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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., 1989-1992
All rights reserved.
Version 9228A
July 08, 1992
by David H. Ransom, Jr.
Rancho Palos Verdes, California, USA
BBS: (310) 541-7299
Program STSORBIT PLUS Satellite Orbit Simulation Page i
TABLE OF CONTENTS
-----------------
INTRODUCTION ......................................................1
HARDWARE AND SOFTWARE REQUIREMENTS ................................5
PROGRAM DESCRIPTION ...............................................6
STSORBIT PLUS FILES ...............................................8
PROGRAM SETUP AND USAGE NOTES .....................................10
Slow Computers and 80x87 Mach Coprocessor Chips .................10
Using a RAM Disk ................................................11
Starting Program STSORBIT PLUS ..................................12
Predicting Visible Satellite Passes .............................13
Known STSPLUS Problems and Bugs .................................15
PROGRAM OPERATION .................................................18
THE STSORBIT PLUS GROUND TRACK DISPLAY ............................20
World Maps ......................................................20
Quadrant Maps ...................................................20
Zoom Maps .......................................................21
Location Maps with Isocontours ..................................22
Tracking Station Maps with Isocontours ..........................22
Big Clock Options ...............................................23
Satellite Motion Maps ...........................................23
On-line Help (F1 Key) ...........................................24
Satellite Position and Orbit Projections ........................24
User's Circle of Visibility .....................................25
Spacecraft Circle of Visibility .................................25
TDRS Satellite Features .........................................26
Ground Tracking Stations and .TRK Files..........................26
ACTIVE KEYS DURING GROUND TRACK DISPLAY ...........................30
STSORBIT PLUS MAIN MENU ...........................................33
F1 Program STSORBIT PLUS Demonstration .........................33
F2 Read NASA/NORAD 2-Line Elements .............................34
F3 Read Prior Mission Information from *.INI File ..............37
F4 Enter New Orbital Information ...............................37
F5 Adjust Orbital Parameters ...................................39
2-Line Elements Model .......................................39
Simple Orbital Model ........................................40
F6 Set Elapsed Time Option (2-line elements only)...............41
F7 Set FILENAMES and Paths .....................................42
F8 Set Program TIME and DATE....................................42
F9 DOS Shell ...................................................45
F10 Set STSORBIT PLUS Program Options and Features ..............46
ENTER Resume Mission ...........................................46
ESC Quit STSORBIT PLUS and Save Current Mission ..............46
PROGRAM OPTIONS AND FEATURES MENU .................................47
F1 Program STSORBIT PLUS Information ...........................47
F2 Set New Local Coordinates ...................................47
F3 Set Display Features ........................................49
F6 Set Map Center and Size .....................................49
F7 Set for SLOW COMPUTER or NO COPROCESSOR .....................50
F9 Set UTC Time Offset and Daylight Flag .......................50
Program STSORBIT PLUS Satellite Orbit Simulation Page ii
F10 Enable/Disable Printer Logging ..............................51
SET DISPLAY FEATURES ..............................................53
F1 Display LOCAL Circles of Visibility .........................53
F2 Display TDRS Coverage .......................................53
F3 Enable/Disable Additional Map Grid Lines ....................54
F4 Display Tracking Stations ...................................54
F5 Show Ascending & Descending Node Data .......................54
F6 Display Spacecraft Circle of Visibility .....................54
F7 Display South Atlantic Anomaly Zone .........................55
F8 Display Terminator, Sun and Spacecraft Lighting .............55
F9 Select Distance Units: NM or KM .............................56
F10 Select Satellite Coordinates: RA/DEC, AltAz or XYZ ..........56
STSORBIT PLUS'S ORBITAL MODELS ....................................57
ADJUSTING ORBITAL PARAMETERS (Simple Orbital Model) ...............59
STSORBIT PLUS Revision History ....................................61
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 recommended, and a math coprocessor
chip will significantly improve performance. Some users report acceptable
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, for simulating a
Space Shuttle mission, and for general satellite tracking using NASA/NORAD
2-Line Orbital Elements.
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. When used with NASA/NORAD 2-Line
Elements, 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 Soviet MIR Space Station, may be displayed. 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.
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 as well. One problem is that of 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 and the size and resolution of its monitor. The NASA wall
map shows essentially the entire globe in a cylindrical projection;
STSORBIT uses a cylindrical projection but restricts 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.
Initially, and as a consequence of a lack of accurate orbital data for
Program STSORBIT PLUS Satellite Orbit Simulation Page 2
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 NASA/NORAD 2-Line Elements
via modem from TS Kelso's Celestial BBS. Until HST, I had been content to
update 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 may be manually 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 suggestions; Bill Anderson and Jeff
Ehmen, 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 NASA 2-line elements and thereby maintain
significantly improved accuracy over long periods of time. As an incidental
benefit, the ground tracks of other satellites (such as the Russian space
station MIR) could also be displayed. At present, the orbital model (SGP4)
used with 2-line elements is accurate only for low Earth orbits. Deep space
orbits, defined as orbits having an orbital period greater than or equal to
225 minutes, require a more complex orbital model (SDP4) which takes into
account solar and lunar perturbations for best accuracy. STSPLUS calculates
data and displays a ground track for deep space objects but the accuracy of
these data has not been validated; it is believed to be "reasonably"
accurate.
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 NASA 2-line elements. This would allow
both the higher accuracy of the NASA 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, Sun 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, 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 --
to the point where some slower computers not equipped with a math
coprocessor were unable to keep up. I have therefore essentially "frozen"
the original STSORBIT program (except for minor updates) and created a 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 3
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". 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. Most recently, Intelsat used STSPLUS
operationally in May of 1992 at their Mission Control Center in Washington,
DC, and at five tracking stations around the world during the STS-49
mission, the maiden flight of Endeavour and the rescue/reboost of the
INTELSAT-VI satellite.
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; my interest in space has
continued to this day. The desire to "keep in touch" with our Space Shuttle
missions was one of the principal 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 goal.
For those who are 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 9600 baud. NASA SpaceLink, located at the NASA Marshall Space Flight
Center, 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 graphics
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.
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 1987 or so. The Celestial BBS may be
reached at (513) 427-0674 and is located near Dayton, Ohio.
Program STSORBIT PLUS Satellite Orbit Simulation Page 4
Special thanks to Paul Traufler for his friendship and encouragement
over the past several years. 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 strongly recommend TRAKSAT for the serious satellite tracker.
My thanks as well for Paul's help in upgrading STSORBIT to use the
NASA/NORAD 2-Line Elements.
Thanks also to Rob Matson for offering comments and code to help me
implement some of STSPLUS's more exotic features. Rob coind the phrase
"isocontours" to describe the circle of equal satellite altitude around a
location. Rob's fine program, SKYMAP, generates high accuracy printed star
maps with or without satellite tracks.
Finally, my thanks to all those individuals who have taken the time to
write or leave a message on my BBS with comments and suggestions. While I
haven't implemented every suggestion, many are now included and the
feedback is most welcome.
For current orbital information (if a mission is in progress), current
NASA/NORAD 2-line element sets, and the most recent versions of STSORBIT,
STSPLUS, TRAKSAT, and SKYMAP, call my RPV ASTRONOMY BBS at (310) 541-7299.
If the BBS has not answered after the third ring, hang up, wait TWO
MINUTES, then call back; the system has a power controller and if the
system is off it takes that long for the computer to start up and do its
housekeeping chores. The system has well over 1,000 regular users and is
often busy, so please be patient.
If you do not have access to a modem, you may send US$10.00 as a
donation to cover materials, postage and handling for a copy of the current
version of STSORBIT PLUS; please specify 5-1/4" 360K or 3-1/2" 720K disks.
Please allow two to three weeks for shipment.
David H. Ransom, Jr.
7130 Avenida Altisima
Rancho Palos Verdes, CA 90274
Program STSORBIT PLUS Satellite Orbit Simulation Page 5
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 all features will
execute as described and in real time. Performance with 386/387 and 486
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 math coprocessor chip
VGA color display
Hard disk
RAM disk with at least 500K space
The 287/387 math coprocessor chip is HIGHLY RECOMMENDED and is
required for some processors to operate in real time. The calculations
relating to orbital mechanics are very complex and STSPLUS will use the
coprocessor chip if one is equipped; performance is improved by about an
order of magnitude. Other "fast" processor and coprocessor combinations may
yield acceptable performance. A SLOW MODE is provided to accommodate slower
machines. However, math coprocessor chips are now reasonably inexpensive,
particularly for 286 systems, and the performance improvement is impressive
and well worth the modest cost. As an example, my vintage Zenith laptop is
equipped with an 80C88 processor and an 8087 math coprocessor and is just
able to keep up in real time when running at a clock speed of 8 MHz
(although map drawing times are very slow). However, an 8 MHz 286 (AT-
class) computer without a math coprocessor is NOT able to execute the
program correctly except in the SLOW mode and 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 adapters, the display is in color. Because of its
improved vertical resolution, the VGA is recommended over the EGA. A
monochrome VGA 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 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 recommended for performance in program and file loading
and for storage of orbital elements files. A RAM disk with sufficient space
to hold the program and its various data files is also recommended for
improved performace, especially for reduced map drawing times. However, the
program will execute correctly on floppy disk based systems with 640K base
memory provided the system is otherwise equipped as suggested.
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. Third party memory
management programs and Digital Research DRDOS 6.0 may experienc problems
with internal memory allocation performed by the Microsoft BASIC Compiler;
however, I'm told that the latest release of DRDOS 6.0 works correctly.
Program STSORBIT PLUS Satellite Orbit Simulation Page 6
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. Little of this information is 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 to initialize a tracking program.
Given the geographical coordinates of the Kennedy Space Center, assuming a
circular orbit, and using the typical altitude and inclination of a Space
Shuttle orbit, the data should be sufficient to give at least a rough idea
of the Shuttle's position for the first several orbits. After that,
additional information is required if the position is going to be very
close.
Fortunately, NASA does announce the orbital altitude (for non-military
missions at least) and this information is usually reported in the media.
The reader is cautioned that the popular press and television often (but
not always) convert the orbital altitude to statute miles with the
inevitable confusion resulting. If a television viewer has access to NASA
Select Television on Satcom F2R, Transponder 13, he will periodically see
Mission Control Center's huge wall map on which the current position of the
Space Shuttle is always displayed. Using this display, the careful viewer
can make a visual estimate of the longitude of the ascending or descending
node, the point at which the orbit crosses the Earth's equator in the
Northbound or Southbound direction respectively. Not exactly high-tech data
acquisition, but better than nothing at all!
Given all of these uncertainties, I did not feel it necessary or
worthwhile to try to hone the mathematics of my "simple" orbital model in
program STSORBIT beyond that required to give an approximate position in
real time. Coincident with the Hubble Space Telescope mission I added the
J2 perturbation factor for improved accuracy. As an example, STSORBIT was
used to track STS-31, Discovery and the Hubble Space Telescope, and gave an
accurate position over more than 25 orbits.
Within a day of launch, the NASA/NORAD 2-line elements are usually
available and will yield a more accurate position over longer time periods
provided no orbital maneuvers are made. Using NASA/NORAD 2-line elements is
quite simple. No adjustment of orbital parameters is necessary when using
the 2-line elements. All that is required is to obtain the current 2-line
elements file (from my BBS or elsewhere), enter the name of the file (for
example, NASA877.TXT) and the name of the desired satellite (i.e. "HST" for
Hubble Space Telescope or "STS" for the Space Shuttle). STSPLUS takes care
of all the rest. The 2-line element set available at the time of this
release of STSPLUS is included in the program files. The data for each
satellite included in the 2-line element set 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. Users who prepare their own 2-line element files are cautioned to
make certain no extraneous lines are included, that the satellite name is
on a single line, and that the two data lines exactly conform to the 69-
Program STSORBIT PLUS Satellite Orbit Simulation Page 7
character/line NASA/NORAD format.
STSPLUS displays a portion of the Earth using a cylindrical
projection of the surface area. For the full world map, this extends almost
from one pole to the other; a small area near each pole (approximately five
degrees) is omitted to maintain optimum map proportions. The map shows most
of the Earth's land boundaries, and continental areas and major seas and
oceans are easily recognizable. Twelve quadrant maps display one quarter of
the Earth, and zoom maps may be selected which display a field of view
adjustable from 180 degrees to 45 degrees. With the quadrant and zoom maps,
automatic map generation may be enabled to endure that the satellite is
displayed. The display shows the selected satellite as a small symbol or
icon, the projected low-Earth orbit ground track for approximately the next
two orbits (three hours), and the ground track for the past orbit (one and
a half hours).
The program may be operated in real time, in simulated time, or in
"fast time", which is ten or sixty times normal time. For the "simple
orbital model", the orbital parameters may be manually entered or adjusted
for the desired mission. A pre-programmed demonstration may be run to
permit the user to become familiar with the program and its display. The
lower section of the screen displays current data about the mission in
progress.
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 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:
STSPLUS.EXE Main program (required)
STSPLUS.DOC Documentation (not required)
STSPLUS.ICO Icon for WINDOWS 3 (optional)
STSPLUS.KEY STSPLUS Active Keys (optional)
STSPLUS.MVF World map data (required)
STSPLUS.TRK NASA Tracking Stations (optional)
STSPLUS.CTY City coordinates (optional)
STSPLUS.INI Initialization data (optional)
MSHERC.COM Hercules driver (required for HGC)
NASAnnn.TXT 2-Line Elements (optional)
NASA.TRK NASA Tracking Stations (not required)
USSR.TRK Soviet Tracking Stations (not required)
INTELSAT.TRK INTELSAT Tracking Stns (not required)
SPACENTR.TRK Other Tracking Stations (not required)
README STSPLUS Confidential Questionnaire
QUICK.DOC Quick Start Instructions
MAK2LINE.EXE MAK2LINE Utility Program (optional)
MAK2LINE.DOC MAK2LINE Documentation (optional)
Files noted as "(required)" must be in the current default directory for
program operation. Files noted as "(optional)" do not need to be in the
default directory when STSPLUS is operated but provide additional features
or information if present. In order to minimize the disk space required,
all .EXE files have been compressed with PKWare's PKLITE Professional.
These files require a brief additional time to begin execution since they
are decompressed "on the fly" at load time.
Program MAK2LINE was written at the request of local amateur radio
enthusiasts to facilitate converting Keplerian orbital elements, received
by ham broadcast or via voice link, to the 2-line format. It is available
separately from my bulletin board system and is included with program
registration (see file README).
*** 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 prior version of STSPLUS,
all data will be ignored and the program must be initialized as if
being run for the first time.
Program STSORBIT PLUS Satellite Orbit Simulation Page 9
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 NASAnnn.TXT (where "nnn" will be a number such as "014") is a set
of NASA/NORAD 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 posted on my bulletin board system two or three times
per week. 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.
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. File NASA.TRK is the same
as file STSPLUS.TRK; if you wish to use a different TRK file, use Function
Key F7 from the Main Menu to select the desired file.
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 filetype .TXT are normally 2-line orbital elements. Some common
satellite name abbreviations are: "STS" = Space Shuttle; "HST" = Hubble
Space Telescope; "GRO" = Gamma Ray Observatory; and, "MIR" = Soviet MIR
Space Station.
Program STSORBIT PLUS Satellite Orbit Simulation Page 10
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 program features may be used to advantage.
Slow Computers and 80x87 Math Coprocessor Chips
-----------------------------------------------
STSPLUS has been designed for 80286/80287 or better computers eqipped
with an EGA or VGA color display. While the program can be executed on
older 8088 (XT-class) computers equipped with the 8087 math coprocessor or
on 286 or better computers without a math coprocessor, performance is
seriously degraded. But it would seem that warnings and suggestions can
NEVER convince people that the calculations required for orbital mechanics
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. I really don't want to hear from users how slow this
program can be on older machines; I recommend the original STSORBIT if you
want the best performance from an 8088 computer. The following table
illustrates the difference the processor and a math coprocessor chip make.
Processor Speed Coprocessor Time (secs)
---------------------------------------------
486 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 display. All data were
resident in memory (no disk operations required). All tests were made using
the same display options (most were enabled and the SLOW MODE was OFF).
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 really acceptable, and NONE of the
computers without the math coprocessor chip can operate in real time unless
the SLOW MODE is ON.
If, in spite of these data and hints, you insist on using STSPLUS on
your old clunker, here are a few cautions and reminders.
1. Especially at startup and when redrawing the maps, long time delays
can be expected -- on the order of minutes in some cases. Status
messages are presented on the screen during some of these delays so
users will at least know the program is working. Note also that the
Program STSORBIT PLUS Satellite Orbit Simulation Page 11
.EXE file is compressed to save disk space and is decompressed at load
time; this may cause a delay on any system, with or without a math
coprocessor.
2. The original CGA display, even when equipped with a color monitor, can
display reasonable resolution graphics (320x640) ONLY in monochrome.
Your color CGA monitor buys you nothing for graphics that are quite
inferior to the EGA and VGA. If you have a monochrome monitor, be sure
to include the "/M" command line option to force monochrome. The
program may otherwise fail with or without an error message.
3. If you don't have a math coprocessor or are using a slow computer, be
SURE to enable the SLOW MODE using Function Keys F10+F7. Even a 286 or
386 computer may be unable to keep up with the calculations in the
normal mode. The clue is to watch the LOCAL and SIMULATION times at
the lower left of the screen; if these times are not within one or two
seconds of each other, you must use the SLOW MODE. The SLOW MODE
changes the screen update interval to once every 10 seconds from once
every second to allow more time for calculations.
4. Even with the SLOW MODE, you may not be able to turn on all the
options and features you'd like to use and still keep up. Some
features, such as the solar terminator, may have to be disabled. Too
bad, but only a math coprocessor chip can solve that problem for 286
computers and there is no solution for 8088 computers running at the
original 4.77 MHz. Experiment with your computer to see what features
permit proper operation.
Using a RAM Disk
----------------
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 probably use
memory that STSPLUS (as well as most other programs) may need to operate
correctly. The basic files required for operation of STSPLUS require a
minimum of about 256K of RAM disk; additional map or satellite data files
could as much as double that amount. A RAM disk of at least 500K is
therefore recommended. The actual size RAM disk you can provide will be
dependent upon how much memory is equipped in your computer.
In order to use the RAM disk effectively, all essential files must be
copied from your hard disk to the RAM disk. The following program files are
recommended:
STSPLUS.EXE STSPLUS Main Program file
STSPLUS.INI STSPLUS Initialization file
STSPLUS.MVF STSPLUS Map file
STSPLUS.CTY STSPLUS City file (optional)
STSPLUS.TRK STSPLUS Tracking Station file (optional)
In addition, you must copy all 2-line orbital elements files you plan to
use, files such as NASAnnn.TXT, GSFCnnn.TXT, and so forth. Remember that
all RAM disk files are lost when you turn off your computer! I recommend
that you build a batch file which copies all of the files from the hard
disk to the RAM disk and, when you are finished with STSPLUS, copies the
Program STSORBIT PLUS Satellite Orbit Simulation Page 12
file STSPLUS.INI back to your hard disk. Saving STSPLUS.INI on the hard
disk ensures that the next time you run STSPLUS, the previous settings will
be restored.
The following is a sample batch file which will copy the STSPLUS files
from the hard disk (drive F: and subdirectory STSPLUS in this example) to
the RAM disk (drive J: in this example), run program STSPLUS with the /R
(resume) option, then copy the STSPLUS.INI file back to the original drive
on the hard disk. Many variations are possible to suit individual needs.
J:
COPY F:\STSPLUS\STSPLUS.EXE
COPY F:\STSPLUS\STSPLUS.INI
COPY F:\STSPLUS\STSPLUS.MVF
COPY F:\STSPLUS\STSPLUS.CTY
COPY F:\STSPLUS\STSPLUS.TRK
COPY F:\STSPLUS\NASA*.TXT
COPY F:\STSPLUS\GSFC*.TXT
COPY F:\STSPLUS\STS*.TXT
STSPLUS /R
COPY STSPLUS.INI F:\STSPLUS
Starting Program STSORBIT PLUS
------------------------------
Versions of STSPLUS prior to 9219 attempted to read the file
STSPLUS.INI even if it had been created by a prior version. Since the
format of that file changes from time to time, STSPLUS now ignores the
STSPLUS.INI file unless it was created or written by the current version.
If the file does not exist, STSPLUS will automatically create it.
To start program STSPLUS, enter one of the following commands:
STSPLUS Automatic monitor, CGA/HGC/EGA/VGA
STSPLUS /EGA Force EGA (or lower) monitor
STSPLUS /CLK Use 43 or 60 lines for graphics display of
data and large clock characters. NOTE: This
feature available with EGA and VGA displays
ONLY! It is ignored for CGA/HGC monitors.
STSPLUS /CGA Force CGA monitor
STSPLUS /M Force monochrome operation, EGA/VGA
STSPLUS /R Resume last mission automatically
Only one display option (/EGA or /CGA or /M) may be used. 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 13
* * * * *
Hercules Graphics Card USERS NOTE:
----------------------------------
Run the program MSHERC prior to running STSPLUS. This Microsoft
program works with compiled BASIC programs to enable use of the Hercules
Graphics Card. One user reported that setting the HGC to FULL and selecting
Page Zero (using software supplied with the HGC) was sufficient for proper
operation with program STSPLUS. At least one HGC "clone" user reported
improper operation.
* * * * *
If you have already run STSPLUS (or if you have file STSPLUS.INI)
and simply wish to resume that same mission, use the /R (resume) command
line option:
STSPLUS /R
STSPLUS will sense the monitor type, enable color for EGA and VGA systems,
read the map data as usual, 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
plotting has started will return to the Main Menu.
Predicting Visible Satellite Passes
-----------------------------------
One of the best 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 three 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.
There are a number of satellite tracking programs, most notably Paul
Traufler's TRAKSAT, which can generate a tabular output for a given
satellite or group of satellites telling when and where the satellite will
be visible. STSPLUS does not have those tabular capabilities and relies
instead on its graphics capabilities to make pass predictions quick and
easy. Here are a series of suggestions to help you check for visible passes
for a satellite of interest.
1. Set up STSPLUS for the desired satellite. First, use Function Keys
F10+F3+F5 to set the satellite ground track to LINE or BOTH (rather
than DOTS). This makes the ground track more visible on the zoom map
displays. Then use Function Key F2 to select the satellite's 2-line
orbital elements from the available satellites. Typical files have
names like NASA971.TXT or GSFC037.TXT or, for the space shuttle,
STS45N03.TXT. The numbers will change from time to time or mission to
mission. Use one of the quadrant maps or the world map to make sure
that the satellite is correctly displayed.
Program STSORBIT PLUS Satellite Orbit Simulation Page 14
2. 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 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 simply means above his 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
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.
3. The geometry of the pass and the attitude and geometry of the
spacecraft is 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; large solar panels can reflect
enough light to appear the most brilliant objects in the sky while
large but rounded spacecraft seem all but invisible.
4. Given otherwise good conditions and favorable weather, the single most
important factor is spacecraft apparent altitude during a pass. This
is the spacecraft's apparent elevation above your local horizion.
Depending upon local conditions, an altitude of at least 5 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 and haze (except
when looking out over the Pacific Ocean).
5. After altitude, the azimuth is the number which describes the
direction from the viewer to the spacecraft at any moment. This is
given in the sense NESW, North to East to South to West, in degrees.
For a good pass after sunset, for example, an azimuth ranging from 60
to 150 degrees would indicate a pass moving generally from the
Northeast to the Southeast, ideal lighting conditions with the Sun in
the West.
6. Now to look for a visible pass using STSPLUS. Use Function Keys F8+F3
to select a local time shortly after sunset. For example, if sunset
will occur at 17:30, set the local time to 18:00 and select the date
desired to test. Now begin the display and press the "L" key to obtain
the Location Map display centered on your viewing location. (If you
have a second location set into STSPLUS, press "L" again to toggle
between the two locations.) Notice the concentric spacecraft altitude
isocontour rings spaced at 10 degree intervals and centered on your
location. The outermost ring is 0 degrees, the approximate point at
which the spacecraft will appear over your horizon. Press "PgUp" or
"PgDn" to select a different zoom factor for the map. The ground track
will be drawn against this map background. If you see no ground track,
Program STSORBIT PLUS Satellite Orbit Simulation Page 15
there will be no visible passes that evening (or dawn)! A good visible
pass will arc in toward your location and reach a peak altitude of 40
or more degrees, which should be easily visible even over most local
obstructions. Since as many as three sequential ground tracks may be
shown, be sure you know which one occurs at what time!
7. Once you have found a visible pass which looks promising, pause the
display with Function Key F6. This freezes the satellite on your
display while still generating the altitude ("Alt") and azimuth
("Azm") values. Move the satellite back and forth along its ground
track with the "+" and "-" keys and adjust the time step (1, 10, or 60
seconds) with Function Key F4. Now you can position the satellite at
the point you expect it to become visible, reach its highest altitude,
and disappear from view and record the time, altitude, and azimuth for
each of these events. The spacecraft lighting is shown as an asterisk
("*") next to the "Orbit #" if the satellite is in sunlight; for color
displays, the satellite icon is bright white in sunlight, yellow in
partial shadow, and dim white in full shadow (umbra). If the lighting
conditions are favorable and you are using reasonably current 2-line
orbital elements, this method is just about foolproof.
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 to minimize such bugs, 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 modes for the CGA are 320 x 200 which is inadequate for STSPLUS.
1. As quite a few users have reported, the FAST modes did NOT operate
correctly with automatic map generation enabled. Beginning with
Version 9226, enabling FAST modes (X10 and X60), will automatically
disable automatic map generation. Press TAB to restore automatic map
generation.
I use the FAST modes successfully in conjunction with the PAUSE to
move a satellite back and forth on the Location Map (while the map is
displayed select PAUSE with F6, then set the desired time increment
using F4, and then use the "+"/"=" and "-" keys to move the satellite)
to determine the altitude and azimuth of a pass. Once the PAUSE is
released, the time will return to normal. Another alternative is to
determine the approximate time of interest and then use simulated time
(F8+F3 on the Main Menu) to display that time. Depending upon the
speed of your computer, it's pretty simple to select another time if
Program STSORBIT PLUS Satellite Orbit Simulation Page 16
you guess wrong. Return the program to real time with F8+F1 from the
Main Menu.
2. 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.
3. 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. 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 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.
4. Some users report problems with certain Terminate and Stay Resident
(TSR) programs for which the only remedy is to remove the offending
TSR. This usually requires a "trial and error" approach to pinpoint
the TSR causing the problem. The best method is to remove ALL such
programs from your AUTOEXEC.BAT file, including 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. One user reports a problem on an IBM PS/2 when his mouse is
active (but I regularly execute STSPLUS on different computers with my
mouse active!).
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 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. 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 17
[The program GRAFTABL.COM is included as part of DOS in most cases.]
8. Finally, as noted elsewhere, all computers are NOT equal. There are
some computers which will not execute these programs 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 PDS BASIC
compiler 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 a
workaround for these problems; check with the manufacturer.
Program STSORBIT PLUS Satellite Orbit Simulation Page 18
PROGRAM OPERATION
-----------------
The program 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, 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. Once STSPLUS has started, the display type
may not be changed without halting 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. Use the SLOW option on the Set
Program Options Menu (F10+F7) if the program has difficulty operating on
your system.
STSPLUS selects the icon or symbol used to graphically represent the
satellite based upon the mission name. Names which start with the letters
"STS" will use the space shuttle icon and all other missions will use an
icon resembling the Hubble Space Telescope.
STSPLUS first reads in the map coordinates from file STSPLUS.MPT,
which must be in the current drive and directory. These coordinates are
converted to screen coordinates for the type of monitor detected and stored
internally so that they need only be read once. After map coordinates have
been loaded, the initial title screen is shown on the display.
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 the following section is then displayed. Press any
key to proceed to the Main Menu immediately.
Program STSORBIT PLUS Satellite Orbit Simulation Page 19
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
Last Mission = STS-45 [STS45J13]
(C) Copyright David H. Ransom, Jr., 1989-1992
All rights reserved.
Program STSORBIT PLUS Satellite Orbit Simulation Page 20
THE STSORBIT PLUS GROUND TRACK DISPLAY
--------------------------------------
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. Six different map displays are
available: World, Quadrant, Zoom, Location, Tracking Station, and Satellite
Motion. 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.
World Maps
----------
The STSPLUS 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. 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
includes approximately 30,000 vector pair coordinates describing the
world's coastlines, islands, and major rivers. (The rivers are not
displayed on the world maps to avoid "cluttering" the display.)
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.
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. A full
world map is available which is quite similar in appearance to the original
display. I happen to think it is a big improvement, but that's a matter of
personal opinion.
However, some geographic details are still difficult to distinguish,
Program STSORBIT PLUS Satellite Orbit Simulation Page 21
even on a VGA display. STSPLUS includes twelve quadrant maps, each overing
1/4 of the Earth's surface. 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.
Zoom Maps
---------
Although I was pleased with the enhanced maps using the Quadrant Mode,
the vector map file contains 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 45 degrees
across the screen, six times better than the 180 degree quadrant maps. This
approaches the practical limit for the vector database. 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.
Press the "Z" key to enable Zoom Mode. STSPLUS will use the current
position of the satellite to select the center of the map. 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 45 degrees, roughly the limit for
acceptable maps given the vector data being used). 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 the TAB key to enable or disable automatic map generation (the map
will always be redrawn). When automatic map generation is enabled, the
Program STSORBIT PLUS Satellite Orbit Simulation Page 22
letter "A" appears in the upper right corner of the screen next to the map
width or field of view. Zoom field of view is limited to 45, 60, 75, 90,
120, and 180 degrees.
During Mission STS-48, I found the Zoom Mode extremely effective in
helping me to distinguish various coastlines and rivers, even on my poor
old Zenith CGA/LCD laptop! The only problem with all of this is that I am
now approaching the limit of an 80C88 with 8087 math coprocessor (8 MHz at
that!) in terms of its ability to get the calculations done in the time
allowed.
Location Maps with Isocontours
------------------------------
By popular request, especially from the amateur radio community, I
have added the Location Map with Isocontours. (Isocontours is a description
coined by Rob Matson for his SkyMap program and for which he supplied
sample code.) Press the "L" key when the map display is present to select
this display. The map will be drawn with the current 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. 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
displayed at the lower right of the screen (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. Pressing
the "T" key will select this map mode. STSPLUS calculates which of the
available tracking stations is nearest to the current 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 23
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
included in the current TRACKING STATION file. Several different tracking
station files are included with 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.
Since this map mode uses the ZOOM map algorithms, the usual zoom map
features (PgUp, PgDn, Home, End) are active.
Big Clock Options
-----------------
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.
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. The big clocks are then placed below the standard data
instead of overwriting the regular data area.
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 ground 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 the EGA mode); the current map is always displayed
and the new map is drawn "off screen" and updated every ten seconds (or as
frequently as the capability of the processor will permit). Users with slow
computers or computers without math coprocessors may prefer this display
because, once the map has been drawn the first time, a complete map is
always displayed. For VGA users, the vertical map resolution in this mode
is reduced from 400 lines to 280 lines.
The Satellite Motion Map is enabled by pressing the "M" key when the
map is displayed. When switching to this map mode, the message "Switching
to EGA Dual-Page Mode ..." is displayed on the screen; all EGA and VGA
systems display the Satellite Motion Map in EGA resolution: 640 x 350
pixels. The complete map is then drawn off-screen and will require the
"usual" time during which the screen will be unchanged. (My 386 systems
update every 10 seconds but my 286 systems can only manage every 20 or 30
seconds -- and they all have math coprocessors!) As with other zoom modes,
the zoom magnification may be adjusted by pressing the Hone, End, PgUp, or
PgDn keys. Note that ONLY the "M", Home, End, PgUp, PgDn, and ENTER keys
are active while the Satellite Motion Map is displayed; press the "M" key
or ENTER to return to normal operation.
Program STSORBIT PLUS Satellite Orbit Simulation Page 24
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:
F1=Resume Data F6=Pause (+,-) TAB=Auto Maps On/Off L=Location Maps
F2=Sat Blink 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: Home,
F5=MET/T+Epoch F10=Sat Coordinates PgUp,PgDn STSPLUS Version 9228
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.
Satellite Position and Orbit Projections
----------------------------------------
The focus of the display, and the reason for program STSORBIT, 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 Function Key F2 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 predicted ground track
is shown as a series of light green dots, and the past ground track is
shown as light red dots. These dots are plotted at one minute intervals and
"move" as the spacecraft or satellite changes position; one new dot is
Program STSORBIT PLUS Satellite Orbit Simulation Page 25
added to the predicted track each minute and one dot is removed from the
past track at the same time.
The ground track may optionally be omitted, be shown as a light green
line, or be shown with both dots and line.
User's Circle of Visibility
---------------------------
Centered around the user's geographic location, and marked with a
small cross on EGA and VGA systems, is a magenta "circle" of the
approximate line of sight visibility for the mission in progress. The
"circle" appears on the display approximately as a circle near the Equator
and as a rounded triangle in higher latitudes. These strange shapes are
entirely an artifact of the map projection; if projected on the surface of
a sphere, they would be true circles. 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 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 usually 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 NASAnnn.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 using the same
alrorithm as for the user's circle of visibility. Like the user's circle,
the spacecraft circle appears on the display as an ellipse 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
at the same rate as the spacecraft symbol, normally every ten seconds.
Program STSORBIT PLUS Satellite Orbit Simulation Page 26
Comparisons with 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 shown on NASA Select
Television.
TDRS Satellite Features
-----------------------
TDRS Satellite features are shown only on HGC, EGA and VGA monitors.
The three TDRS satellites (Tracking and Data Relay Satellites), used for
most communications to and from the Space Shuttle and the Hubble Space
Telescope, are each shown as a dot inside a small yellow circle on the
Equator. There are three TDRS satellites in geosynchronous orbit, TDRS East
at approximately 72 degrees West longitude and the TDRS West Cluster
consisting of two satellites at approximately 170 degrees West longitude.
Both of the TDRS West Cluster satellites have partially failed but between
them they can provide the facilities of a fully operational satellite.
Each TDRS location provides communications coverage for almost half of
the Earth. However, since the ground station is at White Sands, New Mexico,
the coverage overlaps to provide good communications. This, in turn, means
that there is a narrow band, known by NASA as the Zone of Exclusion, off
the East coast of Africa which is not covered by either TDRS. Four slightly
curved vertical red lines on the display show the limits of coverage for
each TDRS location. With the map centered on the United States and scanning
from left to right, the red coverage lines are acquisition of TDRS East,
loss of TDRS West, loss of TDRS East, and acquisition of TDRS West.
During most of an orbit, the satellite being used for communications
will be shown in the data block opposite the title "Com:"; the messages
"TDRS-West" or "TDRS-East" will appear. Approximately five minutes before
the spacecraft reaches loss TDRS East, the message will change to "LOS
5:07" with the numbers indicating the minutes:seconds until anticipated
signal loss. Once the signal is lost, the message will change to "AOS 7:35"
to show the time remaining until acquisition by TDRS West. The algorithm
used for the calculation of the TDRS coverage is very approximate but is
usually accurate to within approximately 30 seconds.
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. Files STSPLUS.TRK and NASA.TRK contain 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. 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 27
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.
The shape of the antenna range "circle of visibility" varies as a
function of the latitude and is an artifact of the map projection; if
projected on a sphere, they would be 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. For all systems except CGA, the locations of the
three TDRS (Tracking and Data Relay Satellite) are shown as small circles
on the Equator at -41 degrees and at -171 degrees; on CGA displays the TDRS
coverage is NOT shown in order to avoid confusing the display.
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 Gwam
VAN -120.57,34.73 Vandenberg, CA
YAR 115,-29 Yargidy, 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
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"
"Yargidy, 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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 28
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 USSR.TRK (data courtesy
Ellwood Marshall). With the breakup of the Soviet Union, some of these
installations may no longer be active.
"Baikonur Cosmodrome",63.3392,45.9235,0,"BAI
"Dzhusaly USSR",63.85,46.15,0,"DZH"
"Kalingrad Control Ctr",37.816,55.916,0,"KAL"
"Plesetsk Cosmodrome",40.7,45.9235,0,"PLS"
"Petropavlovsk USSR",158.933,53.216,0,"PTR"
"Tbilisi USSR",44.75,41.66,0,"TBL"
"Ulan Ude USSR",107.683,51.983,0,"ULN"
"Ussuriysk USSR",132.15,43.8,0,"USS"
"Yevpatoria USSR",33.3666,45.2166,0,"YEV"
Other nations also have facilities for satellite launches. As of early
1992, file SPACENTR.TRK includes the following locations:
"Alcantara LC Brazil",-44.3999,-2.3999,0,"ALC"
"Esrange,Kiruna Sweden",21.067,67.883,0,"ESR"
"Jiuquan Space LC China",100.033,40.83,0,"JIU"
"Kagoshima Center Japan",131.083,31.25,0,"KAG"
"Kourou Space Ctr Fr.Gu",-52.7669,5.23,0,"KOU"
"San Marco Platform",40.2,-2.9329,0,"SMP"
"Sriharikota Ctr India",80.25,13.78,0,"SRI"
"Tanegashima SC Japan",130.967,30.4,0,"TAN"
"Xichang Space LC China",102.217,27.967,0,"XUC"
The first mission of Endeavour, STS-49, was in May, 1992. This
dramatic and exciting mission captured the INTELSAT VI (F3) satellite,
stranded in a useless orbit by its booster rocket failure since January,
1990, and attached a new booster rocket which placed the satellite in its
proper orbit. STSPLUS was used operationally during the mission by
Intelsat, another "first" for the program. Intelsat used its own ground
tracking stations for communications with INTELSAT VI (F3); the ground
stations which participated in the mission are listed in file INTELSAT.TRK
(information courtesy Dee Smith):
"Paumalu, Hawaii",-158.0342,21.6711,157.86,"PAU"
"Tangua, Brazil",-42.7845,-22.7442,35.38,"TAN"
Program STSORBIT PLUS Satellite Orbit Simulation Page 29
"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. Note that although
the two quoted strings at the beginning and end of each line are not
presently used, they are required for proper operation. 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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 30
ACTIVE KEYS DURING GROUND TRACK DISPLAY
---------------------------------------
The following table lists the various keys which are active when the
tracking display is shown on the screen. Some of these features are more
fully described elsewhere.
ENTER Return to Main Menu (cancel this 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 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; use the TAB key to restore automatic map generation.
F5 When using 2-line elements, the elapsed time may be switched
between "T+Epoch" and "MET" by using the "T" command. If no
launch time and date have been entered, this command will have no
effect.
F6 Enable/Disable PAUSE mode; only the local date and time are
updated. The plot is frozen at the current position and the "+"
and "-" commands are enabled.
F7 Enable or disable the spacecraft circle of visibility.
Program STSORBIT PLUS Satellite Orbit Simulation Page 31
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.
NOTE: Since this "-" or reverse feature was implemented primarily
for testing and demonstration, the ground track logic does not
recognize these reverse movements and will become slightly
confused. To restore the ground track and current times properly,
press ENTER TWICE to stop the display and then to resume the
mission.
TAB Enable or disable automatic map generation. When automatic map
generation is enabled, 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.
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.
W,0 Select World Map display, showing the full world from +85 degrees
North latitude to -85 degrees South latitude. 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 32
Q Select Quadrant Map display, showing 180 degrees field of view
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 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. 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 zoom map with the satellite centered. 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.
R Resynchronize MET or T+Epoch with Local Time. Resets plot to real
time.
NOTE: The Resynchronization feature was originally intended only
for testing and should only be performed when the simulated time
and local times are reasonably close to each other. The plot may
otherwise have some extraneous pixels left around! This feature
has not been extensively tested. To restore the ground track
completely, press ENTER to stop the display and return to the
Main Menu, then press ENTER again to resume the mission.
Program STSORBIT PLUS Satellite Orbit Simulation Page 33
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 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
F1 Program STSORBIT PLUS Demonstration
F2 Read NASA/NORAD 2-Line Elements (from *.TXT File)
F3 Read Prior Mission Information (from *.INI File)
F4 Enter New Orbital Information (Simple Orbital Model)
F5 Adjust 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 (STS-45 [STS45J13])
ESC Quit STSORBIT PLUS and Save Current Mission
Select desired function:
F1 Program STSORBIT PLUS Demonstration
------------------------------------------
The F1 command may be used to demonstrate the operation of STSPLUS and
to verify that the program will operate correctly. No other information is
required. The demonstration automatically sets up the data to simulate a
mission and clears the screen. A slight delay may follow while the program
calculates the initial parameters of the orbit. Then the world map is
drawn, the ground track for the first three orbits (approximately) is drawn
as a series of dots (green for color monitors), and mission data is
displayed at the bottom. Mission Elapsed Time (MET) is set to shortly
before launch time and counts down to zero.
When MET reaches zero, the shuttle symbol appears over Cape Canaveral.
For CGA and HGC systems, the shuttle will blink; for EGA and VGA systems,
the shuttle will be steady. At first the shuttle will move along the ground
track very slowly, simulating the ascent phase of the mission. After about
ten minutes the shuttle reaches orbital altitude and proceeds along the
ground track normally, passing a dot every minute. Press F4 (for Fast time)
once or twice to speed up the progress of the simulation. Press ENTER to
return to the Main Menu.
Data are displayed by STSPLUS in several standard formats:
Program STSORBIT PLUS Satellite Orbit Simulation Page 34
4/05/1990 Date in month/day/year
14:33:00 Time in hours:minutes:seconds
3/09:23:15 MET in days/hours:minutes:seconds
-69.34 Longitude and Latitude in degrees
WEST longitude and SOUTH latitude are negative
320.50 nm Altitude in nautical miles
F2 Read NASA/NORAD 2-Line Elements from *.TXT File
------------------------------------------------------
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 "NASA014.TXT" where the "014"
corresponds to the particular NASA 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 (the example
has been edited to show only 8 lines):
Select NASA/NORAD 2-Line Elements File
Enter 2-Line Filename [STS50N38.TXT]:
Use ARROW KEYS or press ENTER to use the current
default file as shown in square brackets [...].
16 Available .TXT files in directory E:\STSPLUS
COS851R.TXT STS49N12.TXT
GSFC035.TXT STS49N16.TXT
GSFC055.TXT STS49N19.TXT
GSFC071.TXT STS49N26.TXT
GSFC096.TXT STS49N28.TXT
GSFC097.TXT STS49N29.TXT
GSFC100.TXT STS49R05.TXT
GSFC101.TXT STS50N38.TXT
The list of files is sorted in alphabetical order then displayed using
up to five columns. The default filetype is ".TXT". 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, STS50N38.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
Program STSORBIT PLUS Satellite Orbit Simulation Page 35
ENTER.
STSPLUS defaults the drive and directory to the current directory, the
one from which STSPLUS is being executed. However, some users prefer to use
a separate directory for 2-line elements files. To specify a different
drive and/or directory, enter the drive (followed by a colon) and the
desired directory (followed by a trailing backslash, "\"). The specified
drive, directory, and filename are saved in file STSPLUS.INI and will be
used the next time STSPLUS is executed. The following examples illustrate
this method:
D:\ Use the root directory on drive D:
\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
Although STSPLUS defaults to "*.TXT", you may use this command to
temporarily specify a different filename and filetype mask if desired.
If no files with filetype .TXT (or files corresponding to the current
filename and filetype mask) are found in the specified directory, the
following error message will be displayed:
No .TXT files found in specified drive/directory: E:\JUNK
Press any key to continue ...
where the filetype, ".TXT" in the example above, is the default filetype or
whatever filetype was specified. 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" 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/Number [STS...]:
(Enter '*' to match any satellite name)
STSPLUS will normally display the first three characters of a
satellite name, enclosed in square brackets, as the default choice. If no
prior satellite has been selected, the satellite name will default to
Program STSORBIT PLUS Satellite Orbit Simulation Page 36
"STS..." for space shuttle missions (provided the filename begins with
"STS") and to "HST..." for all other satellites; otherwise, it will be the
first three letters of the currently selected satellite. 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;
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 errors that might otherwise yield an incorrect position!
Program STSORBIT PLUS Satellite Orbit Simulation Page 37
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 NASAnnn.TXT is an ASCII file; it may be
helpful to view 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.
As a point of interest, the NASA 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 Read Prior Mission Information from *.INI File
-----------------------------------------------------
The F3 command displays all files in the current directory with a
filetype of .INI and then prompts the user to enter the name of the desired
data file. File STSPLUS.INI is the file which has the data from the last
time the program was run; to use file STSPLUS.INI, press ENTER. STSPLUS
will automatically supply the filetype .INI if you do not include it. If
the requested file is not present, an error will be reported. To create new
command to copy STSPLUS.INI into a file with a the desired name.
STSPLUS also expects your computer clock to be set to the correct
local time and date; use the DOS TIME and DATE commands. See the F10+F10
command below for information on setting the UTC Zone Offset. Of course,
you could "fool" STSPLUS by setting your computer to a desired time and
date using the DOS TIME and DATE commands, but be aware that for most
computers using MS-DOS/PC-DOS 3.3 or greater the hardware clock is also set
with these commands. Instead of setting your computer clock to some
fictitious time, use STSPLUS's internal time setting functions (F8 on the
Main Menu) to set a desired simulation time. This method does not affect
your computer's internal hardware or software clocks.
F4 Enter New Orbital Information (Simple Orbital Model)
-----------------------------------------------------------
The F4 command uses the "simple" orbital model and allows the user to
enter the orbital altitude, inclination, launch time, and launch date
using your local time or UTC (Coordinated Universal Time) or GMT (Greenwich
Mean Time, essentially identical to UTC for the purposes of this program)
to determine the orbital parameters. If you enter the time and date using
local time, it will internally be converted to UTC so that the .INI file
will be valid in any time zone. To manually enter orbital data, you will be
prompted for the required information.
Program STSORBIT PLUS Satellite Orbit Simulation Page 38
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
Enter mission title: STS Mission Simulation
Enter orbit altitude (nm): 160.00 nm ( 296.52 km)
Enter orbit inclination (deg): 28.450 degrees
Enter Launch Time (HH:MM:SS): 15:58:12 PST 23:58:12 UTC
Enter Launch Date (MM/DD/YYYY): 4/08/1992 4/08/1992
Press ENTER to accept, SPACE BAR to repeat: _
The sample above illustrates the data required to generate the simple
orbital model. A brief discussion follows for each item.
Enter mission title:
Enter the title of the mission, such as "STS-45 ATLANTIS" without the
quotation marks. If you press ENTER, the title "STS Mission Simulation"
will be used.
Enter orbit altitude (nm):
[Add 'km' for altitude in kilometers.]
Enter the orbit altitude (or average orbit altitude for non-circular
orbits), in nautical miles. If you wish to use kilometers, add the letters
"KM" (upper or lower case) at the end of the number.
Enter orbit inclination:
Enter the inclination of the orbit in degrees; a decimal fraction is
allowed. For example, STS-30 was flown at an inclination of 28.85 degrees
and STS-28 used an inclination of 57 degrees. Press ENTER to use the
default value of 28.45 degrees.
Enter Launch Time (HH:MM:SS):
[Press ENTER for ASAP; add 'U'or 'G' for UTC/GMT]
Enter the time in the format shown using 24-hour notation and local time.
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). 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 39
entered as 16:00:00 or 4:00 PM. Press ENTER for "launch" ASAP, as soon as
possible; depending upon the system, this will be in from 30 to 60 seconds
from the current time.
Enter Launch Date (MM/DD/YYYY):
[or press ENTER for TODAY]
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
full four digit year may be used OR you may use 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 use today's date.
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.
F5 Adjust Orbital Parameters
--------------------------------
ADD/CHANGE LAUNCH DATE AND TIME (2-line elements)
The full F5 command assumes the "simple" orbital model and is
abbreviated when using NASA 2-line elements; only the LAUNCH DATE and
LAUNCH TIME may be set when NASA 2-line elements have been selected; all
other orbital parameters are included in the 2-line elements and may not be
altered within STSPLUS. A 2-line element set must have been previously
loaded using the F2 command on the Main Menu before the launch date and
time may be set or changed.
Since estimated NASA 2-line elements are usually available prior to a
launch, and actual 2-line elements within about 24 hours after a launch
(and are far more accurate than the manually entered "simple orbital
data"), those data should be used when available. However, since most
events occuring during a space shuttle mission follow the MET (Mission
Elapsed Time) timeline, the time elapsed since launch, it is convenient to
show MET. This requires that you obtain the launch date and launch time
independent of the 2-line elements and manually enter that data into
STSPLUS. Note that STSPLUS retains the launch date and time information
from one set of 2-line elements to another. Be sure to reset these data
when you change from one mission to another!
Enter Launch Time (HH:MM:SS):
[Press ENTER for ASAP; add 'U'or 'G' for UTC/GMT]
Enter the time in the format shown using 24-hour notation and local time.
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). 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 40
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 for "launch" ASAP, as soon as
possible; depending upon the system, this will be in from 30 to 60 seconds
from the current time.
Enter Launch Date (MM/DD/YYYY):
[or press ENTER for TODAY]
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
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 use today's date.
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.
Once the launch date and time have been set, this information is
saved in file STSPLUS.INI. Remember, when changing from one satellite to
another this information is NOT cleared automatically.
ADJUST ORBITAL PARAMETERS (Simple Orbital Model)
When the orbital parameters change in mid-mission for the "simple"
orbital model, use this command to adjust the orbital period/altitude,
orbital longitude, and time along orbital track. This technique allows the
"launch time" to remain correct, which in turn assures that Mission Elapsed
Time is correct, while adjusting the orbital parameters so that the
position is displayed correctly in later orbits. The following items may be
adjusted; in each case, the required units or input format is shown in
parentheses (...) and the current value of the item is shown within square
brackets [...]. Press ENTER to leave an item unchanged.
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
Enter MISSION TITLE [STS Mission Simulation]: STS Mission Simulation
Enter LAUNCH TIME (HH:MM:SS) [23:58:12 UTC]: 16:58:12 PDT 23:58:12 UTC
Enter LAUNCH DATE (MM/DD/YYYY) [04/08/1992]: 4/08/1992 4/08/1992
Enter ORBIT INCLINATION (degrees) [28.4500x]: 28.4500
Enter ORBITAL ALTITUDE (nm) [ 160.00]: 160.00 nm ( 296.52 km)
Enter LONGITUDE adjust (deg) [ 0.000x]: 0.000
Program STSORBIT PLUS Satellite Orbit Simulation Page 41
Enter TIME adjust (min) [ 0.000]: 0.000
Press ENTER to accept, SPACE BAR to repeat:
In order to make these adjustments, the current orbital altitude is
required, along with the longitude and time of one or more equator
crossings (obtained from the NASA Television wall map). NASA is not too
good about making sure that the map is on the screen when the Shuttle makes
an equator crossing (Northbound is Ascending Node, Southbound is Descending
Node); they have a distressing tendency to cut away just before the
crossing. With sufficient patience, however, the data can be interpolated
from the television screen. See the section ADJUSTING ORBITAL PARAMETERS
below for more information.
F6 Set Elapsed Time Option
------------------------------
When using NASA 2-line elements, STSPLUS by default displays the time
elapsed since the epoch date of the elements in the upper right portion of
the data block. This is marked on the display as "T+Epoch". While this
information 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.INI.
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 a previous STSPLUS session
from file STSPLUS.INI. However, since the launch time and date are not
included in the 2-line orbital elements, no validity check can be made; if
you change satellites, be sure to either clear or change the launch time
and date. If no launch time and date are present, you will be prompted for
Program STSORBIT PLUS Satellite Orbit Simulation Page 42
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.
F6 Set FILENAMES and Paths
------------------------------
Function Key F7 allows the user to select the filenames (and drive and
path, if included) for the files that STSPLUS uses to select satellites and
tracking stations.
Select filename to set or press ENTER when done:
F1 Set 2-LINE ELEMENTS filename [NASA975.TXT]
F2 Set TRACKING STATION filename [STSPLUS.TRK]
Enter selection or ENTER:
The current filename is shown in square brackets for each selection. Press
F1 to set the 2-LINE ELEMENTS filename or F2 to select the TRACKING STATION
filename. Press ENTER to leave a filename unchanged. The following is a
typical prompt for filename:
Enter TRACKING STATION filename: _
(Press ENTER to leave unchanged)
If no filetype is entered, STSPLUS will automatically supply ".TXT"
for 2-line elements files and ".TRK" for tracking station 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.
After each entry, the 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
--------------------------------
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 F4 to go to the TIME and DATE Menu:
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
ACTUAL SYSTEM DATE AND TIME SHOWN ABOVE
Program STSORBIT PLUS Satellite Orbit Simulation Page 43
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
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). 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).
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 the F2
command to correctly set your system clock. If the zone abbreviation or UTC
date or UTC time is incorrect, use the Set Program Options command from the
Main Menu (F10+F9) to correctly set the UTC Offset and the Daylight Flag.
Some organizations, NASA for example, continue to use the wording
"Greenwich Mean Time" or "GMT" for what is now usually referred to as
"Coordinated Universal Time" or "UTC" (and sometimes, depending upon the
application, as "UT", "UT1" or "UT2"). STSPLUS uses Coordinated Universal
Time or "UTC", the time used for civil timekeeping and broadcast by radio
stations such as WWV and the BBC. Although technically these different time
standards are not exactly the same, the difference is only a maximum of 0.9
seconds and the program treats them all as identical. STSPLUS defaults to
the abbreviation "UTC" but if you prefer to use "GMT", enter any simulated
time using F3 and include the letter "G" (upper or lower case) at the end.
The time abbreviation at the top of the screen will change from "UTC" to
"GMT" and will continue using that abbreviation until a time is entered
suffixed with "U".
Times are always entered as "HH:MM:SS" where HH is HOURS, MM is
MINUTES, and SS is SECONDS. The time entry format is very flexible. Leading
zeroes are not required. The comma (",") may be used in place of the colon
(":") as a separator if desired. SECONDS or MINUTES and SECONDS may be
omitted if desired. Time entries are assumed to be local time; to enter UTC
or GMT times, add the letter "U" or "G" (upper or lower case) respectively
following the entry. For example, the following are valid time entries:
Entry Interpreted as
------ --------------
12 12:00:00
13,1 13:01:00
4:1:15 04:01:15
1,1,1 01:01:01
13,45U 13:45:00 UTC
1:20g 01:20:00 GMT
Dates are always entered as "DD/MM/YYYY" where DD is DAYS, MM is
Program STSORBIT PLUS Satellite Orbit Simulation Page 44
MONTHS, and YYYY is the full four-digit year. 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 read (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. This
provides a double check that the program has interpreted your entry as you
wished.
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.
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.
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
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.
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 F2 command above to restore the date and time
to "real time".
Program STSORBIT PLUS
Space Shuttle and Satellite Orbit Simulation
Version 9228
Simulated time: 13:00:08 PST 21:00:08 UTC
Simulated date: 11/08/1991 11/08/1991
Program STSORBIT PLUS Satellite Orbit Simulation Page 45
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.
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 9228
Simulated time: 00:17:18 PST 08:17:18 UTC
Simulated date: 10/09/1991 10/09/1991
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.
Press ENTER to return to the Main Menu with the date and time as
displayed on the screen (Current or Simulated).
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.
Program STSORBIT PLUS Satellite Orbit Simulation Page 46
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
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 47
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 9228
Current time: 16:34:24 PDT 23:34:24 UTC
Current date: 04/08/1992 04/08/1992
F1 Program STSORBIT PLUS Information
F2 Set New Local Coordinates (Rancho Palos Verdes, CA)
F3 Select Display Features
F5 OFF Show Ascending & Descending Node Data
F6 ZOOM Set Map Center and Size
F7 OFF Set for SLOW COMPUTER or NO COPROCESSOR
F9 -8.00 Set UTC Time Offset and Daylight Flag
F10 OFF Enable/Disable Printer Logging
ENTER Return to MAIN MENU
Select desired function:
F1 Program STSORBIT PLUS Information
----------------------------------------
Function Key F1 displays information about program STSORBIT PLUS
including the copyright notice, version number, my name and address, and
the telephone number of my RPV ASTRONOMY BBS (Bulletin Board System). The
current version of STSORBIT PLUS is always posted on the BBS. The BBS has a
power controller; if it hasn't answered after the THIRD RING, hang up and
call back in two minutes. The BBS is available 24 hours per day at 9600,
2400 and 1200 baud.
F2 Set New Local Coordinates
--------------------------------
In order to perform the calculations related to satellite visibility
and altitude/azimuth, STSPLUS must know the geographic 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
indicated by the name in parentheses on the Options Menu. The program
provides two methods for setting your own coordinates: reading a file of
Program STSORBIT PLUS Satellite Orbit Simulation Page 48
city names and coordinates (STSPLUS.CTY); or manually entering the
information.
Pressing F2 will display the following reminder:
STSPLUS will search for the CITYNAME you enter anywhere in the city
names in the file. For example, 'SAN' appears in 'SAN FRANCISCO', 'SAN
DIEGO', 'SANTA ANA', 'THOUSAND OAKS', etc. Press ENTER to cancel the
search or enter '*' to enter a new city name and coordinates.
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 search for: 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):
DDD.DDDDD Degrees and decimal fraction
DD,MM.MMM Degrees, minutes and decimal fraction
Program STSORBIT PLUS Satellite Orbit Simulation Page 49
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 complete description below.
F6 Set Map Center and Size
------------------------------
The F6 command selects the size and field of view of the displayed
map. By default, the map is of the full world and is centered on the Prime
Meridian at Greenwich, England at 0 degrees longitude. (Most Americans are
accustomed to viewing the map centered somewhere in the Western Hemisphere,
and this orientation may be selected by pressing the "W" or "0" keys while
the map is displayed.) It is sometimes convenient to shift the map center
when the Space Shuttle is near the edge of the map.
Pressing F6 will select between WORLD, QUAD, and ZOOM maps. Selecting
QUAD will select one of twelve Quadrant Maps showing a field of view
(horizontal size) of 180 degrees. 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. See the sections QUADRANT
MAPS, ZOOM MAPS, and AUTOMATIC MAP GENERATION for additional information.
Program STSORBIT PLUS Satellite Orbit Simulation Page 50
F7 Set for SLOW COMPUTER or NO COPROCESSOR
----------------------------------------------
IMPORTANT NOTE: ALWAYS select the Slow Mode if your computer is
not equipped with a math coprocessor.
When operating in real time, if the seconds
portion of the times shown as "Local:" and
"Simulation:" do not agree to within 1 or 2
seconds, your computer is NOT able to maintain
real time operation without the SLOW MODE!
Press F7 to switch the SLOW MODE between "ON" and "OFF". "ON" means
that the SLOW MODE is active; "OFF" means normal operation.
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 keep up with real time orbital calculations. For example, my
old vanilla Zenith Z-148, operating at 4.77 MHz and no math coprocessor,
takes approximately 4.5 seconds to make a full set of orbital position
calculations; when switched to 8.0 MHz, the same calculations require only
2.5 seconds. In either case, the program gets hopelessly behind itself and
can never catch up when operated in the normal program mode.
While perhaps not the "ideal solution" as compared to having a math
coprocessor, setting STSPLUS for SLOW MODE can help in all but the most
severe cases. Instead of attempting to update its position calculations
every second, the update is slowed to every ten seconds in this mode. This
allows the computer to more or less keep up at a cost of not having data
quite in real time on a second-by-second basis. Except for the frequency of
updates, all program features are unchanged. When STSPLUS is operating in
the SLOW MODE, the phrase "SLO" appears at the lower right of the tracking
display.
Since STSPLUS makes no test to see if it is keeping up with real time
(the program cannot tell the difference between the PAUSE or SIMULATED TIME
modes versus REAL TIME) and since most features are available for all
computer configurations, it is the responsibility of the user to make sure
that the appropriate options have been selected. Even in the SLOW MODE,
certain very slow computers (such as an old XT-class computer running at
4.77 MHz) cannot keep up if the solar terminator is enabled when using the
2-line elements orbital data.
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 51
savings time (summer time in the UK).
When prompted, enter the time offset in hours from your local time to
Coordinated Universal Time. Examples are shown for most time zones in North
America. STSPLUS then asks if you are using daylight savings time; enter
"0" if not, and "1" if so. The sum of these two values is shown on the Main
Menu; for example, if the computer is set to Pacific Daylight Time (UTC
offset is -8.00 hours and Daylight Flag = 1), the sum will be -7.00. For
most time zones in North America, the correct zone abbreviation will be
shown on the ground track display for Local date and time. When you change
your computer from/to daylight savings time, use this command to update
STSPLUS. The following shows the display when using the F9 command:
Set UTC TIME ZONE OFFSET and DAYLIGHT FLAG
STSPLUS must know the difference between your local time zone
and Coordinated Universal Time (UTC), also sometimes known as
Greenwich Mean Time (GMT). With this information, STSPLUS can
automatically adjust launch or Epoch times and dates for your local
time zone. In addition, STSPLUS must know if your computer is now set
to STANDARD or DAYLIGHT time.
First, enter the difference between your STANDARD time zone and
UTC in hours. Do NOT include the hour for daylight time if you are now
on DAYLIGHT time; it will be entered separately. For most time zones
in the United States and Canada, the entries required are:
Eastern Standard Time EST -5.0
Central Standard Time CST -6.0
Mountain Standard Time MST -7.0
Pacific Standard Time PST -8.0
Enter UTC Offset (hours): -8
Enter DAYLIGHT Flag (0=OFF, 1=ON): 1
Once this information has been entered, it will be saved in file
STSPLUS.INI and will not be requested again. If you change from Standard
to Daylight Time or vice versa, use the F10+F9 command to update the
Daylight Flag. INI files obtained from other users may be from a prior
version of STSPLUS and the time information may have to be corrected.
F10 Enable/Disable Printer Logging
-------------------------------------
I have found it interesting to log the orbital data and the ascending
and descending node information on my printer when analyzing the mission
data over long periods of time. The F10 command toggles the printer logging
function on and off. The first page of the log includes the current orbital
data and subsequent pages contain only node information. In addition to the
information presented on the display, the printer log also calculates the
current orbital time, the time from one ascending (descending) node to the
next, for the third and subsequent nodes. A typical log is shown below.
IMPORTANT: BE SURE THE PRINTER IS TURNED ON PRIOR TO ENTERING THE
F10 COMMAND.
Program STSORBIT PLUS Satellite Orbit Simulation Page 52
STSORBIT: Space Shuttle Tracking Program, Version 9228 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
Adjust Longitude: 9.80
Adjust Orbit Time: 8.40 min
ORBIT
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.
When a printer log is prepared for a satellite using 2-line elements,
the Adjust Longitude and Adjust Orbit Time entries will not be shown in the
header data. 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 for 2-line element simulations. 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 53
SET DISPLAY FEATURES
--------------------
Depending upon the satellte 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 9228
Current time: 09:42:13 PST 17:42:13 UTC
Current date: 04/09/1992 04/09/1992
F1 ON Display LOCAL Circles of Visibility
F2 OFF 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 NM Select Distance Units: NM or KM
F10 A/A Select Satellite Coordinates: RA/DEC, Alt/Az, XYZ
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. 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 approximate 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
assumes, as is often the case, that TDRS East will be selected when it is
available.
Program STSORBIT PLUS Satellite Orbit Simulation Page 54
F3 Enable/Disable 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, 90 degrees, and -90
degrees shown in blue on color monitors; the Equator and the prime meridian
are shown in bright blue. Turning on the map grid adds lines of longitude
every 30 degrees and lines of latitude every 10 degrees. Displaying the
additional grid lines on monochrome monitors usually makes the screen too
"busy" and is not recommended.
In the Quadrant and Zoom Map modes, the spacing of the additional grid
lines is adjusted for the map field of view. For EGA and VGA systems, 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. 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 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.
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 from approximately a circle near the Equator to something
like a rounded triangle at higher latitudes. Near the poles, the "circle"
spreads out across the map. This is an artifact of the map projection;
plotted on the surface of a sphere, it would be a true circle.
This feature may be enabled for all spacecraft using 2-line elements.
When the program is run in the normal mode, the circle of visibility is
Program STSORBIT PLUS Satellite Orbit Simulation Page 55
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. When the program is run in the
SLOW MODE, the radius of the circle of visibility is constant, as
calculated at the moment the ground track display is started. This feature
may also be enabled or disabled during the ground track display using
Function Key F7.
F7 Display South Atlantic Anamoly 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).
F8 Display Terminator, Sun, and SpaceCraft Lighting
-------------------------------------------------------
Many types of observations, especially Earth observations, often
require that the target or terrain be 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 outside 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 is
partially updated every 10 seconds (and is fully updated every 60 seconds)
and the sun is updated every 60 seconds. Because of the additional
calculations and plotting required, these solar features may not be
suitable for slow processors or computers without a math coprocessor. NOTE:
Only the terminator is available with CGA systems.
The terminator 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 sunrise and sunset
are based upon 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 ten minutes or more when
the times are compared against published values or those calculated by my
program ASTROCLK, sunrise being earlier and sunset being later.
The performance of solar panels and certain other instruments on a
spacecraft is dependent upon whether or not the Sun is in view. Similarly,
it is usually impossible to visually see a spacecraft which is not in
sunlight. 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
Program STSORBIT PLUS Satellite Orbit Simulation Page 56
monitors. Note also that the spacecraft lighting is indicated by an
asterisk ("*") next to the "Orbit #"; the asterisk is present when the
spacecraft is in full or partial sunlight and is absent otherwise.
F9 Select Distance Units: NM or KM
--------------------------------------
Spacecraft altitude, range, and satellite geocentric rectangular
coordinates (X, Y, and Z) may be expressed in either nautical miles (nm) or
kilometers (km). This feature selects which units will be displayed for
those data.
F10 Select Satellite Coordinates: RA/DEC, AltAz or XYZ
---------------------------------------------------------
This feature selects between topocentric (horizon) coordinates
(referenced to the Earth's surface and in this case the current local
geographical coordinates), equatorial coordinates for the satellite's
position (Right Ascension and Declination), or geocentric rectangular
coordinates (X, Y, and Z, referenced to the center of the Earth). Press F10
until the desired coordinate system is selected. The abbreviations "R/D",
"A/A", and "XYZ" are used on the menu. You may also use Function Key F10 to
switch between coordinate systems while the ground track display is in
progress. NOTE: The geocentric rectangular coordinates are only available
when using 2-line orbital elements.
For most purposes, such as aiming an antenna or visually spotting the
satellite, the horizon coordinates of Altitude and Azimuth are desired. If
you wish to determine the star background, however, the equatorial
coordinate system of Right Ascension and Declination (referenced to the
epoch of date) is needed. For both of these coordinate systems, the range
from the current local coordinates to the satellite is also given,
expressed in either nautical miles or kilometers as selected by F9 above.
Program STSORBIT PLUS Satellite Orbit Simulation Page 57
STSORBIT PLUS'S ORBITAL MODELS
------------------------------
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 by now 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. Although it may be the only method
available at launch, after about a week the errors can 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, while retaining the capability of using the
simple orbital model (primarily for demonstrations), relies on the 2-line
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
Program STSORBIT PLUS Satellite Orbit Simulation Page 58
space, the "Two Body Problem". These six quantities, often referred to as
Keplerian orbital elements, are included in the NASA/NORAD 2-line element
sets along with other numerical and statistical data. NORAD, the North
American Air Defense Command headquartered in Cheyenne Mountain, Colorado,
(and now known as the U. S. Space Command) developed 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. My own analyses of 2-
line element sets obtained independently from other NASA centers indicate
that NASA and NORAD do not always use the same definition for revolution
(orbit) numbers; NASA frequently gives a number one 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. 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.
For the past several years, T S Kelso has been making the NASA/NORAD
data available as a public service on his Celestial BBS at (513) 427-0674.
The 2-line element sets are prepared by Kelso using data received directly
from NORAD by special arrangement. I regularly post a slightly edited
version of the current element sets on my own RPV ASTRONOMY BBS as file
NASAnnn.TXT, where "nnn" is the NASA 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, also regularly posts
NORAD 2-line elements. 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.
Finally, the NASA SpaceLink BBS in Huntsville, Alabama, (205) 895-
0028, 8 lines @ 300-9600 baud, provides mission information for all space
shuttle missions and current 2-line orbital elements both pre-mission and
while a mission is in progress. In addition, SpaceLink has a wealth of
other NASA information.
Program STSORBIT PLUS Satellite Orbit Simulation Page 59
ADJUSTING ORBITAL PARAMETERS (Simple Orbital Model)
---------------------------------------------------
NOTE: This section applies ONLY if you are using the simple orbital
model for simulation. When using 2-line elements, all orbital
parameters are completely defined by the 2-line elements and may not
be modified from within STSORBIT PLUS. For accurate satellite
tracking, obtain 2-line elements from my BBS or elsewhere.
The original "simple" orbital model used in STSPLUS is imperfect, to
say the least. The data generally available from NASA prior to launch often
does not describe upcoming shuttle orbits at all precisely. In particular,
STSPLUS's initial orbital calculations, those related to the time from
liftoff to orbital insertion, are more or less guesswork. Once a mission is
established in orbit, it may be therefore desirable to adjust the orbital
parameters to make STSPLUS's displayed ground track correspond more closely
to that displayed on the wall map in Mission Control Center. To make the
adjustment, use the following procedure:
1. Start program STSPLUS. After the map data has been read in, select the
program options command, F10, then press F5 to enable display of the
data for the ascending and descending nodes. Enter the original launch
time and orbital data using the F4 command or restore prior data using
the ENTER key or F3 command if no adjustments have been entered. The
plot will appear on the screen.
2. Observe the crossing time and longitude of the node of interest and
calculate the difference from the desired crossing time. Note that
NASA performs all orbital calculations referenced to the Ascending
Node, the point at which the ground track crosses the Equator in a
North-bound direction. In order to view a given node crossing
repeatedly, you may find it convenient to reset the DOS clock to a
minute or two prior to the expected time.
HINT: Use the F9 command to go back to DOS, then use DOS's TIME
command to set the clock. BE SURE TO RESET YOUR COMPUTER CLOCK WHEN
YOU HAVE COMPLETED ALL ORBITAL ADJUSTMENTS!
3. When adjusting orbital parameters, it is preferable to adjust the TIME
before adjusting the LONGITUDE. This is because the longitude of the
node is affected by the rotation of the Earth (by 15 degrees per hour)
when the time is changed. Calculate the difference between the time of
the observed node crossing and the time of crossing plotted by
STSORBIT. If the observed time is earlier than the plotted time, the
time adjustment must be positive, otherwise it must be negative. The
time must be calculated in minutes and decimal fractions of a minute.
4. Press ENTER to return to the Main Menu, then press F5 to enter
adjusted data. Enter the new orbital altitude in nautical miles (or
altitude in kilometers by adding "km"); usually, the orbital altitude
has not changed and you should press ENTER to leave this item
unchanged.
5. Press ENTER to leave the longitude adjustment set at zero.
Program STSORBIT PLUS Satellite Orbit Simulation Page 60
6. Enter the calculated time difference for the node crossing as the time
adjustment (in minutes).
7. Press ENTER to leave the launch time unchanged.
8. Inspect the data displayed to be sure it is correct. If it is not,
press the SPACE BAR to re-enter data; if it is correct, press ENTER to
accept the data. STSPLUS will immediately begin plotting the new
ground track. If necessary, interrupt the plot with the ENTER key,
reset your computer's clock, return to STSPLUS, and press ENTER to
resume current mission.
9. Again observe the plotted time of crossing and repeat from Step 4 if
the time is not correct. If the time is correct, note the longitude of
the node and calculate the difference from the observed longitude. If
the plotted longitude is less than the observed longitude, the
adjustment must be positive, otherwise it must be negative. The
longitude adjustment must be entered in degrees and decimal fractions
of a degree.
10. Press ENTER to return to the Main Menu, then press F5 to enter
adjusted data. Enter the calculated longitude adjustment, then press
ENTER twice to leave the time adjustment and launch time unchanged.
11. Inspect the data displayed to be sure it is correct. If it is not,
press the SPACE BAR to re-enter data; if it is correct, press ENTER to
accept the data. STSPLUS will immediately begin plotting the new
ground track. If necessary, interrupt the plot with the ENTER key,
reset your computer's clock, return to STSORBIT, and press ENTER to
resume current mission.
12. This procedure should enable you to set the orbital parameters with
considerable accuracy. However, even minor changes of the orbit in
flight can cause a significant cumulative error in the ground track
displayed by STSPLUS. If all this seems like too much effort, just
enjoy the program "as it comes from the box"!
Program STSORBIT PLUS Satellite Orbit Simulation Page 61
STSORBIT PLUS Revision History
------------------------------
Each released version of STSPLUS uses a four digit revision code such
as 9218. 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 9228A -- July, 1992
---------------------------
-In response to many user requests, I have improved the 2-line elements
file directory functions using F2 from the Main Menu. The list of available
files is now alphabetized and you may use the ARROW KEYS to move through
the list. The selected file is highlighted and is shown as the new default
file. See the section "F2 Read NASA/NORAD 2-Line Elements" for a complete
explanation.
-Corrected a bug that displayed the incorrect city label for the primary
location if the Location Map for the second location was last displayed.
Thanks again to Joel Runes for spotting this one!
-Corrected a minor bug that caused the "BAD CHECKSUM ..." error message to
scroll off the screen when reading 2-line elements (F2). The message now
appears in RED following the File Record Number.
Version 9228 -- July, 1992
--------------------------
-Fixed bug when too many .TXT files were present and the list overflowed
the available screen columns and aborted with "BASIC PDS Error 5". The file
listing now stops when the screen is full (and some files may therefore NOT
be displayed).
-Changed screen mode for EGA and VGA monitors to use 43 or 50 lines for
display of available .TXT files. Screen returns to 25 lines after file
search. This slows the display slightly but greatly increases the number of
files that may be displayed on EGA and VGA systems.
-Fixed bug associated with help screen (F1 with the map displayed) which
caused big clocks to overwrite the help information and then display only
changed digits when F1 was pressed again.
-Changed the satellite elements data display shown when selecting 2-line
elements to add the acceleration/drag and to move the Element Set Number to
the top of the data for clarity.
-Changed colors for satellite position data (Range, Altitude, Azimuth, etc.
Program STSORBIT PLUS Satellite Orbit Simulation Page 62
at the right of the data block) such that when the satellite is in view of
the current location, the color is LIGHT GREEN, otherwise YELLOW (all map
modes except TRACKING STATION) or LIGHT RED (TRACKING STATION).
-Corrected Location Map so that the primary location and name are displayed
when the map is centered on the secondary location.
Version 9227C -- June, 1992
---------------------------
-This version NOT released publicly.
-The Big Clock mode has been added for all display monitors -- for those of
us who want big characters due to impaired eyesight. This displays UTC date
and time, Local date and time, or MET/T+Epoch in large characters and is
enabled by Function Key F2 (see following item).
-Changed the operation of Function Key F2 while map is displayed. Instead
of controlling the satellite blink (which may now only be controlled by the
"B" key), F2 now selects the Big Clock mode. The Big Clock modes are
selected in the following order:
0 No clock displayed
1 UTC date and time
2 Local date and time
3 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.]
-Changed the extended clock feature to use command line option "/CLK"
instead of "/60". In this mode, the text portion of the map display uses 43
(EGA) or 60 (VGA) lines instead of the normal 25 lines and positions the
clocks below the normal data block. This feature now operates correctly on
both EGA and VGA systems but when enabled, the Motion Map is disabled.
-Various minor cosmetic changes.
Version 9227B -- June, 1992
---------------------------
-Corrected persistent bug present in Versions 9226/9227/9227A which caused
the program not to recognize Hercules (HGC) monitors even after MSHERC was
executed. Thanks to Roger Guilemette for reporting the problem.
-Corrected problem when second location was present and displayed on the
Location Map. Switching back to World/Quadrant/Zoom maps gave altitude and
aximuth data for second location instead of standard location.
-Corrected Location Map for second location to remove overprinting of the
local name on top of the second location's name. Thanks to Joel Runes!
-Moved location names to above location in the Location Map to avoid
overprinting the altitude data.
-Added circle of visibility for second location (if present).
-Modified the block number "5" so as not to be confused with "6".
-Various minor cosmetic repairs.
Program STSORBIT PLUS Satellite Orbit Simulation Page 63
Version 9227A -- June, 1992
---------------------------
-This has NOT been a good day. Just as soon as I released Version 9227,
another bug was reported. Versions 9226 and 9227 will not execute on an EGA
system, reporting that they do not recognize the monitor type. This has now
been repaired. Thanks to Roger Pettengill for reporting the problem!
Version 9227 -- June, 1992
--------------------------
-Removed a "Clear Screen" that caused the MOTION MAP not to work in Version
9226. It never fails that I seem to break something while fixing something
else. For some reason, that got missed in testing ... sorry!
-The standard program version now can be used in Read/Only Networks. Set up
the program the way you wish, then edit STSPLUS.INI so that the version
number on the first line is negative, e.g. "-9227" instead of "9227". With
the STSPLUS.INI file set up this way, the program will NEVER write a new
Remind users to use the command line "STSPLUS /R" for immediate startup.
-As an experimental test, VGA users ONLY may include the command line
option "/60" to force 60-line mode and display a large clock at the bottom
of the data block. (Not yet configured for use with the Motion Map!!)
Version 9226 -- June, 1992
--------------------------
-Corrected (I think) a problem in zoom mode which caused the program to
hang on startup using the command "STSPLUS /R" if the time was prior to the
time of epoch. Thanks to Joel Runes for reporting this one!
-Corrected a bug with higher inclination orbits which caused the map to be
redrawn repeatedly near the poles. I've only seen the problem with orbit
inclinations greater than 60 degrees AND with automatic map generation
enabled. The problem was related to the map centering and map projection.
-By popular request, I've restored the "feature" which allows the user to
interrupt map drawing by pressing ENTER. This slows down map drawing
slightly but so many folks have complained since I removed it ...
-Corrected the circle of visibility algorithms to correctly plot circles
which overlap a pole. The "overlap" portion of the circle appeared near the
opposite pole instead of where it belonged! Thanks to Don Nicholson for
pointing out the error!
-Because of frequent user complaints, setting fast time (X10 or X60 using
F4 while the map is displayed) will now disable automatic map generation. I
recommend using fast time ONLY on the world map, or using it when PAUSE is
enabled. Press TAB to restore automatic map generation.
-Changed the algorithm for calculating orbit numbers to account for the
drag and other effects that caused the orbit number calculation to fall
behind by approximately 0.1 orbits every 15 days (measured from the Epoch
of the elements) for satellites in low Earth orbits. The "new and improved"
algorithm is now accurate to better than 0.01 orbits when the simulation is
started for either real or simulated time (SLOW MODE not enabled).
-If the SLOW MODE is enabled, the new orbit number algorithm is only used
when elements are loaded ("/R" command line option or F2 from the Main
Menu) to avoid additional processor delays. In SLOW MODE, the initial
calculation is done once for real time and some error will be noted in the
orbit number if simulated time is set days different from real time.
Program STSORBIT PLUS Satellite Orbit Simulation Page 64
-Corrected a 1 pixel vertical error in plotting which occured under certain
circumstances. The TDRS satellites, for example, were sometimes plotted 1
pixel above the equator.
-Improved the map centering logic to avoid an occasional incorrect map
center (usually quadrant maps) which was followed by an immediate redraw.
-Improved ascending and descending node logic to (hopefully) eliminate
spurious data which was displayed under certain circumstances.
-Fixed a minor bug in printer output where five digit orbit numbers were
incorrectly displayed as "%11007" instead of "11007".
-In response to user requests, I have added an additional status message,
"Recalculating Map and Position data ...", which appears on what was
previously a blank screen before the actual map is drawn. The message
doesn't even appear on my 486/33 but is visible for about 15 seconds on a
vintage 8MHz 8088 with no coprocessor.
-Repaired a minor bug that set the default satellite name to the last
satellite found in a file when the satellite being searched for was not
found. The original satellite default name is now restored correctly.
-Repaired the demo (F1 on the Main Menu) so the correct mission name and
icon are used. The "countdown" may now be terminated with ENTER.
-The format of the data printed with the LOG function has been changed to
avoid numeric overflow of the ORBIT field and the columns changed. The
NORAD number has been added to the initial data block.
-Only minor updates and changes to the main documentation.
Version 9219 -- April, 1992
---------------------------
-Version 9219 corrects a minor bug in the circles of visibility for the
user's location, the alternate location, and the tracking stations. These
circles were incorrectly shaped in Version 9218 due to a minor error in the
formula that crept in during testing. (The circle of visibility for the
spacecraft was correctly shaped and all numerical data was correct.)
-Versions 9204 through 9218 ignored bad checksums in 2-line elements but
did not read the data correctly. This has now been repaired and a bad
checksum on either data line is reported but otherwise ignored and the data
read correctly.
-Several minor typos were corrected in this documentation.
Version 9218 -- April, 1992
---------------------------
-Version 9218 is the initial formal release of program STSORBIT PLUS and
now includes complete program documentation. The beta releases included
only update notes to the original STSORBIT 9134 documentation. While the
STSORBIT PLUS documentation borrows heavily from that original STSORBIT
documentation, many sections are new or have been rewritten and updated.
-I had planned to modify STSPLUS for dual satellite operation but this
proved more difficult than expected. After many hours of work, I have put
that feature aside, at least for the present. The basic structure of the
program does not lend itself to multiple satellites; this is particularly
true of the multi-layered graphics features. The processor workload was
also increased substantially, making things even more difficult for the
many users without a math coprocessor chip. Finally, given the other
demands on my time, a complete rewrite from scratch would simply require
too long. I'm sorry to disappoint those who asked for that feature ...
Program STSORBIT PLUS Satellite Orbit Simulation Page 65
especially the folks working on Mission STS-49.
-In order to eliminate problems due to changes from one program version to
another, STSPLUS now ignores all data from different versions of file
STSPLUS.INI and the program must be initialized as if being run for the
first time. Only .INI files written by the same program version will be
accepted. Trying to maintain backward compatibility with all prior versions
of the .INI file has become both difficult and time consuming -- and has
not always been successful. Too many problem reports have been due to
corrupt or incompatible .INI files, sometimes from versions dating back
several years.
-There have been many changes from Beta Version 9206, too many to describe
in detail here. Even "seasoned users" of STSPLUS should check this
documentation carefully!
Beta Versions 9139 thru 9206
----------------------------
-Beta versions released for testing and comment. Version numbers included
9139, 9145, 9146, 9148, 9202, 9203, 9204, and 9206. Significant changes and
improvements were incorporated in these releases, often the result of user
feedback. Many thanks to those who sent in bug reports and suggestions!
Beta Version 9137 -- September, 1991
------------------------------------
-Initial public beta version.