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Program STSORBIT
Space Shuttle and Satellite Orbit Simulation
Version 9027
July 01, 1990
by David H. Ransom, Jr.
Rancho Palos Verdes, CA
BBS: (213) 541-7299
Program STSORBIT Space Shuttle Orbit Simulation Page i
TABLE OF CONTENTS
-----------------
INTRODUCTION ......................................................1
PROGRAM DESCRIPTION ...............................................4
THE STSORBIT GROUND TRACK DISPLAY .................................6
STSORBIT'S ORBITAL MODELS .........................................8
STSORBIT FILES ....................................................10
STARTING PROGRAM STSORBIT .........................................11
STSORBIT MAIN MENU ................................................14
F1 Program STSORBIT Demonstration (STS-29) .....................14
F2 Read NASA/NORAD 2-Line Elements .............................15
F3 Read Prior Mission Information from *.INI File ..............16
F4 Enter New Orbital Information ...............................16
F5 Adjust Orbital Parametrers ..................................17
F9 DOS Shell ...................................................18
F10 Set STSORBIT Program Options ................................18
ENTER Resume Prior Mission .....................................18
ESC Quit STSORBIT (Save Current Mission) .....................19
PROGRAM OPTIONS MENU ..............................................20
F1 Program STSORBIT Information ................................20
F2 Set New Local Coordinates ...................................20
F3 Enable/Disable Additional Map Grid Lines ....................22
F4 Display NASA Tracking Stations ..............................22
F5 Show Ascending & Descending Node Data .......................23
F6 Set Map Center (USA/Europe) .................................23
F7 Set for SLOW COMPUTER or NO COPROCESSOR .....................23
F8 Set/Reset Satellite Symbol Blinking .........................24
F9 Set UTC Time Offset and Daylight Flag .......................24
F10 Enable/Disable Printer Logging ..............................25
USING DISPLAY OPTIONS .............................................27
ADJUSTING ORBITAL PARAMETERS ......................................29
STSORBIT REVISION HISTORY .........................................31
Program STSORBIT Space Shuttle Orbit Simulation Page 1
INTRODUCTION
------------
Program STSORBIT is an orbital tracking and display program for use
during Space Shuttle missions, for simulating a Space Shuttle mission, or
for general satellite tracking using NASA/NORAD 2-Line Elements. STSORBIT
is free for non-commercial use. Use it if you like it, discard it if you
don't. There are no warranties of any kind. If you wish to use STSORBIT
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 program STSORBIT.
Program STSORBIT is intended to display the approximate orbital
position and ground track of the Space Shuttle on a global map during a
typical NASA mission. When used with NASA/NORAD 2-Line Elements, other
satellite ground tracks may also be displayed. An IBM-compatible computer
is required. When used with an EGA or VGA video adapter, the display is in
color; CGA and HGC systems can only present graphics in monochrome. In the
past, NASA has not published or made available very precise information as
to the orbital parameters either before or during a "normal" mission;
recently, however, more accurate data has been published in magazines such
as Aviation Week and in various NASA publications. NASA now also releases
the "2-Line Elements", classical orbital elements which enable much more
precise calculation of orbital positions. Military missions, of course, are
almost completely blacked out. It is something of a challenge, therefore,
to devise a program which will at least come close and which, as more or
different information becomes available, will permit the program's data to
be updated "on the fly". The primary objective is to present an interesting
and attractive real time graphics display of a Space Shuttle mission or
satellite ground track, rather than to generate mathematically precise
positional information.
The initial premise of 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 attempted to do that
same task, but each fell short of my objectives for one reason or another;
since then other programs have appeared which produce similar information,
most notably Paul Traufler's excellent TRAKSAT. 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 +80 degrees to -80 degrees in order to achieve reasonable
proportions and vertical resolution while at the same time showing
recognizable land features.
As a consequence of the basic inaccuracies relative to the orbital
parameters of a Space Shuttle mission while it is in progress, I did not
originally try to be especially precise with respect to the orbital
mathematics. Additionally, mathematical complexity must be held to a
reasonable minimum if older computers not equipped with a math coprocessor
are to be able to maintain the presentation in real time. The higher
resolution and color graphics available with more advanced displays such as
the EGA and VGA greatly enhance the program, but my Zenith laptop computer
Program STSORBIT Space Shuttle Orbit Simulation Page 2
emulates the older CGA graphics display in (blue) monochrome. Therefore, in
order to use my own program on all of my computers, STSORBIT maintains
compatibility with all three display standards. Recently, compatibility
with HGC (Hercules Graphics Card) has been improved.
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. 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 orbital model.
The accuracy of that model degrades rapidly after ten or twenty orbits and,
although it may be the only method available at the start of a mission,
more accurate data is now readily available within a day or so of launch.
Beginning with Version 9022, therefore, STSORBIT was modified to also read
orbital data from these 2-line elements and maintain significantly improved
accuracy over longer periods of time. As an incidental benefit, the ground
tracks of other satellites (such as the Russian space station MIR) may now
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). STSORBIT calculates data and
displays a ground track for deep space objects but the accuracy of these
data has not been tested. The SDP4 orbital model may be added to STSORBIT
at a later time.
A brief biographical note: I am a retired physicist and engineer who
has 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, 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. If
STSORBIT 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.
In addition to individual users all over the world, STSORBIT is also
being used in an educational setting in several instances. 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.
As with most of the programs which I have written recently that are
intended for public distribution, STSORBIT was first written using
Microsoft's QuickBASIC, Version 4.50. (The current versions use Microsoft
BASIC Compiler Version 7.00 for improved performance.) While not
necessarily the most efficient language that might have been used, BASIC is
by far the best known computer language, the single language available to
almost any programmer regardless of experience or computer environment, and
is relatively inexpensive. Many of the SUB and FUNCTION procedures in
STSORBIT have been lifted more or less intact from my program ASTROCLK.
While not included as part of the public program distribution, the complete
program, including source code, is available by mail (see below).
For others 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.
Program STSORBIT Space Shuttle Orbit Simulation Page 3
NASA SpaceLink, supervised by Bill Anderson of the NASA Marshall Space
Flight Center, provides a wealth of information on NASA and its projects.
In addition to educational materials, 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, available 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 bulletin board system (BBS).
Special thanks to Paul Traufler whose programs STS95 and TRAKSAT not
only demonstrate excellent accuracy but his documentation also spells out
the factors which generate the major perturbations to low Earth orbits.
While the accuracy of STSORBIT still does not quite equal Paul's method, it
has been substantially improved. My thanks as well for Paul's help in
upgrading STSORBIT to use the NASA/NORAD 2-Line Elements.
My thanks also to Brian K. Jones and his program SUNMAP (available on
my BBS), an interesting program in its own right, for the initial map
coordinate data file used in that program. SUNMAP served as a demonstration
that a reasonable world map display WAS possible, particularly on EGA and
VGA monitors, and encouraged me to start this STSORBIT project.
Finally, thanks as well to all those individuals who have taken the
time to call me or leave a message on my BBS with comments and suggestions.
While I haven't been able to implement every suggestion, many are now
included.
For current orbital information (if a mission is in progress), current
NASA/NORAD 2-line element sets, and the most recent version of the program,
call my bulletin board system (BBS) at (213) 541-7299. If the BBS has not
answered by 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 boot and do its housekeeping chores. If you do not have
access to a modem or if you wish the full source code for STSORBIT, you may
send US$10.00 to cover materials, postage and handling for a copy of the
latest version; please specify 5-1/4" 360K or 3-1/2" 720K disks.
David H. Ransom, Jr.
7130 Avenida Altisima
Rancho Palos Verdes, CA 90274
Program STSORBIT Space Shuttle Orbit Simulation Page 4
PROGRAM DESCRIPTION
-------------------
A typical Space Shuttle orbit is nearly, but almost never exactly,
circular with an altitude of approximately one hundred and sixty nautical
miles plus or minus thirty nautical miles and an inclination of from 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, Mission Control Center does occasionally announce the
orbital altitude, which is usually in the neighborhood of about one hundred
and sixty nautical miles; 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. Whenever practical, I generate the information required by STSORBIT
as an initialization file, for example HST.INI for the Hubble Space
Telescope, which may be read directly by the program and which uses the
most current data. These .INI files are normally posted on my BBS during a
mission. When orbital parameters change during a mission, as was the case
with STS-31, new .INI files are posted as soon as the new data are
determined.
Within a day or two 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, NASA710.TXT) and the name of the desired satellite
(HST for Hubble Space Telescope). STSORBIT takes care of all the rest. The
2-line element set available at the time of this release of STSORBIT 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"
Program STSORBIT Space Shuttle Orbit Simulation Page 5
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-character/line format.
Particularly with the relatively low resolution (640x200) of a CGA
monitor, the display errors alone are significant; using an EGA or VGA
monitor improves the vertical resolution by about a factor of two (640x350
or 640x480, respectively), but does nothing to improve the horizontal
resolution. The HGC (Hercules Graphics Card) has also been included; HGC
users will note that of the 720 horizontal pixels available, only the left
640 pixels are used in the present code. Higher resolution monitors are
available (at a price!) but are not in general use and so are not suitable
for a program such as STSORBIT which is intended for public distribution.
STSORBIT displays a portion of the Earth using a cylindrical
projection of the surface area almost from one pole to the other; a small
area near each pole (approximately ten degrees) is omitted to maintain
optimum map proportions. The map shows most of the Earth's land boundaries,
and continental areas and major oceans are easily recognizable. At any
time, the display shows the Space Shuttle or satellite as a small symbol,
the projected orbit for approximately the next three orbits (or four and a
half hours), and the orbit track for the past orbit (or one and a half
hours).
The program may be operated in real time or in "fast time", which is
ten or sixty times normal time. For "simple" orbits, the orbital parameters
may be manually entered or adjusted for the desired mission, or 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 Space Shuttle Orbit Simulation Page 6
THE STSORBIT GROUND TRACK DISPLAY
---------------------------------
The STSORBIT ground track display consists primarily of a map of the
world extending from approximately +80 degrees to -80 degrees using a
linear cylindrical projection. Omitting the two 10 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).
Centered around the user's geographic location is a magenta "circle"
of the approximate line of sight visibility for the mission in progress.
The circle appears on the display as an ellipse because of the scaling
factors used by the map projection. The radius of this circle of visibility
is calculated for each satellite based upon its current altitude and the
user's elevation above mean sea level. 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/earth/satellite/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 of 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 pass overhead, such
a satellite's altitude 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.
The world map consists of a series of some 7500 coordinate pairs. When
used with an EGA or VGA color monitor, the coastal outlines are in cyan,
the equator and longitude grid are in blue, the Space Shuttle or satellite
is in white, the projected orbit is in green, and the past orbit track is
in red. On HGC, EGA and VGA monitors, the two TDRS satellites (Tracking and
Data Relay Satellites), used for most communications to and from the Space
Shuttle, are shown as a dot inside a small circle in yellow on the equator,
and the various NASA ground tracking stations (and their approximate
antenna range) may be displayed. CGA and monochrome monitors, of course,
display everything in a single color.
Orbital calculations are performed every second in real time and every
ten or sixty seconds in "fast time", and the position of the Space Shuttle
or satellite symbol is updated every ten (real time or X10) or every sixty
(X60) seconds. The predicted orbit and past orbit track markers are updated
every sixty seconds, primarily to avoid "cluttering" the display with too
Program STSORBIT Space Shuttle Orbit Simulation Page 7
many dots scattered around. Each dot therefore represents one minute of
time along the orbit. When the program is first started, three hours of
predicted orbits are traced and the program "catches up" to real time. As
the mission continues, the orbit track will be left behind until
approximately six hours of ground track are visible, one and a half hours
of past ground track and four and a half hours of predicted ground track.
Thereafter, the past and predicted ground track will "move" as time passes,
with one dot of past ground track removed from the display each minute as a
new dot of predicted ground track is added to the display.
Program STSORBIT Space Shuttle Orbit Simulation Page 8
STSORBIT'S ORBITAL MODELS
-------------------------
The initial version of STSORBIT was 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 with an orbital inclination of zero degrees. For orbits with
low inclinations, as is typical for launches from Kennedy Space Center,
these 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, 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 element sets.
Not only are the data readily available publicly, but they are relatively
accurate and are updated regularly. 2-line element sets for non-military
space shuttle missions are typically available by the second or third day
of the mission.
Six quantities are required by classical gravitational theory to
completely characterize the orbit of one body about another in time and
space, the "Two Body Problem". These six quantities, often referred to as
Keplerian orbital elements, are included in the NASA/NORAD 2-line element
sets along with other numerical and statistical data. NORAD, the North
American Air Defense Command headquartered in Cheyenne Mountain, Colorado,
Program STSORBIT Space Shuttle Orbit Simulation Page 9
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 suggest 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.
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
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. 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 downloaded by Kelso directly from NASA Goddard
Space Flight Center by special arrangement. I regularly post a slightly
edited version (certain introductory text material is removed so that the
file may be used directly by programs such as STSORBIT) of the current
element sets on my own RPV ASTRONOMY BBS as file NASAnnn.TXT, where "nnn"
is the NASA 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.
Program STSORBIT Space Shuttle Orbit Simulation Page 10
STSORBIT FILES
--------------
STSORBIT is normally distributed in archived format using either the
PAK or ZIP format. The following files are usually included:
STSORBIT.EXE Main program (required)
STSORBIT.DOC Documentation (not required)
STSORBIT.MAP World map data (required)
STSORBIT.CTY City coordinates (optional)
STSORBIT.INI Initialization data (optional)
MSHERC.COM Hercules driver (required for HGC)
NASAnnn.TXT 2-Line Elements (optional)
STS35.INI HST Sample File (optional)
STS35.TXT HST 2-Line Elements (optional)
STS386.PIF Windows 3.0 (386 enhanced mode)
STS286.PIF Windows 3.0 (normal mode)
README STSORBIT Confidential Questionnaire
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 STSORBIT is operated but provide additional features
or information if present. If file STSORBIT.INI is not present it will be
created.
Program MSHERC must be executed before running STSORBIT for systems
equipped with Hercules Graphics Cards or Hercules Graphics Plus Cards.
STSORBIT will otherwise report an error and remind the user to run MSHERC.
File NASAnnn.TXT (where "nnn" will be a number such as "713") is a set
of NASA/NORAD 2-line elements as of the program release date. 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. File
HST.TXT is the 2-line element data for the Hubble Space Telescope extracted
from the NASAnnn.TXT file. File HST.INI contains simple orbital model data
for the Hubble Space Telescope; the launch time and date must be corrected
to reflect the date actually launched.
The two PIF files have been tested with Microsoft Windows Version 3.0.
File STS386.PIF uses the 386 enhanced mode and file STS286.PIF uses the
normal mode. Since a PIF file includes specific filename and directory
information, each file will have to be edited to reflect the drive,
directory, and filenames actually in use. (The samples included use drive
I: and subdirectory STSORBIT.)
Program STSORBIT Space Shuttle Orbit Simulation Page 11
STARTING PROGRAM STSORBIT
-------------------------
To start program STSORBIT, enter one of the following commands:
STSORBIT (any monitor, CGA/HGC/EGA/VGA)
STSORBIT /EGA (force EGA or lower monitor)
STSORBIT /CGA (force CGA monitor)
STSORBIT /M (force monochrome operation, EGA/VGA)
STSORBIT /EUR (center map on Prime Meridian)
STSORBIT /R (resume last mission automatically)
STSORBIT /S (force shuttle icon for speed)
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, force the shuttle icon, and force
EGA mode:
STSORBIT /R/S/EGA
* * * * *
Hercules Graphics Card USERS NOTE:
----------------------------------
Run the program MSHERC prior to running STSORBIT. This Microsoft
program works with QuickBASIC 4.5 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 STSORBIT. At least one HGC "clone" user reported
improper operation.
* * * * *
If you have already run STSORBIT (or if you have file STSORBIT.INI)
and simply wish to resume viewing that same mission, use the /R command
line option. STSORBIT 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 STSORBIT.INI, is
used to initialize the program. Once started in this manner, pressing the
ENTER (or RETURN) key after plotting has started will return to the Main
Menu.
European users, or those users accustomed to viewing a map of the
world centered on the Prime Meridian at zero degrees longitude (Europe),
may include the /EUR by itself or in addition to other options.
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
Program STSORBIT Space Shuttle Orbit Simulation Page 12
used to force monochrome operation. However, if you wish to operate
STSORBIT 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. STSORBIT
depends upon Microsoft QuickBASIC 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 QuickBASIC 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. Naturally, the operation of the program is enhanced by the use
of a color monitor. The vertical resolution is also adjusted depending upon
the type of adapter which has been detected. The program checks for the
presence of a math coprocessor and will use it if found. Once STSORBIT 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 new
option selection(s).
STSORBIT normally 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. However, the "other
satellite" symbol has approximately three times as many pixels (dots) as
does the space shuttle symbol and therefore takes longer to draw and erase.
If you are using a slower computer or one not equipped with a math
coprocessor, using the "/S" option may improve performance by forcing the
use of the space shuttle symbol. The /S option may be used by itself or in
combination with other options.
STSORBIT first reads in the map coordinates from file STSORBIT.MAP,
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. For slower processors,
systems equipped only with floppy disks, or systems without a math
coprocessor, this may take several minutes; there are over 7,500 sets of
coordinates to process for the world map. By processing the map data as it
is loaded, the time to subsequently display the map is much reduced. As the
map coordinates are being read, the initial title screen is shown on the
display. The "Percent processed" shows how much of the map data has been
processed so far. To cancel program STSORBIT at this point and return to
DOS, press ESC.
Program STSORBIT
Space Shuttle and Satellite Orbit Simulation
Version 9027
by David H. Ransom, Jr.
Current time: 17:11:42
Current date: 06/23/1990
Last Mission = HST [NASA710]
Loading STSORBIT Map Data
Program STSORBIT Space Shuttle Orbit Simulation Page 13
Please wait ...
Percent processed = 70.4%
When all of the map coordinates have been read from disk and
processed, the program presents its Main Menu which allows the user to
select the desired program function. Press the Function Key corresponding
to the function desired.
Program STSORBIT Space Shuttle Orbit Simulation Page 14
STSORBIT MAIN MENU
------------------
Once the map coordinates have been stored internally, STSORBIT
presents its Main Menu:
Program STSORBIT
Space Shuttle and Satellite Orbit Simulation
Version 9027
Current time: 17:12:28
Current date: 06/23/1990
F1 Program STSORBIT Demonstration (STS-29)
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 Orbital Parameters (Simple Orbital Model)
F9 DOS Shell (CAUTION: DOS Version 3.x ONLY!)
F10 Set STSORBIT Program Options
ENTER Resume Prior Mission (HST [NASA710])
ESC Quit STSORBIT (Save Current Mission)
Select desired function: _
F1 Program STSORBIT Demonstration (STS-29)
----------------------------------------------
The F1 command may be used to demonstrate the operation of STSORBIT
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 computer's "bell" sounds and 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 several minutes the shuttle reaches
orbital altitude and proceeds along the ground track normally, passing a
dot every minute. Press F (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 STSORBIT in standard formats:
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
Program STSORBIT Space Shuttle Orbit Simulation Page 15
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. Typical files from my BBS system have names such as
"NASA710.TXT" where the "710" corresponds to the particular NASA data set
and may change several times per week. A sample file is included with the
normal distribution of STSORBIT.
Entering the F2 command will display the following prompts:
Read NASA/NORAD 2-Line Element File
Press ENTER to enter the current default
name as shown in square brackets [...].
Enter 2-Line Filename [NASA710.TXT]:
Enter desired Satellite Name [HST]:
In each case, pressing ENTER will select the default choice shown
inside the square brackets. For the example shown, the defaults are the
file NASA710.TXT and the satellite HST. If you wish to change the
information (or if no default is shown), enter the required information
followed by ENTER. For the filename, if no filetype is included, STSORBIT
will automatically add ".TXT". For the satellite, only sufficient letters
to unambiguously identify the desired satellite, upper or lower case, are
required. For example, "Alou" would select "Alouette 1". Once this
information has been entered, STSORBIT will attempt to locate the specified
file and the data for the requested satellite. Once a satellite matching
the requested name is found, the data is displayed:
Satellite Name: HST
Elements File: NASA710.TXT
Satellite Rec #: 91
Elements Epoch: 90144.02899116
Rev at Epoch: 438
Satellite Number: 20580
Launch Year: 1990
Launch Number: 37
Launch Piece: B
Element Number: 68
Inclination: 28.4702
RA of Ascend Node: 43.2557
Eccentricity: .0006169
Arg of Perigee: 241.1778
Mean Anomaly: 118.8166
Mean Motion: 14.84320861
Press ENTER to ACCEPT this satellite, OR
Press any other key to REJECT and continue searching: _
Program STSORBIT Space Shuttle Orbit Simulation Page 16
If this is the satellite you wish, press ENTER and the data will be
entered into STSORBIT. If, on the other hand, a different satellite is
desired, press any other key (such as the SPACE BAR) and STSORBIT 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 NASA710.TXT is an ASCII file; it may be
helpful to print the file to show the available satellite names.
Once the satellite has been selected, STSORBIT will require a brief
time to calculate certain required orbital parameters, then will proceed
directly to the display of the ground track.
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 STSORBIT.INI is the file which has the data from the last
time the program was run; to use file STSORBIT.INI, press ENTER. STSORBIT
will automatically supply the filetype .INI if you do not include a
filetype. If the requested file is not present, an error will be reported.
To create new .INI files, enter the desired data then exit STSORBIT and use
the DOS COPY command to copy STSORBIT.INI into a file with a the desired
name.
Two additional .INI files are included (more may be added later),
STS28.INI and STS30.INI; these were launched in August 1989 and May 1989
respectively. Since Space Shuttle missions normally last only five to ten
days, using these files at later dates will generate "unusual" mission
elapsed times and orbit numbers! Note that the launch time in these files
has been converted to Universal Time (UT); prior releases (Version 9019 and
earlier) of these files included the launch time in PACIFIC standard or
daylight time.
STSORBIT also expects your computer clock to be set to the correct
local time and date; use the DOS TIME and DATE commands. See the Z command
below for information on setting the UTC Zone Offset. Of course, you may
"fool" STSORBIT by setting your computer 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.
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, and launch date/time to determine
the orbital parameters. To manually enter orbital data, you will be
prompted for the required information.
Enter mission title:
Enter the title of the mission, such as "STS-30 ATLANTIS" without the
quotation marks. If you press ENTER, the title "STS Mission Simulation"
Program STSORBIT Space Shuttle Orbit Simulation Page 17
will be used.
Enter orbit altitude (nm):
Enter the orbit altitude (or average orbit altitude for non-circular
orbits), in nautical miles.
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 is expected to have an inclination of 57 degrees. Press ENTER
to use the default value of 28.00 degrees.
Enter Launch Date (MM/DD/YYYY):
Enter the date in the format shown. The full four digit year is required
and be sure to use the SLASH "/" rather than the MINUS "-" as the
separator; STSORBIT'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.
Enter Launch Time (HH:MM:SS):
Enter the time in the format shown using 24-hour notation and local time.
One or two digit numbers may be used as required. [The comma is also
acceptable as a separator in place of the colon.] You may omit seconds [or
minutes and seconds] if desired. For example, an entry of "16" will be
entered as 16:00:00 or 4:00 PM. Press ENTER for "launch" ASAP, as soon as
possible; depending upon the system, this will be in from 30 to 60 seconds
from the current time.
Normal or fast time (N,f):
If the "launch" has not yet occurred, this prompt will allow you to select
normal time (x1), x10, or x60 fast time for the display. Press ENTER to
select normal time. If you change your mind during the display, use the F
command to toggle the time (see below).
F5 Adjust Orbital Parameters (Simple Orbital Model)
-------------------------------------------------------
The F5 command uses the "simple" orbital model and is NOT available
when using 2-line elements. 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 Space Shuttle Orbit Simulation Page 18
Enter LAUNCH DATE (MM/DD/YYYY) [05/15/1990]:
Enter LAUNCH TIME (HH:MM:SS) [21:45:00]:
Enter ORBITAL ALTITUDE (nm) [ 187.23]:
Enter LONGITUDE adjust (deg) [ 0.000]:
Enter TIME adjust (min) [ 0.000]:
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. In the case of STS-30, the orbital time at
Orbit 34 changed to 90.85 minutes and the longitude of the descending node
was approximately -36 degrees, crossing at 2/2:18:00 MET. See the section
ADJUSTING ORBITAL PARAMETERS below for more information.
F9 DOS Shell (CAUTION: DOS Version 3.x ONLY!)
-------------------------------------------------
If a system function is desired at the Main Menu, press F9 to execute
QuickBASIC's DOS SHELL function. This will return you to a DOS prompt and
most DOS commands may be executed immediately. One of the most frequent
reasons to return to DOS is to adjust the system time or date using the DOS
commands TIME and DATE. Users of DOS Versions 3.3 and higher should be
aware that the TIME and DATE commands for these DOS versions now set not
only the SOFTWARE clock in DOS but also the HARDWARE clock.
When the Shell is executed, STSORBIT remains in memory and the map
data will not be re-read when you return. Enter "EXIT" (without the
quotation marks and followed by ENTER) at the DOS prompt when you wish to
return to STSORBIT. CAUTION: The QuickBASIC 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 Program Options
-----------------------------------
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 Prior Mission
---------------------------
Pressing ENTER resumes the current mission shown in parentheses at the
right. In the example shown, the 2-line elements file used for the data is
shown in the square brackets. 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
Program STSORBIT Space Shuttle Orbit Simulation Page 19
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 your computer's time).
ESC Quit STSORBIT (Save Current Mission)
-------------------------------------------
Press ESC (the key marked "ESC" or "Esc", not the letters E+S+C) to
quit program STSORBIT. If you press ESC to quit the program and have
manually entered orbital data, STSORBIT will save all required mission data
in file STSORBIT.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 STSORBIT, 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 STSORBIT.INI, but the map data is lost and will
be re-read when you next use program STSORBIT. NOTE: If you have neither
entered data (with the E command) nor read a previously saved .INI file
(with the F command), no data will be saved when you exit STSORBIT.
Program STSORBIT Space Shuttle Orbit Simulation Page 20
PROGRAM OPTIONS 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
Space Shuttle and Satellite Orbit Simulation
Version 9027
Current time: 17:12:58
Current date: 06/23/1990
F1 Program STSORBIT Information
F2 Set New Local Coordinates (Rancho Palos Verdes, CA)
F3 OFF Enable/Disable Additional Map Grid Lines
F4 ON Display NASA Tracking Stations
F5 OFF Show Ascending & Descending Node Data
F6 USA Set Map Center (USA/Europe)
F7 OFF Set for SLOW COMPUTER or NO COPROCESSOR
F8 ON Set/Reset Satellite Symbol Blinking
F9 -7.00 Set UTC Time Offset and Daylight Flag
F10 OFF Enable/Disable Printer Logging
ENTER Return to MAIN MENU
Select desired function:
F1 Program STSORBIT Information
-----------------------------------
Function Key F1 displays information about program STSORBIT including
the version number, my name and address, and the telephone number of my RPV
ASTRONOMY BBS (Bulletin Board System). The current version of STSORBIT is
always posted on the BBS. The BBS has a power controller; if it hasn't
answered by the THIRD RING, hang up and call back in two minutes.
F2 Set New Local Coordinates
--------------------------------
In order to perform the calculations related to satellite visibility
and altitude/azimuth, STSORBIT must know the geographic coordinates for the
user's location. 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 city names and coordinates
(STSORBIT.CTY); or manually entering the information.
Pressing F2 will display the following reminder:
STSORBIT will search for the CITYNAME you enter anywhere in the city
Program STSORBIT Space Shuttle Orbit Simulation Page 21
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, STSORBIT will
attempt to match that group of characters anywhere in the names which
appear in the city file. 'SAN' matches 'SAN diego' as well as '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, OR
Press SPACE to search for next city: _
If the city displayed is the one desired, press ENTER and the data
will be entered into STSORBIT and subsequently saved in file STSORBIT.INI.
If you wish to search further in the file, press the SPACE BAR.
NOTE: The elevations contained in file STSORBIT.CTY are all zero
except for Rancho Palos Verdes, CA and Calaveras County, CA, locations
for which I have accurate elevations above mean sea level. If you know
the correct elevation, edit the file using any ASCII text editor and
change the last number on the line. STSORBIT.CTY contains
approximately 720 cities and uses a different format than the .CTY
files for program ASTROCLK. If users send me their correct elevations
(or additional cities they wish added), I will incorporate that data
into subsequent versions of file STSORBIT.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
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 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
Program STSORBIT Space Shuttle Orbit Simulation Page 22
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, STSORBIT 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 STSORBIT.CTY (Y/n): _
Press "Y" or ENTER to append the data or press "N" to not modify the file.
F3 Enable/Disable Additional Map Grid Lines
-----------------------------------------------
This command is not available for CGA systems. The world map normally
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.
F4 Display NASA Tracking Stations
-------------------------------------
The F4 command enables/disables the display of NASA's 14 ground
tracking stations; this command is not available for CGA monitors. Each
ground tracking station is shown as a small symbol surrounded by a "circle"
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.
The antenna range circle is displayed on the screen as an ellipse
because of the scaling factors used by the map projection. Some of these
ground tracking stations are scheduled to be shut down in the near future
due to budgetary constraints. For all systems except CGA, the locations of
the two 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 ground tracking stations which are shown along
with their abbreviations and approximate map coordinates (longitude,
latitude):
Program STSORBIT Space Shuttle Orbit Simulation Page 23
MIL -81,28 Merritt Island, FL
BDA -64,32 Bermuda
DKR -17,14 Dakar
ACN -14,-8 Ascension Island
MAX -5,41 Central Spain
IOS 56,-5 Indian Ocean
HAW -156,20 Hawaii
GWM 145,14 Gwam
VAN -122,35 Vandenberg, CA
YAR 115,-29 Yargidy, Australia
CAN 149,-36 Canberra, Australia
GDX -116,34 Goldstone, CA
CTS -105,38 Colorado Springs, CO
AGO -71,-34 Santiago, Chile
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 MET and longitude
of the most recent ascending and descending nodes. This information is
useful when comparing STSORBIT's data against other sources such as the
wall map in Mission Control.
F6 Set Map Center (USA/Europe)
----------------------------------
The F6 command changes the center of the displayed world map. By
default, the map is centered on the United States at 90 degrees West
longitude. Most Americans are accustomed to viewing the map in that
orientation, but it is sometimes convenient to shift the map center when
the Space Shuttle is near the edge of the map. If you prefer to have the
map centered at the prime meridian or zero degrees (Greenwich, England),
use the F6 command or use the /EUR command line option when starting
STSORBIT. Each time you use the F6 command the map center is changed to the
alternate meridian and the map data is re-read from disk.
F7 Set for SLOW COMPUTER or NO COPROCESSOR
----------------------------------------------
Particularly since the addition of the calculations related to 2-line
element sets, 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 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.
Program STSORBIT Space Shuttle Orbit Simulation Page 24
While perhaps not the "ideal solution" as compared to having a math
coprocessor, setting STSORBIT 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 five 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 STSORBIT is operating in
the Slow Mode, the phrase "SLO" appears at the lower right of the tracking
display (above "RNG:").
F8 Set/Reset Satellite Symbol Blinking
------------------------------------------
The symbol representing the space shuttle or satellite is normally
blinking for CGA and HGC systems in order that it may more readily be
identified on the monochrome display. On EGA and VGA systems the symbol is
bright white which normally is easily located. However, some users may find
the blinking symbol distracting and it also requires additional computing
time to draw and erase the symbol. STSORBIT may automatically defeat
blinking in slower computers. NOTE: Use the "B" command to toggle the
blinking on or off while the ground track is displayed.
F9 Set UTC Time Offset and Daylight Flag
--------------------------------------------
STSORBIT uses UT (Universal Time, formerly known as GMT or Greenwich
Mean Time) and which is approximately the same as UTC (Coordinated
Universal Time), for certain functions such as launch time. This permits
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 UT in order to
obtain your local time, and whether or not you are currently using daylight
savings time (summer time in the UK).
When prompted, enter the time offset in hours from your local time to
Universal Time. Examples are shown for most time zones in North America.
STSORBIT 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 (UT offset is
-8.00 hours and Daylight Flag = 1), the value shown 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. The values are saved in
file STSORBIT.INI. When you change your computer from/to daylight savings
time, use this command to update STSORBIT. The following shows the display
when using the Z command:
Set UTC TIME ZONE OFFSET and DAYLIGHT FLAG
STSORBIT must know the difference between your local time zone
and Universal Coordinated Time (UTC), also sometimes known as
Greenwich Mean Time (GMT). With this information, STSORBIT can
automatically adjust launch or Epoch times and dates for your local
time zone. In addition, STSORBIT must know if your computer is now set
to STANDARD or DAYLIGHT time.
Program STSORBIT Space Shuttle Orbit Simulation Page 25
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
STSORBIT.INI and will not be requested again. If you change from Standard
to Daylight Time or vice versa, use the F10 command to update the Daylight
Flag. INI files obtained from other users may be from a prior version of
STSORBIT 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. When printer logging is enabled and the ground track is displayed,
the word "LOG" will appear in yellow at the right of the text area. A
typical log is shown below. BE SURE THE PRINTER IS TURNED ON PRIOR TO
ENTERING THE F10 COMMAND.
STSORBIT: Space Shuttle Tracking Program, Version 9027 Page 1
ORBITAL DATA for STS-31 Discovery/HST
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
ORBITAL
LOCAL DATE TIME ORBIT LONG MET TIME
04/28/1990 20:32:52 Ascend Node: 70 -69.95 4/14:58:07 1:36:55
04/28/1990 21:20:52 Dscend Node: 70 97.64 4/15:46:35 1:36:55
04/28/1990 22:09:52 Ascend Node: 71 -94.77 4/16:35:02 1:36:55
Program STSORBIT Space Shuttle Orbit Simulation Page 26
When a printer log is prepared for 2-line orbits, the Adjust Longitude
and Adjust Orbit Time entries will not be shown in the header data. The
Launch Date and Launch Time entries are replaced by Epoch Date and Epoch
Time. Note also that the orbit altitude shown is the altitude at the start
of the log and will not be correct for subsequent entries if the satellite
has an elliptical orbit (high eccentricity).
A printer log may be prepared in advance by enabling printer logging
from the Main Menu with the F10 command, then starting the ground track
display with ENTER, pressing the F key twice to set STSORBIT in the X60
fast time mode, and allowing the simulation to run for the desired length
of time. When a sufficient number of orbits has been logged, press ENTER
twice to return to the Main Menu and to then resume the simulation in real
time. While the ground track is active the "L" command performs the same
function as the F10+F10 command to enable or disable printer logging.
Program STSORBIT Space Shuttle Orbit Simulation Page 27
USING DISPLAY OPTIONS
---------------------
Once the orbital display is in progress, a number of keys are active:
ENTER Return to Main Menu (cancel this simulation)
B Toggle the BLINK mode of the space shuttle symbol between
blinking and steady.
F Toggle FAST mode from x1 to x10 to x60 to x1, etc.
R Resynchronize MET or T+Epoch with Local Time. Resets plot to
real time.
NOTE: The Resynchronization was 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.
P 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.
+ 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.
- 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 convused. 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.
L 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 Pause command is active in the normal as well as the "catch up"
modes. The Fast and Resynchronize commands are only active during the
normal plotting mode. The simulated time, taking into account any fast time
that may have been in effect up to that point, is shown at the lower left
of the screen. For reference, the launch or epoch time and the actual local
time (as determined by the computer's internal DOS clock) are also
displayed. The MET (Mission Elapsed Time) or T+Epoch display at the lower
right of the screen shows the current elapsed time in the mission and will
Program STSORBIT Space Shuttle Orbit Simulation Page 28
include an additional message, "(x10)" or "(x60)", when fast time is in
effect.
When using 2-line elements or when the launch has already occurred
(you have entered a date and time that is in the past), the program goes
back approximately two hours then "catches up" and plots the position of
the Space Shuttle as it does so. The program plots a point for each minute
during that time, so it can take a few minutes to get up to real time.
Computers with 8088 processors and/or without a math co-processor may
require a considerable time for this process. Once the plot reaches the
current time, it will slow to real time and resume normal plotting. Using
this technique, you may re-plot the orbit after receiving improved orbital
information or resume a plot after an interruption.
Program STSORBIT Space Shuttle Orbit Simulation Page 29
ADJUSTING ORBITAL PARAMETERS
----------------------------
The original "simple" orbital model used in STSORBIT 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,
STSORBIT'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 STSORBIT'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 STSORBIT. 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.
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,
Program STSORBIT Space Shuttle Orbit Simulation Page 30
press the SPACE BAR to re-enter data; if it is correct, press ENTER to
accept the data. STSORBIT 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.
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. STSORBIT 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 STSORBIT. If all this seems like too much effort, just
enjoy the program "as it comes from the box"!
13. During the course of a non-military mission, I normally watch NASA
Select TV (if I'm around!) and post updated .INI files from time to
time on my BBS. You may call the BBS and download the updated .INI
files; these files typically have names such as STS31A.INI, STS31B.INI
and so forth. Use the F3 command to read the updated .INI file into
program STSORBIT. Also, within a day or two of a Space Shuttle launch,
the 2-line elements for the mission will usually be available on my
BBS.
Program STSORBIT Space Shuttle Orbit Simulation Page 31
STSORBIT REVISION HISTORY
-------------------------
Program STSORBIT underwent multiple revisions during the first days of
the STS-30 Atlantis/Magellan mission (May 1989) and the process was
repeated during the STS-28 Columbia mission (August 1989). At one point, I
was releasing new versions every couple of hours! Lacking any equations or
data for the first minutes of a typical mission, the first tries were
largely guesswork and needed to be refined considerably. After all of that,
comparison of STSORBIT's plot with the NASA wall map data (as seen on NASA
Select Television) and interpolation of that data shows good agreement
through about the first ten orbits. However, after orbital maneuvers, such
as occur with the deployment of a satellite or spacecraft, the initial data
is much less accurate. Unfortunately, the NASA wall map is not always on
the screen and orbital information may otherwise be difficult to obtain
during the first day or two of a mission.
The launch of the Hubble Space Telescope (May 1990) and the
availability of the NASA/NORAD 2-Line Element Sets has prompted a major
revision of the program at Version 9022 to permit accurate tracking over
longer periods of time using these data. This has required a major rewrite
of the program which required many days of effort. As with any major
software change, not all problems and bugs are detected in the first
releases. User feedback and patience will be appreciated.
Each released version of STSORBIT uses a four digit revision code
such as 8916. 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. 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 STSORBIT through all
of the minor twists and turns that usually accompany the evolution of such
a program. It illustrates the tortuous process of maintaining and refining
a program as ideas and problems are reported from every quarter. The early
versions were rushed to meet the launch schedules, probably too much so.
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.
9027 7/01/90
-----------------
-Rewrote main menu to use Function Keys and added new secondary menu for
program options. Special keys used during map display are unchanged.
-Documentation extensively revised to reflect menu changes and additional
features.
-Added Slow Mode for very slow computers or systems without a math
coprocessor. Position calculations performed every five seconds rather than
every second when in this mode.
-Added circle of visibility to map showing the approximate area about the
observing location through which the current satellite may be seen.
-Added Range, Altitude and Azimuth to current position calculations.
-Added local observing coordinates and ability to read STSORBIT.CTY with
approx. 720 city locations. NOTE: The city file includes the local
Program STSORBIT Space Shuttle Orbit Simulation Page 32
elevation but all elevations are set to zero since I don't have that
information. Location data may also be input manually.
-Added graphics clipping to restrict graphics to map area for orbits with
high inclinations. (Example: Alouette)
-Adjusted top edge of map to top of screen.
-Revised CGA HST icon for faster drawing and better proportions.
-"/R" is now sufficient for RESUME command line option.
-Added "/S" command line option to force space shuttle icon. Requires less
time to draw than HST icon for slower computers.
-Adjusted blink timing for more reliable blinking. If computational delays
are too great (especially 2-line orbits which require more than twice the
calculation time compared to simple orbits), blinking is defeated.
-Two sample PIF files are included for use with Windows 3.0, one for 386
enhanced mode and one for normal mode. Files must be edited to set correct
drive/directory names.
9023 6/03/90
-----------------
-Added an icon resembling the Hubble Space Telescope to be used when the
mission title does NOT begin with the letters "STS". Space Shuttle icon is
unchanged.
9022B 5/31/90
-----------------
-Corrected two errors with the E command: QuickBASIC Error 11 (again!) and
typographical error causing altitudes entered in km to be zero.
-Eliminated the R Command since that function is now obtained by pressing
the ENTER key to resume the current mission, or by using the 2 or F
commands to load files.
-Meridian longitude numbers (0, -90, etc.) at top of map removed to yield
approximatly 5% more range in latitude.
-Orbit number calculations changed so that both orbital models agree with
NORAD; first ascending node after launch starts orbit 1. NASA often counts
the first partial orbit as orbit 1; STSORBIT now always counts this as
orbit 0. Preliminary, pre-launch 2-line elements from NASA also often have
the orbit count 1 higher than subsequent elements with the first ascending
node set at orbit 2.
-Changed from QuickBASIC V4.5 to BASIC Compiler V7.0 for optimized code and
more flexible error handling.
-Improved error processing for 2-line files.
9022A 5/30/90
-----------------
-Fixed the R command so that with NASA 2-line elements the program would
not abort with QuickBASIC error 11 upon initial entry.
-Fixed the D command so that it would not abort with QuickBASIC Error 11.
-Fixed a minor bug for "old style" (not NASA 2-line) simulations that
caused the simulation date and time to be incorrect if the current time was
prior to the launch time.
-Reduced search time in NASA 2-line elements files.
-Corrected a number of typographical and spelling errors in this doc.
9022 5/28/90
-----------------
-This is a MAJOR UPGRADE in performance and features. STSORBIT may now be
Program STSORBIT Space Shuttle Orbit Simulation Page 33
used with NASA/NORAD 2-Line Elements which yield far more accurate orbital
information over long periods. Much of the original code has been rewritten
and an almost equal amount has been added. Many thanks to Paul Traufler for
his assistance.
-IMPORTANT NOTE: Version 9022 is a BETA RELEASE. While considerable testing
has been performed and no major problems are known at this time, minor bugs
may remain. In particular, error checking associated with the new 2-line
elements features is minimal in this version. To avoid errors, be sure the
2-line elements file name and the satellite name are correct. Comments and
problem reports will be appreciated!
-Because some of the software adapted for this version of STSORBIT was
originally written by others and is private, the source code is not
available for this version.
-Upon first time entry, STSORBIT now requests UT (Greenwich Mean Time)
offset in hours and whether or not daylight savings time is in effect. Both
parameters are now saved in the .INI file.
-Local time and date now updated while loading map data.
-Map coordinates file converted from ASCII to binary, duplicate data points
removed, and renamed to STSORBIT.MAP. File size and map loading time are
more than cut in half. Users of prior versions may delete file STSORBIT.DAT
since it is no longer used.
-Internal timekeeping switched from local time to UT in order to allow .INI
files to be exchanged across time zones without conversion. Users
exchanging .INI files should use the "F" command to read in foreign .INI
files (rather than copying them to file STSORBIT.INI) to avoid accidentally
changing the UT Time Zone on their system. NOTE: Old .INI files (Version
9019 or earlier) will be automatically converted to UT; STSORBIT assumes
they were created in the time zone and daylight status now in use and
therefore the data should be verified!
-Launch time and simulation time displays now show UT rather than local
time. Local time display now includes the appropriate time zone
abbreviation for US time zones (PST/PDT, etc.) and GMT/BST (Greenwich Mean
Time/British Summer Time) for UK.
-When STSORBIT is first entered, pressing RETURN at the Main Menu resumes
the last mission (if present) rather than generating an error.
-Missing cursor on Main Menu repaired.
-Various minor cosmetic changes.
9019 5/06/90
-----------------
-This is primarily a DOCUMENTATION UPDATE. The Main Menu text has been
completely rewritten. Various other minor changes and clarifications.
-Added information on NASA SpaceLink.
-README questionnaire added to package.
-Added input and display of orbit altitude in kilometers.
-Cleared screen prior to exit if no .INI update required.
-Several minor cosmetic changes.
9017A 4/27/90
-----------------
-Added L command to enable printer logging to record orbital information
and ascending and descending node information.
-Added B command to toggle shuttle symbol blinking for all display types.
9017 4/24/90
Program STSORBIT Space Shuttle Orbit Simulation Page 34
-----------------
-Added code to cause shuttle icon to flash once per second. Applies ONLY to
CGA and HGC displays.
-Fixed position of longitude labels at top of screen for Hercules Graphics
Card.
-Added reminder to execute MSHERC before running STSORBIT if using Hercules
Graphics Card.
-STSORBIT is now one year old!
9015 4/12/90
-----------------
-Added code for calculation of the J2 factor, the perturbation of low
orbits due to the non-spherical shape of the Earth and consequent
gravitational field variation. I confess that the J2 factor contributed a
far greater error that I had supposed, amounting to as much as 5-7 degrees
per day. The accuracy of the longitude of the nodes is improved by
approximately an order of magnitude.
[Intermediate revision notes removed to save space. Available on request.]
8916 4/24/89
-----------------
-Initial BETA VERSION Release.