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Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
(Enhanced Version for 286/386/486 Computers)
(C) Copyright David H. Ransom, Jr., 1989-1993
All rights reserved.
Version 9320
May 07, 1993
by David H. Ransom, Jr.
Rancho Palos Verdes, California, USA
Bulletin Board Systems
----------------------
RPV ASTRONOMY BBS
(310) 541-7299 @ 14400/9600/2400 Baud
RPV HOTLINE BBS
(310) 544-8977 @ 2400/1200 Baud
Program STSORBIT PLUS Satellite Orbit Simulation Page i
TABLE OF CONTENTS
-----------------
INTRODUCTION ......................................................1
HARDWARE AND SOFTWARE REQUIREMENTS ................................6
PROGRAM DESCRIPTION ...............................................7
STSORBIT PLUS FILES ...............................................8
STSPLUS MAP PROJECTIONS AND DATABASES .............................11
PROGRAM SETUP AND USAGE NOTES .....................................13
DOS 5.0 CONFIG.SYS Setup ........................................13
Using a RAM Disk ................................................14
Copying Files for STSORBIT PLUS .................................15
Slow Computers and 80x87 Math Coprocessor Chips .................16
Starting Program STSORBIT PLUS ..................................18
Predicting Visible Satellite Passes .............................19
Predicting Satellite Passes with STSPLUS ......................20
Predicting Satellite Passes with TRAKSTAR .....................22
Printing Graphics Screens .......................................25
Known STSPLUS Problems and Bugs .................................25
PROGRAM OPERATION .................................................28
STSORBIT PLUS SATELLITE TRACKING FEATURES .........................30
Orthographic Projection Maps ....................................30
Rectangular Projection World Maps ...............................31
Rectangular Projection Quadrant Maps ............................31
Rectangular Projection Zoom Maps ................................32
Location Maps with Isocontours ..................................33
Tracking Station Maps with Isocontours ..........................33
Location and Features Labels ....................................34
Big Clock Options ...............................................36
Satellite Motion Maps ...........................................36
Satellite Position and Orbit Projections ........................37
Satellite Visibility ............................................38
User's Circle of Visibility .....................................38
Spacecraft Circle of Visibility .................................39
SUN and Solar Features ..........................................40
TDRS Satellite Features .........................................41
Ground Tracking Stations and .TRK Files..........................44
Event Timers and Audible Alarms .................................46
Pausing the Ground Track Display (F6 Key) .......................49
Using FAST Time (F4 Key) ........................................49
On-line Help (F1 Key) ...........................................50
ACTIVE KEYS DURING GROUND TRACK DISPLAY ...........................51
STSORBIT PLUS MAIN MENU ...........................................54
F1 Convert Keplerian Data to 2-Line Format .....................55
Example Data Input and Output ...............................57
Received Keplerian Orbital Data Form ........................59
F2 Read NASA/NORAD 2-Line Elements .............................60
F3 Data Output and Pass Prediction Selections ..................63
Setting up Position and State Vector Data Output ............66
Setting up Tabular Pass Predictions .........................69
Data Mode 1: Azimuth/Elevation Data Format ..................73
Program STSORBIT PLUS Satellite Orbit Simulation Page ii
Data Mode 2: Latitude/Longitude Data Format .................74
Data Mode 3: Topocentric RA/DEC Data Format .................75
Data Mode 4: Ascending Node Data with State Vector ..........76
Data Mode 5: X-Y-Z Cartesian State Vector, 2 Data Lines .....78
Data Mode 6: X-Y-Z Cartesian State Vector, Comma Delim ......80
Data Mode 7: X-Y-Z Cartesian State Vector, Labeled Data .....82
Data Mode 9: Pass Predictions ...............................84
F4 Calculate Satellite Positions with TRAKSTAR .................86
F5 Set Launch Time and Date ....................................86
Using File STSPLUS.LTD for Launch Date & Time ...............87
F6 Select Time Since Epoch or Mission Elapsed Time .............88
F7 Set FILENAMES and PATHS .....................................89
F8 Set Program TIME and DATE....................................89
F1 Restore System Date and Time .............................91
F2 Set DOS System Clock .....................................91
F3 Set Simulated Date and Time using Calendar Method ........92
F4 Set Simulated Date and Time using MET ....................93
F9 Display Current RIGHTIME Corrections .....................93
F10 Set UTC OFFSET and DAYLIGHT Flag ........................94
F9 DOS Shell ...................................................94
F10 Set STSORBIT PLUS Program Options and Features ..............94
ENTER Resume Mission ...........................................94
ESC Quit STSORBIT PLUS and Save Current Mission ..............95
PROGRAM OPTIONS AND FEATURES MENU .................................96
F1 Program STSORBIT PLUS Information ...........................96
F2 Set New Local Coordinates ...................................96
F3 Set Display Features ........................................98
F4 Select Satellite Coordinates ................................98
F5 Show Ascending & Descending Node Data .......................99
F6 Set Map Projection and Size .................................99
F7 Enable/Disable EVENT TIMERS .................................99
F8 Enable/Disable Audible ALARMS ...............................100
F9 Set UTC Time Offset and Daylight Flag .......................100
F10 Enable/Disable Printer Logging ..............................101
SET DISPLAY FEATURES ..............................................103
F1 Display LOCAL Circles of Visibility .........................103
F2 Display TDRS Coverage .......................................103
F3 Display Additional Map Grid Lines ...........................104
F4 Display Tracking Stations ...................................104
F5 Display Ground Track: DOTS/LINE .............................104
F6 Display Spacecraft Circle of Visibility .....................105
F7 Display South Atlantic Anomaly Zone .........................105
F8 Display Terminator, Sun and Spacecraft Lighting .............105
F9 Display Map Locations and Features ..........................106
F10 Display Lakes and Rivers ....................................106
Preparing 2-Line Elements using VEC2TLE by Ken Ernandes ...........107
STSORBIT PLUS's Orbital Model .....................................109
Accurate Time and the Personal Computer ...........................111
Methods for Setting DOS Time ....................................112
Maintaining Accurate DOS Time ...................................113
Programs TIMESET and RIGHTIME ...................................115
Computer Bulletin Board Systems ...................................119
STSORBIT PLUS Revision History ....................................121
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 286 or better
computer (AT-class IBM compatible) is required. A math coprocessor chip
is STRONGLY RECOMMENDED and will significantly improve performance; the
math coprocessor chip is REQUIRED for acceptable performance when using the
orthographic projection. Some users report "usable" performance on an XT-
class machine WITH a math coprocessor. 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. 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 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.
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 2
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 J. Ernandes written specifically for this
purpose.
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 3
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 4
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 5
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 or RPV HOTLINE BBS (see title page for numbers 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 90274
Program STSORBIT PLUS Satellite Orbit Simulation Page 6
HARDWARE AND SOFTWARE REQUIREMENTS
----------------------------------
An AT-class computer equipped with a 286 processor (running at 8 MHz)
and a 287 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 386/387 and 486DX
systems will be considerably superior to 286 systems. Note that NO TESTING
is performed on systems not equipped with a math coprocessor chip. The
following minimum hardware is recommended:
286/386/486 IBM-compatible computer
287/387/487 math coprocessor chip
VGA color display
Hard disk with up to 3MB available
RAM disk with at least 500K space
The 287/387 (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, and a variety of other information. The data are
sufficiently accurate (given good 2-line orbital elements, of course!) that
the program has been used operationally by NASA and Intelsat.
Program STSORBIT PLUS Satellite Orbit Simulation Page 8
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.ICO Icon for WINDOWS 3 (optional)
STSPLUS.KEY STSPLUS Active Keys (optional)
STSPLUS.LOC Map Locations & Features (optional)
STSPLUS.LTD Satellite Launch Dates (optional)
STSPLUS.TRK NASA Tracking Stations (optional)
STSPLUS.CTY City Coordinates (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 (optional)
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 Confidential Questionnaire
QUICK.DOC Quick Start 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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 9
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 9242, 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.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 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 10
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 TLEnnn.TXT files.
Program STSORBIT PLUS Satellite Orbit Simulation Page 11
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 12
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 13
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:
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
As the example times 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 CONFIG.SYS files, selected by a batch
file or other methods, can optimize performance for various applications.
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
CONFIG.SYS:
DEVICE=C:\DOS\HIMEM.SYS
DOS=HIGH
Program STSORBIT PLUS Satellite Orbit Simulation Page 14
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. 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*.*) and the
locations and features file (STSPLUS.LOC or whatever alternate filename(s)
will be used) 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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 15
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:
copy /b \sop\stsplus*.loc 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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 16
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 SOP9320A.EXE and/or SOP9320B.EXE), create the STSPLUS
directory as above then log into the STSPLUS directory and unpack the files
with the commands:
C:
CD \STSPLUS
A:SOP9320A
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 1.1 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 80286/80287 or better computers equipped
with an EGA or VGA color display. While the program can be executed on some
older 8088 (XT-class) computers equipped with the 8087 math coprocessor,
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 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 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 8088 (XT-class) and 80286 (AT-class)
computers, this makes a tremendous difference AND for a very modest cost,
often well under $100. Some users report problems with coprocessor chips
Program STSORBIT PLUS Satellite Orbit Simulation Page 17
manufactured by IIT and USLI; 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 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)
---------------------------------------------
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
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. 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. 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 80387SX
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 18
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 display, 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.
Starting Program STSORBIT PLUS
------------------------------
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 19
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
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. If 2-line
elements were used, that file must also be present. Once started in this
manner, pressing the ENTER key after the map is displayed will return to
the Main Menu.
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 20
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 21
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 22
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
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
RPV Hotline BBS
(310) 544-8977
1200/2400 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 23
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 24
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 25
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:
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 frequently hear about is that the 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.
1. STSORBIT PLUS has been run extensively on systems using Microsoft DOS
3.3 and 5.0 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 5.0! Users report memory allocation problems with
some earlier versions of Digital Research DRDOS 6.0 and certain third
party memory allocation programs. A typical symptom of this kind of
problem is that you cannot return to DOS without either an error
message or the computer freezing.
2. Note that not all computers (especially older CGA systems) will
Program STSORBIT PLUS Satellite Orbit Simulation Page 26
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 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.]
3. 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 the DOS 5 "DOSSHELL",
to make sure the program will work with your computer. Similarly,
delete all special memory and device drivers from your CONFIG.SYS
file. For DOS 5.0, add 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 on different
computers with my mouse active!).
4. Several users have reported occasional "BASIC Error 11" problems;
BASIC reports this error as "Division by Zero". The only way I have
been able to reproduce this error is to restart the program using the
command line "STSPLUS /R" after I have deleted the 2-line file used on
the prior run; to avoid this error, do not use the "/R" command line
option and select a new 2-line file using F2. This error may also be
the result of a memory limitation (with multitasking enabled?) or it
may be a BIOS problem associated with a specific computer.
5. All VGA adapter cards are not equal, in case any of you had some
illusions left. In at least one case, the aspect ratio of the 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 displays. So far as I know,
there is no remedy. Early VGA cards (the 449 card from Zenith is an
example) are not always recognized as VGA; the card is not register
compatible with the IBM standard and is recognized as EGA instead.
6. 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.
7. 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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 27
[The program GRAFTABL.COM is included as part of DOS in most cases.]
8. Some math coprocessor chips have caused problems. In at least two
reported cases, early version 386SX math coprocessor chips from IIT
did not execute correctly and generated random errors; ITT replaced
the suspect chips and the problems disappeared. On a 40MHz 386SX
system, a USLI 387SX chip did not operate correctly; a Cyrix 387SX
chip cured the problem. No problems have been reported for Intel or
Cyrix chips.
9. Finally, as noted elsewhere, all computers are NOT equal. There are
some computers which will not execute STSPLUS under any circumstances.
Tandy is the most common offender followed by Leading Edge. Some
models from these 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 is sometimes an update or workaround
for these problems; check with the manufacturer.
Program STSORBIT PLUS Satellite Orbit Simulation Page 28
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 29
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9320
RighTime Version 2.53 detected!
Current time: 15:02:17 PST 23:02:17 UTC
Current date: 02/28/1993 02/28/1993
Last Mission = Hubble Space Telescope
2-Line Elements File = F:\TLE\TLE147.TXT
CPU Type = 80386DX or 80387SX
NDP Type = 80387DX or 80387SX
Display = VGA Color
(C) Copyright David H. Ransom, Jr., 1989-1993
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 30
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 31
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 32
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 33
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 34
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 rectangular projection. Since
this map mode uses the ZOOM map algorithms, the usual zoom map features
(PgUp, PgDn, Home, End) are active.
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 (".") 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
locations to avoid this problem! If you wish to add your own locations
Program STSORBIT PLUS Satellite Orbit Simulation Page 35
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 magnitudes. All labels are automatically centered with respect to
longitude.
There is no restriction on the length of the location name. However,
avoid long names if possible so as to avoid location names displaying on
top of one another or "cluttering" the display.
IMPORTANT NOTE: The program performs no error checking on the contents of
file STSPLUS.LOC. 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 file STSPLUS.LOC. 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 36
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 37
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 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 38
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 39
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+F3+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 40
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 41
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.
TDRS Satellite Features
-----------------------
TDRS Satellite features are shown only on HGC, EGA and VGA monitors.
When TDRS coverage is enabled (F10+F3+F2), the three 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 each shown as a dot inside a small yellow circle on the
Equator. As of May, 1993, there are five TDRS satellites in geosynchronous
orbit, 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 6.87
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 150 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 Terminal is at White Sands,
New Mexico, the coverage has been slightly overlaped to provide good ground
communications. 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 TDRS for low Earth orbits.
Two red "circles" on the display show the limits of coverage for each TDRS
location. Each circle, whose shape may be quite distorted when using
Program STSORBIT PLUS Satellite Orbit Simulation Page 42
rectangular projection, encloses an area where a TDRS satellite is out of
range of the satellite 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 in minutes for TDRS
East and TDRS West. The method used for the calculation of the TDRS
coverage normally accurate to about 10 seconds (assuming accurate 2-line
elements for the satellite and for the TDRS). However, spacecraft attitude
can cause loss of 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 make a quick mental calculation to determine the
status; if the AOS time is larger than the LOS time, the satellite is in
communication.
STSPLUS can sound an audible alarm (three beeps) 30 seconds prior to
TDRS AOS or LOS. Use F10+F3+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
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 currentlyu 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 May, 1993, the TDRS assignments are:
Program STSORBIT PLUS Satellite Orbit Simulation Page 43
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 -150W On-orbit spare
* Original NASA letter designation at launch
STSPLUS will use TDRS 4 and TDRS 5 by default and approximate positions as
of 1 OCT 1992 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 4 or letters A through D or E. Use the
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
successively displaying the two satellites. To do this, press F2 from the
Main Menu, select a 2-line elements file which includes the TDRS satellites
(the TLEnnn.TXT file from my BBS is one such file), then for each TDRS
satellite enter the NORAD number and display the satellite. The new
position data will be used for subsequent AOS/LOS calculations and saved in
file STSPLUS.INI.
If you wish to change the default TDRS satellites, you must edit file
STSPLUS.INI. Use a standard ASCII editor; if you use a word processor, use
the "non-document" mode. CAUTION: STSPLUS does no error checking on file
STSPLUS.INI and errors may cause unpredictable performance; if that
happens, delete file STSPLUS.INI, run the program, and start over. The TDRS
information is included in lines 6 and 7 of the file:
19883,"TDRE",-2.87065876318583D-02,-40.9568653303904
21639,"TDRW",1.11188496191951D-02,-174.185413704575
For each line, the data are NORAD#, TDRS abbreviation, and the latitude and
longitude of the sub-satellite point. If you wish to use a different TDRS
satellite, changing the NORAD number in file STSPLUS.INI to the number
desired is sufficient; run STSPLUS, select the new TDRS satellite (by NORAD
number) for display, and all data will be updated. If you wish to change
the TDRS abbreviation, remember that STSPLUS performs NO ERROR CHECKING on
file STSPLUS.INI on the assumption that it wrote the file itself. The TDRS
abbreviation MUST be exactly 4 characters long and be enclosed in double
quotation marks as shown above!
In theory, any satellite could be substituted for one or both of the
TDRS satellites; in practice, since STSPLUS assumes the "TDRS" satellite is
"stationary" in geosynchronous orbit, this makes little sense except in a
few cases. For example, substituting MIR (NORAD #16609) for one of the TDRS
satellites would indicate in the AOS/LOS data when direct, line-of-sight
communications was possible between MIR and the active satellite (such as a
Space Shuttle) but the data would be reasonably accurate for only a few
minutes at most since MIR is in motion.
Program STSORBIT PLUS Satellite Orbit Simulation Page 44
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 45
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"
"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"
Program STSORBIT PLUS Satellite Orbit Simulation Page 46
"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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 47
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 48
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!
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 49
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.
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 50
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.
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 F8=SUN and Term 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 9320
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 51
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 52
F7 Enable or disable the spacecraft circle of visibility.
F8 Enable or disable the SUN, solar terminator, and spacecraft
lighting feature. NOTE: The SUN and spacecraft lighting are not
available on CGA systems.
F9 Change units of distance between kilometers (km) and nautical
miles (nm).
F10 Change satellite coordinates between Altitude and Azimuth, Right
Ascension and Declination, and Geocentric Rectangular (XYZ)
systems.
+ 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. (NOTE: The "="
key may be used instead of "+" to avoid 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 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 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.
PgDn When in one of the zoom modes, decreases the field of view down
to a minimum of 45 degrees. Press rapidly to execute multiple
zoom steps without redrawing the map for each keypress.
Home When in one of the zoom modes, returns the field of view to 75
degrees (rectangular projections) or the full globe (orthographic
projections).
End When in one of the zoom modes, returns the field of view to the
last zoom factor used prior to pressing the HOME key.
B Toggle the BLINK mode of the satellite symbol between blinking
and steady.
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 53
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 45 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 (rectangular 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.
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 54
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 9320
Current time: 15:47:28 PST 23:47:28 UTC
Current date: 03/11/1993 03/11/1993
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 Display MET & Launch Times (now 2-Line Epoch Times)
F7 Set FILENAMES and Paths
F8 Set program TIME and/or DATE
F9 DOS Shell (CAUTION: DOS Version 3.x+ ONLY!)
F10 Set STSORBIT PLUS Program Options and Features
ENTER Resume Mission (MIR Space Station)
ESC Quit STSORBIT PLUS and Save Current Mission
Select desired function:
During operation of STSPLUS, data are displayed by STSPLUS in several
standard formats:
4/05/1990 Date in month/day/year
14:33:00 UTC Coordinated Universal Time in hours:mins:secs
06:33:00 PST 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 55
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 "IAU 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 56
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 IAU (International Astronomical Union) 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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 57
As noted elsewhere, orbital elements have a limited lifetime. How long
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 IAU 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 58
EXAMPLE DATA OUTPUT
-------------------
Satellite Data has been entered as:
Satellite Name (15 chars max): Sts-55
NORAD Number (NNNNN): 00055
IAU 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 59
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: __ __ __ __ __
IAU 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 60
F2 Read NASA/NORAD 2-Line Elements from *.TXT/*.TLE Files
-------------------------------------------------------------
In order to read the NASA/NORAD 2-line elements, you must have a file
with that data. A current file is included in the standard distribution of
STSPLUS. These files have names such as "TLE147.TXT" where the "147"
corresponds to the particular US Space Command Prediction Bulletin number
from T. S. Kelso's Celestial BBS and may change several times per week.
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 61
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:
\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)
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;
Program STSORBIT PLUS Satellite Orbit Simulation Page 62
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
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: STS-50
Satellite NORAD Number: #22000
Elements File: STS50N38.TXT
Elements File Record#: 1
(*)
Element Set Number: 38
Elements Epoch: 92187.57342677
05 JUL 1992 @ 13:45:44 UTC
Orbit # at Epoch: 159
Launch Year: 1992
Launch Number: 34
Launch Piece: A
Inclination: 28.467
RA of Ascend Node: 275.07
Eccentricity: .0007237
Arg of Perigee: 340.7929
Mean Anomaly: 19.153
Mean Motion: 15.91359642
Acceleration/Drag: -.00032668
BSTAR Drag: -.000097874
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 63
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
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
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). Each function is assigned a "Data
Mode" number:
1 = Azimuth, Elevation, Range
2 = Latitude, Longitude, Orbit Altitude
Program STSORBIT PLUS Satellite Orbit Simulation Page 64
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)
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
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,
Program STSORBIT PLUS Satellite Orbit Simulation Page 65
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 66
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.
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]:
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:
Program STSORBIT PLUS Satellite Orbit Simulation Page 67
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
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 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)
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 (Data Modes 1-3 and 5-
7), 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]:
Program STSORBIT PLUS Satellite Orbit Simulation Page 68
(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.
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 69
and return to the Main Menu.
Setting Up Tabular Pass Predictions
-----------------------------------
Tabulation of predicted passes is always displayed on the screen and
may optionally be sent to a destination device. 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.
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,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. 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
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)
Program STSORBIT PLUS Satellite Orbit Simulation Page 70
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 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)
9 = Tabular Line-of-Sight Predictions
Press the "9" number key to select tabular 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 tabular Line-of-Sight predictions, the data are displayed on the
screen as calculated and optionally 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 71
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 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.
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
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.
Each time predicted passes are requested, the list begins with the
Program STSORBIT PLUS Satellite Orbit Simulation Page 72
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 73
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 74
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 75
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 76
Data Mode 4: Ascending Node Data with State Vector
--------------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 14
22640 93126.01064687500 05/06/1993 00:15:19.89 UTC 151 -28.97484
-20700626.50033 -7017763.71702 99.48729
7171.14632550111 -21154.38143121826 12116.07993705963
0.00041435000 0.00000000000 0.00011400000
22640 93126.07331099537 05/06/1993 01:45:34.07 UTC 152 -52.06526
-20757257.66786 -6847814.66865 108.75000
6998.06013681081 -21212.45538276647 12116.17608786654
0.00041435000 0.00000000000 0.00011400000
22640 93126.13597488427 05/06/1993 03:15:48.23 UTC 153 -75.15575
-20812516.70863 -6677355.28046 86.99262
6824.43127187151 -21269.13033360731 12116.26910764658
0.00041435000 0.00000000000 0.00011400000
22640 93126.19863854167 05/06/1993 04:46:02.37 UTC 154 -98.24631
-20866398.57582 -6506396.67448 34.34157
6650.27110334244 -21324.40060661349 12116.35898369872
0.00041435000 0.00000000000 0.00011400000
22640 93126.26130208334 05/06/1993 06:16:16.50 UTC 155 -121.33639
-20918833.55553 -6335163.80849 72.08828
6475.87348993044 -21378.17509121208 12116.44570353700
0.00041435000 0.00000000000 0.00011400000
NOTES:
1. Data Mode 4 records the data when the Ascending Node is detected. The
data is recorded when the latitude switches from negative to positive
on the Northbound equator crossing to an accuracy of 0.01 seconds.
2. 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.
3. The units of measure for the state vector may be determined by the
tens digit of the Data Mode in the initial header line:
4 Kilometers and kilometers per second
14 Feet and feet per second
24 Nautical miles and nautical miles per second
4. The NASA Day-of-Year format is shown first 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. Also included
is the more conventional notation for date and time (UTC).
5. Five successive data samples are shown for feet and feet per second.
6. The following FORTRAN-like format statements may be used to read the
Program STSORBIT PLUS Satellite Orbit Simulation Page 77
four lines of data in this mode for all units of measure:
First Line:
-----------
Catalog #: I5
2X
Date/Time: F17.11
2X
Date: A10
2X
Time: A11
1X
Zone: A3
2X
Rev Number: I6
Longitude: F15.5
CR/LF
Second Line:
------------
20X
X: F15.5
4X
Y: F15.5
4X
Z: F15.5
CR/LF
Third Line:
-----------
23X
Xdot: F18.11
1X
Ydot: F18.11
1X
Zdot: F18.11
CR/LF
Fourth Line:
------------
23X
Ndot/2: F18.11
1X
Ndot/3: F18.11
1X
B-Star: F18.11
CR/LF
Program STSORBIT PLUS Satellite Orbit Simulation Page 78
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 79
4X
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 80
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 81
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 82
Data Mode 7: Precision X-Y-Z Cartesian State Vector, Labeled Data
-----------------------------------------------------------------
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 7
Satellite Name: Hubble Space Telescope
Catalog Number: 20580
Epoch Date/Time: 93110.05034722222
04/20/1993 01:12:30 UTC
ECI X: 1512.86585008771 km
Y: 6802.10451969805 km
Z: -98.64567159224 km
Xdot: -6.48159140528 km/sec
Ydot: 1.48930990107 km/sec
Zdot: 3.60688654153 km/sec
Ndot/2 (Drag): 0.00002579000
Ndot/3: 0.00000000000
B-Star: 0.00023093000
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 17
Satellite Name: Hubble Space Telescope
Catalog Number: 20580
Epoch Date/Time: 93110.05115740740
04/20/1993 01:13:40 UTC
ECI X: 3462003.87590686000 ft
Y: 22593825.70095322000 ft
Z: 504853.92724508480 ft
Xdot: -21612.97193927312 ft/sec
Ydot: 3031.49503449803 ft/sec
Zdot: 11826.09008591681 ft/sec
Ndot/2 (Drag): 0.00002579000
Ndot/3: 0.00000000000
B-Star: 0.00023093000
STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 27
Satellite Name: Hubble Space Telescope
Catalog Number: 20580
Epoch Date/Time: 93110.05196759259
04/20/1993 01:14:50 UTC
ECI X: 319.37381540774 nm
Y: 3742.62290007086 nm
Z: 218.95997503174 nm
Xdot: -3.59376884632 nm/sec
Ydot: 0.19075561766 nm/sec
Zdot: 1.93381830034 nm/sec
Ndot/2 (Drag): 0.00002579000
Ndot/3: 0.00000000000
B-Star: 0.00023093000
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 83
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:
7 Kilometers and kilometers per second
17 Feet and feet per second
27 Nautical miles and nautical miles per second
One example is shown above for each unit of measure.
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. 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 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. The Date/Time is also
"decoded" and given in the more conventional "MM/DD/YYYY HH/MM/SS"
format for clarity using Coordinated Universal Time (UTC/GMT).
Program STSORBIT PLUS Satellite Orbit Simulation Page 84
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 85
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 86
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 87
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 88
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 Select Time Since Epoch or Mission Elapsed Time
------------------------------------------------------
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 "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.
The F6 command may be used to switch the display between Time Since
Epoch ("T+Epoch") and Mission Elapsed Time ("MET"). The command description
on the Main Menu indicates which mode will be selected if Function Key F6
is pressed:
F6 Display MET & Launch Times (now 2-Line Epoch Times)
F6 Display 2-Line Epoch Times (now MET & Launch Times)
The first example (the default) indicates that MET will be displayed if the
function key is pressed; the second example indicates that the display will
return to Time Since Epoch if the function key is pressed. (The elapsed
time option may also be switched at any time during the tracking display by
pressing Function Key F5.)
The F6 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, you will be prompted for the information
as if you had pressed function key F5 (see above). The F6 command is
inactive unless you have read in 2-line elements using function key F2.
Program STSORBIT PLUS Satellite Orbit Simulation Page 89
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: [F:\TLE\]
F2 Set TRACKING STATION filename: [STSPLUS.TRK]
F3 Set MAP DATABASE FILES path: [F:\STSPLUS\]
F4 Set FEATURES LABEL filename: [F:\STSPLUS\STSPLUS.LOC]
F5 Set TRAKSTAR path: [F:\STSPLUS\]
Enter selection or ENTER:
Press the indicated function key for the item you wish to change. The
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. 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 (for example:
"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 Satellite Orbit Simulation Page 90
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9320
Current time: 14:52:24 PST 22:52:24 UTC
Current date: 03/10/1993 03/10/1993
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
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 91
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 are entered as "MM/DD/YYYY" or "MM/DD/YY" 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 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 Satellite Orbit Simulation Page 92
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9320
Current time: 19:59:10 PST 03:59:10 UTC
Current date: 02/24/1993 02/25/1993
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 PST
Enter DATE (MM/DD/YYYY): 4/08/1992
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 9320
Current time: 19:59:10 PST 03:59:10 UTC
Current date: 02/24/1993 02/25/1993
Press ENTER to leave an item unchanged
Enter SIMULATED TIME [12:05:06]: 13:00:00 PST 21:00:00 UTC
Enter SIMULATED DATE [11/11/1991]: 11/09/1991 11/09/1991
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 93
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
entered.
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9320
Simulated time: 00:17:18 PST 08:17:18 UTC
Simulated date: 10/09/1992 10/09/1992
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 94
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.
F10 Set UTC OFFSET and DAYLIGHT Flag
---------------------------------------
You may change the UTC Offset and/or the setting of the Daylight Flag
using F10. The prompts are self-explanatory; see the section "Program
Options and Features, Set UTC Offset and Daylight Flag" for a detailed
description of the UTC Offset and Daylight flag.
F9 DOS Shell (CAUTION: DOS Version 3.x+ 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. 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 3.0 or higher! Systems with less than 640K memory may fail to
execute the shell and applications requiring large amounts of memory
may also fail.
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.
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 95
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 96
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 9320
Current time: 19:59:10 PST 03:59:10 UTC
Current date: 02/24/1993 02/25/1993
F1 Program STSORBIT PLUS Information
F2 Set New Local Coordinates (Rancho Palos Verdes, CA)
F3 Select Display Features
F4 A/A Select Satellite Coordinates: RA/DEC, Alt/Az or XYZ
F5 OFF Show Ascending & Descending Node Data
F6 ORTHO Set Map Projection and Size
F7 OFF Enable/Disable EVENT TIMERS
F8 ON Enable/Disable Audible ALARMS
F9 -7.00 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 coordinates for the
user's location. The name of the current location is shown in parentheses.
When STSPLUS is first started, the default coordinates are set to Rancho
Palos Verdes, California, near Los Angeles. The current location is
Program STSORBIT PLUS Satellite Orbit Simulation Page 97
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 names and coordinates (STSPLUS.CTY); or manually entering the
information.
Pressing F2 will display the following reminder:
STSPLUS searchs STSPLUS.CTY for the CITYNAME you enter anywhere in the
city names. 'SAN' appears in 'SAN DIEGO', 'SANTA ANA', 'THOUSAND OAKS.
Press ENTER to delete SECOND LOCATION, or enter '*' to manually enter
a city name and coordinates (and optionally add it to STSPLUS.CTY).
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 city file. For example, 'SAN' matches 'SAN diego' as well as
'SAN jose' 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, the name 'ran' was entered for the search.
Enter CITYNAME to match: ran
Processing record 1
City Name: Rancho Palos Verdes CA
Latitude: 33.7675
Longitude: -118.4033
Elevation: 186 meters
Press ENTER to ACCEPT this city as your location, OR
Press TAB to also display this city's location, OR
Press SPACE to search for next city: _
If the city displayed is the one you wish to use as your local
coordinates, press ENTER. If you wish to display this city as a second
location on the display, press TAB. The data will be entered into STSPLUS
and subsequently saved in file STSPLUS.INI. If you wish to search further
in the file, press the SPACE BAR.
NOTE: The elevations contained in file STSPLUS.CTY are almost all zero
except for Rancho Palos Verdes, CA for which I have accurate elevation
above mean sea level. 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 800 cities. If
users send me their correct elevations (or additional cities they wish
added), I will incorporate that data into subsequent versions of file
STSPLUS.CTY.
To enter location data manually, press "*" (without the quotation
marks) followed by ENTER. 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):
Program STSORBIT PLUS Satellite Orbit Simulation Page 98
DDD.DDDDD Degrees and decimal fraction
DD,MM.MMM Degrees, minutes and decimal fraction
DD,MM,SS.SS Degrees, minutes, seconds and fraction
Note that SOUTH latitude and WEST longitude must be entered as NEGATIVE
numbers as measured south of the Equator or west of the Prime Meridian at
Greenwich, respectively. 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 or meters as appropriate,
regardless of the 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, OR
Press SPACE to cancel this data: _
Press ENTER to accept the data as shown or SPACE to cancel the data and
return to the Options 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 file, or press "N" to not
modify the STSPLUS.CTY file.
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.
F4 Select 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).
Alt/Az Altitude and Azimuth. 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).
Program STSORBIT PLUS Satellite Orbit Simulation Page 99
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.
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.
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 45
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 100
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
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 UTC Time 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 101
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:
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.
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 102
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 9320 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 103
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 9320
Current time: 19:59:10 PST 03:59:10 UTC
Current date: 02/24/1993 02/25/1993
F1 ON Display LOCAL Circles of Visibility
F2 ON Display TDRS Coverage
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 Coverage
----------------------------
This command will display the communications coverage for
the Tracking and Data Relay Satellites (TDRS) EAST and WEST. The coverage
boundaries overlap between the East and West TDRS satellites and Mission
Control may select either satellite during the overlap period. STSPLUS
Program STSORBIT PLUS Satellite Orbit Simulation Page 104
displays the areas covered by each satellite and the times for acquisition
and loss of signal (AOS and LOS). See the section "TDRS 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
108 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,
especially CGA, 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 rectangular
map modes (EGA and VGA systems only), each grid line is labeled at the left
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
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 105
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
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:
Program STSORBIT PLUS Satellite Orbit Simulation Page 106
* 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 107
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 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 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 (formerly NORAD) 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 IAU Designation is assigned by the International
Astronomical Union 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 individual or agency and have no effect on
Program STSORBIT PLUS Satellite Orbit Simulation Page 108
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
file, performs limited error checking on these data, then displays and
writes the generated 2-line elements file. The initial public release of
VEC2TLE, Version 9319, 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.
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,
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 validated and tested in conjunction with STSPLUS
using NASA ECI state vectors (provided courtesy Willie Musty, Mission
Support, Rockwell International, Downey, CA) during 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. See the
documentation for VEC2TLE for additional discussion and references.
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 109
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 110
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 111
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 Candad 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 112
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 113
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 RIGHTIME 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 114
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 115
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 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, 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 116
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 117
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 118
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 119
Computer Bulletin Board Systems
-------------------------------
Timely 2-line orbital elements are essential for accurate satellite
tracking. In addition to my own bulletin board systems (see title page for
numbers), four other bulletin board systems provide authoritatve data for
the general public. Most files on these systems are compressed to reduce
downloading time and must be decompressed before use.
For the past several years, Major 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) 427-0674, 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 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.
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) 306-0010, 4 lines @ 1200 and 2400
baud. The OIG database contains elements for some 7000+ satellites and is
updated every weekday morning except holidays. Elements for popular
satellites are posted in seven ".DAT" files (with the NORAD number only in
the first line of data rather than the more usual satellite name or IAU
identification) and all other satellites are available on a query basis. I
regularly post a combined and sorted set of the .DAT data as file
GSFCnnn.ZIP on my own RPV ASTRONOMY BBS where "nnn" is a number like "170".
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 120
@ 300-2400 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. 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 121
STSORBIT PLUS Revision History
------------------------------
Each released version of STSPLUS uses a four digit revision code such
as 9320. 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 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 122
(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!
-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.
Version 9316 -- April 1993
--------------------------
-This is a BETA MAINTENANCE UPDATE not released publicly.
-Added Data Output Function #5, "Precision XYZ State Vector (km)", to
generate full precision state vectors. The position and velocity data are
in km and km/sec. The format is similar to Data Output Function #4 except
that it requires two data lines per state vector.
-Help is now available in all display modes by pressing Function Key F1.
Press F1 again to return to normal data display.
-The default (and minimum) magnification for the End key in orthographic
modes has been changed from 100 to 150. Thus, pressing the End key will
return to the prior magnification or to MAG=150, whichever is greater.
-Added missing minus sign on large character MET during the last 24 hours
prior to launch time. Display was "0/00:01:00" instead of "-0/00:01:00".
-Corrected the latitude for Mauritius in file STSPLUS.LOC. The latitude was
missing a minus sign! Changed the "trigger" magnitude for Athens, Greece to
500 from 2000 following a user complaint. Also corrected the longitude for
Luxor, Egypt which was off just that little bit ...
-Various minor cosmetic changes.
Version 9314 -- March 1993
--------------------------
-This is a MINOR UPDATE to correct several problems. Except for these
notes, the documentation is essentially unchanged.
-Corrected a bug with F6 on the Main Menu. Switching between MET and T+E
using F6 changed the label but NOT the data. (F5 worked correctly when the
ground track is displayed.) Thanks to Paul Ferrante for reporting the bug.
-Corrected (again!) a format error in file STSPLUS.OBS which is created for
Program STSORBIT PLUS Satellite Orbit Simulation Page 123
use with TRAKSTAR. For names shorter than 20 characters, the numerical data
was shifted left. Thanks to Michael Simmons for helping track down the bug!
-Corrected the CPU identification displayed for 386 processors to "80386DX
or 80386SX". Due to a typo, the SX processor was shown as "80387SX".
-Corrected the spelling of Yarragadee, Australia. Thanks to Elwood Marshall
for the correction.
Version 9311 -- March 1993
--------------------------
-This is a FULL RELEASE with updated documentation, and includes all
changes listed here as well as those made in Preliminary Versions 9307
through 9310. Please see the update notes below for details.
-Added F1 to the Main Menu, Convert Keplerian Elements to 2-Line Format,
which incorporates the features formerly provided separately in my program
MAK2LINE. See new text for discussion and for a form which may be used to
transcribe data received by voice or modem.
-Repaired a bug which caused the Location Map isocontours to be drawn at
the wrong location when a second location was enabled in orthographic mode.
Thanks to Paul Ferrante for reporting the problem!
-Added Function Key F9 to the Time and Date Menu (F8 from the Main Menu) to
show the last system TIMESET and the current RIGHTIME corrections. This
menu item will not appear if program RIGHTIME is not detected.
-Added additional code to maintain the prior state of RIGHTIME per Tom
Becker. Thanks, Tom!
-Various minor cosmetic changes.
-Documentation updated.
Version 9310 -- March 1993
--------------------------
-This is a MAINTENANCE UPDATE and also includes several improvements to
Version 9309. Users updating from Version 9250 should also read the notes
for Version 9309 below.
-In my rush to release Version 9309 of STSPLUS prior to STS-55, I neglected
to finish updating the code for F2 (Read 2-line elements). Hopefully, that
code has now been repaired correctly ... sorry!
-STSPLUS is now "aware" of program RighTime by Tom Becker. Audible alarms
in prior versions would perform unpredictably when RighTime was active
because MS BASIC uses the hardware clock's timer functions for "music"
(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.
-Added the flashing message "calculating ..." during Pass Prediction
calculations so that users with slow computers (especially those without a
Program STSORBIT PLUS Satellite Orbit Simulation Page 124
math coprocessor) will know that the process is continuing. Users with 286
computers and no math coprocessor report delays up to tens of minutes for
satellites with low mean motions!
Version 9309 -- February 1993
-----------------------------
-This is a PRELIMINARY RELEASE of a major update for STSPLUS and the first
public release since Version 9250. This version is being released as an
UPDATE ONLY for Versions 9250 and 9307; the full version will be released
shortly, complete with full documentation, pending the results of testing
for this preliminary release. See also the update notes for Version 9307
below. Comments and suggestions are invited, particularly with respect to
the new Data Output and Pass Prediction features.
-Function Key F3 on the Main Menu, Pass Predictions and Data Output, has
been rewritten and improved.
-Added Line-of-Sight Pass Predictions for the current satellite. Use F3
from the Main Menu and select Data Format 9. Pass predictions are made for
48-hour blocks and for up to 99 passes. Users may immediately display a
listed pass by entering the pass number. STSPLUS then automatically sets
SIMULATED TIME to the middle of the pass and switches to the ground track
display. See the section "Pass Predictions and Data Output" for additional
information. The capability to use TRAKSTAR or other external tabular pass
prediction software has been retained for those who prefer that technique.
-Improved and refined the Data Output capabilities introduced in Beta
Version 9307. Added FILE Data Output to file STSPLUS.LOG, and PRINTER Data
Output to printer LPT1:.
-Modified F2 on the Main Menu (Read 2-line Elements) to require the "#"
symbol when entering the NORAD number; enter the NORAD number as "#20580".
This now permits satellite names such as "1993 012A" to be found correctly;
prior versions would treat such an entry as a NORAD number and the search
would fail.
-Entering a full drive and path specification in addition to a filename
with F2 on the Main Menu (Read 2-line Elements) will now correctly set the
path without the need to use F7 (Set Paths and Filenames). Root directories
("C:\") are now processed correctly. Press ESC to cancel.
-Added text section titled "Time and the Personal Computer" which offers
information on setting and maintaining the PC clocks over long periods of
time. Includes information on programs TIMESET and RIGHTIME.
Version 9307 -- February 1993
-----------------------------
-This is a BETA TEST VERSION, not released publicly.
-Added Function Key F3 to the Main Menu. This provides data output on the
selected COM port with specified data items. Three different data formats
have been implemented so far.
-Removed the original Function Key F3 (Read .INI file) from the Main Menu.
Use F2 to read 2-line elements and/or set file names. In Version 9250, the
satellite data was not being read when the .INI file was changed. This was
caused by logic changes to speed up initialization of the program. Also,
reading "foreign" .INI files sometimes caused problems.
-Corrected a bug which caused a new launch time/date NOT to be added to
file STSPLUS.LTD if the curret satellite's NORAD number was less than the
last NORAD number in the file.
Program STSORBIT PLUS Satellite Orbit Simulation Page 125
-In response to a request by Maj. T.S. Kelso, USAF, who prepares the 2-line
orbital elements which I post on my RPV ASTRONOMY BBS, I have changed the
name of that file from "NASAnnn.TXT" to "TLEnnn.TXT". The default file
which STSPLUS looks for has been similarly changed. Since the orbital data
in the file does NOT come from NASA but from US Space Command, the use of
"NASA" in the filename was confusing and did not give credit where it was
due.
-Corrected a minor bug which caused five pixels to be restored incorrectly
under the starbord (right) wing of the space shuttle icon.
-Modified the operation of Function Key F5 from the Main Menu to ADD or
UPDATE new launch time and date in file STSPLUS.LTD rather than to append
the new data at the end of the file. This assures that the satellite is
included only once in the file and that the new or updated information is
always read correctly. Prior versions required the user to manually edit
the file to remove multiple entries.
-Adjusted the maximum angle displayed for the isocontours (concentric
circles of satellite visibility) on the Location Map in orthographic mode
to take satellite altitude into account.
-Corrected the STSPLUS.OBS file format for use with TRAKSTAR. The data was
correct but the spacing caused TRAKSTAR to sometimes read the data
incorrectly. Thanks to Michael Simmons for reporting the problem!
-Corrected the latitude of Sao Paulo, Brazil in file STSPLUS.LOC. It was
one degree off to the South and wound up in the Atlantic Ocean ...
Version 9250 -- December 1992
-----------------------------
-This is a MAINTENANCE AND FEATURES UPDATE.
-In response to numerous suggestions, I have redesigned and enlarged the
space shuttle icon and switched from a profile to a plan view to make the
icon easier to find on the screen. The new icon has almost three times as
many pixels and takes more time to draw. Comments are invited!
-In response to many user requests, I have improved file selection logic
for 2-line elements using F7 from the Main Menu to "remember" the path and
save it in file STSPLUS.INI. Users may now keep all 2-line elements files
for STSPLUS and other tracking programs in a separate directory.
-While the default filetype for 2-line elements is still ".TXT", the
program now also searches for filetype ".TLE".
-Event timers (showing AOS and LOS for the local station, TDRS, etc.) are
now enabled by F10+F7 from the Main Menu.
-I have added the Location Map in orthographic mode; press "L" while an
orthographic map is displayed. The projection used for the Location Map is
now based upon the current projection, rectangular or orthographic, when
"L" is pressed.
-Improved resolution of spacecraft lighting from 10 seconds to 1 second and
the Sun's position is now calculated every 10 seconds instead of every 60
seconds.
-Spacecraft lighting icon and symbol (to the right of "Orbit #:" in the
data block) now indicate the full range of solar illumination:
* Bright White Full sunlight
+ Yellow Partial sunlight (penumbra)
- Light Red Refracted sunlight
White Full shadow (umbra)
Note that LIGHT RED and the "+" and "-" symbols have been added to
distinguish refracted sunlight from partial sunlight.
Program STSORBIT PLUS Satellite Orbit Simulation Page 126
-In response to several user requests, I have added AOS and LOS event
timers for orbital sunrise and sunset, displayed when the solar features
are enabled. In order to avoid excessive delays during the ground track
plotting (when the timers are set up), I have used a simpler algorithm for
orbital sunrise and sunset than that used during program operation. The
simpler algorithm is usually accurate to about plus or minus 15 seconds.
The actual spacecraft lighting is calculated dynamically and is both more
accurate and takes into account the non-spherical shape of the Earth.
-After several user comments about the "big clocks", I have again tweaked
the shape of the large digit "5" (back to what I started with) and modified
the "6" to better distinguish it from the "5".
-In order to free a display line in orthographic mode, the map drawing time
and map database file information have been combined on a single line (e.g.
"EARTH4 10.91") at the bottom of the display block.
-STSPLUS now automatically detects the type of processor and math
coprocessor; if no math coprocessor chip is detected, the program displays
a caution message at startup. The SLOW MODE is now automatically set or
reset depending upon the presence or absence of the math coprocessor and
the menu selection for the SLOW MODE has been removed.
-Performance may be improved if a memory manager such as EMM386, QEMM386 or
386MAX is NOT used! See the section "PROGRAM SETUP AND USAGE NOTES" for
specific information.
-Changed the grid spacing in orthographic mode, MAG=200, to 10 degrees from
5 degrees to make the display a bit less cluttered.
-STSPLUS is now compiled using Microsoft Visual Basic for DOS.
-Updated this documentation. Added the sections "SUN and Solar Features",
"Event Timers and Audible Alarms", and "F5 Display Ground Track:
DOTS/LINE". Moved the section "F5 Show Ascending & Descending Node Data"
to the proper place in the text.
-Corrected a bug which caused a minus sign (if present on Y or Z) to
persist when changing from XYZ to Alt/Az or RA/DEC satellite coordinates.
-Various minor cosmetic changes.
-Version 9249 was a limited release beta version.
Version 9245 -- October, 1992
-----------------------------
-This is a MAINTENANCE UPDATE, correcting several bugs and adds the launch
date and time capability.
-Added file STSPLUS.LTD which contains the NORAD number and launch date
(Julian date, UTC) for selected satellites. A sample entry appears as:
22194,2448918.21503472,0
This example is 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 last parameter is reserved and should be set to zero. Launch date and
time may be appended to file STSPLUS.LTD when entered using F5 from the
Main Menu. See the section "Using File STSPLUS.LTD for Launch Date & Time"
for a complete discussion.
-Corrected a misplaced statement which caused "BASIC PDS Error = 5" when
the Satellite Motion Map was requested from rectangular modes.
-Changed future dots on ground track to LIGHT GREEN when only dots are
shown to avoid confusion with solar terminator. (That's what it was
supposed to be but I messed up ...)
-Changed satellite circle of visibility on the Satellite Motion Map to
Program STSORBIT PLUS Satellite Orbit Simulation Page 127
solid white (from light white dots) for greater clarity.
-Added a default magnification of 200 for the End key.
-Corrected the coordinates for Shanghi, China, in STSPLUS.LOC.
Version 9244A -- October, 1992
------------------------------
-On rectangular projections, the LAUNCH TIME and LAUNCH DATE were shown
incorrectly. The calculations for MET were correct.
Version 9244 -- October, 1992
-----------------------------
-Version 9244 is a MAINTENANCE UPDATE which adds several new features in
addition to repairing a number of bugs which have been discovered as a
result of the addition of the orthographic map mode and other new features
such as enhanced TDRS coverage. This is still "early in the game" following
the major rework associated with the addition of orthographic projection.
Comments, suggestions, and bug reports will be appreciated.
-Added EGA dual-page Satellite Motion Map to orthographic modes, available
ONLY for EGA and VGA systems. Press "M" while the orthographic map is
displayed. Press "M" or ENTER to return to normal map modes. PgUp, PgDn,
Home, and End are the only other keys which are active with the Satellite
Motion Map.
-In response to MANY requests, I have restored the "red dots" for past
orbital ground track. (My original method no longer worked when I added the
orthographic projection.)
-AOS/LOS for secondary location now available in orthographic mode and in
rectangular mode with "/CLK" command line option AND when large clock is
selected for MET/T+Epoch (using F2 when the map is displayed). Finding
display space is getting very difficult, particularly in normal rectangular
modes! Primary location is labeled "STN1" and secondary location is labeled
"STN2".
-The PAUSE mode has FINALLY been repaired so that it operates correctly.
Press F6 while the map is displayed to enter PAUSE, press ENTER to resume
normal operation. Use the "+" and "-" keys to advance or retard the time,
and use F4 to set the time step. See the section "Pausing the Ground Track
Display" for a full description.
-The FAST mode has also been repaired so that it works more or less in the
manner intended. Press F4 while the map is displayed to enter FAST mode.
Note that 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. See the section "Using FAST Time" for a full
description.
-Corrected a problem with TDRS coverage when updating from one version to
another. The TDRS AOS/LOS labels read ":" instead of "TDRE:" and "TDRW:"
and the AOS/LOS calculations could be incorrect or blanked out. (The TDRS
data were not being set up correctly.) As a work-around, the problem could
be corrected by deleting file STSPLUS.INI and restarting the program.
-Corrected a crash with "BASIC PDS Error 5" which occurred under certain
circumstances when drawing circles of visibility in orthographic mode. (An
array index was being overrun.)
-Corrected a minor bug in the AOS/LOS logic that limited the time
resolution to 2 seconds instead of 1 second (4 seconds instead of 2 seconds
Program STSORBIT PLUS Satellite Orbit Simulation Page 128
when the SLOW flag is set). Thanks to Joel Runes for spotting the problem!
-Various minor cosmetic bugs.
NOTE: Version 9243 was a beta version released on a limited basis to
individuals who had problems and/or registered the program
immediately before and during Mission STS-52. Version 9243
included some of the changes noted above for Version 9244.
Version 9242 -- October, 1992
-----------------------------
-Version 9242 is primarily a Maintenance Update, correcting a number of
minor bugs and documentation errors. However, several "new and improved"
features have also been added as a result of continued testing and user
requests. Thanks to everyone who sent in encouragement and suggestions!
-In response to MANY user requests, I have added an interface (via F4 from
the Main Menu) to TS Kelso's new satellite prediction program TRAKSTAR.
Download TRAKSTR2.ZIP (filename for Version 2.15) from RPV ASTRONOMY BBS or
from Celestial BBS (see text for telephone number). CAUTION: TRAKSTAR uses
UTC time rather than LOCAL time! See text for full description and setup
instructions.
-By popular request, I've added an audible warning for AOS and LOS at the
user's location. The AOS warning occurs 2 minutes prior to AOS, and the LOS
warning occurs 30 seconds prior to LOS. Audible warnings are enabled and
disabled using F10+F8 from the Main Menu. Past versions of Microsoft's
compilers have caused the system clock to lose time when "music" was
played; I would appreciate feedback from users if this feature causes
problems.
-A similar (but shorter) audible warning has also been added for TDRS
coverage. The TDRS warnings occur 30 seconds before AOS or LOS if TDRS
coverage and audible alarms are both enabled.
-AOS and LOS clocks now change to YELLOW if the time is 2 minutes or less,
as stated in the documentation. A minor bug has been repaired that caused
the AOS or LOS clocks to sometimes "freeze" at 00:00 or 00:01 when no
future event was detected.
-AOS and LOS calculations have been improved in precision by a factor of
two and the average time required for the calculations has decreased by
about 5:1 using a binary search algorithm. This may be just an exercise in
performance improvement since factors such as antenna pointing errors and
atmospheric conditions may introduce errors of up to tens of seconds!
-When launch time and data have been entered and Mission Elapsed Time is
selected for display, the HOURS:MINUTES for MET will appear at the bottom
of the data block in large digits for orthographic modes. (When MAG is
greather than 100, seconds are not displayed because of space limitations.
The full MET, including days, is always displayed near the top of the data
block in normal characters.)
-Corrected error when changing to/from DAYLIGHT TIME using F8+F10 from the
Main Menu. If the Daylight setting is changed, STSPLUS now asks if you wish
to adjust your DOS clock. CAUTION: Setting the DOS clock may NOT execute
correctly for 8088 computers! (Prior versions required exit from the
program and restart before the time was shown correctly.)
-Corrected the satellite coordinates when orthographic mode was selected
with the second city displayed. (V9240 displayed the primary location name
but the data for the secondary location.)
-Corrected a problem (which left the screen black most of the time and then
Program STSORBIT PLUS Satellite Orbit Simulation Page 129
was redrawn immediately) when Motion Map was requested (by pressing "M")
from other than Zoom Mode.
-Corrected TDRS AOS/LOS title placement error with "/CLK" command line
option.
-Meridian drawing algorithm adjusted to (hopefully) always draw the lines
of equal longitude to the bottom or top of the map in orthographic mode.
-Added a test for field overflow in the first derivative of mean motion
(dx/dt, the parameter following the epoch on Line 1). Field overflow is
indicated by a numeric field of ".********" and it is now set to a value of
1 or -1 depending upon the leading sign. This is often an indication that
the satellite has decayed or soon will decay.
-Corrected the default directory upon return from DOS using F9 on the Main
Menu. (Default directory was left where the user last logged and file
STSPLUS.INI was written there instead of where it belonged.)
-Corrected file list to show CIS.TRK instead of USSR.TRK and updated the
distribution files accordingly.
-Description of TDRS satellite locations in the text corrected.
-Description of MCX, MCP, and XYZ map database files corrected to restore a
line of text that was dropped by my word processor.
Version 9241 was released for beta testing only.
Version 9240 -- October, 1992
-----------------------------
*********************
* IMPORTANT NOTES *
*********************
After almost four years, I have at last discontinued support
for the simple orbital model in STSORBIT PLUS. Users who wish
to continue using the simple orbital model must use prior
versions of STSPLUS or use the original STSORBIT program. I
plan to add manual generation of estimated 2-line orbital
elements for the Space Shuttle in the next release of STSPLUS.
Motion maps are available only with rectangular projection.
The FAST modes are still not really repaired. Maybe I'll get
around to that in the next release ...
The South Atlantic Anomaly (SAA) is disabled for
orthographic modes until I digitize a better model from
NASA's Mission Charts.
-Version 9240 is a MAJOR UPGRADE and is the initial public release with the
orthographic projection techniques used in my program ORTHOGRAPHIC EARTH
VIEW.
-While the principal new feature is the orthographic projection, that
addition affected almost all parts of the program and many different
routines have been updated or modified. I have also rewritten the AOS/LOS
code for TDRS and the user's location. Although considerable beta testing
has been performed, there are surely a few bugs that have not yet been
discovered. Special thanks to Joel Runes for his help with the beta
Program STSORBIT PLUS Satellite Orbit Simulation Page 130
versions! Comments and bug reports are welcome.
-Added Orthographic Projection maps and new map databases. Orthographic
maps are selected using the letter "O" when the map is displayed or by
selecting "ORTHO" using F10+F6 from the Main Menu. PgUp, PgDn, Home, and
End may be used to select the magnification factor. See the text for a full
description.
-A math coprocessor is REQUIRED for the orthographic maps. Orthographic
maps require MUCH more computation time. Most computers not equipped with a
math coprocessor chip, even 386 systems, will yield poor or unacceptable
performance in orthographic modes. Typical orthographic map drawing times
range from 5 or 10 seconds for a 486DX/33 to 600 seconds or more for an
8088 without a math coprocessor!
-All rectangular projection map routines have been rewritten to use the new
indexed map database files and the maximum zoom factor has been increased
to a field of view of 30 degrees. This yields much improved map detail at
higher zoom factors and decreases the map drawing time in most cases. The
old map database file, STSPLUS.MVF, may be deleted.
-Because of their size, the high detail map database files cannot be
downloaded from the RPV ASTRONOMY BBS except for callers with 9600 or
faster baud modems. See file README for additional information on these
files.
-The TDRS sub-satellite coordinates are now included in STSPLUS.INI and may
be updated by displaying the appropriate satellite. For TDRS East display
NORAD #19883, and for TDRS West display NORAD# 21639. See the section "TDRS
Satellite Features" for additional information. Thanks to Jim Henderson of
NASA White Sands (and others) for the suggestion.
-Changed TDRS coverage algorithm to reflect actual coverage as a function
of satellite altitude above the Earth's surface. Provided current TDRS
position data is used, accuracy should now be on the order of tens of
seconds. Prior versions assumed a "customer" satellite orbital altitude of
approximately 160 miles.
-Added location and features labels to all maps, enabled or disabled by
F10+F3+F9 from the Main Menu. Labels are contained in file STSPLUS.LOC. See
the section "Location and Features Labels" for additional information.
-Rewrote the time base algorithms to better accomodate slower computers and
the longer calculation times required in orthographic modes. The program
now operates correctly even when the map drawing and updating times are
longer than ten seconds. Updating of the spacecraft circle of visibility,
for example, will occur at ten second intervals if the necessary
calculations and screen operations can be performed in less than one
second; if not, the update interval will be adjusted as necessary.
-Partly because of the new timebase algorithms, the ground track has been
changed. The "minute marker" dots are now yellow when DOTS+LINES are
enabled and the dots no longer change color. (A synchronization problem.)
-Changed the algorithm for the Circle of Visibility to correctly calculate
near the poles. The new algorithm is now used in all map projections. Users
who complained about the circles of visibility for high inclination orbits
will find them now correct -- although somewhat slower. The algorithm was
adapted from FORTRAN code generously supplied by Paul Traufler. Thanks
yet again, Paul!
-Changed most circle of visibility plotting routines from double to single
precision and used in-line code to improve performance.
-Added a black dot on the satellite icons to show the center of the icon.
-Corrected a fatal error if the map data files were missing. This problem
was frequently caused by using an old version of PKUNZIP (earlier than
Program STSORBIT PLUS Satellite Orbit Simulation Page 131
Version 1.10) which could not unpack the map data file, the only file which
used the most recent compression algorithm. No error message was displayed
and the computer had to be rebooted. (Users who downloaded the program from
NASA SpaceLink BBS often had this problem since NASA had the wrong version
of PKUNZIP posted -- which they corrected at my request!)
-Corrected an error in the internal tracking station data which caused a
fatal Basic PDS Error 3 ("Syntax Error") if file STSPLUS.TRK was missing.
-Changed "current file" display to use inverse video when selecting 2-line
elements files. The color change used in prior versions did not show on
monochrome systems!
-Corrected a bug in the 2-line file selection logic that prevented entry of
a specific filename and improved the error trapping.
-Corrected the longitude of Cape Canaveral in STSPLUS.CTY so that it was
not out in the Atlantic Ocean. (Thanks to all of you who reported it!)
-Increased internal STACK size to 6144 bytes (vs. 3072) in the hope of
eliminating some reported memory problems (which I can't duplicate).
-Corrected a minor bug in the (25 line modes only) large character display
of MET/T+Epoch if the days were four characters; the time was shifted left
one digit. Days may now range from -999 to +9999. Also eliminated a double
minus sign if MET or T+Epoch was negative.
-Corrected a minor bug in satellite coordinates if a distance was greater
than -99999.99 km/nm. The display wrapped because of field overflow. The
distance is now shown as -NNNNNN.N (one less digit to the right of the
decimal point) for large distances. Most folks won't notice this one!
-Corrected a minor bug in large character negative MET/T+Epoch that caused
the time to be green for one second before turning red under certain
circumstances.
-Corrected an occasional bug which caused the colors to go awry or to
monochrome.
-Various minor cosmetic bugs.
(Intermediate update notes deleted to save space, available on request.)
Beta Version 9137 -- September, 1991
------------------------------------
-Initial public beta version.
