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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.