1800,145.8800,1
18129,21.1800,29.3800,1
19216,435.4950,145.9000,-1 (AO-13)
Program STSORBIT PLUS Satellite Orbit Simulation Page 65
19216,144.4500,435.9650,-1
19216,1269.4750,435.8600,-1
19216,435.6190,2400.7290,-1
20437,145.9750,435.0700,1 (UO-14)
20439,145.9000,437.02625,1 (PACSAT)
20441,1265.0000,437.0751,1 (WO-18)
20441,1265.0000,437.1258,1
20442,145.8400,437.15355,1 (LO-19)
20480,145.9550,435.8500,-1 (FO-20)
21087,435.0160,145.9870,1 (AO-21)
21087,435.0620,145.8920,-1
21087,435.0830,145.9060,-1
21089,21.2400,29.4400,1 (RS-12/13)
21089,21.2400,145.9400,1
21089,145.4400,29.4400,1
21575,145.9000,435.1200,1 (UO-22)
22077,145.9000,435.1670,1 (KO-23)
22077,145.9000,435.1200,1
22825,145.8500,436.8000,1 (AO-27)
NOTE: The center frequencies listed above are preliminary, based upon
available information. For example, the uplink frequencies for the
first entry for RS-10 and the entry for FO-20 have been adjusted up by
5KHz to compensate for an apparent transponder bias. These data will
be coordinated by Ken Ernandes, N2WWD. Ken may be contacted through my
RPV Astronomy BBS at (310) 541-7299 or on CompuServe at 70511,3107.
Users who have carefully calibrated their receivers and transmitters
and who have updated information are encouraged to contact Ken.
SAREX, the Shuttle Amateur Radio EXperiment, is frequently assigned to
Space Shuggle flights. The following uplink and downlink frequencies have
been assigned for that flight (data as of April 1994):
UPLINK DOWNLINK NOTES
-------------------------------------------
VOICE: 144.91 MHz 145.55 MHz EXCEPT EUROPE
144.93
144.95
144.97
144.99
144.70 MHz 144.55 MHz EUROPE ONLY
144.75
144.80
PACKET: 144.49 MHz 145.55 MHz WORLDWIDE
NASA adds the following note with respect to the voice uplink: "The
astronauts will not favor any one of the above frequencies. Therefore, the
ability to talk with an astronaut depends on selecting one of the above
frequencies chosen by the astronaut." (Information courtesy NASA Spacelink
BBS as of April, 1994) Thus, for a station in North America, the user may
add the following entries to file STSPLUS.FRQ:
Program STSORBIT PLUS Satellite Orbit Simulation Page 66
00059,144.91,145.55,1
00059,144.93,145.55,1
00059,144.95,145.55,1
00059,144.97,145.55,1
00059,144.99,145.55,1
00059,144.49,145.55,1
where "00059" must be replaced by the actual NORAD number assigned to the
flight. A temporary NORAD number corresponding to the flight number,
illustrated by "00059" in the example above, is usually used until the
permanent NORAD number is assigned (although some sources use a different
method to assign a temporary NORAD number -- check the TLEs). However, if a
temporary NORAD number is used during the initial portion of the flight,
the data in file STSPLUS.FRQ must later be updated to the permanent NORAD
number when that number is used in the TLEs in order for STSPLUS to
recognize the flight's frequency list. A typical set of TLEs for a Space
Shuttle are shown with the NORAD number and Eccentricity noted:
STS-65
1 23173U 94039A 94203.67836573 .00310904 40043-6 28999-3 0 371
2 23173 28.4640 263.1143 0006121 89.0653 314.1440 16.10872029 2244
--+-- ---+---
| |
| +----- Eccentricity (=0.0006121)
|
+------------------------------ NORAD Number
Because different sources of 2-line elements (TLEs) may use different
names for the same satellite, numerous satellites may have similar names,
and some payloads (especially amateur radio transponders) are "piggybacked"
on a primary satellite with a different name, always use the NORAD Number
if possible when searching a file for the TLEs. The MIR Space Station,
NORAD Number #16609, can be mistaken for numerous MIR debris objects ("DEB"
or "D" appears in the first line of the TLEs). For AO-13, for example,
press F2, select the desired TLE filename, then enter "#19216" (without the
quotation marks but WITH the pound sign) as the satellite name. This method
will ALWAYS find the data if they are present in the file. Once the data
are found, STSPLUS displays them as usual. If there is only one entry in
file STSPLUS.FRQ for the satellite, STSPLUS will immediately draw the map
after ENTER is pressed to approve the satellite and its data. However, if
more than one entry for the satellite is present, and STSPLUS is currently
in the Doppler Shift Mode, STSPLUS will display a list of the available
preset frequencies and request the user to select one:
Preset Frequency Selections for 19216
# UpLink DnLink Mode
---------------------------------
1 435.4950 145.9000 -1
2 144.4500 435.9650 -1
3 1269.4750 435.8600 -1
4 435.6190 2400.7290 -1
Enter Desired Preset Frequency Selection Number [1]:
Program STSORBIT PLUS Satellite Orbit Simulation Page 67
Enter the desired preset frequency selection number followed by ENTER. If
you wish selection #1, you may simply press ENTER. Entering a number less
than 1 or greater than the highest selection number will also pick
selection #1.
Note that when STSPLUS is NOT in the Doppler Shift Mode, no list of
preset frequency selections is displayed and STSPLUS automatically picks
selection #1 (to avoid bothering folks who are not interested in the
Doppler Shift Mode).
Program STSORBIT PLUS Satellite Orbit Simulation Page 68
ACTIVE KEYS DURING GROUND TRACK DISPLAY
---------------------------------------
The following table lists the various keys which are active when the
ground track display is shown on the screen. Some of these features are
more fully described elsewhere.
ENTER Return to Main Menu (cancel the simulation).
F1 On-line HELP. Press F1 to display a help screen in the lower
portion of the screen. Press F1 again to resume normal data
display.
F2 Selects the Big Clock mode. These modes are selected in the
following order:
0 No clock displayed
1 UTC date and time
2 Local date and time
3 STN/TDRS AOS/LOS and MET or T+Epoch (select with F5)
Note that not all computers (especially older CGA systems) will
display the extended graphics characters used for the large clock
characters. The symptom of this problem is that the lower left
portion of the data block is mostly blank after pressing F2. If
you have this problem and your computer is running DOS 3.x or DOS
5.0, enter the command "GRAFTABL" at the DOS prompt before
running STSPLUS or include the line "GRAFTABL" in your
AUTOEXEC.BAT file; this sets the "code page" to enable the
computer to display the extended graphics characters. [The
program GRAFTABL.COM is included as part of DOS in most cases.]
F3 Enable or disable printer logging. If logging is enabled, the
word LOG appears in the lower right of the screen. Be sure the
printer is turned on BEFORE using the L command. The "L" command
automatically enables the display of ascending and descending
node information.
F4 Toggle FAST mode from x1 to x10 to x60 to x1, etc. When either of
the fast modes is enabled, "(x10)" or "(x60)" will appear at the
upper right of the data block in red. This feature operates in
both the normal (real or simulated time) and PAUSE modes. When
x10 or x60 fast modes are used, automatic map generation is
disabled in rectangular projections; use the TAB key to restore
automatic map generation.
F5 Switches the elapsed time between "T+Epoch" and "MET". If no
launch time and date have been entered, this command will have no
effect.
F6 Enable PAUSE mode. The plot is frozen at the current position and
the "+" and "-" keys are enabled. The "=" key may be used instead
of the "+" key to avoid use of the SHIFT KEY. Press ENTER to
resume normal operation using the current simulated time. (NOTE:
To return to REAL TIME after the PAUSE mode, press ENTER after
Program STSORBIT PLUS Satellite Orbit Simulation Page 69
leaving PAUSE to return to the Main Menu, then press F8+F1.)
F7 Enable or disable the spacecraft circle of visibility.
F8 Switches program operation between NORMAL and DOPPLER SHIFT
modes. (Orthographic projection only; see text for details.)
F9 Change units of distance between kilometers (km) and nautical
miles (nm).
F10 Change satellite coordinates between Altitude/Elevation and
Azimuth (Topocentric), Right Ascension and Declination
(Equatorial), and X-Y-Z (Geocentric Rectangular, also known as
ECI or Earth-Centered Inertial) coordinate systems. If a Target
Satellite has been selected, F10 may also be used to display
Relative Range and Velocity between the Primary and Target
Satellites.
+/= During PAUSE mode only, "+" moves the satellite to the NEXT
calculated position based upon the FAST mode then in effect:
simulated time is advanced 1, 10, or 60 seconds. The "=" key may
be used instead of "+" to avoid use of the SHIFT KEY.
- During PAUSE mode only, "-" moves the satellite to the PREVIOUS
calculated position based upon the FAST mode then in effect:
simulated time is backed up 1, 10, or 60 seconds.
TAB In rectangular map modes only, enable or disable automatic map
generation. Automatic map generation is ALWAYS enabled in
orthographic modes. When automatic map generation is enabled in
rectangular map modes, the letter "A" will appear in the upper
right of the display screen. Pressing the TAB key will always
cause the map to be redrawn.
PgUp NORMAL OPERATION: When in one of the zoom modes, increases the
field of view up to a maximum of 180 degrees. Press rapidly to
execute multiple zoom steps without redrawing the map for each
keypress.
DOPPLER SHIFT MODE: Increases the "RECV" frequency by 1 KHz. Hold
down or press rapidly for large frequency changes.
PgDn NORMAL OPERATION: When in one of the zoom modes, decreases the
field of view down to a minimum of 30 degrees. Press rapidly to
execute multiple zoom steps without redrawing the map for each
keypress.
DOPPLER SHIFT MODE: Decreases the "RECV" frequency by 1 KHz. Hold
down or press rapidly for large frequency changes.
Home NORMAL OPERATION: When in one of the zoom modes, returns the
field of view to 75 degrees (rectangular projections) or the full
globe (orthographic projections).
DOPPLER SHIFT MODE: Restores the UpLink and DnLink center
Program STSORBIT PLUS Satellite Orbit Simulation Page 70
frequencies to the original values read from file STSPLUS.FRQ.
End NORMAL OPERATION: When in one of the zoom modes, returns the
field of view to the last zoom factor used prior to pressing the
HOME key.
DOPPLER SHIFT MODE: (not used and inactive)
UP NORMAL OPERATION: (not used and inactive)
DOPPLER SHIFT MODE: Increases the "RECV" frequency by 100 Hz.
Hold down or press rapidly for larger frequency changes.
DOWN NORMAL OPERATION: (not used and inactive)
DOPPLER SHIFT MODE: Decreases the "RECV" frequency by 100 Hz.
Hold down or press rapidly for larger frequency changes.
B Toggle the BLINK mode of the satellite symbol between blinking
and steady. NOTE: On most systems, the satellite symbol will
appear to blink very briefly as it is erased and redrawn even
when BLINK is OFF.
O Select Orthographic Projection (the LETTER "O" not the digit
zero). PgUp, PgDn, Home, and End are active to select the
magnification.
W,0 Select World Map display, showing the full world from +85 degrees
North latitude to -85 degrees South latitude using rectangular
projection. If automatic map generation is disabled, pressing "W"
or "0" will toggle between the two world map displays.
Q Select Quadrant Map display, showing 180 degrees field of view
(rectangular projection) and selected so as to approximately
center the satellite.
1-9 Select the indicated Quadrant Map. Automatic map generation is
!@# disabled when a specific quadrant map is selected. See the chart
in the section Quadrant Maps for the map numbers.
Z Select Zoom Map display, showing from 180 to 30 degrees field of
view (rectangular projection) and selected so as to approximately
center the satellite. The default is 75 degrees.
L Select Location Map display, showing concentric isocontours for
your location. If a second location has been enabled, press "L"
again for that location.
T Tracking Station Map display, showing concentric isocontours for
the tracking station closest to the current ground track position
of the satellite using the current projection. Uses the data in
the current TRACKING STATION file to select the tracking
station(s); if the file is not found, STSPLUS defaults to an
internal set of tracking stations. Use F7 from the Main Menu to
select the TRACKING STATION filename.
Program STSORBIT PLUS Satellite Orbit Simulation Page 71
M Satellite Motion Map display, available on EGA and VGA systems
only. Displays a map with the satellite centered using the map
projection in effect when the key is pressed. In rectangular
modes, the map is shown in zoom. Maps are drawn "off screen" and
a complete map is always displayed. The map is updated every 10
seconds or as rapidly as the computer processor will permit.
While the Satellite Motion Map is displayed, the following keys
are active: ENTER, "M", "Home", "End", "PgUp", and "PgDn"; these
keys perform the same functions as during the normal display
except that the "M" key cancels the Satellite Motion Map and
returns to normal display.
Program STSORBIT PLUS Satellite Orbit Simulation Page 72
STSORBIT PLUS MAIN MENU
-----------------------
Once the map coordinates have been stored internally, STSORBIT PLUS
presents its Main Menu:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
F1 Convert Keplerian Data to 2-Line Format
F2 Read NASA/NORAD 2-Line Elements (.TXT/.TLE Files)
F3 Pass Predictions and Data Output
F4 Tabular Satellite Positions (TRAKSTAR by TS Kelso)
F5 Set Launch Time and/or Launch Date
F6 Set/Read/Save TDRS and Real Time Satellites
F7 Set FILENAMES and Paths
F8 Set program TIME and/or DATE
F9 DOS Shell (CAUTION: DOS 3.x or higher ONLY!)
F10 Set STSORBIT PLUS Program Options and Features
ENTER Resume Mission (Mir)
ESC Quit STSORBIT PLUS and Save Current Mission
Select desired function:
WHILE MAP IS DISPLAYED: F1 = HELP ENTER = Main Menu
During operation of STSPLUS, data are displayed by STSPLUS in several
standard formats:
26 JUL 1994 Date in day/month/year format
02:01:57 UTC Coordinated Universal Time in hours:mins:secs
19:01:57 PDT Local Time in hours:mins:secs (abbr. may vary)
3/09:23:15 MET in days/hours:minutes:seconds
320.50 nm Distance in nautical miles
551.37 km Distance in kilometers
-69.34 Angles in degrees; WEST longitude and SOUTH
latitude are negative.
Note that latitudes and longitudes also include "N" and "E" for positive
values respectively, and "S" and "W" for negative values respectively. This
convention, which may seem redundant, has been used to avoid possible
confusion; there are a number of representations for latitude and longitude
in common use which use different sign conventions. Azimuth (heading) is
given in the sense North-East-South-West where North is 0 degrees, East is
90 degrees, and so forth. The degree symbol is shown on the display for
all angles but has been omitted from this documentation because it may not
print correctly on all printers.
Program STSORBIT PLUS Satellite Orbit Simulation Page 73
F1 Convert Keplerian Data to 2-Line Format
----------------------------------------------
This function provides a means to individuals without modems to
receive the so-called "Keplerian Orbital Elements" by voice or other means
and reliably convert those data to the "2-Line Element" format as required
by STSPLUS and other satellite tracking programs. However, more data is
included in the 2-line orbital element set than is usually distributed as
the Keplerian orbital elements; this means that the missing data must
either be obtained from other sources or be set to a specified value or
zero. These instructions and the example and sample form which follows will
help the unskilled user to do these tasks.
This conversion function has but a single purpose: to prepare 2-line
orbital elements from Keplerian orbital elements by means of user keyboard
input. Since the program is designed only to transcribe valid data from one
format to another, no error checking is performed and the program makes no
tests of the "reasonableness" of the various data and parameters. The user
is therefore cautioned to check his data before using this program, or to
use the resulting data with caution until it has been verified.
The information shown below is usually included in the Keplerian
orbital elements as received via modem or voice (amateur radio or
telephone). This sample is an actual file for Space Shuttle Flight STS-55
launched in early 1993 as received via modem direct from the NASA Johnson
Space Center prior to launch:
Satellite: STS-55
Catalog number: 00055
Epoch time: 93073.67556033 =====> (14 MAR 93 16:12:48.41 UTC)
Element set: JSC-003
Inclination: 28.4697 deg
RA of node: 228.7025 deg Space Shuttle Flight STS-55
Eccentricity: .0003812 Prelaunch Keplerian Elements
Arg of perigee: 314.2100 deg Launch: 14 MAR 93 15:00 UTC
Mean anomaly: 45.8202 deg
Mean motion: 15.90487610 rev/day G. L. Carman
Decay rate: 1.2020e-03 rev/day~2 NASA Johnson Space Center
Epoch rev: 2
If you compare the information required by STSPLUS (as shown in the
example on the following page) with that above, several items are missing
or may be in a slightly different format. Here are some suggestions.
1. A sample form is included in this documentation which will assist you
when receiving Keplerian orbital information by voice or by amateur
radio link. Note that the form includes lines for "Int'l Designation"
and "BSTAR Drag"; these items are frequently omitted and must be
determined independently (see below).
2. The Catalog Number (often referred to as the NORAD Number) is assigned
by US Space Command at Cheyenne Mountain after a satellite has been
successfully launched. Initial or pre-launch Keplerian elements may
use the mission number or some other convenient number for this item.
Most tracking programs will accept any number here. STSPLUS uses the
Catalog number to keep track of launch date and time; if the Catalog
number used for a mission changes, the launch date and time must be
Program STSORBIT PLUS Satellite Orbit Simulation Page 74
entered again.
3. The Epoch time is the instant for which the Keplerial elements have
been calculated and is NOT the same as the launch date and time.
Launch date and time is shown separately, is NOT part of the 2-line
elements, and must be entered in STSPLUS using F5 from the Main Menu.
4. The International Designation is often not assigned until well after a
flight is in progress; press ENTER to use all spaces for this item.
5. For the 2-line orbital element set, the element set number (shown as
"JSC-003" in the example above) MUST be numeric. For this example,
enter "3" or "003". Most tracking programs will accept any number for
this item, up to a maximum of FOUR DIGITS.
6. The "Epoch Rev/Orbit" is the orbit number at the epoch (the instant
when the data is taken). Up to FOUR DIGITS may be entered here but
except for the orbit number on displays, this number has no effect on
the propagated orbit. NASA assigns Orbit/Rev 1 to the first partial
orbit following launch; US Space Command usually (but not always)
assigns Orbit/Rev 0 to the first partial orbit and the orbit number
for space shuttle missions must usually be adjusted to conform to NASA
convention.
7. When the program asks for "NDOT2 Drag/Decay", the information being
requested is the "Decay rate" in the Keplerian elements. It may be
entered in the form shown in the example or as a decimal fraction such
as ".002102" (which is identical to the "2.10200e-03" in scientific
notation as used in the example).
8. When the program asks for "NDDOT6 Drag", press ENTER to insert a value
of zero. This should be satisfactory for most satellites and most
tracking programs.
9. When the program asks for "BSTAR", you may press ENTER to insert a
value of zero. This will be satisfactory for times very close to the
Epoch Time for the elements. However, as time progresses the satellite
may lag behind the propagated (projected) ground track if no value is
avaialble for BSTAR. For space shuttle missions, NASA often assigns a
default value of "25599-3" or ".00025599". A value from a prior set of
2-line elements may also be used.
10. After all data have been entered, STSPLUS will request the filename to
which the 2-line orbital data is to be written. Enter the full
filename and filetype, such as "TESTSAT.TXT". The file will be written
to the drive and directory set using F7+F3 from the Main Menu. DO NOT
INCLUDE A DRIVE OR DIRECTORY; THAT IS ADDED AUTOMATICALLY! An existing
file with the same name will be overwritten.
11. If you make a mistake during the data entry process, you may use the
BACKSPACE key until ENTER has been pressed. If you wish to cancel the
program without writing the data to a file, press ENTER when asked for
the filename and the data will be discarded.
As noted elsewhere, orbital elements have a limited lifetime. How long
Program STSORBIT PLUS Satellite Orbit Simulation Page 75
that lifetime may be depends primarily upon the orbital altitude. Low Earth
orbit (LEO) satellites, especially those such as the space shuttle and
Russian space station, are frequently maneuvered to maintain the desired
orbit. Orbital elements for these satellites may be valid for only days or
sometimes even hours. Orbital elements for higher orbital altitudes, say
above 1,500 km, tend to be valid for much longer -- up to weeks. Satellites
in very high or geosynchronous orbits exhibit usually long term orbital
stability. The Bottom Line: The accuracy with which any tracking program
can determine a satellite's position is primarily dependent upon having
accurate orbital elements!
Finally, a word about the NDOT2 and BSTAR parameters. A satellite's
orbit is completely and accurately determined at the epoch time without
NDOT2 and BSTAR. These two parameters determine various adjustments as the
orbit is propagated in time and are a function of such things as orbital
altitude, spacecraft attitude and cross-sectional area, atmospheric density
changes due to sunspot activity, and so on. Both US Space Command and
Johnson Space Center have been known to "tweak" these values for a variety
of reasons, usually because the orbit is in a state of change due to
maneuvers and/or excessive drag.
NOTE: A positive exponent for BSTAR, which indicates high acceleration
and is somewhat unusual (and often an indication of "tweaking"), is NOT
handled correctly and must be manually edited. The resulting elements may
not propagate accurately for more than a few hours.
EXAMPLE DATA INPUT
------------------
Enter 2-LINE ELEMENTS
Enter the required data as prompted. Most essential data is included in the
Kelplerian Orbital Data available to amateur radio enthusiasts. Other data
may be inserted if available or may be omitted if not. Accuracy may be
affected, see documentation.
Enter Satellite Name (15 chars max): sts-55
Enter NORAD Number (NNNNN): 55
Enter Int'l Designation (8 chars max):
Enter Epoch Time (YYDDD.TTTTTTTT): 93073.67556033
Enter Element Set Number (NNN): 3
Enter Inclination (DDD.DDDD): 28.4697
Enter RA of Ascend Node (DDD.DDDD): 228.7025
Enter Eccentricity (.NNNNNNN): .0003812
Enter Arg of Perigee (DDD.DDDD): 314.21
Enter Mean Anomaly (DDD.DDDD): 45.8202
Enter Mean Motion (NN.NNNNNNNN): 15.9048761
Enter Epoch Rev/Orbit (NNN): 2
Enter NDOT2 Drag/Decay (.NNNNNNNN): .001202
Enter NDDOT6 Drag (NNNNN-N): 00000-0
Enter BSTAR (NNNNN-N): 36300-3
Program STSORBIT PLUS Satellite Orbit Simulation Page 76
EXAMPLE DATA OUTPUT
-------------------
Satellite Data has been entered as:
Satellite Name (15 chars max): Sts-55
NORAD Number (NNNNN): 00055
Int'l Designation (8 chars max):
Epoch Time (YYDDD.TTTTTTTT): 93073.67556033
Element Set Number (NNN): 3
Inclination (DDD.DDDD): 28.4697
RA of Ascend Node (DDD.DDDD): 228.7025
Eccentricity (.NNNNNNN): .0003812
Arg of Perigee (DDD.DDDD): 314.2100
Mean Anomaly (DDD.DDDD): 45.8202
Mean Motion (NN.NNNNNNNN): 15.90487610
Epoch Rev/Orbit (NNN): 2
NDOT2 Drag/Decay (.NNNNNNNN): .00120200
NDDOT6 Drag (NNNNN-N): 00000-0
BSTAR (NNNNN-N): 36300-3
Sts-55
1 00055U 93073.67556033 .00120200 00000-0 36300-3 0 33
2 00055 28.4697 228.7025 0003812 314.2100 45.8202 15.90487610 23
Enter FILENAME for 2-Line Elements:
Program STSORBIT PLUS Satellite Orbit Simulation Page 77
RECEIVED KEPLERIAN ORBITAL DATA FORM
------------------------------------
This form is provided as a convenience to users receiving Keplerian
orbital data via voice link (amateur radio or telephone). Each set of
underline characters indicates an expected character; the decimal point is
shown where expected (if appropriate for the item). Make multiple copies of
this form prior to a mission.
Satellite: __ __ __ __ __ __ __ __ __ __ __ __ __ __ __
Catalog Number: __ __ __ __ __
Int'l Designation: __ __ __ __ __ __ __ __
Epoch Time: __ __ __ __ __ . __ __ __ __ __ __ __ __
Element Set: __ __ __ __
Inclination: __ __ __ . __ __ __ __
RA of Node: __ __ __ . __ __ __ __
Eccentricity: . __ __ __ __ __ __ __
Arg of Perigee: __ __ __ . __ __ __ __
Mean Anomaly: __ __ __ . __ __ __ __
Mean Motion: __ __ . __ __ __ __ __ __ __ __
Decay Rate: . __ __ __ __ __ __ __ __
BSTAR Drag: __ __ __ __ __ - __
Epoch Rev: __ __ __ __
Program STSORBIT PLUS Satellite Orbit Simulation Page 78
F2 Read/Update NASA/NORAD 2-Line Elements from *.TXT/*.TLE Files
--------------------------------------------------------------------
In order to read or update the NASA/NORAD 2-line elements, you must
have a file with data for the appropriate satellites. A current file is
included in the standard distribution of STSPLUS. These files have names
such as "TLE360.TXT" where the "360" corresponds to the particular US Space
Command Prediction Bulletin number from T. S. Kelso's Celestial BBS and are
usually updated several times per week. This and other TLE files are
available from my BBS and from various other sources including CompuServe
and INTERNET.
Select/Update Preset Frequency Selections
-----------------------------------------
STSPLUS reads file STSPLUS.FRQ for preset frequency selections for the
current satellite each time the program is started. STSPLUS will re-read
file STSPLUS.FRQ each time F2 is used to select or update the current
primary satellite. When the Doppler Shift Mode is active (selected using F8
while the map is displayed) and more than one preset frequency selection is
available for the satellite, STSPLUS will present a list of available
selections and the user may choose the desired selection. The following is
a sample list of preset frequency selections for AO-13, NORAD #19216:
Preset Frequency Selections for 19216
# UpLink DnLink Mode
---------------------------------
1 435.5325 145.9375 1
2 144.4625 435.9275 1
3 1269.5475 435.9325 1
4 435.6280 2400.7380 1
Enter Desired Preset Frequency Selection Number [1]:
Enter the desired preset frequency selection number followed by ENTER. If
you wish selection #1, you may simply press ENTER. Entering a number less
than 1 or greater than the highest selection number will also pick
selection #1. If you wish to change your preset frequency selection, you
must be in the Doppler Shift Mode -- press F8 while the map is displayed.
Return to F2 on the Main Menu, re-select the desired satellite, then choose
the desired preset frequency selection. See the section "Satellite
Communications and Amateur Radio" for additional information on the Doppler
Shift Mode.
NOTE: When STSPLUS is NOT in the Doppler Shift Mode, no list of preset
frequency selections is displayed and STSPLUS automatically picks selection
#1 to avoid bothering folks who are not interested in the Doppler Shift
Mode.
Update Current TDRS and Real Time Satellites
--------------------------------------------
Program STSORBIT PLUS Satellite Orbit Simulation Page 79
Once Secondary Satelliets (TDRS, Static, and Real Time) have been
selected (using F6+F1 from the Main Menu), it is necessary to periodically
update the 2-line elements ("TLEs") for these satellites so that the
calculated positions are accurate. Naturally, this is also true for the
primary satellite being tracked. TLEs have a limited lifetime. For higher
altitude satellites such as geosynchronous satellites, 4 to 8 weeks is
probably sufficient unless the satellite is being maneuvered (although I
usually do this task at least weekly since I have the data). For low Earth
orbit satellites, even when the satellite is not being maneuvered, I
recommend a maximum interval of about two weeks; if the satellite is being
maneuvered, such as is usually the case with the Space Shuttle, daily
updates may be required. The Secondary Satellite display (F6+F1) flags real
time satellites whose elements are more than 10 days old, and static
satellites whose elements are more than 60 days old.
To update 2-line elements for the primary satellite and all Secondary
Satellites, press F2 from the Main Menu and select the desired file as
described in the following section. Then enter the satellite name as "&" to
request TLE update mode. The TLE file will be scanned and all satellite
TLEs will be updated if their Epoch Time is later than those presently
stored. The entire process takes only a few seconds. The following prompt
illustrates the "Update" selection:
Select NASA/NORAD 2-Line Elements File
Enter 2-Line Filename [GSFC315.TXT]: GSFC315.TXT
Enter Satellite Name/#nnnnn [#20638]: &
(Enter '*' to match any satellite name, '&' for AUTO UPDATE)
As STSPLUS updates TLEs, a list of the satellites for which new TLEs have
been loaded is displayed:
Automatic TLE updates for:
Satellite 8: Norad# 22920 HST Solar Array @ 93355.87870989
Satellite 10: Norad# 22076 TOPEX @ 93357.21248411
Satellite 12: Norad# 21987 EUVE @ 93356.85536486
Satellite 7: Norad# 21701 UARS @ 93353.94360770
Satellite 11: Norad# 21225 GRO @ 93356.46954065
Satellite 9: Norad# 20638 ROSAT @ 93353.77650216
Satellite 13: Norad# 20580 HST @ 93357.18124168
Satellite 6: Norad# 16609 MIR @ 93356.89342327
Press any key to continue ...
The satellite number indicates the "slot" in the Secondary Satellite
configuration, or "P" for the Primary Satellite. In the example shown, the
TLEs for eight satellites were updated to the Epoch Times (YYDDD.DDDDDDDD)
indicated. The satellites are listed in the order found in the TLE file.
The updated TLEs will be saved in file STSPLUS.INI. Press ENTER to return
to the Main Menu.
Program STSORBIT PLUS Satellite Orbit Simulation Page 80
Read NASA/NORAD 2-Line Elements from a File
-------------------------------------------
For both "Read" and "Update" functions, pressing F2 will display a
list of all available files with default filetypes ".TXT" and ".TLE". The
following example has been edited to show only 8 files:
Select NASA/NORAD 2-Line Elements File
Enter 2-Line Filename [TLE147.TXT]:
Use ARROW KEYS, press ENTER to use the current default file
shown in square brackets [...], or press ESC to CANCEL.
8 matching files in directory F:\TLE
GPS.TXT
GROUP000.TLE
GSFC198.TXT
GSFC199.TXT
MIR.TLE
TLE141.TXT
TLE146.TXT
TLE147.TXT
The list of files is sorted in alphabetical order by filename then
displayed using up to five columns. The display mode is adjusted for the
maximum number of lines permissible for the active monitor type: 25 lines
for CGA and HGC, 43 lines for EGA, and 50 lines for VGA. The maximum number
of files which may be displayed for each monitor type is shown in the
following table:
Screen File Max
Monitor Lines Lines Files
----------------------------------
VGA 50 42 210
EGA 43 35 175
CGA/HGC 25 17 85
To accept the default file shown in the square brackets, TLE147.TXT in
the example, press ENTER. To manually enter a filename, type the name (the
filetype .TXT will be appended if no filetype is typed) and press ENTER. To
select one of the displayed files, use the ARROW KEYS (UP, DOWN, LEFT,
RIGHT), Home, End, PgUp, or PgDn to move through the list until the desired
file is highlighted and shown in the square brackets, then press ENTER. To
cancel the function and return to the Main Menu, press ESC.
STSPLUS defaults the drive and directory to the current directory, the
one from which STSPLUS is being executed. However, some users prefer to use
a separate directory for 2-line elements files. To specify a different
drive and/or directory, enter the drive (followed by a colon) and the
desired directory (followed by a trailing backslash, "\"). The specified
drive, directory, and filename are saved in file STSPLUS.INI and will be
used the next time STSPLUS is executed. The following examples illustrate
this method:
D:\ Use the root directory on drive D:
Program STSORBIT PLUS Satellite Orbit Simulation Page 81
\ELEMENTS\ Use the current drive and directory
\ELEMENTS\
C:\TLE\ Use drive C: and directory \TLE\
Failing to include the trailing backslash will cause STSPLUS to interpret
what you intended as a directory to be a filename! The complete path with
filename and filetype mask may also be entered:
C:\TLE\*.TXT Use .TXT files on Drive C: and directory TLE
D:\TLE\*.* Display all files on drive D: and directory
\TLE\
F:\TLE\TLE*.TXT Use drive F:, directory \TLE\ and all files
matching "TLE*.TXT"
Although STSPLUS defaults to filetypes "*.TXT" and "*.TLE", you may use
this command to temporarily specify a different filename and filetype mask
if desired.
If no files with filetype .TXT or .TLE (or files corresponding to the
current filename and filetype mask) are found in the specified directory,
the following error message will be displayed:
No matching files found in specified drive/directory: E:\JUNK
Press any key to continue ...
To specify NO fileltype, enter the filename followed by a period, i.e.
"ELEMENTS.". Any desired filetype may be used, but the program will always
default to ".TXT" and ".TLE" each time F2 is used.
If you include a drive (such as "D:") and/or directory (the directory
MUST be followed by a trailing backslash, "\"), and the drive or directory
cannot be found, the following error message will be displayed:
Drive or path error: E:\JUNK
Press any key to continue ...
Once the file has been selected, a default satellite name will appear
in the next prompt:
Enter 2-Line Filename [STS50N38.TXT]: STS50N38.TXT
Enter Satellite Name/#nnnnn [STS...]:
(Enter '*' to match any satellite name, '&' for AUTO UPDATE)
STSPLUS will normally display the first three characters of a
satellite name or the full NORAD number, enclosed in square brackets, as
the default choice. If no prior satellite has been selected, the satellite
name will default to "STS..." for space shuttle missions (provided the
filename begins with "STS") and to "HST..." for all other satellites;
otherwise, it will be the first three letters or full five digit NORAD
number of the currently selected satellite. NORAD numbers are always
prefixed with the "#" character. If you wish to change the information (or
if no default is shown), enter the required information followed by ENTER.
For the satellite name, only sufficient letters to unambiguously identify
Program STSORBIT PLUS Satellite Orbit Simulation Page 82
the desired satellite, upper or lower case, are required. For example,
"Alou" would select "Alouette 1". However, note that entering "MIR" could
select "MIRANDA" before it finds "MIR" depending upon the ordering of the
2-line elements within the file. Alternatively, you may enter the NORAD
number for the desired satellite by entering "#" followed by the number;
leading zeroes may be omitted.
Once the information has been entered, STSPLUS will attempt to locate
the data for the requested satellite. If a satellite matching the requested
name is found, the data for that satellite are displayed. Certain non-
essential data are not always included in the 2-line elements and may be
replaced by spaces, indicated by "(n/a)".
Satellite Name: Mir
Satellite NORAD Number: #16609
Elements File: TLE233.TXT
Elements File Record#: 315
(*)
Element Set Number: 201
Elements Epoch: 93206.84472440
25 JUL 1993 @ 20:16:24.188 UTC
Orbit # at Epoch: 42516
Launch Year: 1986
Launch Number: 17
Launch Piece: A
Inclination: 51.6213
RA of Ascend Node: 25.384
Eccentricity: .0004375
Arg of Perigee: 244.4461
Mean Anomaly: 115.6366
Mean Motion: 15.58931226
Acceleration/Drag: .00007676
BSTAR Drag: .000099999
Press ENTER to ACCEPT this satellite, OR
Press any other key to REJECT and continue searching:
(*) This line is normally blank. However, one of the following
messages will appear here if a checksum error is detected in the
element set:
BAD CHECKSUM in line 1 ignored!
BAD CHECKSUM in line 2 ignored!
BAD CHECKSUM in both lines ignored!
In all three cases, STSPLUS will accept the data and attempt to use
it. Be advised, however, that the checksums are included to help
detect data errors that might otherwise yield an incorrect position!
Serious errors may even cause STSPLUS to abort with an error message.
For convenience, the Elements Epoch (the instant at which these
orbital elements were calculated) is shown in two formats: the first format
is that used in the 2-line elements, YYDDD.DDDDDDDD; and the second format
is the same time converted into conventional date and time notation. You
Program STSORBIT PLUS Satellite Orbit Simulation Page 83
may thus see immediately how old the elements are and take this into
account when evaluating the satellite's projected position.
If this is the satellite you wish, press ENTER and the data will be
entered into STSPLUS. If, on the other hand, a different satellite is
desired, press any other key (such as the SPACE BAR) and STSPLUS will
search for another name matching the requested satellite. For example,
there are a number of NAVSTAR Global Positioning Satellites usually
included in the file with official names such as "GPS-0001", "GPS-0002",
"GPS BII-01" and so forth; requesting "GPS" will allow you to cycle through
all the available choices. The file TLEnnn.TXT is an ASCII file; it may be
helpful to view or print the file to see the available satellite names.
Once the satellite has been selected, STSPLUS will require a brief
time to calculate certain required orbital parameters, then will proceed
directly to the display of the ground track. However, if the current
calculated altitude of the satellite is less than 75 nautical miles, the
satellite has probably decayed. STSPLUS will display the following message
before returning to the Main Menu:
Satellite MIR DEB (#22209) indicates a current altitude less than
75 nautical miles and has probably decayed. STSORBIT PLUS can NOT
process the orbital data for this satellite!
Use Function Key F2 from the Main Menu to select another
satellite and verify the satellite NAME and NORAD NUMBER.
Press any key to return to the Main Menu ...
As a point of interest, the 2-line elements for the Space Shuttle
Mission STS-50 used in the example above are as follows:
STS-50
1 22000U 92 34 A 92187.57342677 -.00032668 00000-0 -97874-4 0 380
2 22000 28.4670 275.0700 0007237 340.7929 19.1530 15.91359642 1596
Program STSORBIT PLUS Satellite Orbit Simulation Page 84
F3 Data Output and Pass Prediction Selections
-------------------------------------------------
By popular request, STSPLUS has been enhanced to send selected data
for the current satellite to other equipment via a serial port (COM1 or
COM2), to a file (STSPLUS.LOG), or to the printer (LPT1). Validation of the
serial port output has been accomplished using two computers and a "Null
Modem" cable. Three classes of data may be selected for output: current
position data in three formats, precision Earth-centered inertial ("ECI")
state vectors in four formats, and tabular Line-of-Sight pass predictions
(which are also displayed on the screen).
The precision state vector outputs have been carefully coordinated
with Ken Ernandes so that they may be used as input to his program VEC2TLE,
Version 9331 or later. Using these state vectors and VEC2TLE, the user may
generate 2-line elements at any desired time (including just after the
ascending node) for use with STSPLUS or other satellite tracking programs.
With these programs, the user has a very powerful set of tools which can
be used for a variety of analytical and display purposes. Cross validation
of the two programs during Space Shuttle missions STS-56 and STS-55, as
well as comparison with US Space Command data of comparable epoch,
demonstrated high accuracy and excellent correlation.
Each Data Output function is assigned a "Data Mode" number:
1 = Azimuth, Elevation, Range
2 = Latitude, Longitude, Orbit Altitude
3 = Right Ascension, Declination
4 = Ascending Node Data with State Vector
5 = Precision X-Y-Z State Vector (2-Line Data)
6 = Precision X-Y-Z State Vector (Comma Delimited)
7 = Precision X-Y-X State Vector (Labeled Data)
8 = Doppler Shift Frequency Predictions
9 = Tabular Line-of-Sight Predictions
The current position data and precision state vectors are generated while
the ground track map is displayed; for all Data Modes EXCEPT #4, data
output may be logged continuously, for a specified time (UTC/GMT or local
time), or for a specified time span (UTC/GMT or local time). Data Mode 4
records data ONLY at the Ascending Node, e.g. when the Northbound equator
crossing is detected. The predicted pass data is calculated "off-line"
using UTC/GMT or local time, and is displayed on the screen as well as
being sent to the selected output destination.
Current position data include the UTC date/time and are generated for
local horizon coordinates (altitude and azimuth), geographic coordinates
(geocentric latitude, longitude, and orbital altitude), and topocentric
equatorial coordinates (right ascension and declination calculated for the
user's location). Precision X-Y-Z Earth-centered inertial state vectors
(ECI position and velocity components) are generated as two numeric data
lines, single line comma delimited, and multi-line labeled data. The
details for each data output format are given in following sections.
The precision ECI X-Y-Z state vectors, generated by STSPLUS for the
true equator and equinox of date, have been extensively tested and
validated in conjunction with Ken Ernandes' program VEC2TLE during Space
Shuttle missions STS-56 and STS-55 in early 1993. For example, the
combination of the two programs, STSPLUS and VEC2TLE, may be used to
Program STSORBIT PLUS Satellite Orbit Simulation Page 85
convert data between 2-line and ECI formats with very high accuracy. State
vectors from STSPLUS may be read by VEC2TLE and converted into 2-line
elements, then in turn read again by STSPLUS with essentially exact
conversions. VEC2TLE has also been used during STS-56 and STS-55 to convert
real time state vectors ("M50" or Mean of 1950) supplied courtesy Willie
Musty of Mission Support, Rockwell International, into 2-line elements
equal in accuracy to those generated by US Space Command (and made
available four to eight hours sooner!). See the separate text section
describing VEC2TLE.
Note that the timing accuracy for Data Mode 4 is a fixed at 0.01
seconds, regardless of the time step (X1, X10, or X60) then in effect.
STSPLUS detects the Ascending Node data when the latitude switches from
negative to positive on the Northbound crossing of the Equator. An
iterative process is then used to refine the time to the nearest 0.01
seconds and the data at that time are recorded.
Potential applications for the position data include automatic antenna
pointing systems, off-line high precision plotting, and widespread
distribution of the data within a large facility or via modem. ECI state
vectors may be used in real time to create 2-line elements for a specified
epoch to full precision. Users who develop applications to utilize these
data are invited to contribute their programs and documentation for general
use. Since these are new features for STSPLUS, comments and suggestions are
welcome.
Although STSPLUS retains the capability of performing off-line pass
predictions with TS Kelso's TRAKSTAR or other satellite tracking software,
many users have requested that a similar feature be incorporated directly
into STSPLUS. Pass predictions may only be calculated for satellites having
a mean motion greater than 1.5; this eliminates satellites in near
geosynchronous or higher orbits, but since such satellites don't move much
that does not represent a significant constraint. The satellite's orbit is
examined for 48 hours, starting at the current real or simulated time, with
a sampling interval which ranges from 10 to 60 seconds depending upon the
orbit. Because of this "granularity" in the search algorithm, it is
possible to skip passes whose duration is less than the sampling interval.
Since those brief passes would barely peek above the user's horizon, they
are thus not significant. Pass predictions may be continued in 48 hour
segments until 99 passes have been displayed. Since a typical satellite may
have from about two to seven passes in a 24 hour period, the passes may be
examined for a considerable time into the future.
Predicted pass data are calculated using the current satellite for
Line-of-Sight visibility; that is, when the satellite is in line of sight
to the user's location and without consideration of lighting effects. Since
STSPLUS users are about equally divided between those who track satellites
visually and those who use electronic equipment such as amateur radio, this
method provides data for all users. Passes which occur near local sunrise
or sunset may be tested for lighting constraints and/or ground visibility
by displaying the ground track for the pass or other means. Dates and times
may be displayed in Coordinated Universal Time (UTC/GMT) or in local time.
Note that the date for each pass is given only for AOS (Acquisition of
Signal); it is possible for the pass to span 00:00:00 hours (midnight) for
the time scale in use with a consequent date change during the pass for MAX
VISIBILITY and/or LOS (Loss of Signal).
Prediction calculations may require some time; calculation delays are
noted with the message "calculating ...". Using a processor equipped with a
Program STSORBIT PLUS Satellite Orbit Simulation Page 86
math coprocessor chip, each 48 hour block may require from less than 10
seconds to a minute or more. However, users without math coprocessor chips
will experience significant delays -- minutes or even tens of minutes! The
following table lists typical calculation times for various processors (all
with math coprocessors!) using the Russian MIR Space Station:
286/287 386SX/387SX 486DX
8 MHz 20 MHz 33 MHz
---------------------------------------------------
MIR 60 sec 30 sec 6 sec
The data output feature MUST be enabled with F3 each time STSPLUS is
run; it is NOT automatically restarted when the "/R" (RESUME) command line
option is used.
**********
* NOTE *
**********
Users are reminded that when data output is sent to the file
STSPLUS.LOG, a considerable volume of data may be accumulated
over long periods of time. It is possible to completely fill a
disk with this data! The file should be periodically copied to
other media or deleted to avoid this problem.
Setting Up Position and State Vector Data Output
------------------------------------------------
Data output of position and state vectors ONLY occurs while the
ground track is displayed; no data are generated until the ground track is
actually in progress! The appropriate data are sent to the destination
device at the selected data interval (continuous), at a specified time, or
at the selected data interval over a specified time span covering no more
than 24 hours.
************************
* IMPORTANT REMINDER *
************************
STSPLUS generates Earth-Centered Inertial ("ECI") state vectors
for the true equator and equinox of date. Other software and
various agencies may use different coordinate systems. In
particular, NASA uses the mean equator and equinox of the
Besselian year 1950 ("Mean of 1950", "M50" or "B1950").
Astronomers and other agencies may use the mean equator and
equinox of the Julian year 2000 ("Mean of 2000" or "J2000").
Other agencies, such as the DOD C-Band Radar Network, use a time-
independent coordinate system ("Earth-fixed Greenwich" or "EFG")
for predicted state vectors prior to a launch. Users must take
care that the appropriate coordinate system is used for each
application and/or perform the required conversions.
Program STSORBIT PLUS Satellite Orbit Simulation Page 87
STSPLUS sets up certain initial default parameters for data output and
displays the current parameters each time F3 is pressed, as shown in the
following example:
STSORBIT PLUS Data Output Parameters:
Data Output: STSPLUS.LOG
Data Format: 7 = Precision X-Y-Z State Vector
Data Interval: 60 seconds (continuous)
Data Units: Kilometers, Multi-Line Labeled
Accept Parameters [Y,n,x]:
For Data Modes 8 and 9, the final prompt includes the option to display the
data on the screen:
Accept Parameters [Y,n,s,x]:
To cancel data output and return to the Main Menu, press "X". If the
current parameters are correct, press "Y" (or ENTER) to accept them. If the
parameters are to be changed or if a specified time or time span is
desired, press "N" to be prompted for new parameters. In each case, the
default value which will be used if ENTER is pressed will be shown in
square brackets; if more than one choice is shown, separated by commas, the
first choice will be used if ENTER is pressed. The user must first select
the data output device or destination by pressing the indicated key:
Select Output [F,p,1,2]:
F = File STSPLUS.LOG
P = Printer LPT1:
1 = Serial Port COM1:
2 = Serial Port COM2:
Pressing ENTER or the letter "F" (upper or lower case) will select the FILE
output and the data will be sent to the file STSPLUS.LOG. If the file does
not exist, it will be created; if the file already exists, the data will be
appended to the existing data. Press the letter "P" to direct the data to
the printer on LPT1. Press "1" or "2" to direct the data to one of the two
serial ports.
When a serial port (COM1: or COM2:) is selected, the user next selects
the data rate to be used for communications with the external equipment.
Only the four data rates shown below the prompt are supported. Use the
first character of the desired rate to select it, or press ENTER to use the
data rate shown in the square brackets:
Select DATA RATE [9600]:
(300, 1200, 2400, 9600)
STSPLUS automatically sets the communications parameters to "8,N,1"; these
are fixed and may not be altered. These communications parameters select 8
data bits per transmitted byte, NO parity, and 1 stop bit. Most external
equipment will operate satisfactorily with these parameters.
STSPLUS requires several additional items of information before it can
send data to the external equipment, file or printer. The first is the data
format to be used. Eight different data formats are available. The next
Program STSORBIT PLUS Satellite Orbit Simulation Page 88
prompt lists the formats and shows the current default in square brackets:
Select Data to Output [7]:
1 = Azimuth, Elevation, Range
2 = Latitude, Longitude, Orbit Altitude
3 = Right Ascension, Declination
4 = Ascending Node X-Y-Z State Vector
5 = Precision X-Y-Z State Vector (2-Line Data)
6 = Precision X-Y-Z State Vector (Comma Delimited)
7 = Precision X-Y-X State Vector (Labeled Data)
8 = Doppler Shift Frequency Predictions
9 = Tabular Line-of-Sight Predictions
Press the number key corresponding to the desired Data Mode or press ENTER
to select the choice shown in square brackets. See the Data Mode Formats in
the following sections for specific details on the data included in each
data mode.
For current position and state vector formats except Data Mode 4, the
desired time interval between successive sets of data must be also
selected. (Data Mode 4 records data immediately after the Ascending Node
and does not use the time interval parameter.) Any interval between 1 and
900 seconds may be selected (that is, up to 15 minutes maximum). Add the
letter "T" or "t" if you wish the data to be logged for a specific time or
time span. Note also that this is the DESIRED time interval; if your
computer is too slow to complete its calculations in that time, the
interval will be longer. In other words, STSPLUS will generate the
requested data no more frequently than the interval requested but may take
longer, depending upon what has to be done each time. In response to the
prompt, press ENTER to accept the default value shown in square brackets or
type the desired numerical value (in seconds) followed by ENTER:
Data Interval (secs) [60]:
(Min = 1 sec, Max = 900 secs; Add 'T' for timer)
If a value less than 1 second is entered, 1 second will be substituted; if
a value greater than 900 seconds is entered, 900 will be substituted. If
"T" is entered by itself, the default value shown in square brackets will
be used for the Data Interval.
If "T" is appended to the desired interval or is entered by itself,
STSPLUS requests the Start Time for logging:
Start Time (HH:MM:SS):
(Add 'U' or 'G' for UTC/GMT)
Enter the desired LOCAL Start Time or add the letter "U" or "G" for UTC/GMT
time. STSPLUS will reformat the entered time and add the appropriate time
zone designation, then prompt for the Stop Time:
Start Time (HH:MM:SS): 08:45:00 PDT
Stop Time (HH:MM:SS):
(Press ENTER for Stop Time = Start Time)
Enter the desired Stop Time using the SAME time scale used for Start Time,
or press ENTER to use the Start Time. STSPLUS will reformat the entered
time and add the appropriate time zone designation.
Program STSORBIT PLUS Satellite Orbit Simulation Page 89
Stop Time (HH:MM:SS): 08:50:00 PDT
When Start Time equals Stop Time, only one set of data will be recorded.
Reasonable care is required when setting up these times. If the current
time (real or simulated) is past the Start Time, data will be recorded
immediately. Times may be set to less than 24 hours into the future.
When state vectors are requested (Data Modes 5 through 7), STSPLUS
must also know the desired units of measure, kilometers ("km" or "KM"),
feet ("ft" or "FT"), or nautical miles ("nm" or "NM"):
Data Units [KM,ft,nm]:
(Press 1st letter to select)
Press the first letter of the desired units of measure or press ENTER for
the current default units of measure (shown in capital letters in the
prompt, "KM" in the example above).
STSPLUS now displays the new parameters for approval:
STSORBIT PLUS Data Output Parameters:
Data Output: STSPLUS.LOG
Data Format: 7 = Precision X-Y-Z State Vector
Data Interval: 60 seconds, 08:45:00-08:50:00 PDT
Data Units: Kilometers, Multi-Line Labeled
Accept Parameters [Y,n,x]:
If no Start and Stop Times have been entered, "(continuous)" will appear in
place of the Start and Stop Times.
As before, press "Y" (or ENTER) to accept the parameters and enable
data output, "N" to re-enter the parameters, or "X" to cancel data output
and return to the Main Menu.
Setting Up Tabular Pass Predictions
-----------------------------------
STSPLUS provides two Data Modes, 8 and 9, to generate tabular pass
prediction data. These two Data Modes may also be used simply to display
passes of interest (with the generated data not used or discarded).
8 = Doppler Shift Frequency Predictions
---------------------------------------
Data Mode 8, Doppler Shift Frequency Predictions, displays
upcoming satellite passes over the user's primary location for 48-hour
periods. When a pass is selected and displayed, the map is drawn with
simulated time set to just before the beginning of the pass. As the
pass proceeds, the Doppler Shift information is calculated and sent to
the selected output device.
Program STSORBIT PLUS Satellite Orbit Simulation Page 90
9 = Tabular Line-of-Sight Predictions
-------------------------------------
Data Mode 9, Tabular Line-of-Sight Predictions, displays (and
optionally sends to an output device) data for upcoming satellite
passes over the user's primary location during 48-hour periods. The
user may select a particular pass and cause simulated time to be set
to the middle of the pass. The map is drawn and the user may view the
pass to determine any additional information of interest.
The appropriate data are displayed and sent to the destination device at
the selected data interval (continuous), at a specified time, or over a
specified time span covering no more than 24 hours. The user may simply
view the tabular pass information or he may select a specific pass to view
on the map.
Data Mode 8, the Doppler Shift Frequency Predictions, can be
particularly helpful in preparing for a satellite amateur radio contact by
printing the resulting frequency predictions for use during the contact. In
this data mode, the tabular data are generated as a selected pass is
displayed; the data include date and time, satellite geodetic coordinates
(latitude and longitude), horizon coordinates (elevation and azimuth), and
the frequency differences from the specified uplink and downlink center
frequencies. See the format description for Data Mode 8 below for
additional details. The pass selection list is NOT sent to the output
device in this Data Mode.
STSPLUS sets up certain initial default parameters for tabular pass
predictions and displays the current parameters each time F3 is pressed, as
shown in the following example:
STSORBIT PLUS Data Output Parameters:
Data Output: STSPLUS.LOG
Data Format: 9 = Tabular Line-of-Sight Predictions
(Using PDT for times)
Accept Parameters [Y,n,s,x]:
To cancel data output and generate pass predictions on the screen
ONLY, press "X". If the current parameters are correct, press "Y" (or
ENTER) to accept them or press "S" if output to the screen only is desired.
If the parameters are to be changed or if a specified time is desired,
press "N" to be prompted for new parameters. In each case, the default
value which will be used if ENTER is pressed will be shown in square
brackets; if more than one choice is shown, separated by commas, the first
choice will be used if ENTER is pressed. The user must first select the
data output device or destination by pressing the indicated key:
Select Output [F,p,1,2]:
F = File STSPLUS.LOG
P = Printer LPT1:
1 = Serial Port COM1:
2 = Serial Port COM2:
Pressing ENTER or the letter "F" (upper or lower case) will select the FILE
Program STSORBIT PLUS Satellite Orbit Simulation Page 91
output and the data will be sent to the file STSPLUS.LOG. If the file does
not exist, it will be created; if the file already exists, the data will be
appended to the existing data. Press the letter "P" to direct the data to
the printer on LPT1. Press "1" or "2" to direct the data to one of the two
serial ports.
When a serial port (COM1: or COM2:) is selected, the user next selects
the data rate to be used for communications with the external equipment.
Only the four data rates shown below the prompt are supported. Use the
first character of the desired rate to select it, or press ENTER to use the
data rate shown in the square brackets:
Select DATA RATE [9600]:
(300, 1200, 2400, 9600)
STSPLUS automatically sets the communications parameters to "8,N,1"; these
are fixed and may not be altered. These communications parameters select 8
data bits per transmitted byte, NO parity, and 1 stop bit. Most external
equipment will operate satisfactorily with these parameters.
STSPLUS requires several additional items of information before it can
send data to the external equipment, file or printer. The first is the data
format to be used. Five different data formats are available. The next
prompt lists the formats and shows the current default in square brackets:
Select Data to Output [7]:
1 = Azimuth, Elevation, Range
2 = Latitude, Longitude, Orbit Altitude
3 = Right Ascension, Declination
4 = Ascending Node X-Y-Z State Vector
5 = Precision X-Y-Z State Vector (2-Line Data)
6 = Precision X-Y-Z State Vector (Comma Delimited)
7 = Precision X-Y-X State Vector (Labeled Data)
8 = Doppler Shift Frequency Predictions
9 = Tabular Line-of-Sight Predictions
Press the "8" or "9" number key to select one of the pass predictions or
press ENTER to select the choice shown in square brackets. See the Data
Mode Formats in the following sections for specific details on the data
included in each data mode.
For tabular line-of-sight predictions, STSPLUS must know the time zone
for which data is to be displayed. The choices are UTC/GMT or the LOCAL
time zone:
Use UTC or PDT time [PDT]:
(Use LEFT LETTER of abbreviation to select);
Depending upon the user's choice when the UTCOffset was set, either "UTC"
or "GMT" will be displayed along with the abbreviation for the local time
zone. Use the left-most letter of the desired time zone, or press ENTER to
accept the time zone shown in the square brackets ("[PDT]" in the example).
STSPLUS now returns to the initial parameter display and again asks if
the parameters are correct. As before, press "Y" to proceed with pass
predictions AND sending the data to the specified destination device, "N"
to change parameters, or "X" return to the Main Menu and display the pass
predictions on the screen WITHOUT sending the data to a destination device.
For both pass prediction modes, the data are displayed on the screen
Program STSORBIT PLUS Satellite Orbit Simulation Page 92
as calculated and optionally (for Line-of-Sight Predictions ONLY) sent to
the selected destination device. The following is an edited sample of the
screen display:
---------16609 AOS-------- ---MAX VISIBILITY-- ------LOS------
# UTC Date UTC Time Azm UTC Time Alt Azm UTC Time Azm Duration
1 02/23/1993 03:05:56 171.5 03:09:39 7 125.1 03:13:23 78.4 0:07:27
2 02/23/1993 04:40:12 230.2 04:45:23 70 318.8 04:50:32 44.9 0:10:20
3 02/23/1993 06:17:58 281.3 06:22:02 9 333.9 06:26:07 26.7 0:08:09
4 02/23/1993 07:57:27 328.5 07:59:40 2 354.4 08:01:53 20.3 0:04:26
5 02/23/1993 09:34:31 339.1 09:37:34 4 15.9 09:40:38 52.7 0:06:07
6 02/23/1993 11:09:57 325.6 11:14:46 21 34.8 11:19:35 103.4 0:09:38
7 02/23/1993 12:46:00 302.3 12:50:56 29 229.0 12:55:55 155.6 0:09:55
8 02/24/1993 02:12:22 131.7 02:13:17 0 121.3 02:14:12 110.9 0:01:50
9 02/24/1993 03:43:39 212.0 03:48:44 42 132.6 03:53:48 53.7 0:10:09
10 02/24/1993 05:20:25 263.7 05:25:02 16 327.6 05:29:40 31.9 0:09:15
11 02/24/1993 06:59:36 314.0 07:02:22 3 347.0 07:05:09 20.0 0:05:33
12 02/24/1993 08:37:54 340.4 08:40:18 2 8.7 08:42:43 37.0 0:04:49
13 02/24/1993 10:13:30 331.3 10:17:49 12 28.7 10:22:09 85.8 0:08:39
14 02/24/1993 11:49:11 311.8 11:54:20 79 224.7 11:59:31 137.0 0:10:20
15 02/24/1993 13:26:53 273.2 13:29:57 4 236.4 13:33:01 199.8 0:06:08
Elapsed time = 27 seconds
Repeat for NEXT 48 HOURS or DISPLAY PASS [N,y,pass#]:
The final prompt for Doppler Shift Frequency Predictions is similar:
Repeat for NEXT 48 HOURS or CALCULATE DOPPLER [N,y,pass#]:
The column headings indicate the data displayed. "16609" indicates that the
data is for NORAD number 16609, the MIR Space Station. "AOS" is Acquisition
of Signal or when the satellite rises above the user's true horizon. "MAX
VISIBILITY" is the maximum altitude above the user's true horizon that the
satellite reaches during the pass. "LOS" is Loss of Signal or when the
satellite sets below the user's true horizon. "#" is an arbitrary pass
number for this set of calculations. The format for the data sent to the
destination device is slightly different from that displayed; see the Data
Mode 9 format description below.
For Line-of-Sight Pass Predictions, the user may select either UTC/GMT
or LOCAL date and times for pass predictions. If other than UTC is
selected, substitute the appropriate time zone abbreviation as required.
The date is given only for AOS; since passes may span 00:00:00 hours for
the selected time zone, the actual date for MAX VISIBILITY and/or LOS may
have to be incremented.
Times are calculated to the nearest second, altitudes are rounded to
the nearest degree, and azimuths are rounded to the nearest tenth of a
degree. Azimuth is always calculated in the sense NESW where North = 0
degrees, West = 90 degrees, etc. Note that the degree symbol will appear on
the display for all "Azm" and "Alt" data but has been deleted in the sample
above in order to maintain compatibility with various printers; the actual
display is thus four columns wider than the example above.
Press ENTER while the passes are being calculated to stop the
calculations. When all calculations for the current 48 hour block have been
completed, the time elapsed for the calculations is displayed and the user
is asked if another set of calculations is desired of if a particular pass
should be displayed. Press "N" or ENTER to return to the Main Menu, or
Program STSORBIT PLUS Satellite Orbit Simulation Page 93
press "Y" to perform the next 48 hour block of calculations. The
calculations will be stopped when 99 passes have been listed. Typically,
from four to sixteen passes are listed for each 48 hour block, the number
being related to the characteristics of the current satellite's orbit. If
additional passes beyond that time are desired, set simulated time (F8+F3
from the Main Menu) to the desired start time and repeat the predictions.
To display a particular pass, enter the listed pass number. Passes are
assigned arbitrary numbers from 1 to 99 beginning with the first pass which
occurs during or subsequent to the current real or simulated time. Any pass
number may be selected, from pass #1 to the last listed pass shown on the
screen. (Attempting to enter a pass number larger than the last one shown
will cause the computer to "beep" and the prompt will be repeated.) STSPLUS
will set simulated time to approximately 30 seconds prior to the mid-point
of the selected pass and prepare the display. The pass may then be examined
for details of lighting, ground track, and so forth. STSPLUS displays "VIS"
next to the orbit inclination if a visual sighting may be possible. While
examining the pass, use F6 to PAUSE the display, then use the "+" or "-"
keys to adjust the simulated time forward or backward. The default time
step is one second; press F4 to select a different time step: 1, 10, or 60
seconds. Press ENTER to return to normal operation from the PAUSE mode.
For Doppler Shift Frequency Predictions only, the displayed pass
begins just before AOS (Acquisition of Signal) instead of near the maximum
elevation. Doppler shift frequency data will be sent to the output device
only after AOS is reached and until LOS (Loss of Signal) is reached. The
user may use "fast time" to speed up the operation but there may be some
loss of accuracy. Press ENTER once the pass has been completed to return to
the Main Menu.
Each time predicted passes are requested, the list begins with the
first pass which occurs at or subsequent to the current real or simulated
time. Note that STSPLUS automatically sets simulated time to display a
predicted pass, and that new simulated time remains in effect until the
user returns to the Main Menu, at which point the time is restored to the
real or simulated time in effect BEFORE the pass prediction was displayed.
Repeated use of pass predictions will therefore generally produce the same
list of passes; however, if sufficient time elapses between predictions
that a pass "comes and goes", new pass numbers will be displayed.
Program STSORBIT PLUS Satellite Orbit Simulation Page 94
Data Mode 1: Azimuth/Elevation Data Format
------------------------------------------
1 2 3 4 5
0123456789012345678901234567890123456789012345678901234
-------------------------------------------------------
02/10/1993 13:58:09 20580 -2.472 248.222 1675 [CR/LF]
-----+---- ----+--- --+-- ----+--- ----+--- ---+---
| | | | | |
| | | | | +--- Range
| | | | |
| | | | +----------- Aximuth
| | | |
| | | +--------------------- Elevation
| | |
| | +------------------------------ NORAD #
| |
| +-------------------------------------- UTC Time
|
+------------------------------------------------- UTC Date
UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy
UTC Time: Current time in Universal Coordinated Time, hh:mm:ss
NORAD #: Satellite NORAD Number
Azimuth: Azimuth in degrees to satellite in the sense NESW
Elevation: Elevation to satellite in degrees above true horizon
Range: Range from User Location to Satellite in km
[CR/LF]: Each data line is terminated with a CR and LF in addition to
the 54 printing characters shown, for a total of 56
characters per data line.
Program STSORBIT PLUS Satellite Orbit Simulation Page 95
Data Mode 2: Latitude/Longitude Data Format
-------------------------------------------
1 2 3 4 5
0123456789012345678901234567890123456789012345678901234
-------------------------------------------------------
02/11/1993 13:46:40 20580 -5.182 155.667 593 [CR/LF]
-----+---- ----+--- --+-- ----+--- ----+--- ---+---
| | | | | |
| | | | | +--- Orbit Altitude
| | | | |
| | | | +----------- Longitude
| | | |
| | | +--------------------- Latitude
| | |
| | +------------------------------ NORAD #
| |
| +-------------------------------------- UTC Time
|
+------------------------------------------------- UTC Date
UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy
UTC Time: Current time in Universal Coordinated Time, hh:mm:ss
NORAD #: Satellite NORAD Number
Latitude: Geodetic Latitude in degrees of sub-satellite point
(satellite ground track)
Longitude: Geodetic Longitude in degrees of sub-satellite point
(satellite ground track)
Orbit Alt: Altitude in kilometers of the satellite above the Earth's
surface
[CR/LF]: Each data line is terminated with a CR and LF in addition to
the 54 printing characters shown, for a total of 56
characters per data line.
Program STSORBIT PLUS Satellite Orbit Simulation Page 96
Data Mode 3: Topocentric RA/DEC Data Format
-------------------------------------------
1 2 3 4
01234567890123456789012345678901234567890123456
-----------------------------------------------
02/11/1993 13:47:20 20580 7.111 -25.941 [CR/LF]
-----+---- ----+--- --+-- ----+--- ----+---
| | | | |
| | | | +----------- DEC
| | | |
| | | +--------------------- RA
| | |
| | +------------------------------ NORAD #
| |
| +-------------------------------------- UTC Time
|
+------------------------------------------------- UTC Date
UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy
UTC Time: Current time in Universal Coordinated Time, hh:mm:ss
NORAD #: Satellite NORAD Number
RA: Topocentric Right Ascension in hours
DEC: Topocentric Declination in degrees
[CR/LF]: Each data line is terminated with a CR and LF in addition to
the 46 printing characters shown, for a total of 48
characters per data line.
NOTES:
1. Topocentric coordinates give the right ascension and declination as
seen from the current user's location on the surface of the Earth.
2. Coordinates are equator and equinox of date.
Program STSORBIT PLUS Satellite Orbit Simulation Page 97
Data Mode 4: Ascending Node X-Y-X State Vector
----------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 4
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93206.71622934028
07/25/1993 17:11:22.215 UTC
ECI X: 6083.74442210995 km
Y: 2969.71930867257 km
Z: 0.01043524694 km
Xdot: -2.09290827983 km/sec
Ydot: 4.27922666083 km/sec
Zdot: 6.01892329735 km/sec
Ndot/2 (Drag): 0.00056174000
Nndot/6: 0.00000000000
B-Star: 0.00071196000
ElSet #: 196.00000000000
Rev @ Epoch: 42514.00433526011
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 14
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93206.71622934028
07/25/1993 17:11:22.215 UTC
ECI X: 19959752.12027331000 ft
Y: 9743154.40544174400 ft
Z: 34.23630116129 ft
Xdot: -6866.48346437341 ft/sec
Ydot: 14039.42991197058 ft/sec
Zdot: 19747.08480675116 ft/sec
Ndot/2 (Drag): 0.00056174000
Nndot/6: 0.00000000000
B-Star: 0.00071196000
ElSet #: 196.00000000000
Rev @ Epoch: 42514.00523843931
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 24
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93206.71622934028
07/25/1993 17:11:22.215 UTC
ECI X: 3284.95919120368 nm
Y: 1603.52014507239 nm
Z: 0.00563458372 nm
Xdot: -1.13008006471 nm/sec
Ydot: 2.31059754904 nm/sec
Zdot: 3.24995858388 nm/sec
Ndot/2 (Drag): 0.00056174000
Nndot/6: 0.00000000000
B-Star: 0.00071196000
ElSet #: 196.00000000000
Rev @ Epoch: 42514.00325144509
Program STSORBIT PLUS Satellite Orbit Simulation Page 98
NOTES:
1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered
inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis
is pointing toward the vernal equinox, the Z-Axis is pointing toward
the North Pole, and the Y-Axis is mutually orthogonal to the other
axes in a right-handed axis system. All coordinates are for true
equator and equinox of date.
2. The units of measure for the state vector may be determined by the
tens digit of the Data Mode in the initial header line as well as
being indicated with the data:
4 Kilometers and kilometers per second
14 Feet and feet per second
24 Nautical miles and nautical miles per second
3. One data item is given per line, labeled as shown in the examples. The
data in the first four lines (Satellite Name, Catalog Number, and two
lines of Date/Time) begin in column 25. The remaining numeric data
items begin in column 21 and use a FORTRAN-like format statement
F21.11.
4. The Catalog Number is given first as the NORAD Number ("16609" in the
example) and then as the International Designation ("86017A"). The
International Designation is from 1 to 3 letters. Some 2-line elements
omit the International Designation, in which case that portion will be
blank.
5. Note that the Date/Time is presented on two lines in two different
formats. The first format is the NASA Day-of-Year ("DOY") format,
YYDDD.DDDDDD, since that is the format used by NASA/JSC for X-Y-Z
state vectors for the Space Shuttle, in 2-line elements, and in
program VEC2TLE. In the DOY format, time is counted from midnight
(00:00 UTC) each day. Some calculations may require instead the Julian
Date format which counts time from noon (12:00 UTC) each day. The
Date/Time is also "decoded" and given in the more conventional
"MM/DD/YYYY HH/MM/SS.SSS" format for clarity using Coordinated
Universal Time (UTC/GMT).
6. The ElSet Number is specified in the 2-line elements used to generate
the ground track and is always given as an integer. Note that ElSet
Numbers may not necessarily follow in sequence and that different
sources will use different sequences of ElSet numbers.
7. The Rev Number at Epoch (the orbit number at the time the data is
sampled) is based upon the Rev Number specified in the 2-line elements
used to generate the ground track. The fractional part is calculated
by STSPLUS geometrically from the ascending node. Note that US Space
Command uses a different orbit numbering convention than does NASA for
space shuttle missions; US Space Command usually specifies the first
(partial) orbit number as Rev 0, while NASA specifies that orbit
number as Rev 1. For satellites which have been in orbit for long
periods of time, the Rev Number may be arbitrary.
Program STSORBIT PLUS Satellite Orbit Simulation Page 99
Data Mode 5: Precision X-Y-Z Cartesian State Vector, 2 Data Lines
-----------------------------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 5
20580 93110.043125 4920.98348 4440.02814 -2158.84295
-4.02147461570 5.78870948196 2.74131815428
20580 93110.043171 4904.85124 4463.14112 -2147.85724
-4.04461763461 5.76773962933 2.75148946765
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 15
20580 93110.045081 13656864.66720 17514322.54968 -5452252.42794
-16168.27686974290 15789.75251859515 10248.33566657315
20580 93110.045139 13575822.39276 17593013.13238 -5400930.14914
-16248.48336702945 15686.35334359047 10280.38786725583
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 25
20580 93110.046829 1817.50246 3234.50460 -631.72242
-3.02340746009 2.05326951871 1.82336359537
20580 93110.046991 1774.96638 3262.87575 -606.12299
-3.05304428709 1.99966800523 1.83360328215
NOTES:
1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered
inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis
is pointing toward the vernal equinox, the Z-Axis is pointing toward
the North Pole, and the Y-Axis is mutually orthogonal to the other
axes in a right-handed axis system. All coordinates are for true
equator and equinox of date.
2. The units of measure for the state vector may be determined by the
tens digit of the Data Mode in the initial header line:
5 Kilometers and kilometers per second
15 Feet and feet per second
25 Nautical miles and nautical miles per second
3. The NASA Day-of-Year format is used here for date and time since that
is the format used by JSC for X-Y-Z state vectors and also in 2-line
elements. In the DOY format, time is counted from midnight (00:00 UTC)
each day. Some calculations may require instead the Julian Date format
which counts time from noon (12:00 UTC) each day.
4. Two successive data samples are shown for each data mode.
5. The following FORTRAN-like format statements may be used to read the
two lines of data in this mode for all units of measure:
First Line:
-----------
Catalog #: I5
2X
Date/Time: F15.9
X: F15.5
4X
Program STSORBIT PLUS Satellite Orbit Simulation Page 100
Y: F15.5
4X
Z: F15.5
CR/LF
Second Line:
------------
23X
Xdot: F18.11
1X
Ydot: F18.11
1X
Zdot: F18.11
CR/LF
Program STSORBIT PLUS Satellite Orbit Simulation Page 101
Data Mode 6: Precision X-Y-Z Cartesian State Vector, Comma Delimited
--------------------------------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 6
0,0,20580,93110.0476041667,2982.28779295502,6229.01725815628,-940.796339818487,
-5.85010701911522,3.3199940892324,3.46047048985284
0,0,20580,93110.0476851852,2941.25120957693,6252.07713790904,-916.54588610151,
-5.87454395677527,3.2685046500327,3.46815363454982
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 16
0,1,20580,93110.0482060185,8771281.06140276,20969911.6226162,-2491608.1429704,
-19762.0576284838,9623.02409449012,11524.6952898439
0,1,20580,93110.0482638889,8672341.7437806,21017717.5456987,-2433947.77946384,
-19813.4647395816,9499.28476766938,11539.2506632381
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 26
0,2,20580,93110.0493865741,1103.65585656622,3591.279279101,-214.476932551084,
-3.4057330597861,1.1598790254898,1.9344163566285
0,2,20580,93110.049537037,1059.27271053518,3605.99939807939,-189.308779132495,
-3.42231018081901,1.10471766926502,1.93751948609809
NOTES:
1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered
inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis
is pointing toward the vernal equinox, the Z-Axis is pointing toward
the North Pole, and the Y-Axis is mutually orthogonal to the other
axes in a right-handed axis system. All coordinates are for true
equator and equinox of date.
2. The units of measure for the state vector may be determined by the
tens digit of the Data Mode in the initial header line as well as the
second parameter in the comma delimited data string:
Data Param
Mode #2 Units
-----------------------------------------------------------
6 0 Kilometers and kilometers per second
16 1 Feet and feet per second
26 2 Nautical miles and nautical miles per second
3. The comma delimited data are generated as a single line terminated by
CR/LF. The examples above have been split into two lines for printing
purposes.
4. The data are written in a single data line in the following order,
separated by a comma between items:
Epoch Flag, always zero signifying equator and equinox of date.
Units Flag (see Note 1 above)
Catalog/NORAD number
Date (YYDDD.DDDDDDDD... format)
ECI X
ECI Y
ECI Z
Program STSORBIT PLUS Satellite Orbit Simulation Page 102
ECI Xdot
ECI Ydot
ECI Zdot
5. Line length will vary as a function of the data.
6. Two successive data samples are shown for each data mode.
Program STSORBIT PLUS Satellite Orbit Simulation Page 103
Data Mode 7: Precision X-Y-Z Cartesian State Vector, Labeled Data
-----------------------------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 7
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93192.11956018518
07/11/1993 02:52:10.000 UTC
ECI X: -3441.20195444797 km
Y: -3110.29870646026 km
Z: 4920.32069520120 km
Xdot: 2.90216455238 km/sec
Ydot: -6.74909064951 km/sec
Zdot: -2.23710677970 km/sec
Ndot/2 (Drag): 0.00008567000
Nndot/6: 0.00000000000
B-Star: 0.00011546000
ElSet #: 167.00000000000
Rev @ Epoch: 42286.31052536559
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 17
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93192.12233796297
07/11/1993 02:56:10.000 UTC
ECI X: -8617248.92526347200 ft
Y: -15077459.08108566000 ft
Z: 13806887.09734187000 ft
Xdot: 12614.26230523560 ft/sec
Ydot: -18214.71804776612 ft/sec
Zdot: -12006.04438377176 ft/sec
Ndot/2 (Drag): 0.00008567000
Nndot/6: 0.00000000000
B-Star: 0.00011546000
ElSet #: 167.00000000000
Rev @ Epoch: 42286.35385448637
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 27
Satellite Name: MIR Space Station
Catalog Number: 16609 86 17 A
Epoch Date/Time: 93192.12280092592
07/11/1993 02:56:50.000 UTC
ECI X: -1333.74601094830 nm
Y: -2598.74977950943 nm
Z: 2190.96899536823 nm
Xdot: 2.14691236531 nm/sec
Ydot: -2.86693936350 nm/sec
Zdot: -2.09121400862 nm/sec
Ndot/2 (Drag): 0.00008567000
Nndot/6: 0.00000000000
B-Star: 0.00011546000
ElSet #: 167.00000000000
Rev @ Epoch: 42286.36107600650
Program STSORBIT PLUS Satellite Orbit Simulation Page 104
NOTES:
1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered
inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis
is pointing toward the vernal equinox, the Z-Axis is pointing toward
the North Pole, and the Y-Axis is mutually orthogonal to the other
axes in a right-handed axis system. All coordinates are for true
equator and equinox of date.
2. The units of measure for the state vector may be determined by the
tens digit of the Data Mode in the initial header line as well as
being indicated with the data:
4 Kilometers and kilometers per second
14 Feet and feet per second
24 Nautical miles and nautical miles per second
3. One data item is given per line, labeled as shown in the examples. The
data in the first four lines (Satellite Name, Catalog Number, and two
lines of Date/Time) begin in column 25. The remaining numeric data
items begin in column 21 and use a FORTRAN-like format statement
F21.11.
4. The Catalog Number is given first as the NORAD Number ("16609" in the
example) and then as the International Designation ("86017A"). The
International Designation is from 1 to 3 letters. Some 2-line elements
omit the International Designation, in which case that portion will be
blank.
5. Note that the Date/Time is presented on two lines in two different
formats. The first format is the NASA Day-of-Year ("DOY") format,
YYDDD.DDDDDD, since that is the format used by NASA/JSC for X-Y-Z
state vectors for the Space Shuttle, in 2-line elements, and in
program VEC2TLE. In the DOY format, time is counted from midnight
(00:00 UTC) each day. Some calculations may require instead the Julian
Date format which counts time from noon (12:00 UTC) each day. The
Date/Time is also "decoded" and given in the more conventional
"MM/DD/YYYY HH/MM/SS.SSS" format for clarity using Coordinated
Universal Time (UTC/GMT).
6. The ElSet Number is specified in the 2-line elements used to generate
the ground track and is always given as an integer. Note that ElSet
Numbers may not necessarily follow in sequence and that different
sources will use different sequences of ElSet numbers.
7. The Rev Number at Epoch (the orbit number at the time the data is
sampled) is based upon the Rev Number specified in the 2-line elements
used to generate the ground track. The fractional part is calculated
by STSPLUS geometrically from the ascending node. Note that US Space
Command uses a different orbit numbering convention than does NASA for
space shuttle missions; US Space Command usually specifies the first
(partial) orbit number as Rev 0, while NASA specifies that orbit
number as Rev 1. For satellites which have been in orbit for long
periods of time, the Rev Number may be arbitrary.
Program STSORBIT PLUS Satellite Orbit Simulation Page 105
Data Mode 8: Doppler Shift Predictions
--------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 8
Satellite Name: AO-27
Catalog Number: 22825 93061C
Uplink Center Frequency: 145.85000 MHz
Dnlink Center Frequency: 436.80000 MHz
Freq Diff in Hz
MM/DD TIME Sat Lat Sat Lon Sat Elv Sat Azm Uplink DnLink
------------------------------------------------------------------------
07/31 18:21:00 UTC 56.992 -102.805 1.748 19.947 -3171 9497
07/31 18:22:00 UTC 53.549 -104.703 5.777 22.118 -3135 9388
07/31 18:23:00 UTC 50.085 -106.353 10.523 24.984 -3062 9170
07/31 18:24:00 UTC 46.604 -107.814 16.339 29.016 -2926 8764
07/31 18:25:00 UTC 43.109 -109.129 23.770 35.186 -2673 8005
07/31 18:26:00 UTC 39.603 -110.330 33.417 45.735 -2189 6555
07/31 18:27:00 UTC 36.088 -111.439 44.547 65.985 -1291 3865
07/31 18:28:00 UTC 32.565 -112.475 50.407 101.881 63 -188
07/31 18:29:00 UTC 29.035 -113.452 43.796 136.739 1389 -4161
07/31 18:30:00 UTC 25.501 -114.381 32.707 155.928 2247 -6730
07/31 18:31:00 UTC 21.962 -115.271 23.276 165.962 2707 -8108
07/31 18:32:00 UTC 18.419 -116.131 16.011 171.851 2949 -8832
07/31 18:33:00 UTC 14.873 -116.966 10.302 175.688 3080 -9223
07/31 18:34:00 UTC 11.326 -117.782 5.625 178.391 3150 -9435
07/31 18:35:00 UTC 7.777 -118.584 1.638 180.406 3186 -9543
NOTES:
1. The header information gives the satellite name and catalog number,
the Epoch Date/Time of the TLEs, and the center frequencies for the
Uplink and the Downlink (usually in units of MHz) as read from file
STSPLUS.FRQ (if present) or the default value of 100 MHz.
2. One data line is generated for each time step. For the date, only the
month and day ("MM/DD") are given in order to accommodate line length
restrictions. The time is given in Coordinated Universal Time (UTC).
3. The satellite geodetic coordinates, latitude and longitude, are given
in degrees. Negative latitude is South, negative longitude is West.
4. The satellite horizon coordinates, elevation and azimuth, are given in
degrees and the sense is NESW, North = 0, East = 90, etc.
5. The doppler shift calculations are shown as the frequency difference
(in Hz) from the corresponding center frequency (in MHz, shown in the
header) at 60 second intervals throughout the pass.
Program STSORBIT PLUS Satellite Orbit Simulation Page 106
Data Mode 9: Pass Predictions
-----------------------------
--------#20580 AOS-------- --MAX VISIBILITY-- ------LOS------
# UTC Date UTC Time Azm UTC Time Alt Azm UTC Time Azm Duration
1 02/27/1993 03:58:09 205.1 04:03:00 9 157.9 04:07:52 110.8 0:09:43
-+ ---------+--------- --+-- ----+--- -+ --+-- ----+--- --+-- ----+---
| | | | | | | | |
Pass # | | | | | | | |
| | | | | | | |
+----------+ | | | | | | |
| | | | | | | |
| +---------------------+ | | | | | |
| | | | | | | |
| +----- AOS Azimuth (degrees) | | | | | |
| | | | | | |
+-------- AOS Date/Time | | | | | |
(mm/dd/yyyy hh:mm:ss) | | | | | |
| | | | | |
+---------------------------------+ | | | | |
| | | | | |
| +-------------------------------------+ | | | |
| | | | | |
| | +--------------------------------------+ | | |
| | | | | |
| | +-- MAX Azimuth (degrees) | | |
| | | | |
| +----- MAX Altitude (degrees) | | |
| | | |
+-------- MAX Time (hh:mm:ss) | | |
| | |
+-----------------------------------------------------+ | |
| | |
| +----------------------------------------------------------+ |
| | |
| +----- LOS Azimuth (degrees) |
| |
+-------- LOS Time (hh:mm:ss) |
|
Total Pass Duration (hh:mm:ss) --+
NOTES:
1. When the Data Output mode is set up for pass predictions, dates and
times for pass predictions may be selected for UTC/GMT or local time
and the selected time zone abbreviation and time scale will be used.
Substitute the appropriate abbreviation for "UTC" as required if other
than UTC has been selected. When UTC or GMT is selected, the Data Mode
will be given as "9"; when local time is selected, the Data Mode will
be given as "19".
2. The Pass # is an arbitrary number assigned by STSPLUS during the pass
calculations and is a function of the real or simulated time at which
the calculations are performed. If the real or simulated time is
changed, the pass numbers may change and different passes may be
Program STSORBIT PLUS Satellite Orbit Simulation Page 107
shown.
3. The satellite NORAD number is included in the heading, "20580" in the
sample above.
4. The Date (UTC/GMT or local) is given only for AOS. Since a pass may
span 00:00:00 hours, the date for MAX VISIBILITY and/or LOS may have
to be incremented from that shown for AOS.
5. All azimuths ("Azm") have been rounded to the nearest 0.1 degree; the
MAX VISIBILITY altitude ("Alt") has been rounded to the nearest
degree.
Program STSORBIT PLUS Satellite Orbit Simulation Page 108
F4 Calculate Satellite Positions with TRAKSTAR
--------------------------------------------------
Tabular predictions for the currently selected satellite may be made
by using TRAKSTAR by Dr. TS Kelso. STSPLUS has been arranged to operate
seamlessly with TRAKSTAR by simply pressing Function Key F4 from the Main
Menu. All data required by TRAKSTAR is automatically supplied by STSPLUS.
See the section above "Predicting Satellite Passes with TRAKSTAR" and the
TRAKSTAR documentation for full information.
F5 Set Launch Time and Date
-------------------------------
Orbital data for the satellite must be loaded using the F2 command on
the Main Menu before the launch date and time may be set or changed. Once
saved in file STSPLUS.LTD, the launch date and time will be automatically
read from that file each time the satellite is selected (see below).
********************
* IMPORTANT NOTE *
********************
LAUNCH TIME AND DATE MUST EITHER BE INCLUDED IN FILE STSPLUS.LTD
OR BE MANUALLY ENTERED FOR EACH SATELLITE OR MISSION SINCE THAT
INFORMATION IS NOT INCLUDED IN 2-LINE ELEMENTS.
Launch date and time are most important for manned missions such as
the Space Shuttle since the mission timeline is reckoned using Mission
Elapsed Time. However, MET may be used whenever actual launch date and time
are known. The only requirement is that 2-line orbital elements must be
available for the satellite. Since launch date and time are NOT included in
the 2-line orbital elements, this means that you obtain the launch date and
launch time independently and manually enter that data.
Pressing F5 to enter launch date and time begins with the prompt:
Enter Launch Time (HH:MM:SS):
[Add 'U'or 'G' for UTC/GMT]
Enter the time in the format shown using 24-hour notation. Add the letter
"U" to signify UTC (Coordinated Universal Time) or the letter "G" to
signify GMT (Greenwich Mean Time, essentially identical to UTC for the
purposes of this program). Use no suffix for local time; it will be
internally converted to UTC/GMT. If you enter "U" or "G", the abbreviation
used in the menus will be set to "UTC" or "GMT" respectively. One or two
digit numbers may be used as required. [The comma is also acceptable as a
separator in place of the colon.] You may omit seconds [or minutes and
seconds] if desired. For example, an entry of "16" will be entered as
16:00:00 or 4:00 PM. Press ENTER to leave the entry unchanged.
Enter Launch Date (MM/DD/YYYY):
[Enter '*' to clear LAUNCH DATE]
Enter the date in the format shown. Note that if you requested UTC or GMT
when entering the time, the date is interpreted as the UTC/GMT date. The
Program STSORBIT PLUS Satellite Orbit Simulation Page 109
full four digit year may be used OR two digits as in "92". Be sure to use
the SLASH "/" rather than the MINUS "-" as the separator; STSPLUS's
internal date algorithms will interpret the minus sign as just that and
some rather strange dates can result! You may also use relative dates: -1
will use the prior day, +2 will use two days hence, and so forth. Press
ENTER to leave the date unchanged. Press "*" (followed by ENTER) to clear
the launch date and time; this does NOT remove it from file STSPLUS.LTD.
Press ENTER to accept, SPACE BAR to repeat:
When all data have been entered, the program pauses for your approval. If
all data are correct, press ENTER. Press the SPACE BAR to start over. You
are next asked if you wish to save this data:
Add/Update this data in file STSPLUS.LTD [Y,n]:
Press "Y", "y" or ENTER to add or update the data in file STSPLUS.LTD (see
below). Press "N" or "n" to use the data but not add or update it in file
STSPLUS.LTD. Adding or updating the data to file STSPLUS.LTD makes sure
that the launch date and time data will be available the next time this
particular satellite is selected.
Using File STSPLUS.LTD for Launch Date & Time
---------------------------------------------
An alternative and automatic method to set launch date and time is to
use file STSPLUS.LTD. This file contains the NORAD number and launch date
and time (UTC Julian date) for selected satellites. A sample entry appears
as:
22194,2448918.21503472,0
--+-- -------+-------- +
| | |
| | +--- (Reserved, must be present)
| |
| +------------- Launch Date (UTC Julian date)
|
+------------------------ NORAD Number
The Sample above shows the data for Space Shuttle mission STS-52 (NORAD
#22194) and corresponds to a launch date and time of 22 OCT 1992 @ 17:09:39
UTC. The file is in standard ASCII format and may be edited with any
standard editor; word processor users use the "non-document" mode. Use care
when manually editing the file as STSPLUS performs NO ERROR CHECKING!
Estimated 2-line orbital elements are usually available prior to a
Space Shuttle launch, and actual 2-line orbital elements within about 8 to
12 hours after a launch. Note, however, that the NORAD number is not
assigned until actual launch and a "dummy" NORAD number is used for
estimated pre-launch elements; for example, "00052" for STS-52. Once the
launch has taken place, the permanent NORAD number is assigned. This change
in NORAD number will require either that file STSPLUS.LTD be edited OR that
a new entry be made. Note that there are still a few satellites around with
low NORAD numbers!
Program STSORBIT PLUS Satellite Orbit Simulation Page 110
If file STSPLUS.LTD is present and if the selected satellite is found,
the launch time and date will be set and Mission Elapsed Time (MET) will be
used automatically; otherwise, T+Epoch (T+E) will be used. When MET is
displayed, it may be changed to T+E by pressing F6 from the Main Menu
(below) or F5 while the map is displayed.
File STSPLUS.LTD is read each time a new satellite is selected using
F2 from the Main Menu. If file STSPLUS.LTD is NOT present, the launch date
and time will be saved in file STSPLUS.INI and must be MANUALLY MAINTAINED
as in versions prior to 9245! If you wish to use the old method, rename or
delete file STSPLUS.LTD.
F6 Set/Read/Save TDRS and Real Time Satellites
--------------------------------------------------
STSPLUS is able to display up to 32 additional TDRS (or other
geosynchronous/geostationary) or Real Time satellites. The first menu
selection allows the user to select the desired satellite for each of the
sixteen available "slots" as well as abbreviation, mode, and icon/label
color. Note that these features are enabled and disabled using F10+F3+F2
from the Main Menu. The following menu is displayed:
TDRS and Real Time Satellite Maintenance Menu
F1 Display/Modify satellite assignments
F2 Save SCF Satellite Configuration File
F3 Read SCF Satellite Configuration File
F4 Select new PRIMARY SATELLITE
F5 Select new TARGET SATELLITE
F6 Clear Static and Real Time Satellites
Press function key for desired choice or ENTER for Main Menu:
Press ENTER to return to the Main Menu, or press the desired function key
to select the indicated function.
Before the current position of each satellite can be calculated, 2-
line elements must be read or updated using F2 from the Main Menu. After
this has been performed once, the position will be calculated based upon
those 2-line elements. The user is reminded that the 2-line elements should
be updated periodically so that the calculated position accurately reflects
the actual position.
NOTE: Users of prior versions of STSPLUS will note that Function Key F6
has been reassigned for its present function. Switching between
MET and T+Epoch may now be accomplished ONLY by pressing F5 while
the ground track is displayed.
F1 Display/Modify Satellite Assignments
----------------------------------------
This menu selection displays the current TDRS and Real Time Satellite
assignments and option selections as a table:
Program STSORBIT PLUS Satellite Orbit Simulation Page 111
--------------------------------------------------------------------------
TDRS and Real Time Satellite Setup
Sat# NORAD# Abbr Mode Color Size Label Vis Color Chart
1 19883 TDRE Static 10 o 3 ON
2 21639 TDRW Static 10 o 3 ON 1 = XXXXX
3 22314 TDR5 Static 2 o 3 ON OFF 2 = XXXXX
4 19548 TDR2 Static 2 o 3 ON OFF 3 = XXXXX
5 13969 TDR1 Static 2 o 3 ON OFF 4 = XXXXX
6 16609 MIR Primary 12 o ON ON 5 = XXXXX
7 21701 UARS Real Time 13 o ON OFF 6 = XXXXX
8 20580 HST Real Time 14 o ON OFF 7 = XXXXX
9 20638 ROSAT Real Time 13 o ON OFF 8 = XXXXX
10 22076 TOPEX OFF 13 o ON OFF 9 = XXXXX
11 0 (not used) 10 = XXXXX
12 0 (not used) 11 = XXXXX
13 0 (not used) 12 = XXXXX
14 0 (not used) 13 = XXXXX
15 0 (not used) 14 = XXXXX
16 0 (not used) 15 = XXXXX
Enter Satellite # to edit or press ENTER when done:
(The maximum Satellite # available is 32)
--------------------------------------------------------------------------
NOTE: The first two satellite slots, #1 and #2, are reserved for the
standard TDRS East and TDRS West satellites, currently NORAD
Numbers 19833 and 21639. Instead of conventional circles of
visibility, these two satellites generate commumications coverage
circles. Assigning different satellites, especially satellites
which are not geostationary, may produce unpredictable results.
The Satellite Setup table headings indicate:
Sat# Satellite Assignment Number, 1 to 32. If an asterisk ("*")
appears to the right of the number, the epoch (date) of the
associated orbital elements is more than 10 days (Real Time)
or 60 days (Static) old as in this example:
8* 22920 ARRAY Real Time 14 o ON OFF
and the following caution note will appear at the bottom of
the display:
* 2-Line Elements more than 10 (Real Time) or 60 (Static)
days old!
The caution note has no effect on orbital caculations and is
simply a reminder that the orbital elements may be out of
date and may or may not be valid. Use F2 from the Main Menu
with "&" as the satellite name to update TLEs from a current
data file.
NORAD# The NORAD Number of the assigned satellite, or "0" if no
satellite is assigned to this slot.
Program STSORBIT PLUS Satellite Orbit Simulation Page 112
Abbr The five character abbreviation assigned to this satellite.
Use only letters and numbers; the common satellite name or
NORAD Number are the recommended choices. This abbreviation
will be used as a label on the map if the Label is ON. May
be left blank.
Mode Five mode classifications are available:
Primary Primary satellite selected for full
tracking, selected using F2 or F6+F4
(below). The primary satellite may not
be present in the satellite list.
Static Geosynchronous or geostationary
satellites (including TDRS). Plotted
when map is drawn and NOT updated.
Real Time Satellites tracked dynamically; updated
every second (386/387 or higher), every
ten seconds (286 or no coprocessor).
OFF The satellite is included in the data
but is not plotted. Used to temporarily
disable satellite slots.
(not used) Unassigned satellite slot(s).
Color A number selected from the Color Chart at the right which
indicates the color to be used to display the satellite icon
and label (if enabled). Each "XXXXX" in the Color Chart
appears on color monitors as a bar of the corresponding
color. The "o" character to the right of the number is
displayed as a small diamond in the selected color.
Size For Static satellites only, selects the relative size of the
icon used to represent the satellite. Values may range from
3 to 6. This column is blank for Real Time satellites since
the icon size is fixed for these satellites.
Label May be set to "ON" or "OFF" to indicate if the satellite
abbreviation is to be displayed. The label color will be the
same as that selected for the satellite.
Vis May be set to "ON" or "OFF" to indicate if the satellite
circle of visibility is to be drawn. The circle of
visibility is drawn only for Static satellite on normal maps
but is drawn for all satellites on Motion maps.
Color The color chart displays the 15 available icon and label
Chart colors (BLACK is omitted). When a monochrone display is used
and the "/M" command line option is specified, two levels of
gray will normally be displayed instead of colors. Each
color is assigned a standard color number which is used for
all data entries.
Program STSORBIT PLUS Satellite Orbit Simulation Page 113
As indicated by the prompt, simply press ENTER if all data in the
Satellite Setup is correct. You will return to the F6 menu above. If you
wish to add a satellite or change the selections for an existing satellite,
enter the satellite slot number (Sat# in the left column of the table). The
following prompts will be displayed in turn:
Enter NORAD Number:
(Enter 0 to clear the satellite entry)
STSPLUS expects the NORAD number for the desired satellite. This number
will be used to "capture" the 2-line elements when this satellite is
subsequently displayed.
Enter Satellite Abbreviation:
Enter any desired abbreviation, 5 characters or less, or the NORAD number.
Use only letters, numbers, and the period ("."), dash ("-"), and comma
(",") with no leading spaces. The Satellite Abbreviation is used as the
satellite label on the map display (see below) and may be left blank if
no label is desired.
Enter Mode (0=STATIC, 1=REAL TIME, 2=OFF):
Enter "0", "1", or "2". STATIC satellites are drawn each time the map is
redrawn on the screen. REAL TIME satellites are updated every 1 or 10
seconds (depending upon the processor/coprocessor present) or as often as
the processor can complete the required calculations. Satellites set to OFF
and not processed but their data is retained so that they may be returned
to STATIC or REAL TIME subsequently.
Enter satellite color (1 to 15):
Enter the number for the desired color, as shown on the Color Chart at the
right of the screen. An illegal color number will default to YELLOW.
Display satellite Label (0=NO, 1=YES):
Enter "0" or "1". The label will be displayed directly below the satellite
icon in the same color as that selected for the icon in the preceeding
step. For Real Time satellites, the label is only drawn when the map is
redrawn and remains stationary EXCEPT when using the Motion Map (in which
case it follows with the icon).
Display Cir of Visibility (0=NO, 1=YES):
Enter "0" or "1". The circle of visibility is drawn (when enabled) for all
Static satellites, and also for all Real Time satellites when using the
Motion Map.
When a new satellite is entered, a double asterisk ("**") will appear
at the right for that satellite slot. This is to remind the user to display
the ground track for that satellite so that 2-line elements may be stored
in the TLE memory associated with that slot. The following message will
also appear below the chart:
Program STSORBIT PLUS Satellite Orbit Simulation Page 114
** Update TLEs (F2+'&') or display ground track for this satellite!
When STSPLUS adds a new Secondary Satellite, a skeletal 2-line element set
(TLE) is saved which includes only the NORAD number. Before the satellite
can be tracked, real TLEs must be present. This may be accomplished by
updating the TLEs using F2 from the Main Menu and selecting AUTO UPDATE
(satellite name entered is "&"). Alternatively, the satellite ground track
may be displayed; to display the ground track, press F2 from the Main Menu,
select the file of 2-line elements which includes the satellite in
question, and enter the NORAD Number ("#nnnnn", where "nnnnn" is the NORAD
Number). In either case, the 2-line elements will be saved for future use.
Although 2-line elements are saved for all TDRS and Real Time
satellites, the user is reminded that these elements have a limited
lifetime. That lifetime varies considerably from satellite to satellite.
For geosynchronous satellites, 4 to 8 weeks is probably reasonable; for
other active satellites, 1 to 2 weeks should be an upper limit before new
elements are used. Use F2 from the Main Menu and enter the satellite name
as "&" to scan through the 2-line elements file and update all elements
which are more recent than those now saved.
F2 Save SCF Satellite Configuration File
-----------------------------------------
Users may wish to switch among several sets of TDRS and Real Time
satellites from time to time. Since it can be tedious to re-enter all the
information repeatedly, STSPLUS can save and read Satellite Configuration
Files, identified by the filetype .SCF. All parameters are saved and
restored, exactly as if entered at the time. The current satellite
configuration is automatically saved in file STSPLUS.INI each time the
program is exited and is restored when the program is restarted. The
following prompt is displayed:
Save SCF Satellite Configuration File
Enter SCF FILENAME, ENTER to quit:
Current .SCF files are:
STANDARD.SCF
STSPLUS.SCF
STSPLUS displays a list of available SCF files, up to a maximum of 90
files. Press ENTER to cancel the operation. Type the desired filename
with or without the .SCF filetype; STSPLUS automatically appends the
may be no longer than 8 characters.
If the file already exists, STSPLUS will display a warning message:
File STANDARD.SCF already exists! Overwrite [y/N]:
where "STANDARD.SCF" will be the requested file including the .SCF
filetype. Press "Y" or "y" to allow the existing file to be overwritten;
press any other key to cancel the write operation, and then press ENTER to
resume program operation. If the file does not exist, it will be created.
Do not use filename STSPLUS since a sample file by that name is included
with the distribution package (unless you wish to overwrite the supplied
Program STSORBIT PLUS Satellite Orbit Simulation Page 115
file).
F3 Read SCF Satellite Configuration File
-----------------------------------------
See the comments above for saving SCF files. The following prompt is
displayed:
Read SCF Satellite Configuration File
Enter SCF FILENAME, ENTER to quit:
Current .SCF files are:
STANDARD.SCF
STSPLUS.SCF
STSPLUS displays a list of available SCF files, up to a maximum of 90
files. Press ENTER to cancel the operation. Type the desired filename
with or without the .SCF filetype; STSPLUS automatically appends the
may be no longer than 8 characters. If the file does not exist, an error
message will be displayed.
F4 Select New PRIMARY Satellite
--------------------------------
This function allows the user to select a new Primary Satellite, the
satellite for which the data block is calculated, from the list of
Secondary Satellites. The current list of Secondary Satellites is first
displayed:
-------------------------------------------------------
TDRS and Real Time Satellite Setup
Sat# NORAD# Abbr Mode Color Size Label Vis
1 19883 TDRE Static 10 o 3 ON
2 21639 TDRW Static 10 o 3 ON
3 22314 TDR5 Static 2 o 3 ON OFF
4 19548 TDR2 Static 2 o 3 ON OFF
5 13969 TDR1 Static 2 o 3 ON OFF
6 16609 MIR Real Time 12 o ON ON
7 21701 UARS Primary 13 o ON ON
8 22920 ARRAY Real Time 14 o ON OFF
9 20638 ROSAT Real Time 13 o ON ON
10 22076 TOPEX Real Time 13 o ON ON
11 21225 GRO Real Time 13 o ON ON
12 21987 EUVE Real Time 13 o ON ON
13 20580 HST Real Time 14 o ON OFF
14 0 (not used)
15 0 (not used)
16 0 (not used)
Enter New PRIMARY Satellite # or press ENTER to accept:
Program STSORBIT PLUS Satellite Orbit Simulation Page 116
-------------------------------------------------------
Select the satellite which is to be the new Primary Satellite by entering
its Sat# at the prompt, or press ENTER to cancel. Do NOT select a satellite
which displays "**" at the right; valid 2-Line Elements are not available
for that satellite! If "6" is entered for the example shown, the current 2-
Line Elements for MIR will be displayed for approval:
2-Line Elements for new PRIMARY satellite:
MIR
1 16609U 86017A 93351.25309831 .00007289 00000-0 97866-4 0 331
2 16609 51.6188 19.7769 0005725 99.5487 260.6154 15.59089672447666
Accept this Primary Satellite [Y/n]:
Review the 2-Line Elements to be sure that valid elements are present and
that they are for the desired satellite. Press "Y" (or ENTER) to accept the
data shown as the new Primary Satellite, or press any other key to cancel.
F5 Select New TARGET Satellite
-------------------------------
This function allows the user to select a new Target Satellite, the
satellite for which the Relative Range and Velocity may be calculated, from
the list of Secondary Satellites. The current list of Secondary Satellites
is first displayed:
----------------------------------------------------------------------
TDRS and Real Time Satellite Setup
Sat# NORAD# Abbr Mode Color Size Label Vis
1 19883 TDRE Static 10 o 3 ON
2 21639 TDRW Static 10 o 3 ON
3 22314 TDR5 Static 2 o 3 ON OFF
4 19548 TDR2 Static 2 o 3 ON OFF
5 13969 TDR1 Static 2 o 3 ON OFF
6 16609 MIR Real Time 12 o ON ON
7 21701 UARS Real Time 13 o ON ON
8 22920 ARRAY Real Time 14 o ON OFF
9 20638 ROSAT Real Time 13 o ON ON
10 22076 TOPEX Real Time 13 o ON ON
11 21225 GRO Real Time 13 o ON ON
12 21987 EUVE Real Time 13 o ON ON
13 20580 HST Target 14 o ON OFF
14 22917 STS61 Primary 14 o ON OFF
15 0 (not used)
16 0 (not used)
Enter New TARGET Satellite #, '0' to cancel, or press ENTER to accept:
----------------------------------------------------------------------
Select the satellite which is to be the new Target Satellite by entering
its Sat# at the prompt, enter the digit zero ("0") to cancel the current
Program STSORBIT PLUS Satellite Orbit Simulation Page 117
Target Satellite, or press ENTER to cancel and leave the current selection
unchanged. Do NOT select a satellite which displays "**" at the right;
valid 2-Line Elements are not available for that satellite!
If "6" is entered for the example shown, the Target Satellite will be
changed from #20580 (HST) to #16609 (MIR) and the current 2-Line Elements
for MIR will be displayed for approval:
2-Line Elements for new TARGET satellite:
MIR
1 16609U 86017A 93351.25309831 .00007289 00000-0 97866-4 0 331
2 16609 51.6188 19.7769 0005725 99.5487 260.6154 15.59089672447666
Accept this TARGET Satellite [Y/n]:
Review the 2-Line Elements to be sure that valid elements are present and
that they are for the desired satellite. Press "Y" (or ENTER) to accept the
new Target Satellite, or press any other key to cancel. If MIR is
accepted, it will then be used as the Target Satellite and Relative Range
and Relative Velocity with respect to the Primary Satellite (STS-61 in the
example) may be displayed using F10+F4 from the Main Menu OR by pressing
F10 while the map is displayed.
F6 Clear Static and Real Time Satellites
-----------------------------------------
Use this function to clear selected static and/or real time
satellites with slot numbers 3 through 32. STSPLUS asks the user to enter
the first and last slot to clear, and to confirm the operation to avoid
accidental clearing.
NOTE: Slots 1 and 2 are reserved for TDRS satellites and should ALWAYS
contain TDRS or similar geosynchronous satellites. The program may perform
unpredictably if these slots are cleared or have other types of satellites.
F7 Set FILENAMES and PATHS
------------------------------
Function Key F7 allows the user to select the paths and/or filenames
for the various files that STSPLUS uses to select satellites, tracking
stations, and other features:
Select path or filename to set, press ENTER when done:
F1 Set 2-LINE ELEMENTS path: [I:\TLE\]
F2 Set TRACKING STATION filename: [STSPLUS.TRK]
F3 Set MAP DATABASE FILES path: [D:\MAPDATA\]
F4 Set FEATURES LABEL filename: [STSPLUS.LOC]
F5 Set TRAKSTAR path: [D:\STSPLUS\]
F6 Set CITYFILE filename: [STSPLUS.CTY]
Enter selection or ENTER:
Press the indicated function key for the item you wish to change. The
Program STSORBIT PLUS Satellite Orbit Simulation Page 118
current path or filename is shown in square brackets for each selection.
Press ENTER to leave a path or filename unchanged. The following is a
typical prompt for filename:
Enter TRACKING STATION filename: _
(Press ENTER to leave unchanged)
For filenames, enter the full filename including filetype. A drive and
directory may also be included if desired. If no filetype is entered,
STSPLUS will automatically supply ".TRK" for tracking station files, and
".LOC" for features label files. If the desired file has no filetype,
include the period in the filename entered (e.g. "STATION.") to prevent the
automatic addition of a filetype.
For the path selections, enter the desired drive and subdirectory. The
trailing backslash will automatically be added if it is omitted. If the
path cannot be found, an error message will be displayed and the path will
default to the current drive and directory. For best performance, use a RAM
disk for Map Database Files; see the section "Using a RAM Disk" for further
information.
After each entry, the Path and Filenames Menu is again displayed with
the current selections. Press ENTER when done to return to the STSPLUS Main
Menu.
F8 Set Program TIME and DATE
--------------------------------
This menu provides a number of time and date functions for use
with STSPLUS. The program clock may be set to real or simulated time
using several methods, current clock corrections applied by program
RIGHTIME may be displayed, and the UTC OFFSET and DAYLIGHT Flag may be
adjusted.
It is often convenient to set the TIME and DATE within STSPLUS to
something other than the current system time and date, or to return to the
current system time and date if the program time and date have been
changed. Press F8 to go to the TIME and DATE Menu:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
ACTUAL SYSTEM DATE AND TIME SHOWN ABOVE
(Assisted by RIGHTIME)
F1 Restore SYSTEM date and time (use "real time")
F2 Set DOS SYSTEM CLOCK using calendar date and time
F3 Set SIMULATED date and time using calendar date and time
F4 Set SIMULATED date and time using Mission Elapsed Time
F9 Display Current RIGHTIME Corrections
Program STSORBIT PLUS Satellite Orbit Simulation Page 119
F10 Set UTC OFFSET and DAYLIGHT Flag
ENTER Return to MAIN MENU
Select desired function:
The Date and Time Menu, shown above, displays the available time
setting functions along with the actual system date and time as determined
by the DOS software clock in your computer (even if simulated time is in
effect). If program RIGHTIME Version 2.5+ is currently enabled, the message
"(Assisted by RIGHTIME)" will also appear. Both your local date and time,
"PDT" or Pacific Daylight Time in the example, and "UTC" (Coordinated
Universal Time) date and time are displayed. If times have been set using
the letter "G", the abbreviation at the right will be "GMT" (Greenwich Mean
Time).
Press ENTER to return to the Main Menu with the date and time as
displayed on the screen (Current or Simulated).
If you wish to execute STSPLUS in "real time", cancelling any
simulated time that may be in effect, use the F1 command. This will restore
the time and date used for the tracking display to that shown at the top of
the menu. If the actual system date or time displayed is incorrect, use
program TIMESET (if available) or the F2 command to correctly set your
system clock.
Some organizations, NASA for example, continue to use the wording
"Greenwich Mean Time" or "GMT" for what is now usually referred to as
"Coordinated Universal Time" or "UTC" (and sometimes, depending upon the
application, as "UT", "UT1" or "UT2"). STSPLUS uses Coordinated Universal
Time or "UTC", the time used for civil timekeeping and broadcast by radio
stations such as WWV and the BBC. Although technically these different time
standards are not exactly the same, the difference is only a maximum of 0.9
seconds and the program treats them all as identical. STSPLUS defaults to
the abbreviation "UTC" but if you prefer to use "GMT", enter any simulated
time using F3 and include the letter "G" (upper or lower case) at the end.
The time abbreviation at the top of the screen will change from "UTC" to
"GMT" and will continue using that abbreviation until a time is entered
suffixed with "U".
Times are always entered as "HH:MM:SS" where HH is HOURS, MM is
MINUTES, and SS is SECONDS. The time entry format is very flexible. Leading
zeroes are not required. The comma (",") may be used in place of the colon
(":") as a separator if desired. SECONDS or MINUTES and SECONDS may be
omitted if desired. Time entries are assumed to be local time; to enter UTC
or GMT times, add the letter "U" or "G" (upper or lower case) respectively
following the entry. For example, the following are valid time entries:
Entry Interpreted as
------ --------------------------
12 12:00:00 (LOCAL TIME ZONE)
13,1 13:01:00 (LOCAL TIME ZONE)
4:1:15 04:01:15 (LOCAL TIME ZONE)
1,1,1 01:01:01 (LOCAL TIME ZONE)
13,45U 13:45:00 UTC
1:20g 01:20:00 GMT
Dates may be entered as "MM/DD/YYYY" or "MM/DD/YY" (US style) or as
Program STSORBIT PLUS Satellite Orbit Simulation Page 120
"DD.MM.YYYY" or "DD.MM.YY" (European style) where MM is MONTHS (as a number
from 1 to 12), DD is DAYS, and YYYY is the full four-digit YEAR or YY is
the last two digits of the YEAR. Except for the two digit year option, the
full date must always be entered; leading zeroes are not required. The
delimiter used ("/" or ".") determines the method of interpretation:
Entry Interpreted as
--------- --------------
12/8/94 12 AUG 1994
12/8/1994 12 AUG 1994
8.12.94 12 AUG 1994
8.12.1994 12 AUG 1994
The date entered is assumed to be for the same time zone as the time
entered. If local time is entered, the date will be treated as the local
date; if UTC (or GMT) time is entered, the date will be treated as the
UTC/GMT date.
After a time or date entry has been accepted (after you press the
ENTER key), STSPLUS reformats the entry to its standard format, clears the
characters you entered, and replaces them by the standard format in both
local and UTC/GMT time zones. This provides a double check that the program
has interpreted your entry as you wished.
F1 Restore System Date and Time
-----------------------------------
Press F1 to restore the program date and time to the system date and
time. This command reads the DOS clock and restores the program to "real
time" operation. If the program date and time have not been changed with
the F3 or F4 commands, this command will have no effect.
F2 Set DOS System Clock
---------------------------
Press F2 to set the DOS system clock. Use this command if you wish to
change the actual date and time on your system. Note that on many systems
using DOS 3.3 or higher, this command will set BOTH the software clock AND
the hardware clock.
*************
* CAUTION *
*************
This function should NOT be used when program RIGHTIME is
regulating the DOS clocks UNLESS no other method is available.
Use program TIMESET to set the DOS clocks accurately instead!
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
Program STSORBIT PLUS Satellite Orbit Simulation Page 121
CAUTION: This function will change the computer's SYSTEM CLOCK!
Press ENTER to leave an item unchanged
Enter TIME (HH:MM:SS): 16:34:24 PDT
Enter DATE: 20 AUG 1994
Use US Style 'MM/DD/YYYY' or European Style 'DD.MM.YYYY'
Press ENTER to accept, SPACE BAR to repeat: _
The sample above shows the screen after the time and date entries have been
completed. The current ACTUAL system date and time are displayed for
approval. Press ENTER to accept the time and date displayed, or press the
SPACE BAR to repeat the entries.
F3 Set Simulated Date and Time using Calendar Method
--------------------------------------------------------
Press F3 to set a simulated date and time. The date and time may be
either in the past or in the future. This command does NOT affect the DOS
clock in your system! Use the F1 command above to restore the date and time
to "real time".
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
Press ENTER to leave an item unchanged
Enter SIMULATED TIME [12:05:06]: 13:00:00 PDT 20:00:00 UTC
Enter SIMULATED DATE [07/26/1994]: 08 AUG 1994 08 AUG 1994
Use US Style 'MM/DD/YYYY' or European Style 'DD.MM.YYYY'
Press ENTER to accept, SPACE BAR to repeat: _
The sample above shows the screen after the time and date entries have been
completed. The new SIMULATED date and time are displayed (and counting) for
approval. Press ENTER to accept the time and date displayed, or press the
SPACE BAR to repeat the entries.
F4 Set Simulated Date and Time using MET
--------------------------------------------
Press F4 to set a simulated date and time using MET (Mission Elapsed
Time). Note that this command will appear ONLY if the mission name begins
with the letters "STS", signifying a Space Transportation System (Space
Shuttle) mission AND if a launch time and date have previously been
Program STSORBIT PLUS Satellite Orbit Simulation Page 122
entered.
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Simulated time: 00:17:18 PST 08:17:18 UTC
Simulated date: 10/09/1994 10/09/1994
Enter desired Mission Elapsed Time (MET)
Enter MET DAY (NN): 3 day(s)
Enter MET TIME (HH:MM:SS): 04:30:00 MET
Press ENTER to accept, SPACE BAR to repeat: _
The sample above shows the screen after the day and time entries have been
completed. The Mission Elapsed Time is immediately converted to actual date
and time and the current SIMULATED date and time, based upon the MET just
entered, are then displayed (and counting) for approval. Press ENTER to
accept the time and date displayed, or press the SPACE BAR to repeat the
entries.
F9 Display Current RIGHTIME Corrections
-------------------------------------------
If program RIGHTIME has been detected, the "F9" menu item will be
displayed and you may press F9 to display the time since the last TIMESET,
the current WARM correction, and the current COOL correction:
RighTime Version 2.53 detected!
Time Since Last TIMESET: 0 days 08:58:20
Current WARM Correction: -0.01 seconds
Current COOL Correction: -0.35 seconds
Press any key to continue ... _
The version of RIGHTIME is displayed. The time since the last TIMESET is
saved by program RIGHTIME to the nearest 200 seconds and will therefore not
change until that increment is reached. The time is shown as days followed
by hours:minutes:seconds. If more than 7 days has elapsed since the last
TIMESET, an additional message "(TIMESET suggested!)" will also appear. The
WARM and COOL corrections are shown and are updated when the system time is
set using Function Key F1 from this menu, by program TIMESET, or by other
means. Press any key, such as ENTER, to return to the Time and Date Menu.
Program STSORBIT PLUS Satellite Orbit Simulation Page 123
F10 Set UTC OFFSET and DAYLIGHT Flag
---------------------------------------
STSPLUS uses UTC or Coordinated Universal Time, an adjusted version
of Universal Time (which STSPLUS considers the same as GMT or Greenwich
Mean Time), for certain functions such as launch time. The difference
between UT, UT1, UT2 and UTC is never more than 0.9 seconds. UTC is used
because it is the standard for civil timekeeping and agrees with standard
atomic time, TDB or Terrestrial Barycentric Time, used by astronomers.
However, NASA continues to use the GMT designation, a holdover from earlier
days before the introduction of UTC. Using UTC permits critical data to be
used across many time zones without conversion. However, it also means that
STSORBIT must know what number of hours to add to UTC in order to obtain
your local time, and whether or not you are currently using daylight
savings time (summer time in the UK).
When prompted, enter the time offset in hours from your local time to
Coordinated Universal Time. Examples are shown for most time zones in North
America. STSPLUS then asks if you are using daylight savings time; enter
"0" if not, and "1" if so. The sum of these two values is shown on the Main
Menu; for example, if the computer is set to Pacific Daylight Time (UTC
offset is -8.00 hours and Daylight Flag = 1), the sum will be -7.00. For
most time zones in North America, the correct zone abbreviation will be
shown on the ground track display for Local date and time. When you change
your computer from/to daylight savings time, use this command to update
STSPLUS. The following shows the display when using the F9 command:
Set UTC TIME ZONE OFFSET and DAYLIGHT FLAG
STSPLUS must know the difference between your local time zone and
Coordinated Universal Time (UTC), also sometimes known as Greenwich Mean
Time (GMT). With this information, STSPLUS can automatically adjust launch
or Epoch times and dates for your local time zone. In addition, STSPLUS
must know if your computer is now set to STANDARD or DAYLIGHT time.
First, enter the difference between your STANDARD time zone and UTC in
hours. Do NOT include the hour for daylight time if you are now on DAYLIGHT
time; it will be entered separately. For most time zones in the United
States and Canada, the entries required are:
Eastern Standard Time EST -5.0
Central Standard Time CST -6.0
Mountain Standard Time MST -7.0
Pacific Standard Time PST -8.0
Enter UTC Offset (hours): -8
Enter DAYLIGHT Flag (0=OFF, 1=ON): 1
Once this information has been entered, it will be saved in file
STSPLUS.INI and will not be requested again. If you change from Standard to
Daylight Time or vice versa, use the F10+F9 command to update the Daylight
Flag.
If you change the setting of the Daylight Flag, STSPLUS will ask if
you wish to adjust your DOS software clock:
Program STSORBIT PLUS Satellite Orbit Simulation Page 124
You have changed the setting of the Daylight Flag.
Do you wish to adjust your DOS clock to reflect the
change [y/N]:
If you have already made the change at the DOS prompt (or using some other
software) or do not wish to change the DOS clock, press ENTER (or type "N"
followed by ENTER). If you wish to adjust the DOS clock to correspond to
the new setting of the Daylight Flag, press "Y" followed by ENTER. When
STSPLUS changes the DOS clock, it synchronizes the time change to the
nearest second but there may be a small error introduced; only if your
computer is precisely set would the error be detectable.
*************
* CAUTION *
*************
For computers equipped with 80286 or higher processors AND using DOS 3.2 or
higher, changing the DOS clock will ALSO change the hardware clock. 8088-
based computers may or may not have a hardware clock installed and, even if
a hardware clock is present, it may or may not be compatible with the DOS
time setting commands.
F9 DOS Shell (CAUTION: DOS 3.2 or higher ONLY!)
--------------------------------------------------
If a system function is desired at the Main Menu, press F9 to execute
BASIC's DOS SHELL function. This will return you to a DOS prompt and most
DOS commands may be executed immediately. When the Shell is executed,
STSPLUS remains in memory and the map data will not be re-read when you
return. All files used by STSPLUS are closed. However, this means that a
substantial amount of memory is in use and not available to DOS during the
shell operations. Enter "EXIT" (without the quotation marks and followed by
ENTER) at the DOS prompt when you wish to return to STSORBIT.
CAUTION: The BASIC SHELL function is only reliable for versions of DOS
of 3.2 or higher! Systems with less than 640K memory may fail to
execute the shell and applications requiring large amounts of memory
may also fail.
CAUTION: The BASIC SHELL function does NOT perform reliably when
STSPLUS is executed under Windows and a BASIC ERROR or other
unpredictable results may follow! Instead, close STSPLUS and use the
MS-DOS PROMPT function from the FILE MANAGER.
F10 Set STSORBIT PLUS Program Options and Features
-----------------------------------------------------
A number of program features and display options are set using the F10
Program Options Menu. These selections are further described in the section
"Program Options Menu" below.
Program STSORBIT PLUS Satellite Orbit Simulation Page 125
ENTER Resume Mission
---------------------
Pressing ENTER resumes the current mission shown in parentheses to the
right of the command on the Main Menu. The 2-line elements file from which
the data was read is shown in square brackets.
ENTER Resume Mission (STS-41 [STS41F])
Any manually entered data is retained. "ENTER" means the key marked ENTER,
RETURN, or with a left pointing arrow -- but not the backspace or cursor
position keys which may also be marked with arrows! (I am afflicted with
too long a memory; once upon a time this function was known as Carriage
Return and was often shortened to RETURN or even CR. With the advent of
electronic typewriters, video terminals, dot matrix printers and all the
rest, "carriages" have long since disappeared but old habits die hard! Most
PC keyboards are now marked with "ENTER".)
Use ENTER to resume plotting a mission in progress after returning to
the Main Menu to perform some change (such as enabling the node display,
enabling the NASA tracking stations, or adjusting the time or date).
ESC Quit STSORBIT PLUS and Save Current Mission
--------------------------------------------------
Press ESC (the key marked "ESC" or "Esc", not the letters E+S+C) to
quit program STSORBIT PLUS. If you press ESC to quit the program and have
manually entered orbital data, STSPLUS will save all required mission data
in file STSPLUS.INI prior to terminating. This will be the data available
with the ENTER key the next time you execute the program. The demonstration
data will not be saved, preserving any previously saved mission data.
When you have finished with STSPLUS, press ESC at the Main Menu to
return to DOS. The data (and any adjustments you have made) for the current
mission are saved in file STSPLUS.INI, but the map data is lost and will be
re-read when you next use program STSPLUS.
Program STSORBIT PLUS Satellite Orbit Simulation Page 126
PROGRAM OPTIONS AND FEATURES MENU
---------------------------------
A number of program features and display options are set using the F10
Program Options Menu. When used with CGA displays, the features shown below
as selected by function keys F3 and F4 are not available because of the low
resolution of the CGA display. The following Options Menu is displayed when
the F10 command is entered from the Main Menu:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
F1 Program STSORBIT PLUS Information
F2 Set New Local Coordinates (Palos Verdes, CA)
F3 Select Display Features
F4 TGT Set Satellite Coordinates: Ra/Dec, Elv/Azm, XYZ, TARGET
F5 OFF Show Ascending & Descending Node Data
F6 ORTHO Set Map Projection and Size
F7 ON Enable/Disable EVENT TIMERS
F8 OFF Enable/Disable Audible ALARMS
F9 -8.00 Set UTC Time Offset and Daylight Flag
F10 OFF Enable/Disable Printer Logging
ENTER Return to MAIN MENU
Select desired function:
F1 Program STSORBIT PLUS Information
----------------------------------------
Function Key F1 displays information about program STSORBIT PLUS
including the copyright notice, version number, my name and address, and
the telephone number of my RPV ASTRONOMY BBS (Bulletin Board System). The
current version of STSORBIT PLUS is always posted on the BBS. The BBS has a
power controller; if it hasn't answered after the THIRD RING, hang up and
call back in two minutes. The BBS is available 24 hours per day at 9600,
2400 and 1200 baud.
F2 Set New Local Coordinates
--------------------------------
In order to perform the calculations related to satellite visibility
and altitude/azimuth, STSPLUS must know the geographic (geodetic)
coordinates for the user's location. The names of the current PRIMARY and
SECONDARY (if present) locations are shown. When STSPLUS is first started,
Program STSORBIT PLUS Satellite Orbit Simulation Page 127
the default coordinates for the PRIMARY location are set to Palos Verdes,
California, near Los Angeles, and the SECONDARY location is disabled. The
current PRIMARY location is indicated by the name in parentheses on the
Options Menu. The program provides two methods for setting your own
coordinates: reading a file of city or place names and coordinates
(STSPLUS.CTY is the default filename); or manually entering the
information.
Pressing F2 at the Main Menu will display the Local Coordinates Menu:
Current PRIMARY Location: Palos Verdes, CA
Current active CITYFILE: STSPLUS.CTY
F1 Search CITYFILE for PRIMARY location
F2 Search CITYFILE for SECONDARY location
F3 Enter coordinates for PRIMARY location
F4 Enter coordinates for SECONDARY location
ENTER Return to Program Options & Features Menu
Enter desired selection:
Or, if a SECONDARY location is currently enabled, the following Local
Coordinates Menu will be displayed:
Current PRIMARY Location: Palos Verdes, CA
Current SECONDARY Location: Washington (USNO), DC
Current active CITYFILE: STSPLUS.CTY
F1 Search CITYFILE for PRIMARY location
F2 Search CITYFILE for SECONDARY location
F3 Enter coordinates for PRIMARY location
F4 Enter coordinates for SECONDARY location
F5 Clear (disable) SECONDARY location
ENTER Return to Program Options & Features Menu
Enter desired selection:
Press the indicated function key to perform the desired function, or press
ENTER to return to the Program Options & Features Menu. The F5 selection
will only appear if a SECONDARY Location is currently enabled. NOTE: To
change the current active CITYFILE, use F7 from the Main Menu.
NOTE: If the current active CITYFILE is not the one you wish to use,
press ENTER twice to return to the Main Menu and then use F7 to set a
new CITYFILE path and/or name.
F1/F2 Search CITYFILE for Location
----------------------------------
Pressing F1 or F2 will search the current CITYFILE for the full or
partial name (the "CITYNAME") you enter. The following prompt appears:
Enter partial NAME to match:
Program STSORBIT PLUS Satellite Orbit Simulation Page 128
In other words, when you enter a name or partial name, STSPLUS will attempt
to match that group of characters anywhere in the names which appear in the
current city file. For example, 'SAN' matches 'SAN diego' as well as 'SANta
ana" and 'thouSANd oaks'. To get 'SAN FRANCISCO' on the first try, enter
'SAN F' with a space between the 'N' and 'F'. Case is not significant;
upper and lower case letters are treated identically. If you change your
mind and wish to cancel the operation, simply press ENTER by itself. Use
BACKSPACE to make corrections.
To begin the search, enter the desired name after the prompt. In the
example which follows, F2 was pressed and the name 'santa' was entered for
the search:
Processing record 1616
Location: Santa Ana, CA
Latitude: 33.7633
Longitude: -117.8650
Elevation: 20 meters
Press ENTER to ACCEPT this city as your SECONDARY location, OR
Press ESC to cancel, SPACE to search for next location:
If the city displayed is the one you wish to use as your PRIMARY or
SECONDARY location (depending upon which function key you selected, F1 or
F2), press ENTER. The information will be used by STSPLUS and subsequently
saved in file STSPLUS.INI. If you wish to search further in the file, press
the SPACE BAR. If you wish to cancel the search, press ESC to return to the
Local Coordinates Menu.
NOTE: Some of the elevations contained in file STSPLUS.CTY are zero
because the elevation (in meters) above mean sea level was unknown
when the file entry was prepared. If you know the correct elevation
for your location, edit the file using any ASCII text editor and
change the last number on the line. STSPLUS.CTY contains over 2000
cities. If users send me their correct elevations (or additional
cities they wish added), I will incorporate that data into subsequent
releases of file STSPLUS.CTY.
F3/F4 Enter New Coordinates for Location
----------------------------------------
To enter location data manually, press F3 (for the PRIMARY location)
or F2 (for the SECONDARY location). You will be prompted for the city name,
latitude, longitude, and elevation. Latitude and longitude may be entered
using three different formats for convenience (note the use of comma and
decimal point):
DDD.DDDDD Degrees and decimal fraction
DD,MM.MMM Degrees, minutes and decimal fraction
DD,MM,SS.SS Degrees, minutes, seconds and fraction
The decimal point and decimal fraction are not required in any of the
formats. For example, to enter 33 degrees and 17 minutes, type "33,17".
Program STSORBIT PLUS Satellite Orbit Simulation Page 129
Note that SOUTH latitude must be entered as a NEGATIVE number as measured
south of the Equator. Longitudes may be entered as EAST Longitude, the
number of detrees East of the Prime Meridian at Greenwich (0 to 360
degrees) OR as WEST longitude( 0 to -180 degrees), the NEGATIVE number of
degrees West of the Prime Meridian at Greenwich; regardless of the manner
entered, the longitude will be automatically converted to the range of -180
degrees through 180 degrees. The default unit for elevations is meters
above mean sea level; add "F" (upper or lower case without the quotation
marks) if you wish to use feet.
After the elevation has been entered, the data will be displayed for
approval. All data are converted to degrees and decimal fraction or integer
meters as appropriate, regardless of the format or units used on input.
City Name: Rancho Palos Verdes CA
Latitude: 33.7675
Longitude: -118.4033
Elevation: 186 meters
Press ENTER to ACCEPT this city as your PRIMARY location, OR
Press ESC or SPACE to cancel this data:
If you are entering data for the secondary location, the word "SECONDARY"
will appear instead of "PRIMARY" in the prompt. Press ENTER to accept the
data as shown or press ESC or the SPACE BAR to cancel the data and return
to the Local Coordinates Menu. If the data is accepted, STSPLUS will ask if
you wish to append (add) this city/location to the existing file
STSORBIT.CTY so that it will be automatically available thereafter.
Do you with to append this data to file STSPLUS.CTY (Y/n): _
Press "Y" or ENTER to append the data to the current city file shown in the
prompt, OR press "N" to use the data but not modify the current city file.
F5 Clear (disable) Secondary Location
-------------------------------------
If a SECONDARY Location is displayed on the Local Coordinates Menu and
you wish to cancel (disable) that feature, press F5. If the secondary
location is already disabled, the F5 menu item will not be displayed.
F3 Set Display Features
---------------------------
A number of display features may be enabled or disabled using a
separate sub-menu. See the section SET DISPLAY FEATURES below for a full
description.
Program STSORBIT PLUS Satellite Orbit Simulation Page 130
F4 Set Satellite Coordinates
--------------------------------
The F4 command may be used to select the units used to display the
current coordinates for the satellite. The choices are:
Ra/Dec Right Ascension and Declination (Equator and Equinox of
Date).
Elv/Azm Elevation and Azimuth. Elevation (altitude) is the elevation
above the horizon (assuming mean sea level), and azimuth is
the direction in the sense NESW (North to East to South to
West).
XYZ Geocentric Cartesion Coordinates. The X-Axis and Y-Axis are
aligned with the Equator with the X-Axis pointing in the
direction of the Vernal Equinox. The Z-Axis points toward
the North Pole.
TARGET Relative Range and Velocity for a Target Satellite selected
from among the current Secondary Satellites. Use F6+F5 from
the Main Menu to select the Target Satellite BEFORE
selecting this mode. When enabled, the data are displayed im
metric or English units:
TARGET: 20580 Target NORAD Number
Rng: 1661.69 km Relative Range, kilometers
Vel: -1.85 m/s Relative Velocity, meters/second
or:
TARGET: 20580 Target NORAD Number
Rng: 902.55 nm Relative Range, nautical miles
Vel: -6.4 ft/s Relative Velocity, feet/second
NOTE: This mode cannot be enabled if a Target Satellite has
not been selected. Relative Velocity is displayed ONLY if
the Relative Range is less than 5000 kilometers.
For all modes, select the desired units of measure using F9 while the
map is displayed. The desired satellite coordinates may also be selected
using F10 while the map is displayed.
F5 Show Ascending & Descending Node Data
--------------------------------------------
The nodes of an Earth orbit are the points on the ground track where
the path crosses the Equator. The ascending node crosses from South to
North and the descending node crosses from North to South. Orbit numbers
normally increment at the ascending node. This command adds two additional
lines of data at the lower left of the screen giving the time (MET or time
since epoch) and longitude of the most recent ascending and descending
nodes. This information is useful when comparing STSPLUS's data against
other sources such as the wall map in Mission Control.
Program STSORBIT PLUS Satellite Orbit Simulation Page 131
F6 Set Map Projection and Size
----------------------------------
The F6 command selects the size and field of view of the displayed
map. By default, the map is displayed using the orthographic projection,
"ORTHO", shows one complete hemisphere, and is centered so that the
selected satellite is visible. This corresponds to a magnification factor
of 100%.
Pressing F6 will select between WORLD, QUAD, ZOOM, and ORTHO maps.
Selecting WORLD will display the full world using rectangular projection
centered on the Prime Meridian at Greenwich, England at 0 degrees
longitude or at the International Date Line at 180 degrees longitude.
Selecting QUAD will select one of twelve Quadrant Maps showing a field of
view (horizontal size) of 180 degrees using rectangular projection.
Selecting ZOOM will select a Zoom Map with field of view adjustable from 30
degrees to 180 degrees; the default field of view is 75 degrees; the Zoom
Map is approximately centered on the current ground track position of the
satellite. Selecting ORTHO will select the orthographic projection. See the
sections ORTHOGRAPHIC MAPS, QUADRANT MAPS, ZOOM MAPS, and AUTOMATIC MAP
GENERATION for additional information.
F7 Enable/Disable EVENT TIMERS
----------------------------------
Press F7 to enable or disable all event timers. Event timers are
enabled by default if file STSPLUS.INI is present. Especially while the map
is being drawn, the calculations associated with the event times require
appreciable time. If the event timers are disabled, the audible alarms will
also be disabled. See the section "Event Timers and Audible Alarms" for a
full discussion of the event timers.
F8 Enable/Disable Audible ALARMS
------------------------------------
Provided event timers are enabled (above), you may press F8 to enable
or disable audible alarms. Many users allow their computer to run STSPLUS
while performing other tasks and the audible alarm will alert them to an
imminent AOS (Acquisition of Signal) or LOS (Loss of Signal) event
associated with either their local circle of visibility or the TDRS
communications satellites.
For the local circle of visibility, an "up/down" tone sounds six times
two minutes prior to AOS and five tones sound thirty seconds prior to LOS.
Provided TDRS coverage is enabled (F10+F3+F2 from the Main Menu), three
brief tones sound thirty seconds prior to AOS or LOS. Provided Sun features
are enabled (F10+F3+F8), two tones will sound approximately thirty seconds
before orbital sunrise and sunset. The characteristics of the audible tones
will thus allow the user to identify what kind of AOS or LOS event is about
to happen.
Depending upon the computer and the version of DOS being used, "music"
such as these audible alarms may cause the DOS clock to lose a small amount
of time each time an alarm sounds. The amount of time loss is quite small
Program STSORBIT PLUS Satellite Orbit Simulation Page 132
but may accumulate over long periods of time. (The DOS clock may also run
either fast or slow and effectively mask the time loss due to sound
effects.)
F9 Set User-Definable Map Colors
------------------------------------
STSPLUS allows the user to set the colors for certain map features.
These features are the Local Station circle of visibility, the concentric
isocontours used in the Location and Tracking Modes, and the Tracking
Station circle of visibility color. Pressing Function Key F9 displays the
current color assignments (and a color chart on the right of the screen):
Current User-Definable Map Colors
----- 13 Local Station Color
----- 14 Isocontour Color
----- 12 Tracking Station Color
Press ENTER to ACCEPT, SPACE to CHANGE:
The "-----" in the example is a solid line illustrating the map color. The
number to its right is the number used to represent that color. The colors
shown in the example are the default colors. If the colors shown are
acceptable, press ENTER. To change the color assignments, press the SPACE
BAR and the color assignments will be prompted in turn:
Enter color for Local Station: 5
Enter color for Isocontours: 6
Enter color for Tracking Stns: 4
Use the color chart at the right of the screen to select new colors and
enter the corresponding number. Press ENTER to leave a color unchanged. As
each color is assigned, the display sample will change accordingly. When
the last color has been assigned, the initial display will be repeated:
Current User-Definable Map Colors
----- 5 Local Station Color
----- 6 Isocontour Color
----- 4 Tracking Station Color
Press ENTER to ACCEPT, SPACE to CHANGE:
Press ENTER if the new colors are acceptable, or press SPACE BAR again to
change again.
Program STSORBIT PLUS Satellite Orbit Simulation Page 133
F10 Enable/Disable Printer Logging
-------------------------------------
I have found it interesting to log the orbital data and the ascending
and descending node information on my printer when analyzing the mission
data over long periods of time. The F10 command toggles the printer logging
function on and off. The first page of the log includes the current orbital
data and subsequent pages contain only node information. In addition to the
information presented on the display, the printer log also calculates the
current orbital time, the time from one ascending (descending) node to the
next, for the third and subsequent nodes. A typical log is shown below.
IMPORTANT: BE SURE THE PRINTER IS TURNED ON PRIOR TO ENTERING THE
F10 COMMAND.
STSORBIT: Space Shuttle Tracking Program, Version 9435 Page 1
ORBITAL DATA for STS-31 Discovery/HST
NORAD Number: 20580
Launch Date: 04/24/1990
Launch Time: 05:33:52
Orbit Inclination: 28.4695
Orbit Altitude: 329.50 nm
UT DATE UT TIME ORBIT LONG MET TIME
Ascend Node: 04/28/1990 20:32:52 70 -69.95 4/14:58:07
Dscend Node: 04/28/1990 21:20:52 70 97.64 4/15:46:35
Ascend Node: 04/28/1990 22:09:52 71 -94.77 4/16:35:02 1:36:55
When printer logging is enabled and the ground track is displayed, the
word "LOG" will appear in red at the right of the text area. Enabling
printer logging also automatically enagles the display of ascending and
descending node information.
The Launch Date and Launch Time entries are given if that information
has been entered indepentently. The Epoch Date and Epoch Time are always
shown. Note also that the orbit altitude shown is the altitude at the time
the log was started and will not be correct for subsequent entries,
especially if the satellite has an elliptical orbit (high eccentricity).
A printer log may be prepared in advance of a mission by enabling
printer logging from the Set Options Menu (with the F10+F10 command),
setting the desired simulation time (F8+F3 command), then starting the
ground track display with ENTER; once the ground track has appeared on the
screen, pressing the F key twice to set STSPLUS in the X60 fast time mode
will generate the date relatively quickly (although the UT TIME printed may
be off by as much as one minute in the X60 mode). Allow the simulation to
run for the desired length of time, then press ENTER to return to the Main
Menu. While the ground track is active Function Key F3 performs the same
function as the F10+F10 command to enable or disable printer logging.
Program STSORBIT PLUS Satellite Orbit Simulation Page 134
SET DISPLAY FEATURES
--------------------
Depending upon the satellite and personal preferences, a variety of
display features may be enabled or disabled. Not all features are available
with monochrome or CGA monitors. Pressing F3 on the Set Program Options and
Features Menu will display the following menu:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9435
Current time: 19:01:57 PDT 02:01:57 UTC
Current date: 26 JUL 1994 27 JUL 1994
F1 ON Display LOCAL Circles of Visibility
F2 ON Display TDRS and Real Time Satellites
F3 ON Display Additional Map Grid Lines
F4 OFF Display Tracking Stations
F5 BOTH Display Ground Track: DOTS/LINE
F6 ON Display Spacecraft Circle of Visibility
F7 OFF Display South Atlantic Anomaly Zone
F8 ON Display Terminator, SUN, and Spacecraft Lighting
F9 ON Display Map Locations and Features
F10 ON Display Lakes and Rivers
ENTER Return to MAIN MENU
Select desired function:
F1 Display LOCAL Circles of Visibility
------------------------------------------
Function Key F1 enables and disables the local circles of visibility,
centered on your location and a second location (if enabled), and shows the
approximate area within which direct line of sight communication with the
satellite is possible. The circle is calculated at the instant the map is
drawn and may not be accurate over long periods of time for satellites with
highly eccentric orbits. In some situations (geosynchronous satellites, for
example), these circles of visibility cover so large an area that they
simply confuse and clutter the display. Use this command to disable the
circles.
F2 Display TDRS and Real Time Satellites
--------------------------------------------
This command allows the user to display TDRS and/or selected real time
and static satellites. The command cycles through "OFF", "TDRS", "SATS",
and "BOTH". When "TDRS" or "BOTH" is selected,the communications coverage
for the Tracking and Data Relay Satellites (TDRS) or other geosynchronous
Program STSORBIT PLUS Satellite Orbit Simulation Page 135
satellites is also shown. The TDRS coverage boundaries overlap between the
East and West TDRS satellites and Mission Control may select either
satellite during the overlap period. STSPLUS displays the areas covered by
each satellite and the times for acquisition and loss of signal (AOS and
LOS). See the section "TDRS and Real Time Satellite Features" above for a
full discussion of the TDRS coverage features.
F3 Display Additional Map Grid Lines
----------------------------------------
This command is not available for CGA systems. The basic world map
includes the Equator and the meridians at 0 degrees (Prime Meridian) and
180 degrees (International Date Line) shown in bright blue on color
monitors. Turning on the map grid adds additional lines of longitude and
latitude. Displaying the additional grid lines on some monochrome monitors
may make the screen too "busy".
In the Orthographic, Quadrant and Zoom Map modes, the spacing of the
additional grid lines is adjusted for the map field of view. In all
rectangular map modes and for orthographic map modes with MAG > 500 except
for polar and near polar views, each latitude grid line is labeled at the
left and each longitude grid line at the top or bottom of the display
screen.
F4 Display Tracking Stations
--------------------------------
The F4 command enables/disables the display of the tracking stations
included in file STSPLUS.TRK or the current TRACKING STATION filename as
set by Function Key F7 on the Main Menu. If that file is not found,
internal data are used for NASA's 14 original ground tracking stations plus
the NASA Ground Terminal at White Sands, NM. Each tracking station is
located with a small red circle. The circle of visibility is also shown if
that circle has an angular diameter of 90 degrees or less. The circles of
visibility are calculated at the instant the map is drawn and may not be
accurate over long periods of time for satellites with highly eccentric
orbits. For all map modes EXCEPT the World Maps, each tracking station is
also labeled with its 3-character abbreviation. This command is not
available for CGA monitors.
F5 Display Ground Track: DOTS/LINE
--------------------------------------
STSPLUS calculates the ground track for the satellite for a period
from one and one half hours in the past to three hours in the future. Press
F5 to change from one mode to the next. Depending upon the user's
preferences, this function may be used to set the displayed ground track to
any of the following modes:
NONE The ground track is not displayed.
DOTS The ground track is displayed using RED dots for the past
ground track and GREEN dots for the future ground track. The
Program STSORBIT PLUS Satellite Orbit Simulation Page 136
dots are spaced at one minute intervals. As time passes, the
GREEN dots will change to RED.
LINE The ground grack is displayed using a GREEN line.
BOTH The ground track is displayed using a GREEN line with RED
dots for past ground track minute marks and YELLOW dots for
future ground track minute marks. As time passes, the YELLOW
dots will change to RED.
F5 Display Spacecraft Circle of Visibility
----------------------------------------------
STSPLUS can calculate the approximate circle of visibility from the
spacecraft, the area of the Earth's surface which is visible from the
cockpit windows and television cameras or, for unmanned spacecraft, the
direct line of sight visibility from the ground. Note that the shape of the
"circle" varies depending upon the magnification or zoom factor and map
projection being used. With rectangular projection, the shape is
approximately a circle near the Equator and more like a rounded triangle at
higher latitudes; near the poles, the "circle" spreads out across the map.
This is an artifact of the rectangular map projection.
When enabled, the circle of visibility is recalculated every 10
seconds based upon the spacecraft's current altitude. This means that
orbits with a high eccentricity (that is, a highly elliptical orbit whose
apogee and perigee are very different) will exhibit a constantly changing
circle of visibility.
F7 Display South Atlantic Anomoly Zone
------------------------------------------
The South Atlantic Anamoly (SAA) is an area in the southern hemisphere
lying between southern tip of Africa and South America which can cause
severe electromagnetic disturbances on spacecraft. For example, the
semiconductor memory on the Hubble Space Telescope (which regularly passes
through the SAA) was being changed by this phenomenon until a patch was
uplinked to work around the problem. The area is shown on the ground track
as an ellipse for simplicity; its actual outline is more nearly shaped like
a kidney bean. Using NASA Mission Charts for various Space Shuttle
missions as a reference, the SAA is adjusted for spacecraft altitudes from
160 nm to 350 nm (although it extends out to geosynchronous orbits).
SAA coverage is disabled in orthographic modes pending better data and
the development of a mathematical model for use in those modes.
F8 Display Terminator, Sun, and SpaceCraft Lighting
-------------------------------------------------------
This function enables and disables the Sun and related solar features.
See the section "Sun and Solar Features" for a full discussion. STSPLUS
calculates whether the spacecraft is in full sun, penumbra (partial shadow)
or refracted sunlight, or umbra (full shadow) and adjusts the color of the
Program STSORBIT PLUS Satellite Orbit Simulation Page 137
spacecraft icon accordingly: bright white, yellow, and dim white
respectively. This feature is not available on CGA and HGC monitors. The
current spacecraft solar lighting is indicated in the data block (next to
"Orbit #:") by the following symbols:
* Full sunlight
+ Partial sunlight (penumbra)
- Refracted sunlight
Full shadow (umbra)
F9 Display Map Locations and Features
-----------------------------------------
This feature enables or disables the display of the map locations and
features contained in file STSPLUS.LOC if present. See the section
"Location and Features Labels" above for a full discussion.
F10 Display Lakes and Rivers
-------------------------------
This feature enables or disables the display of lakes and rivers on
the map. Removing the lakes and rivers will lessen the time required to
draw a map and can improve screen legibility especially for CGA systems.
(The lakes and rivers are always disabled on the rectangular world map to
avoid cluttering an already busy display!)
Program STSORBIT PLUS Satellite Orbit Simulation Page 138
STSORBIT PLUS's Orbital Model
-----------------------------
The original version of STSORBIT was first prepared without reference
materials of any kind and the simplest possible orbital model was therefore
selected. The primary objective was to duplicate the NASA wall map at
the Mission Control Center in Houston, Texas. This "simple" model assumed
that the orbit was perfectly circular at a specified altitude and
inclination which never degraded due to other factors such as drag or
perturbation. Some simplifying assumptions were incorporated to handle the
initial ascent portion of a mission and the launch site was hard coded to
Cape Canaveral, Florida. With only minor modifications, the program was
essentially unchanged for the next year.
The launch of STS-31 and the Hubble Space Telescope highlighted the
need for improved accuracy because of public interest and the length of the
mission. The orbital calculations were modified (STSORBIT Version 9015) to
include the J2 factor, the perturbation of low Earth orbits due to
variations in the gravitational field related to the non-spherical shape of
the Earth (among other factors); omission of the J2 factor caused errors in
longitude of approximately -5 to -7 degrees per day. That is, the orbital
track drifted Westward from its true position by that amount. More accurate
models of low orbits also include the J3 and J4 perturbation factors,
atmospheric drag, and a host of other less significant items.
Although reasonably accurate for the first day or so of a space
shuttle mission, the "simple" model is by no means ideal. In calculating
the current orbital longitude, for example, the "simple" model assumes a
circular orbit. For orbits with low inclinations, as is typical for
launches from Kennedy Space Center, the errors are not particularly
significant and are probably overshadowed by the fundamental uncertainties
in orbital parameters and by the limitations imposed by display resolution.
Orbits with higher inclinations, as would be the case if near-polar
launches from Vandenburg AFB in California are ever initiated, would have
much larger periodic errors which would be both noticeable and
objectionable. More important for longer missions and for general satellite
tracking is the fact that due to the method used, errors in the orbital
calculations tend to be cumulative. After a day or two, the errors become
unacceptably large.
The real problem with the simple method, of course, is that the Earth
is not a perfect sphere and actual satellite orbits are never perfectly
circular. Satellite orbits are significantly perturbed by the non-spherical
gravitational field of the Earth, by the Sun and Moon, atmospheric drag,
and other factors. Accurate satellite tracking over longer periods of time
therefore demands more accurate data and a more rigorous treatment of
satellite orbits. The only practical alternative is to use the NASA/NORAD
2-line orbital element sets. Not only are these data readily available
publicly, but they are relatively accurate and are updated regularly.
Therefore, STSORBIT PLUS relies on the NORAD SGP4 prediction model and the
2-line orbital element sets for orbit predictions. 2-line element sets for
non-military space shuttle missions are typically available on the same day
as the launch. Amateur astronomers and satellite tracking experts often
generate "unofficial" 2-line element sets even for military missions.
Six quantities are required by classical gravitational theory to
completely characterize the orbit of one body about another in time and
space, the "Two Body Problem". These six quantities, often referred to as
Keplerian orbital elements, are included in the NASA/NORAD 2-line element
Program STSORBIT PLUS Satellite Orbit Simulation Page 139
sets along with other numerical and statistical data. The U.S Space
Command, (formerly NORAD, the North American Air Defense Command)
headquartered in Cheyenne Mountain, Colorado, developed the SGP4 and SDP4
orbital models and the 2-line element format many years ago as part of
their satellite tracking efforts and NASA subsequently adopted the same
format -- more or less. NASA and NORAD do not always use the same
definition for revolution (orbit) numbers; NASA frequently gives a number
one (or two) greater than NORAD, calling the first partial orbit number one
while NORAD calls that same partial orbit number zero. Except for short
duration missions, such as the Space Shuttle, revolution numbers are of no
practical importance.
Having timely and accurate orbital data is of little help without a
computer model or program which can use those data. NORAD has rather
arbitrarily divided satellite orbits into two categories: near Earth orbits
and deep space orbits. Near Earth orbits are defined as those with orbital
periods of 225 minutes or less and deep space orbits are all others.
Computer models are described in the literature for each category. STSORBIT
PLUS employs the SGP4 Near Earth Model only, using a composite of code of
my own combined with translated Fortran and Basic source supplied by Paul
Traufler and C source by Paul Hirose. I plan to add the SDP4 deep space
model in due course. Not only are the near Earth orbits generally of more
interest to observers, but the errors associated with deep space orbits
processed with the SGP4 model (rather than the correct SDP4 model) are not
particularly significant for the purposes of a program such as STSORBIT
PLUS. Further, watching a geostationary satellite orbit on the screen is
not unlike watching grass grow and is about as exciting.
Program STSORBIT PLUS Satellite Orbit Simulation Page 140
Accurate Time and the Personal Computer
---------------------------------------
For a program like STSPLUS, accuracy and precision of the timekeeping
functions are essential. There is a tendency these days to accept whatever
a computer says as the absolute truth without regard for whether or not the
information is even "reasonable". For something as basic as time, even an
experienced computer user may assume that it is correct. This discussion
attempts to compare reality with that expectation.
Given the clock drift and accuracy problems inherent in the design of
the typical IBM-compatible personal computer, frequent time setting and/or
adjustments are required. Accurate time setting would not be practical
for most people without the various time services provided by the National
Institute of Standards and Technology (NIST) and the U.S. Naval Observatory
(USNO). The NIST radio stations WWV and WWVH provide an inexpensive and
convenient means for "ordinary folks" to synchronize clocks and other
equipment. The NIST and USNO Telephone Time Services offer a high precision
standard time calibration source when such accuracy is required. Similar
radio and telephone services are available in Canada and Europe.
Once a computer clock has been set with reasonable accuracy, the
accuracy of the computer's clock will indeed be sufficient for many
applications; if you are using a word processing or spreadsheet program,
knowing the time to within a minute or two is probably adequate. For
programs such as STSPLUS and other time-dependent applications, however,
this level of accuracy simply will not suffice; when used for satellite
tracking, the time should be accurate to within a second. Unless steps are
taken to both set the clock and to maintain its accuracy, this will not be
the case. No matter how accurately the clock on a typical personal computer
is set, it will only be a matter of hours before the time will have drifted
by some seconds. Measured over a number of days, the accumulated errors can
easily amount to a minute or more.
The timekeeping operations of an IBM-compatible computer are actually
performed by two separate and independent functions: a clock-calendar
CMOS integrated circuit and lithium battery combination which maintains the
current time and date in hardware; and, a section of the DOS operating
system software which maintains the current time and date in software. When
computer power is off, the hardware chip continues to operate using its
battery; when the computer is started ("booted"), the operating system
software reads the hardware clock and sets its internal software clock.
Absent special software, the DOS time thereafter relies entirely on the
software clock until the next time the computer is restarted.
Unfortunately, neither of these clocks was designed for accuracy; early
versions of the PC did not even include the hardware/battery arrangement.
Even the typical electric clock, which uses the power line frequency for
its timekeeping reference, is usually far more accurate.
The accuracy of the DOS time at any instant is the result of the
accumulated errors in both clocks. The hardware clock will drift as a
function of time, temperature, voltage, and crystal aging; the software
clock will gain or lose time depending upon the skill with which its
software was written and how well that software "cooperates" with the
balance of the computer's hardware and software. Some software, especially
network and high speed communications software, can prevent the DOS clock
software from incrementing when it should, usually resulting in the DOS
clock losing time. The problem was compounded with the release of DOS
Version 3.3; beginning with that version, the DOS TIME and DATE commands
Program STSORBIT PLUS Satellite Orbit Simulation Page 141
adjust BOTH the hardware and software clocks and thereby potentially
eliminate the hardware clock as even a modestly reliable reference.
Methods for Setting DOS Time
----------------------------
Bearing these considerations in mind, there are a number of approaches
to the DOS time question. The most obvious approach, used by the vast
majority of computer users, is to either ignore the computer clock entirely
or to say "It's close enough". Regardless of the application, I strongly
recommend that the DOS clock be REGULARLY set to the correct time if only
to assure that files are more or less correctly date and time stamped. If
the accuracy of DOS time is important, the computer clock may be set or
synchronized in a number of ways, some of which are described below. In
this context, "ACCURACY" means the accuracy of the time setting operation
and NOT the longer term accuracy and stability of the DOS time.
1. TELEPHONE: Many local telephone companies offer a telephone time
service, usually with a message such as "When you hear the signal the
time will be ... (beep)". I am not aware of any hardware or software
which uses this signal for time setting purposes.
ACCURACY: Generally plus or minus 5 seconds. With the advent of
digital voice response equipment in recent years, the accuracy has
improved to perhaps plus or minus 1 second.
2. COMMERCIAL RADIO: Hourly time signals broadcast on commercial radio
may be used to manually set the time. My experience suggests that the
CBS network time signal is usually reliable.
ACCURACY: Usually within plus or minus 2 seconds, depending upon the
source. Satellite distribution of network feeds add a time delay of
approximately 0.25 seconds per "hop" but some stations, including some
network stations, generate time signals locally.
3. SHORTWAVE RADIO: Time signals are broadcast on shortwave radio
stations WWV and WWVH by the National Institute of Standards and
Technology. These time signals may be used to manually set the time.
WWV and WWVH broadcast on several frequencies: 2.5MHz, 5MHz, 10MHz,
15MHz, and 20 MHz (WWV only). Reception will vary according to your
distance from the transmitter, time of day, and atmospheric
conditions. These time signals are very precise; the only major
variable is the propagation delay, the time it takes the radio signal
to travel from the transmitter to your receiver. The typical
propagation delay is approximately 5 microseconds per mile. Outside
North America, other national radio services such as the British
Broadcasting Company's BBC World Service offer accurate hourly
shortwave time signals.
ACCURACY: Time setting using WWV or WWVH can usually be performed to
within about plus or minus 250 milliseconds, of which up to 25
milliseconds is transmission time and the balance is user response
time. With practice, plus or minus about 100 milliseconds is
practical.
Program STSORBIT PLUS Satellite Orbit Simulation Page 142
4. HEATH GC-1000 MOST ACCURATE CLOCK: The GC-1000 is a combination
digital clock and scanning shortwave radio receiver which may be
equipped with an RS-232 communications port for use with computers and
other electronic equipment. Operation with DC power is available to
maintain accurate time during periods of AC power loss. This is the
only method which provides more or less continuous accurate time
information without telephone toll charges.
ACCURACY: When properly configured for your location, equipped with an
external antenna, used with appropriate computer software, and when
the receiver is locked to one of the WWV (or WWVH) time signals, the
GC-1000 can provide time information and a standard calibration
frequency to an accuracy of plus or minus 10 milliseconds. When signal
lock is lost, the receiver scans the 5MHz, 10MHZ, and 15MHz broadcasts
to reacquire signal and lock. Even after signal lock is lost, the
receiver maintains an accuracy of plus or minus 100 milliseconds for
some hours.
5. NIST/USNO TELEPHONE TIME SERVICE: When real precision and accuracy are
required, the computer clock may be set remotely using the telephone
time service of either the National Institute of Standards and
Technology (NIST, formerly the National Bureau of Standards or NBS) in
Boulder, Colorado, or the U.S. Naval Observatory (USNO) in Washington,
D.C. This method requires a modem connected to a telephone line and is
available for systems using DOS version 3.3 or higher AND equipped
with 80286 processor or higher; some 8088-equipped systems may also
use this method depending upon the type of clock hardware installed
and the version of DOS being used. The recommended method uses the
programs TIMESET and RIGHTIME (see below) although other commercial
and shareware programs may be available.
ACCURACY: This is the most accurate method available for setting and
maintaining the DOS clocks. Depending upon which service is used, NIST
or USNO, whether or not line delay compensation ("lag") is employed,
and the frequency of time setting, the DOS time can be set to within
plus or minus 2 milliseconds. However, since the "time ticks" of the
DOS software clock occur every 55 milliseconds, or 18.2 times per
second, this "granularity" may limit the accuracy of reading the DOS
clocks. See the documentation for programs TIMESET and PRECISION TIME
(below) for additional discussion.
Choose one of the methods suggested or a suitable alternative based
upon your precision and accuracy requirements. Other methods of maintaining
an accurate time standard such as atomic clocks, Global Positioning
Satellite (GPS) time receivers, and NIST time code equipment, are also
available -- for a price. Those methods are beyond the scope of this
documentation.
Maintaining Accurate DOS Time
-----------------------------
Just in case you missed the point earlier, accurately setting DOS time
is only half the battle. Even if the DOS time is set very precisely as
Program STSORBIT PLUS Satellite Orbit Simulation Page 143
discussed above, all that assures is that the time is correct to the
required accuracy at that instant. The problem then becomes one of knowing
how the DOS clocks change or drift with time and how to compensate for
those changes or, alternatively, checking the DOS time frequently enough
that any drift on the part of the DOS clocks is acceptable for the intended
application.
Of the two clocks in a typical personal computer, the hardware clock
is considerably more consistent and reliable. I have checked perhaps a
dozen PC hardware clocks in recent years, and almost all kept reasonably
good time over a period of several days; as expected, none kept "perfect"
time. Typical drift rates ranged from about 3 seconds per day to near zero
seconds per day, with the magnitude and direction of the drift more or less
constant over the period of measurement. The hardware clock is typically
sensitive to both voltage and temperature, both of which undergo
significant change when the computer is turned on or off. Complete
calibration of the hardware clock requires knowledge of its performance
under both circumstances. Once a hardware clock has been calibrated,
its performance may be predicted with reasonable accuracy over periods of
some weeks or more. Crystal aging rates suggest that calibration should be
performed at least monthly.
The hardware clock is normally interrogated only when the computer is
first started or rebooted. The correct time can therefore be predicted at
that moment for a calibrated hardware clock, given the last time that clock
was synchronized with an appropriate time standard. Microsoft provides no
standard software tools for interrogating the hardware clock at other
times except for low level interrupt services. Quite the contrary;
beginning with DOS Version 3.3, using the DOS TIME and DATE commands to set
the DOS software clock will also set the hardware clock and effectively
destroy its usefulness as a calibrated time reference. I am at a complete
loss to understand the reasoning behind this change in DOS; I presume that
users were being "confused" by differences between the hardware and
software clocks; instead of either explaining or fixing the problem,
Microsoft elected to "legislate" the problem away -- a process any
politician would recognize instantly. The only mitigating consideration is
that any really effective solution would probably require hardware as well
as software changes. Blame IBM, I guess.
The software clock provides the only time information readily
accessible to DOS using standard software. Since this clock is maintained
entirely in software, with no reference to the hardware clock except at
bootup, it is at the mercy of other software which may execute from time to
time. The software clock increments its time using "interrupts", a
technique which stops a software process in progress just long enough to do
the required tasks and then resumes the interrupted process. These
interrupts occur every 55 milliseconds. So long as none is missed, the
software clock should keep accurate time -- if the software is written
correctly and if the computer's crystal controlled oscillator is in turn
accurate. It may be that neither of these conditions is true; certainly the
crystal controlled oscillator (quite similar to the one which runs the
hardware clock) was not designed for accuracy or stability. It's original
purpose was solely to generate the necessary timing signals for the
operation of the computer. Cost, not accurate time, was the primary
consideration in its design.
Other software designers have contributed to the problem by writing
software which, deliberately or inadvertently, prevents the software clock
from being updated. Off-brand BIOS firmware can present occasional
Program STSORBIT PLUS Satellite Orbit Simulation Page 144
problems. Local Area Network (LAN) and high speed communications software
are also frequent culprits in this respect. For example, a casual check of
the clock while using a high speed computer-to-computer file transfer
program indicated that the clock was effectively suspended when data
transfers were in progress. In one relatively brief test, the DOS clock
lost about 30 seconds.
As a result of all of these factors, the accuracy of the DOS software
clock can vary wildly from one computer to the next and from one situation
to another. One inexpensive "clone" computer that I'd rather forget
couldn't manage to keep time to better than about 30 seconds per HOUR!
Before planning to use a particular computer as a time reference with
programs like STSPLUS, check the computer hardware and software you intend
to use very carefully.
Programs TIMESET and RIGHTIME
-----------------------------
Two fine shareware programs, TIMESET by Peter Petrakis and RIGHTIME by
Tom Becker, provide all the features required to accurately set and
maintain the computer's hardware and software clocks. Development efforts
on these programs have been carefully coordinated so that they cooperate
with each other. Both programs are copyrighted commercial software
distributed as "shareware" and require registration after an initial
evaluation period. I highly recommend these programs and encourage users to
support the authors and their work. So far as I know, there are no other
comparable programs available at any price!
TIMESET, Version 7.10 or higher, uses the telephone time services of NIST,
USNO, and three European services to precisely set the computer clocks. The
standard distribution also includes several additional time-related utility
programs. It is available on many computer bulletin board systems or direct
from:
Peter Petrakis
Life Sciences Software
8925 271st N.W., Suite 112
Box 1560
Stanwood, Washington 98292 USA
Telephone: (206) 387-9788
RIGHTIME, Version 2.5+, is a program to compensate for the various drift
factors in a computer's hardware and software clocks. When used in
conjunction with TIMESET and properly calibrated, RIGHTIME "learns" the
warm and cool drift factors for a specific computer. As a result, the
clock's can be maintained with an accuracy of a fraction of a second over
long periods of time. It is available on many computer bulletin board
systems or direct from:
Tom Becker
Air System Technologies, Inc.
14232 Marsh Lane, Suite 339
Dallas, Texas 75234 USA
Program STSORBIT PLUS Satellite Orbit Simulation Page 145
Telephone: (214) 402-9660
Tom Becker and Peter Petrakis may be also contacted directly on the Air
Systems Technologies computer bulletin board system in Dallas, Texas. The
BBS always has the latest versions of TIMESET and RIGHTIME available for
download:
Air Systems Technologies BBS
(214) 869-2780
STSPLUS is now "aware" of program RighTime and its use is recommended
for accurate timekeeping. Audible alarms in prior versions would perform
unpredictably when RighTime was active because they use the hardware
clock's timer functions (which RighTime also uses). STSPLUS now detects
RighTime and temporarily disables RighTime while an audible alarm is being
generated and then re-enables RighTime after the alarm has completed,
restoring precise timekeeping. With RighTime active, alarms are generated
in foreground, which may cause a slight delay in screen updating.
*************
* CAUTION *
*************
STSPLUS expects RighTime Version 2.5+; performance with prior
versions of RighTime may yield unpredictable results. If using a
prior version of RighTime, do NOT enable audible alarms!
If RighTime is not present or is not detected, the audible alarms are
generated in background as in prior versions. This usually causes the loss
of several clock ticks in the DOS software clock for each audible alarm.
Although the time loss per audible alarm is very small, the cumulative
error may become significant over extended time periods.
The following descriptive text is extracted with permission from the
documentation for the current versions of TIMESET and RIGHTIME; please
consult the documentation for each program for full details. Although
future versions of both programs are expected to remain compatible with
STSPLUS, they should be tested carefully before regular use.
FEATURES OF TIMESET 7.10
------------------------
TimeSet has been evolving steadily ever since the first version was
released in the summer of 1987. That version and several subsequent ones
could only set a computer's clock from the U.S. Naval Observatory (USNO) in
Washington, D.C. Version 6.00, released in 1990, added ability to use
telephone time signals from the National Institute of Standards and
Technology (NIST) in Boulder, Colorado, making it the first program of its
kind able to address more than one atomic time service. This made it
possible for computer users in the eastern and western United States to
keep down long distance bills by choosing the time service closest to them.
Version 7.10 continues that evolution with a number of new features
Program STSORBIT PLUS Satellite Orbit Simulation Page 146
and supporting utilities:
o TimeSet can now access five atomic clock-based telephone time services
on two continents: the USNO and the NIST in the United States, as
before, and atomic time services in Sweden (National Time and
Frequency Laboratory), Austria (Technical University of Graz), and
Italy (National Electrotechnical Institute). People in European
countries who want to set their computers to an atomic clock no longer
need to make a trans-Atlantic phone call.
o TimeSet 7.10 is designed to interact closely with version 2.5+ of
RighTime (tm), the excellent memory-resident regulator for computer
clocks developed by Tom Becker of Air System Technologies, Inc.,
Dallas. RighTime learns the drift rate in the computer's clock and
continuously applies a correction to compensate for it, and it refines
the correction each time the computer clock is set. A computer with
RighTime installed and trained can maintain system clock accuracy
within a second for at least a week. Furthermore, version 2.46
provides true 0.01-sec resolution in the DOS clock, in contrast to the
normal 0.055-sec resolution. This allows greater accuracy in
timesetting than ever before, indeed the maximum accuracy that can be
obtained with a computer clock. Life Sciences Software and Air System
Technologies cooperated closely during the development of TimeSet 7.10
and RighTime 2.46, with the result that TimeSet can access several
RighTime functions directly.
"TIMESET" is a trademark of Life Sciences Software (TM)
The following is a screen dump of the data displayed by TIMESET:
+------------------- From NIST. Connect time: 11.97 sec. --------------------+
| DATA FOR TIME CALCULATIONS (all data pertain to Coordinated Universal Time) |
| Time data string: 49051 93-03-05 14:07:20 81 0 -.1 051.1 UTC(NIST) |
| Date: 03-05-1993 |
| Julian date: 2449051 |
| Day of year: 064 |
| Hour: 14 Minute: 07 Second: 20 |
| The United States mainland is on standard time. |
| U.S. daylight time begins on 04-04-1993 at 02:00:00 local time. |
+-----------------------------------------------------------------------------+
System clock set: 06:07:20.01
+-----------------------------------------------------------------------------+
| ACTION SUMMARY (at instant of timesetting) |
| Internal delay adjustment: .01 sec. (added to set time) |
| Line delay adjustment: .0511 sec. (precompensated by time service) |
| |
| Universal Time Coordinated: 14:07:20.01 (time at 0x longitude) |
| UTC Date: 03-05-1993, Friday (date at 0x longitude) |
| |
| Local computer time was: 06:07:20.01 (RighTime-assisted) |
| Set to: 06:07:20.01 Pacific Standard |
| Local computer date was: 03-05-1993 |
| Set to: 03-05-1993, Friday, Day 064 of 1993 |
+-----------------------------------------------------------------------------+
Program STSORBIT PLUS Satellite Orbit Simulation Page 147
FEATURES OF RIGHTIME 2.5+
-------------------------
RighTime brings exceptional system time of day clock performance to
the DOS-based AT-class-compatible PC computer with no additional hardware.
With RighTime installed, the standard real time clock system becomes an
Adaptive Mathematically Compensated Crystal-controlled Oscillator based
clock. Under stable conditions, RighTime can produce a system clock that
keeps time within one half second per week or better (some testers have
reported accuracy of 0.07 second per week); this is about 0.8 parts per
million error, or more than 100 times better than an unconditioned crystal
time base alone, or 30 times better than a moderately conditioned one like
a modern watch of quality.
o True one hundredth second DOS clock resolution: the 55-millisecond
barrier is broken! The standard DOS clock resolves to only about 1/18
second; under RighTime v2, the new high resolution DOS clock resolves
to, and increments in, hundredths while the Int 08h and 1Ch tick rate
remains standard.
o RighTime intrinsically sets the hardware clock and solves the midnight
rollover date bug that exists in some DOS versions; this eliminates
the need for other utility programs or drivers that perform these
functions. Unlike DOS alone, the hardware clock seconds transition
will be properly set by RighTime and the time will be set to
hundredths of a second resolution, and these qualities will survive
through rebooting.
o Each time you set the time, RighTime will improve the accuracy of the
clock error corrections and will subsequently improve the accuracy of
the clocks. It should be easy to achieve a worst-case error of less
than 0.5 second per day and under good conditions, less than 0.5
second per week; typical results are much better. Command line
options are provided that allow fine tuning the correction process to
your system. A trimming option provides for offset adjustments in
hundredths of a second.
The following is a screen dump of the data displayed by RIGHTIME:
RighTime: Indicated DOS clock date and time is 1993/03/05 06:04:45.66.
RighTime: Warm correction rate is +2.83 seconds per day.
RighTime: Cool correction rate is +4.27 seconds per day.
RighTime: Current applied DOS-CMOS RTC offset is +0.46 second.
RighTime: Last CMOS RTC adjustment was 0.00 hours ago.
RighTime: Last timeset was 23.33 hours ago.
RighTime: System has been warm 17% of the time since the last timeset.
RighTime: Stack A headroom is 92 bytes; Stack space used is 68 bytes.
Stack D headroom is 100 bytes; Stack space used is 60 bytes.
RighTime: /?=Help; Version 2.53
RighTime: Copyright 1991-93 GTBecker, Dallas 214/402-9660. All Rights
Reserved.
RighTime: Resident and enabled.
RighTime: Selftest passed.
Program STSORBIT PLUS Satellite Orbit Simulation Page 148
Program PRECISION TIME
----------------------
Program PRECISION TIME, a commercial product by Crystalogic, Inc.,
provides in a single program the time setting and time maintenance
functions to keep a PC clock running accurately. An AT-class (80286 or
higher) computer is required and, as with all such programs, the computer's
hardware clock must be "reasonably" stable and predictable with respect to
cold and warm drift rates in order to maintain long term accuracy.
PRECISION TIME is suitable for applications which require an absolute
accuracy of approximately +/-1 second referenced to NIST or USNO;
applications requiring higher accuracy should consider alternative
solutions. The one second granularity of the program's time adjustments may
also cause difficulties for certain applications.
PRECISION TIME ("PTIME") is an "all-in-one" program which calls a
telephone time service (NIST or USNO), sets the computer's hardware and
software clocks, then executes as a TSR (Terminate and Stay Resident)
program to maintain the accuracy of the hardware clock to within one
second. Calling the telephone time service may be performed manually on
demand or at predetermined intervals (1 to 999 days). PTIME "guards"
against inadvertent setting of the time or date EXCEPT by PTIME using a
telephone time service. PTIME may be configured to handle the changes
between Standard Time and Daylight Savings Time automatically. All program
activity may be logged for future reference in a log file, PTIME.LOG.
PTIME is well documented with a printed manual and installs easily and
quickly. Although PTIME does not adjust the hardware clock as frequently
nor to comparable precision as do programs such as RIGHTIME (above), this
may make its internal interface somewhat more robust and reliable in
complex hardware or software environments. During the entire time that
PTIME has been operating on the RPV ASTRONOMY BBS there have been no
failures or system crashes. As the following (edited) excerpt from
PTIME.LOG illustrates, the system clock is updated periodically and is kept
within approximately one second of the correct time as received from NIST:
06/21/1994 07:24:11.00 PTIME - Time adjusted one second backwards.
06/21/1994 10:32:16.01 PTIME - Time adjusted one second backwards.
06/21/1994 13:40:18.01 PTIME - Time adjusted one second backwards.
06/21/1994 16:48:24.03 PTIME - Time adjusted one second backwards.
06/21/1994 19:56:28.03 PTIME - Time adjusted one second backwards.
06/21/1994 23:04:34.00 PTIME - Time adjusted one second backwards.
06/22/1994 02:00:41.04 Time was changed by: Calling an Atomic Clock
Drift amount was: 00:00:00.98
06/22/1994 05:08:42.01 PTIME - Time adjusted one second backwards.
06/22/1994 08:18:49.00 PTIME - Time adjusted one second backwards.
In fact, the error of 0.98 seconds was the largest seen in two months of
operation and, after an initial calibration period, NIST is called only
every five days. (The RPV ASTRONOMY BBS primary computer is always turned
on except for very brief maintenance periods.)
The user may view the current status of PTIME and its adjustments at
any time. The following is an example screen:
Program STSORBIT PLUS Satellite Orbit Simulation Page 149
----------------- Time Adjustments ------------------
Calibration Driver Version: 1.56
Last Sleep Time: 06/22/1994 06:55:28.05
Last Wake Time: 06/22/1994 06:57:37.39
Last Wakeup Adjustment: +0 seconds
Current Time: 17:40:58.10
Seconds Between Adjustments: 11282
Hundredths/Sec to Adjust: -100
Seconds Until Next Adjustment: 7771
Adjustments Handled: 262
Error Count: 0
Last Adjustment 06/24/1994 16:42:29.03
Sleep Time Since Last Call: 129 (0%)
Awake Time Since Last Call: 229151 (100%)
PRECISION TIME is available from:
Crystalogic, Inc.
2525 Perimeter Place Drive, Suite 121
Nashville, TN 37214
Voice: (615) 391-9100
FAX: (615) 391-9997
BBS: (615) 391-8065
As of 1 May 1994, the list price for PRECISION TIME was $79.95 plus
shipping and handling. Contact Crystalogic for current information.
Program STSORBIT PLUS Satellite Orbit Simulation Page 150
Computer Bulletin Board Systems
-------------------------------
RPV Astronomy BBS (310) 541-7299
CELESTIAL BBS (513) 253-9767 <-- Note new number 1/06/94
NASA GSFC OIG RBBS (301) 262-6784 <-- Note new number 7/24/93
NASA Spacelink BBS (205) 895-0028
CSS BBS (905) 458-5907 <-- Note new number 3/15/94
JPL PAO BBS (818) 354-1333
JSC PAO BBS (713) 244-5625
Timely 2-line orbital elements are essential for accurate satellite
tracking. In addition to my own bulletin board systems, five other bulletin
board systems provide authoritatve data for the general public. Some or all
files on these systems are compressed to reduce download time and must be
decompressed before use; compressed files may be recognized by file types
such as ".ZIP", ".ARJ", ".ARC", ".PAK", etc.
I have maintained my RPV Astronomy BBS (computer bulletin board
system) as a public service since 1987, (310) 541-7299, 2400-14400 baud
with 2 lines. The system has some 2000+ files, 150MB, available for
download. During Space Shuttle missions, I post current 2-line elements at
least daily (provided I'm in town!). The system usually also has current 2-
line elements for a large number of satellites in addition to other files
of interest to space and astronomy enthusiasts. The system is very popular
and, therefore, is frequently busy! The RPV Astronomy BBS is open to all
callers but first time callers are granted more limited access and time
than registered users.
Since the mid-1980s, Lt. Col. T. S. Kelso, USAF, has been making the US
Space Command (formerly NORAD) orbital data available as a public service
on his Celestial BBS at (513) 253-9767, 1 line at 1200 to 14400 baud. The
2-line element sets are prepared by Kelso using data received directly from
U.S. Space Command (formerly NORAD) by special arrangement. I regularly
post a concantenated and sorted version of the current element sets on my
own RPV ASTRONOMY BBS as file TLEnnn.ZIP, where "nnn" is a number such as
"420", the current Prediction Bulletin number. Kelso provides data for
several categories of satellites: Amateur Radio, Earth Resources, Manned
Spacecraft, Navigation, Weather, and NASA's 30 Day Specials (which contain
objects launched within the last 30 days and are often easy to spot
visually). More specifically, these include the following satellites or
satellite series: OSCAR, Radio Sputnik, UOSAT, Cosmos, LandSat, SeaSat 1,
SPOT, Mir, Salyut 7, Soyuz, Space Shuttle, NAVSTAR (GPS), GOES, Meteor, and
NOAA.
The Canadian Space Society BBS, (416) 458-5907, 1 line at 1200 and
2400 baud, also regularly posts NORAD 2-line elements. Much of the orbital
data is obtained from Celestial BBS but additional data is generated by Ted
Molczan and his worldwide team of observers. Note that the CSS format is
slightly non-standard, having additional information on the first (title)
line for each satellite, and may have to be edited for use with some
tracking programs. The CSS files also have considerable additional text
material (including current satellite news) before and after the actual 2-
line elements data; this text may have to be edited out before use.
The U.S. Space Command sends all unclassified 2-line elements to the
Orbital Information Group at Goddard Space Flight Center. These elements
are available on the GSFC OIG RBBS, (301) 262-6784, 4 lines @ 1200 and 2400
baud. The OIG database contains elements for some 7000+ satellites and is
Program STSORBIT PLUS Satellite Orbit Simulation Page 151
updated every weekday morning except holidays. Elements for popular
satellites are posted in a file called GROUPTLE.ZIP which contains seven
".TLE" files for some 750+ popular satellites. The data for the entire
database of satellites are available on a query basis. Access time is
limited to 20 minutes per caller per day. I regularly post a combined and
sorted set of the .TLE data as file GSFCnnn.ZIP on my own RPV ASTRONOMY BBS
where "nnn" is a number like "408". Individuals who wish access to the RBBS
must write (include full name and address):
NASA Goddard Space Flight Center
Project Operations Branch/513
Attn: Orbital Information Group
Greenbelt, MD 20771 USA
The OIG RBBS began operation in September, 1991. Until that time, the only
method for obtaining the OIG data was by mail. OIG now plans to discontinue
all mail services in early 1993 and thereafter the only method for
obtaining the OIG data will be via the RBBS.
The NASA SpaceLink BBS in Huntsville, Alabama, (205) 895-0028, 8 lines
@ 300-9600 baud, provides mission information for all space shuttle
missions and (usually) 2-line orbital elements both pre-mission and while a
mission is in progress. 2-line elements for selected satellites are also
available. In addition, SpaceLink has a wealth of other NASA information,
computer programs, teaching materials, and image files.
In January of 1993 the Public Affairs Office at the NASA Jet
Propulsion Laboratory began BBS service related to JPL-supported missions.
Mission status reports and high quality GIF images are the principal files
currently available. The number is (818) 354-1333, two lines at 1200 to
9600 baud.
Program STSORBIT PLUS Satellite Orbit Simulation Page 152
STSORBIT PLUS Revision History
------------------------------
Each released version of STSPLUS uses a four digit revision code such
as 9435. The first two digits indicate the year and the second two digits
indicate the week of the year. In some cases, an additional letter suffix
is added to distinguish changes occurring within the same week or to
identify special versions. A partial week at the beginning or end of the
year is counted as a full week. Using this method, a year will typically
have 53 weeks although it is possible to have 54 weeks in a leap year (1972
is an example). The current year-week revision code is shown on the Julian
Date display, Display Mode 7, in my program ASTROCLK.
This file records the revision history of program STSPLUS through all
of the minor twists and turns that usually accompany the evolution of such
a complex program. It illustrates the tortuous process of maintaining and
refining a program as ideas and problems are reported from every quarter.
These notes may also be helpful to users who are upgrading from one version
to another to find out what has changed.
David H. Ransom, Jr.
Version 9435A -- August 1994
----------------------------
-Version 9435A corrects a problem with certain country codes (such as those
which use the "YY-MM-DD" date format) which still caused "BASIC Error = 5"
in the orthographic mode for Version 9435. The program should now be
independent of the country code.
-Corrected a minor bug with amateur radio satellite frequencies. If the
primary satellite was changed with F6, the frequency file (STSPLUS.FRQ) was
not rescanned and the frequencies from the prior satellite remained.
STSPLUS will now always rescan file STSPLUS.FRQ if the primary satellite is
changed.
Version 9435 -- August 1994
---------------------------
-This release repairs an unfortunate bug which surfaced when I added the
NORAD-style date on the orthographic display. Only users who set DOS to
non-US-style date formats were affected. The problem occurred immediately
when drawing the orthographic map as "BASIC Error = 5" and returned the
user to DOS.
-Added satellite name cross-reference in file STSPLUS.XRF. When TLEs are
read and accepted, STSPLUS now checks for the cross-reference file and, if
the file is present in the current directory, checks for the NORAD Number
of the satellite and a cross-reference name. If found, the new name is
substituted for that found in the TLE file. The file is standard ASCII and
each entry consists of a SPACE, the five-digit NORAD Number, a SPACE, and
then the satellite name. A sample file:
22920 HST Solar Array
22076 Topex/Poseidon
21225 Gamma Ray Observ
20638 Rosat Observatory
20580 Hubble Telescope
Program STSORBIT PLUS Satellite Orbit Simulation Page 153
16609 MIR Space Station
NOTE: The leading space is required for file compatibility with my program
ORBITEL (but is optional for STSPLUS). The NORAD Number MUST be 5 digits;
pad with leading zeroes if necessary. Only one entry is read per satellite.
If the satellite name is longer than 19 characters, only the left 19
characters will be used. This feature may be used to substitute any name
for that given in a TLE file (which is not always consistent from source to
source) or to specify a payload piggy-backed on another satellite (as is
frequently the case with amateur radio transponders). A number of XRF files
are posted on my RPV Astronomy BBS; such files must be renamed for use with
STSPLUS.
-Repaired a minor bug which caused the pass predictions (F3 from Main Menu
to repeat a pass indefinitely when that pass was a grazing pass with a
maximum elevation of less than one degree (0.14 degrees in the test case
reported by Ken Ernandes).
-Corrected a bug in read/save .SCF files (F6 from the Main Menu). If a
fileltype is entered (".SCF" or whatever), it is now ignored and ".SCF" is
automatically appended to the filename. Thanks to Paul Becker for reporting
the problem.
-In response to many requests, the date input routine has been modified to
permit entry in the European style "dd.mm.yyyy" in addition to the US style
"mm/dd/yyyy". The choice of delimiter ("." or "/") determines the method of
interpretation. In both cases, the year may be entered as the last two
digits only, "yy", if desired; "50" through "99" will be interpreted as
"1950" through "1999" and all others as 2000+yy. Dates are displayed as "dd
MMM yyyy" where "MMM" is the English abbreviation for the month.
-All current .SCF files are now displayed for both SAVE and READ functions
(F6+F2 and F6+F3 from the Main Menu).
-Improved backspace processing and error checking when entering TLE
filenames (F2 from the Main Menu).
-Corrected "West Latitude" to "West Longitude" in the data entry section
for local coordinates (F10+F2).
-Various minor cosmetic changes.
-Version 9434 was released as a Beta Version to selected users and included
all changes in Version 9435 EXCEPT the repair to the NORAD-style date bug.
Version 9432A -- August 1994
----------------------------
-As too often happens, a bug was discovered in Version 9432 just after it
was released. The elevation ("Elv") and azimuth ("Azm") in the rectangular
projections either remained at zeroes or at the last value calculated
during orthographic projection. There was no workaround. The problem has
been repaired. My apologies to those who received the defective version.
Version 9432 -- July 1994
-------------------------
-Version 9432 adds several new features and corrects a number of program
errors and/or "bugs". Several minor cosmetic changes were also made.
-Added Data Output Mode 8 to generate tabular output for Doppler Shift
calculations for a selected pass while the tracking map is displayed. Use
F3 from the Main Menu and select Mode 8; setup features are identical to
other modes (output device, interval, etc.). See text for details.
Program STSORBIT PLUS Satellite Orbit Simulation Page 154
-Look angle calculations [elevation ("Elv") and azimuth ("Azm")] during the
tracking map display are more accurate thanks to an improved algorithm
supplied by Ken Ernandes. Users should note that near culmination (maximum
elevation) for passes near the user's zenith (approaching 90 degrees
elevation) there is some uncertainty and ambituity as to azimuth although
the angular error remains very small.
-Changed "Alt" to "Elv" as the label for satellite elevation (altitude)
above mean sea level to conform to standard satellite tracking convention.
-Because STSPLUS is used worldwide, I have reformatted all displayed dates
throughout the program to avoid confusion of the day versus the month. For
orthographic displays, the display now shows the current UTC date and time
("dd MMM hh:mm:ss UTC") and then the local time ("dd mmm hh:mm:ss PDT"
where "PDT" is replaced by the local time abbreviation). For both dates,
the year is implied. The MET/T+E is moved up one line. A typical time
display will show:
15 JUL 19:57:36 UTC
15 JUL 12:57:36 PDT
7/03:14:36 MET
For the Main Menu and rectangular projections, the dates are all given as
"dd MMM yyyy". Data locations are unchanged. A typical date and time will
now be displayed as:
15 JUL 1994 19:57:36 UTC
For all cases, "MMM" is the three letter English abbreviation for the
month, "JAN" for January, "FEB" for February, etc.
IMPORTANT NOTE: Keyboard entry of dates is still in the American
numeric format, "mm/dd/yyyy" or "mm/dd/yy".
-For orthographic projections, the current time using NORAD convention
("yyddd.dddddd") is displayed immediately beneath the current TLE filename:
94196.831667
This provides an immediate method to identify the current year and day-of-
the-year, "94" and "196" respectively in the example above.
-Added an additional data line in orthographic display to show the current
orbital period ("Per'd" using the format "hh:mm:ss") for normal display OR,
for satellites with Eccentricity >= 0.005, satellite Phase, defined as Mean
Anomaly normalized to the range 0-256 ("Phase" using the format "nnn.n")
for use with the Doppler Shift mode [press F8 while the map is displayed]
and satellites which change transponder mode based upon phase. Although
Phase is technically defined as an integer value from 0 through 255,
STSPLUS displays it to one decimal place to alert users to upcoming
phase/transponder changes. Other users may also be interested in two
important Phase or Mean Anomaly angles: Phase=0.0 (Mean Anomaly is 0
degrees) corresponds to perigee and Phase=128.0 (Mean Anomaly is 180
degrees) corresponds to apogee.
NOTE: Mean Anomaly (and therefore Phase) becomes undefined for a
perfectly circular orbit. In practice, satellites with eccentricity
less than 0.005 will display some ambiguity as to Mean Anomaly and
Phase. Note also that the "Elv" is the geodetic elevation (altitude)
of the satellite above Mean Sea Level and NOT the geocentric radius of
the satellite's orbit, the paramter used to determine apogee and
perigee; the difference due to the shape of the Earth is as much as
21 km. See the section "Satellite Communications and Amateur Radio"
for additional discussion!
Program STSORBIT PLUS Satellite Orbit Simulation Page 155
-Repaired the Tracking Station color feature (F10+F9) so that it operates
correctly. Versions 9415/9414 caused the entire screen to turn light red
when the Tracking Station color was changed due to a careless coding error.
-Rewrote the local coordinates code and text (F10+F2) to improve clarity
and add several features. Now uses a function key menu to select action to
perform. Press ENTER to return to prior menu. When entering new
coordinates, an illegal latitude or longitude will cause that coordinate to
be set to zero. Longitude may be entered as East Longitude (0 to +360) or
West Longitude (0 to -180); the longitude is converted if necessary and
stored in the range from -180 to 0 to +180.
-The threshold for generating the "Satellite may have decayed!" message has
been increased to a Mean Motion of 16.4 revs/day to reduce the probability
of the message appearing during low shuttle flights.
-Added code to check for synchronization and data errors in the .INI file
between the "short form" satellite position data and the 2-line elements.
If the NORAD numbers do not agree, the "short form" data will be set to the
TLE NORAD number and the remaining data reset; if TLEs are not present,
dummy TLEs are inserted. Use F6 to verify and/or correct the secondary
satellites, then use F2+& to update data from TLE file(s).
-Adjusted the "trigger" for automatic redraw in orthographic modes with
higher zoom factors to compensate for high speed processors such as the
90MHz Pentium. (Under some circumstances, redraw was being triggered
continuously.)
-Repaired a minor bug that caused the TDRS and Sun AOS/LOS data to be
missing on the rectangular display when Doppler Shift mode had been
selected on the orthographic display.
-Corrected the conversion factor used to convert meters to feet. Thanks to
Steve Lenz for reporting the bug!
-Removed all references to the RPV HOTLINE BBS since that telephone line is
now in rotary with the main number, (310) 541-7299.
-Versions 9424, 9429, and 9431 were beta test versions not released
publicly and included some of the features and changes in this release. For
Version 9424, the precision of Doppler shift frequencies was increased to 5
digits (10 Hz) to the right of the decimal point but this proved confusing
and has been restored to 4 digits (100 Hz).
Version 9415 -- April 1994
--------------------------
-This release repairs a problem in rectangular projections which caused the
Alt/Az calculations to be incorrect. (The data in orthographic projections
were alright.) The problem was traced to a duplicated variable name which
was added to shared common. Only file STSPLUS.EXE is changed.
Version 9414 -- March 1994
--------------------------
-This is a MAJOR UPGRADE, adding new features for satellite communications
and amateur radio, user-definable map colors for certain map features,
improving RA/DEC coordinates, and incorporating several bug fixes.
-See also the notes below for Version 9406 (not released publicly).
ENHANCEMENTS FOR SATELLITE COMMUNICATIONS AND AMATEUR RADIO:
------------------------------------------------------------
Program STSORBIT PLUS Satellite Orbit Simulation Page 156
-By popular request and with the assistance of Ken Ernandes, N2WWD, I have
added Doppler shift calculations for uplink and downlink frequencies. The
calculated uplink (XMIT) and downlink (RECV) frequencies have been tested
in full duplex with RS-10 and yield excellent results. The Doppler shift
calculations are available in orthographic projections ONLY for this
release. See the text for complete discussion.
-The satellite NORAD Number, UPLINK and DOWNLINK frequencies (referenced to
the satellite), and the transponder mode are specified in file STSPLUS.FRQ
in that order, separated by commas and without any leading or trailing
spaces. A sample file might include:
00000,100,100,1 (Default values if sat # not found)
18129,145.8900,29.3900,1 (Parameters for NORAD #18129)
--+-- ----+--- ---+--- +
| | | |
| | | +-- Transponder Mode: 1 = NORMAL
| | | -1 = INVERTED
| | |
| | +------- DownLink Center Frequency (MHz)
| |
| +--------------- UpLink Center Frequency (MHz)
|
+----------------------- Satellite NORAD Number
The first sample line shows the "00000" entry which determines the default
parameters if the satellite is NOT included in file STSPLUS.FRQ. This
should be the FIRST LINE in file STSPLUS.FRQ. The second line gives real
parameters for a specific satellite; the frequencies shown select the Mode
A voice passband for Radio Sputnik 10 (RS-10, piggybacked on COSMOS 1861,
NORAD #18129). The uplink and downlink frequencies should not exceed
99000.0000 MHz to avoid an overflow condition on the display.
-File STSPLUS.FRQ may be created or edited with any ASCII editor; word
processor users, use the "non-document" mode. Note that only minimum error
checking is performed and the user must observe the required format exactly
for each line in the file.
-The Doppler shift calculations replace the TDRS and Sun AOS/LOS data in
the data block to the right of the orthographic map. To enable display of
these frequencies, press F8 while the map is displayed; to return to the
AOS/LOS calculations, press F8 again while the map is displayed. F8 is NOT
active when in PAUSE mode. The following example illustrates the display as
a satellite approaches the ground station (using 1000 MHZ for both
frequencies to show the relative transmit and receive ratios):
UpLink: 1000.0000 Uplink frequency received by satellite
XMIT: 999.9761 TRANSMIT frequency at ground station
DnLink: 1000.0000 Downlink frequency xmitted by satellite
RECV: 1000.0239 RECEIVE frequency at ground station
The XMIT and RECV frequencies will be shown in color on EGA/VGA color
monitors:
RED Satellite is below receiver's horizon
YELLOW Satellite is 5 degrees or less above receiver's horizon
GREEN Satellite is 5 degrees or more above receiver's horizon
Program STSORBIT PLUS Satellite Orbit Simulation Page 157
Transmissions will not normally be possible when RED is shown.
Transmissions MAY be possible when YELLOW is shown. Transmissions should be
practical when GREEN is shown provided the ground station has a clear
horizon in the direction of the satellite.
-STSPLUS includes a "fine tuning" feature for the uplink and downlink
frequencies. While in the Doppler shift calculation mode, the following
keys have a different function from the normal map modes:
UP Arrow Increase RECV frequency by 100 Hz
DOWN Arrow Decrease RECV frequency by 100 Hz
PgUp Increase RECV frequency by 1 KHz
PgDn Decrease RECV frequency by 1 KHz
Home Restore Uplink and DnLink frequencies to those
read in from file STSPLUS.FRQ
End (not used)
If the satellite transponder is NORMAL, the XMIT frequency will be
increased or decreased by the same amount as the RECV frequency. If the
satellite transponder is INVERTED, the amount of change in the XMIT
frequency will be the same magnitude but in the opposite direction as the
change to the RECV frequency.
OTHER SOFTWARE ENHANCEMENTS AND CHANGES IN THIS RELEASE:
--------------------------------------------------------
-In response to numerous user requests, the colors for certain map features
are now user-definable. The assignable features are:
Local Station circle of visibility
Isocontour circles in Location and Tracking Station modes
Tracking Station circles of visibility
From the Main Menu, use F10+F9 to set these colors. The new colors will be
saved in file STSPLUS.INI for future use. To those users who want to
change EVERYTHING, my response is: a) that's a non-trivial programming
exercise, and b) I've spent considerable time designing the program to have
a certain "look and feel" which I wish to retain.
- The Program Features and Options menu has been changed. Function Key F9
is now used for User-Definable Colors (above) and not for setting the UTC
Offset and Daylight Flag. Use F8+F10 from the Main Menu to set the UTC
Offset and Daylight Flag.
-Users are reminded that STSPLUS expects ground station coordinates
(latitude and longitude) in the geodetic coordinate system, as commonly
used on maps (WGS-72 System). Ground station altitude (elevation above Mean
Sea Level) is expected in METERS; if a ground station is significantly
above Mean Sea Level, accuracy will be substantially improved if an
accurate altitude is used. Many cities in file STSPLUS.CTY have ZERO given
as the altitude if no altitude was available in the source(s) used for
preparation of the file. The same comments apply to Tracking Stations in
file STSPLUS.TRK.
-The coordinates for Right Ascension and Declination were incorrect in
prior versions. The ground station's GEODETIC latitude instead of the
GEOCENTRIC latitude was used in the calculations. The error was greatest
(especially the Declination) for ground stations in mid-latitudes as a
satellite approached local zenith. Thanks to Alan Nutley of Australia for
putting me on the track of this one!
-Local horizon coordinates were also affected by the latitude error. The
Program STSORBIT PLUS Satellite Orbit Simulation Page 158
typical error near maximum was one or two degrees in altitude (elevation).
-The keyboard response time has been improved; except when the map is
actually being drawn, response is immediate instead of waiting for the next
second. In the Doppler Shift Mode, the arrow keys and PgUp and PgDn may be
held down to repeat. During rapid key repeats, map and data updates may be
deferred; waiting for a second will allow the map and data to be updated.
-The primary satellite's circle of visibility did not display on the World
Map when the Motion Map (Dual-Page EGA Mode) was enabled. This has been
corrected. Thanks to Todd Sherman for reporting the bug.
-Corrected a problem which caused BASIC ERROR 6 on restart when the SHELL
TO DOS (F9 from the Main Menu) was used and the program was in orthographic
projection.
-Various minor bug fixes and cosmetic changes.
-Versions 9412 and 9413 were BETA VERSIONS released on a limited basis.
-Special thanks to Ken Ernandes, N2WWD, for his assistance and testing of
the satellite communications and amateur radio features!
Version 9406 -- February 1994
-----------------------------
-This version was for Beta Test only and was not released publicly.
-Several users have reported that file STSPLUS.INI sometimes became corrupt
and I have (finally) found and corrected the problem. An array index was
overrunning the bounds of the array and overwriting other data in SHARED
COMMON. This usually only affected the data in secondary satellites but was
potentially more dangerous. The problem also caused some dot colors on the
ground track to be incorrect.
-When no STSPLUS.INI file is present (or when the UTCOffset is set to -99),
the user is automatically asked to set filenames and paths.
-In response to quite a number of user requests, I have added the "/SS"
command line option to force STSPLUS into a "screen saver" mode. In this
mode the program displays the full orthographic globe, ground track and all
selected map features but NO DATA at the right. Use ENTER or ESC to return
to DOS.
-New command line options have been added to control certain display
features (especially from batch files). The new feature status is saved in
file STSPLUS.INI.
+L Include Location and Feature Labels
-L Exculde Location and Feature Labels
+R Include Rivers and Lakes
-R Exclude Rivers and Lakes
+T Include Tracking Stations
-T Exculde Tracking Stations
+V Include Local Circle of Visibility
-V Exclude Local Circle of Visibility
-Because of problems reported with word processors which add the 8th bit to
some characters (and have been used to edit TLE files), I have added code
to strip off the 8th bit in Line 0 of TLEs. However, this is not foolproof,
and users are cautioned to use ONLY editors which do NOT add the 8th bit
and which maintain the "standard" CR/LF at the end of each text line.
Program STSORBIT PLUS Satellite Orbit Simulation Page 159
Version 9405 -- January 1994
----------------------------
-Version 9405 is a MAINTENANCE UPDATE, correcting a number of relatively
minor bugs and updating the documentation to reflect changes in Versions
9403 and 9405.
-Rewrote MET calculations to (hopefully) avoid truncation and rounding
errors which sometimes caused MET to be one second off. The problem was
dependent upon both launch and epoch times.
-Added default filenames and paths if UTCFlag is set to -99. (Setting
UTCFlag to -99 may be used to distribute STSPLUS.INI files when the
ultimate user's time zone is unknown. This procedure forces the user to set
the UTC and DAYLIGHT values, and is NOT recommended for the novice!)
Filenames and paths should ALWAYS be checked and set if necessary using F7
from the Main Menu whenever upgrading to a new version.
-Improved calculation algorithm for "Calculating Orbital Data" phase of
program initialization for satellites with mean motion less than 15 and
greater than 2. The improvement may only be apparent on slower processors
or systems without a math coprocessor.
-Corrected a cosmetic bug which caused the time portion of negative MET to
appear at the left on the next line in rectangular projection modes.
(Missing semicolon!)
Version 9403 -- January 1994
----------------------------
-In response to numerous complaints about BASIC ERROR 6 ("Overflow") when
using Relative Target Tracking with rectangular map projection, I have
corrected a condition while calculating relative velocity which could
generate the overflow error. The error may be related to processor speed
and/or specific 2-line elements and has been difficult to reproduce.
-Corrected several differences between rectangular and orthographic maps so
that rectangular maps are processed as close as practical to the way that
orthographic maps are processed. This eliminated some spurious data that
was displayed momentarily as the rectangular map was first drawn and may
also help avoid the BASIC ERROR 6 problem (above).
-Corrected a cosmetic bug which caused the "s" in "ft/s" and "m/s" to
remain on the screen when switching coordinates from target data to other
coordinates using F10 while the map is displayed.
-Several minor cosmetic changes.
Version 9402 -- January 1994
----------------------------
-Corrected (I hope) a bug which caused BASIC ERROR = 6 when switching from
MET to T+E while using a Target Satellite. The problem was traced to a
variable which was not re-initialized when F5 was pressed while the map was
displayed.
Version 9353 -- December 1993
-----------------------------
-Added Relative Target Tracking (not included in Beta Test Versions 9351
and 9352) to report relative range [km or nm] and velocity [m/s or ft/s]
between the Primary Satellite and a Target Satellite selected from among
the Secondary Satellites. Relative Velocity data is presented ONLY if the
Program STSORBIT PLUS Satellite Orbit Simulation Page 160
Relative Range is less than 5000 km. The Target Satellite is selected with
F6+F5 and the relative tracking data is enabled by F3+F6 from the Main Menu
or F9 while the map is displayed. See text for details.
-The Secondary Satellite code has been modified to save a skeletal TLE when
a new satellite is added. This permits the user to use F2+'&' to update
TLEs INCLUDING the new satellite(s). The warning message for satellites
without TLEs in F6 has been modified to remind users that they may either
update the TLEs or display the satellite ground track.
-I seem to have tracked down an internal timing anomaly that caused errors
in the tracking data of about +/-0.5 seconds. Worst case, this caused an
error in calculated position on the order of tens of meters (about the
length of the space shuttle!) and would not be easily detectable under most
circumstances. Thanks to Ken Ernandes for first reporting the problem
several months ago.
-Corrected a problem which caused the STSPLUS.INI file to become corrupt if
Event Timers were set to OFF. Thanks to Chuck Dean for reporting the bug!
-Corrected a problem with secondary satellites and .SCF files when one or
more secondary satellites was deleted, leaving blank satellite slots.
Secondary satellites may now occupy any slot with or without intervening
blank slots.
-The Primary Satellite is now labeled "Primary" and shown in YELLOW if it
is included in the satellite configuration data (F6+F1).
-When displaying the satellite configuration data (F6+F1), the 2-line
elements are checked for epoch. If the epoch is more than 10 days (Real
Time) or 60 days (Static) prior to the current/simulated time, a flashing
RED asterisk ("*") is shown next to the satellite number and a warning is
shown at the botton of the screen. NOTE: This is a caution warning only;
the elements may or may not still be valid.
-Added an "OFF" mode for Secondary Satellites (F6+F1). The OFF mode permits
one or more satellites to be disabled (not displayed) without removing the
data from the secondary satellite data. All data are retained and the
satellite may be re-enabled at any time. Thanks to Paul Grupp for the
suggestion!
-Added grid labels in the orthographic displays (when Additional Grid Lines
are enabled with F10+F3+F3) for latitude and longitude when the MAG factor
is 500 or greater. Latitude labels are always at the left side of the map;
longitude labels are at the top or the bottom depending upon the map
center. The labels are disabled for polar and near polar maps because of
the projection.
-Changed the plot update interval for secondary satellites to EVERY SECOND
if a 386 or higher processor AND a math coprocessor are present. This
avoids a "leapfrogging" effect between the primary and secondary satellites
during close proximity operations. For other processor/coprocessor
combinations, the plot update interval remains TEN SECONDS as in prior
versions. In all cases, the ground track for secondary satellites is only
plotted every ten seconds in order to avoid cluttering the display.
-Changed the orbit number calculation after considerable debate. The code
used in all prior versions caused the TLE orbit number to be incremented if
the epoch of the TLE was in the latter half of the orbit (at or past the
descending node). The new method increments the TLE orbit number only if
the epoch is within 0.1 orbit of the ascending node. CAUTION: This change
may cause orbit numbers to be different if prior missions are replayed
using TLEs which were adjusted to compensate for STSPLUS' prior orbit
numbering conventions.
-Removed code which translated satellite names. Names beginning with "HST"
Program STSORBIT PLUS Satellite Orbit Simulation Page 161
were changed to "Hubble Space Telescope"; with the jettisoning of the "HST
Solar Array", that debris was being renamed also. A similar problem occured
with MIR debris. If you wish to rename one or more satellites, use my
program ORBITEL (available free on my BBS or for a donation of US$10.00 by
mail).
-Corrected a cosmetic bug which caused stray pixels to appear when a
secondary satellite intersected the circle of visibility for the primary
satellite. Thanks to Joel Runes for spotting the problem.
-Added the International Date Line in orthographic displays as a dotted
bright blue line where it is different from the 180th meridian.
-Corrected a cosmetic bug for map drawing time in orthographic mode. If the
operation spanned midnight, the drawing time overflowed the field with a
number like "%-86300.12", wrapping around to the left side of the screen.
-Removed the function to disable solar features (Sun and Terminator) from
the map using F8 while the map is displayed. The function is now available
ONLY from the Main Menu using F10+F3+F8.
-Changed the "Additional Grid Lines" function, F10+F3+F3, to ON or OFF.
-USSPACECOM has changed the format of the 3-character "Launch Piece"
portion of the International Designator in their 2-line elements (TLE) from
right justified to left justified. This caused STSPLUS to show "(n/a)" for
the launch piece. The data displayed when the elements are presented for
user approval have been changed from numeric to the alpha designation given
in the TLE. In other words, launch piece "B" will be so shown instead of
"2" as in prior versions.
-All references to "IAU Designation" have been changed to "International
Designation" or "Int'l Designation".
-Changed the limits on UTC Offset to allow +13 hours and -13 hours to
conform to civil practice for certain areas in the South Pacific.
-Removed the "FOV" (field of view) data from the orthographic data block.
The calculation was incorrect and misleading.
-Various cosmetic changes and improvements.
Versions 9351 and 9352 were BETA TEST VERSIONS with limited distribution.
A number of minor bugs were reported and have been corrected for this
release:
-Selecting a new Primary Satellite before a map was displayed sometimes
failed.
-Selecting a new Primary Satellite did not set MET correctly. The MET was
calculated for the prior Primary Satellite. Thanks to David Cottle!
-Secondary satellites set to OFF were drawn (but not updated) on the
rectangular projection.
-Corrected a cosmetic bug which caused the thousands digit of MET DAYS not
to be erased when switching large clock times (Mag=100, VGA only) with F2.
Similarly, the colon (":") was omitted when switching from MET to/from T+E
using F2.
Version 9338 -- September 1993
------------------------------
-Repaired a bug in multi-satellite modes which caused a "trail of dots" to
be left behind if the primary satellite icon fell on top of a secondary
satellite icon (such as during close proximity operations).
-Repaired a bug when reading SCF files. In prior versions, the primary
satellite was changed if the SCF file had a different primary satellite.
The primary satellite in the SCF file is now ignored. The format of the SCF
Program STSORBIT PLUS Satellite Orbit Simulation Page 162
file is unchanged to maintain compatibility with prior versions.
-Modified the World and Zoom Maps in rectangular projection so that the
PgDn key switches to Zoom Map (180 degrees) from World Map, and the PgUp
key switches to World Map from Zoom Map (180 degrees).
-Added list of available .SCF files when reading, F6+F3 from the Main Menu.
-Added a warning when writing .SCF files if the requested file already
exists. F6+F2 from the Main Menu. User must now press "Y" to overwrite an
existing file, ENTER or any other key to cancel.
-By user request, modified the small character set (used for labels) to
include the DASH ("-").
-After numerous user complaints, I've finally repaired the BLINK mode so
that for most systems the primary satellite icon will blink on and off once
per second. Press "B" while the map is displayed to toggle the BLINK mode.
-Repaired a minor bug which caused the message "Pause ... press ENTER" not
to be displayed if the map was redrawn during Pause Mode.
-Thanks to the many users who took the time to carefully document these
bugs, enabling me to find and fix them!
Version 9334 -- August 1993
---------------------------
-The maximum number of Static and Real Time satellites is increased to 32.
This permits the entire GPS constellation, currently 25 active Block I and
Block II satellites, to be tracked. The satellite setup display, F6+F1 from
the Main Menu, has been modified to two display pages of 16 satellites
each; the second page of 16 is not displayed if no active satellites are
present.
-Added "Clear Static and Real Time Satellites", F6+F4 from the Main Menu,
to speed reconfiguration of these satellites. It may be used to clear any
block of satellites NOT INCLUDING #1 AND #2 (which are assigned to TDRS
East and TDRS West and must be cleared manually). Users are cautioned that
once cleared, the satellite data for the cleared satellites is lost. If in
doubt, save the current satellite configuration to a SCF file using F2
BEFORE clearing!
-Somehow the "bullseye" was lost in the Tracking Mode for rectangular
projection several releases back. It has now returned. Thanks to Alan Pound
for reporting the problem!
-As an experiment, I changed the color of land boundaries from Light Cyan
to Cyan to make multi-satellites and other display features a little easier
to spot. Feedback welcome!
-When Extra Grid Lines are OFF (F10+F3+F3), changed the color of the grid
lines from Light Blue to Blue and added lines of latitude at +80 and -80
degrees.
-Various repairs to eliminate spurious pixels and other minor problems
associated with multi-satellites.
Version 9333 -- August 1993
---------------------------
-This is a MAJOR UPGRADE, adding multi-satellite capability. This is the
first in a series of upgrades for tracking multiple satellites and
rendezvous missions. Comments, suggestions, and bug reports are welcome!
-Special thanks to Joel Runes for his assistance during beta testing!
-OPERATIONAL HINT: With the addition of multi-satellite tracking, the
Motion Map feature now really comes into its own; press "M" when the normal
Program STSORBIT PLUS Satellite Orbit Simulation Page 163
map is displayed to switch to the EGA Motion Map, press "M" or ENTER to
return to normal map or to the Main Menu. All satellites are updated as
fast as the computer can draw the map. See the notes on a "vanilla" boot
without memory managers for dedicated STSPLUS uses.
-The format of file STSPLUS.INI has been substantially modified and files
from prior versions of STSPLUS will be ignored. The configuration
information must therefore be re-entered.
-Increased to sixteen the number of additional TDRS and real time satellite
positions in file STSPLUS.INI so that all active satellites may be updated
and displayed. Sample data are shown below. See the section "TDRS and Real
Time Satellite Features" for additional information.
19883,"TDRE ", -0.04218, -41.14169,10014
21639,"TDRW ", -0.03643,-174.14074,10014
22314,"TDR5 ", -0.31155,-138.36021,10004
19548,"TDR2 ", 0.05352, -61.66467,10004
13969,"TDR1 ", -6.59117,-170.55876,10004
16609,"MIR ",-17.45706,-178.73251,14115
-TLEs for each active satellite are now saved in the .INI file so that
accurate positions may be calculated dynamically. These TLEs should be
updated periodically.
-TLEs are may now also be saved in and read from special .SCF (Satellite
Configuration File) files so that multiple TDRS and Real Time satellite
configurations may be saved and/or selected. A sample file, STSPLUS.SCF is
included in the standard distribution. Function Key F6 from the Main Menu
is used to display, modify, save, or read these data.
-The 5-character abbreviation of each TDRS satellite may now be used to
label the satellite. The size and color of the icon used to display each
TDRS or real time satellite may now be independently controlled.
-STSPLUS now uses the calculated LATITUDE for the display of all TDRS
satellites. This will cause TDRS1, for example, to appear up to 7 degrees
North or South of the Equator (as of 8/9/93).
-The drive, path, and name of the .CTY file may now be set with F7 from the
Main Menu.
-The Motion Map is now available for the World Map in rectangular
projection. This is helpful with multiple real time satellites.
-Repaired an infrequent bug discovered by Joel Runes which causes the
orthographic map to be redrawn continuously when a) the satellite has a
high eccentricity (.73 in the test case), and b) when the map is being
drawn at approximately the time of perigee. The code has been modified to
take the Eccentricity into account in calculating the map offset time.
-Corrected a minor bug which caused MET in excess of 9999 days to overflow
the assigned format statement for the data block and appear as
"%12038/00:00:00 MET" with the "MET" wrapping around to the left side of
the screen. Obviously, there aren't many satellites with this problem, but
NORAD #00051 is one such. The STSPLUS.LTD entry for this satellite is:
00051,2437158.90208333,0
and the problem was noted because of the pre-launch "temporary" NORAD
number assignment for STS-51.
-A similar problem occured with the large clock displays. In both
projection modes, only the last four days of MET are now displayed (12038
days will display as "2038").
Program STSORBIT PLUS Satellite Orbit Simulation Page 164
-Added a reminder in the text that when entering filenames using F7 from
the Main Menu, a drive and path may also be included if desired. That
capability has been present for some time but was not stated explicitly.
-Changed the precision that the "plain English" display of the elements
Epoch Time is displayed for approval (F2 from the Main Menu) from [rounded]
integer seconds to 0.001 seconds, coordinated with VEC2TLE V9331.
-Several V9332 Beta Versions were released privately for testing.
Version 9331 -- July 1993
-------------------------
-In coordination with Ken Ernandes' VEC2TLE, the data output for Format 7,
ECI State Vector (Labeled Data), has been modified. The data have been
supplemented by the addition of two lines: Element Set Number; and, Rev
Number at Epoch. The International Designation has been added to the
Catalog Number line and the Epoch Time is now given to .001 seconds. The
data output for Format 4 has been changed so that it is identical to Format
7. See text for details.
-Per Ken Ernandes, the Format 4 & 7 label "Ndot/3" is changed to "Nndot/6".
-I have received NO REPORTS from anyone using Data Formats 5 and 6. Those
formats may not continue to be supported indefinitely UNLESS I am informed
of applications which use them.
CAUTION: STSPLUS Version 9331 Data Formats 4 and 7 are NOT compatible
with VEC2TLE Version 9322 when multiple state vectors are generated!
Use a release of VEC2TLE with a version number equal to or greater
than 9331. (However, manually editing the data to remove the Elset and
Rev Number lines can restore compatibility with the older version.)
NOTE: Users are urged to update to VEC2TLE Version 9331 or the current
version, which ever is later! Not only does the current version of
VEC2TLE maintain compatibility with STSPLUS but several important new
features have been added and a bug in Version 9322 which affected data
accuracy under certain circumstances has been repaired.
-The Tracking Station Mode is now active in both Orthographic and
Rectangular projections. The projection used will same as the one which is
active when the "T" key is pressed.
-Repaired a bug which caused the NORAD number displayed in the Pass
Prediction Mode to be incorrect under certain circumstances. Thanks to
Grant Pinto!
-Repaired a bug in the pass prediction logic which caused the MAX
VISIBILITY data to be missstated by a significant amount for certain
satellites, especially ones with higher eccentricities. Thanks to Grant
Pinto for spotting and reporting the bug!
-Changed the default time zone abbreviation for unrecognized (foreign) time
zones from all spaces (which confused the Pass Prediction setup!) to "LCL".
-Corrected a bug using F2 from the Main Menu which showed no 2-line
elements files if no .TXT files were found in the current directory but one
or more .TLE files were present. Thanks to Bob Krohn for reporting the bug.
If no files of either filetype are found, an error is displayed and the
user is returned to the Main Menu.
-Corrected a bug in default paths if the root directory was used. (Path
defaulted to "B:\\" instead of "B:\" for drive B:, etc.)
-Corrected a bug in the NORAD number for F2 from the Main Menu. If the
Program STSORBIT PLUS Satellite Orbit Simulation Page 165
NORAD number was greater than 32767, a negative nunber was shown.
-Disabled RIGHTIME detection for 8086/8088 processors. The detection
process affected the time in certain XT-class machines.
-Corrected a minor bug which caused the "blink" feature for the satellite
icon not to function under certain circumstances.
-Corrected a minor bug which initialized the Location Flag incorrectly for
CGA systems when file STSPLUS.INI was not present. Locations and Features
were displayed even though the menu display indicated they were OFF.
-Various cosmetic changes.
-Most of the changes in this release were included in Beta Version 9329.
Version 9320 -- May 1993
------------------------
-This is a MAJOR UPGRADE, adding new improvements and features along with
high precision state vector data output for use with Ken Ernandes' program
VEC2TLE.
-By popular request, STSPLUS now estimates if a satellite may be visible to
the naked eye or binoculars, and displays "VIS" in bright white next to the
orbit inclination if a visual sighting may be possible. See the section
"Satellite Visibility" for additional discussion.
-Also by popular request, the pass predections (F3, Data Mode 9) have been
enhanced to permit dates and times to be displayed for either UTC/GMT or
LOCAL time. An additional prompt has been added for that selection.
-When displaying predicted passes (F3, Data Mode 9), the satellite is now
approximately centered in the display (instead of being well to one side).
-After considerable confusion and several user comments, I have reworked
the pass prediction logic so that when the user returns to the Main Menu
after the ground track for a predicted pass is displayed, the time is
automatically restored to the real or simulated time in effect BEFORE the
pass prediction was displayed. This means that repeated use of the pass
prediction feature will generally display the same list of numbered passes
and the user no longer needs to restore real time (or reset simulated time)
after displaying predicted passes.
-Corrected a cosmetic bug on pass predictions when an illegal pass number
(greater than the last pass number displayed) was entered at the prompt.
-Added an asterisk ("*") at the left of each event timer when the satellite
is AOS (signal/Sun is being received). This will particularly benefit users
with monochrome or shades of gray.
-Enhanced the Precision X-Y-Z State Vector Data Modes (F3, Data Modes 4
through 7) to include four output formats: multi-line Ascending Node with
state vector, 2 numeric data lines, comma delimited, and multi-line labeled
data. State vectors may now be logged continuously, for a specific time, or
for a specified time span. See text for details.
-Corrected a problem with state vectors being generated at the wrong time
(Data Modes 5 through 7) when the time was entered in UTC and local time
was a different date.
-Removed the low precision state vector data output (F3, Data Mode 4).
-Changed the angle used to calculate the Earth's partial penumbra from 1.2
degrees to 0.3 degrees to better correspond with observed lighting. The Sun
AOS and LOS penumbral calculations were also slightly adjusted; timings
during STS-56 indicated about a 15 to 20 second error before these changes.
-Updated the TDRS information in the section "TDRS Satellite Features" and
all five TDRS satellites are now displayed on the maps at their approximate
locations as of 05/05/93. Thanks to Jim Walls for reminding me!
Program STSORBIT PLUS Satellite Orbit Simulation Page 166
-Corrected a bug which caused "BASIC Error = 5" when the selected satellite
had probably decayed. #22209 MIR Debris was an example in file TLE180.TXT.
STSPLUS now displays a warning message if the satellite has a current
altitude less than 75 nautical miles and then returns to the Main Menu.
-Corrected the conversion from kilometers to feet per Ken Ernandes. (My
original conversion factor was taken from a 40+ year old Handbook of
Chemistry and Physics and was very slightly in error!)
-Repaired (I think...) a truncation problem which sometimes caused MET/T+E
to run one second slow.
-For all those who refuse to read documentation, I added a reminder to the
Main Menu: "WHILE MAP IS DISPLAYED: F1 = HELP, ENTER = Main Menu".
-Special thanks to Ken Ernandes, Joes Runes, and Willie Musty for state
vectors, testing, and validation of the new features in recent versions!
-Version 9319 was released privately for beta testing.
(Intermediate update notes deleted to save space, available on request.)
Beta Version 9137 -- September, 1991
------------------------------------
-Initial public beta version.