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Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation (Enhanced Version for 286/386/486 Computers) (C) Copyright David H. Ransom, Jr., 1989-1993 All rights reserved. Version 9311 March 11, 1993 by David H. Ransom, Jr. Rancho Palos Verdes, California, USA Bulletin Board Systems ---------------------- RPV ASTRONOMY BBS (310) 541-7299 @ 14400/9600/2400 Baud RPV HOTLINE BBS (310) 544-8977 @ 2400/1200 Baud Program STSORBIT PLUS Satellite Orbit Simulation Page i TABLE OF CONTENTS ----------------- INTRODUCTION ......................................................1 HARDWARE AND SOFTWARE REQUIREMENTS ................................6 PROGRAM DESCRIPTION ...............................................7 STSORBIT PLUS FILES ...............................................8 STSPLUS MAP PROJECTIONS AND DATABASES .............................11 PROGRAM SETUP AND USAGE NOTES .....................................13 DOS 5.0 CONFIG.SYS Setup ........................................13 Using a RAM Disk ................................................14 Copying Files for STSORBIT PLUS .................................15 Slow Computers and 80x87 Math Coprocessor Chips .................16 Starting Program STSORBIT PLUS ..................................18 Predicting Visible Satellite Passes .............................19 Predicting Satellite Passes with STSPLUS ......................20 Predicting Satellite Passes with TRAKSTAR .....................22 Printing Graphics Screens .......................................24 Known STSPLUS Problems and Bugs .................................25 PROGRAM OPERATION .................................................28 STSORBIT PLUS SATELLITE TRACKING FEATURES .........................30 Orthographic Projection Maps ....................................30 Rectangular Projection World Maps ...............................31 Rectangular Projection Quadrant Maps ............................31 Rectangular Projection Zoom Maps ................................32 Location Maps with Isocontours ..................................33 Tracking Station Maps with Isocontours ..........................33 Location and Features Labels ....................................34 Big Clock Options ...............................................36 Satellite Motion Maps ...........................................36 Satellite Position and Orbit Projections ........................37 User's Circle of Visibility .....................................37 Spacecraft Circle of Visibility .................................38 SUN and Solar Features ..........................................39 TDRS Satellite Features .........................................40 Ground Tracking Stations and .TRK Files..........................42 Event Timers and Audible Alarms .................................45 Pausing the Ground Track Display (F6 Key) .......................47 Using FAST Time (F4 Key) ........................................47 On-line Help (F1 Key) ...........................................48 ACTIVE KEYS DURING GROUND TRACK DISPLAY ...........................49 STSORBIT PLUS MAIN MENU ...........................................52 F1 Convert Keplerian Data to 2-Line Format .....................53 Example Data Input and Output ...............................55 Received Keplerian Orbital Data Form ........................56 F2 Read NASA/NORAD 2-Line Elements .............................57 F3 Data Output and Pass Prediction Selections ..................60 Data Mode 1: Azimuth/Elevation Data Format ..................66 Data Mode 2: Latitude/Longitude Data Format .................67 Data Mode 3: Topocentric RA/DEC Data Format .................68 Data Mode 4: X-Y-Z Cartesian State Vector ...................69 Program STSORBIT PLUS Satellite Orbit Simulation Page ii Data Mode 9: Pass Predictions ...............................70 F4 Calculate Satellite Positions with TRAKSTAR .................71 F5 Set Launch Time and Date ....................................71 Using File STSPLUS.LTD for Launch Date & Time ...............72 F6 Select Time Since Epoch or Mission Elapsed Time .............73 F7 Set FILENAMES and PATHS .....................................74 F8 Set Program TIME and DATE....................................74 F1 Restore System Date and Time .............................76 F2 Set DOS System Clock .....................................76 F3 Set Simulated Date and Time using Calendar Method ........77 F4 Set Simulated Date and Time using MET ....................78 F9 Display Current RIGHTIME Corrections .....................78 F10 Set UTC OFFSET and DAYLIGHT Flag ........................79 F9 DOS Shell ...................................................79 F10 Set STSORBIT PLUS Program Options and Features ..............79 ENTER Resume Mission ...........................................79 ESC Quit STSORBIT PLUS and Save Current Mission ..............80 PROGRAM OPTIONS AND FEATURES MENU .................................81 F1 Program STSORBIT PLUS Information ...........................81 F2 Set New Local Coordinates ...................................81 F3 Set Display Features ........................................83 F4 Select Satellite Coordinates ................................83 F5 Show Ascending & Descending Node Data .......................84 F6 Set Map Projection and Size .................................84 F7 Enable/Disable EVENT TIMERS .................................84 F8 Enable/Disable Audible ALARMS ...............................85 F9 Set UTC Time Offset and Daylight Flag .......................85 F10 Enable/Disable Printer Logging ..............................86 SET DISPLAY FEATURES ..............................................88 F1 Display LOCAL Circles of Visibility .........................88 F2 Display TDRS Coverage .......................................88 F3 Display Additional Map Grid Lines ...........................89 F4 Display Tracking Stations ...................................89 F5 Display Ground Track: DOTS/LINE .............................89 F6 Display Spacecraft Circle of Visibility .....................90 F7 Display South Atlantic Anomaly Zone .........................90 F8 Display Terminator, Sun and Spacecraft Lighting .............90 F9 Display Map Locations and Features ..........................91 F10 Display Lakes and Rivers ....................................91 STSORBIT PLUS's Orbital Model .....................................92 Accurate Time and the Personal Computer ...........................94 Methods for Setting DOS Time ....................................95 Maintaining Accurate DOS Time ...................................96 Programs TIMESET and RIGHTIME ...................................98 Computer Bulletin Board Systems ...................................102 STSORBIT PLUS Revision History ....................................104 Program STSORBIT PLUS Satellite Orbit Simulation Page 1 INTRODUCTION ------------ Program STSORBIT PLUS is an enhanced version of STSORBIT, my original orbital tracking and display program. As a general rule, a 286 or better computer (AT-class IBM compatible) is required. A math coprocessor chip is STRONGLY RECOMMENDED and will significantly improve performance; the math coprocessor chip is REQUIRED for acceptable performance when using the orthographic projection. Some users report "usable" performance on an XT- class machine WITH a math coprocessor. See the section HARDWARE REQUIREMENTS for additional information and discussion. The program is intended for use during Space Shuttle missions and for general satellite tracking using NASA/NORAD 2-Line Orbital Elements. Both orthographic and rectangular map projections are available, displaying the Earth as a globe or the more traditional "flat" map. Tabular line-of-sight satellite pass predictions may be made from within STSORBIT PLUS and passes of interest may be easily displayed. STSORBIT PLUS is copyrighted software; you are hereby granted a non- exclusive license for non-commercial or educational use only. Agencies of the U.S. Government are also hereby granted a non-exclusive license for internal use. Use STSORBIT PLUS if you like it, discard it if you don't. There are no warranties of any kind. If you wish to use STSORBIT PLUS commercially, write for license information. The only request I make of users is that they take the time to complete and return the confidential questionnaire in file README. The questionnaire gives users a chance to offer comments and suggestions, and lets me know that people use and appreciate STSORBIT PLUS. Registration of STSORBIT PLUS is inexpensive and optional -- but will be appreciated and will encourage me to continue supporting and enhancing the program. Program STSORBIT PLUS (which I will usually refer to as STSPLUS from here on) is intended to display the position and ground track of an orbiting satellite on a selection of maps ranging from a full map of the world to zoom maps showing considerable detail. The program has special features implemented at the request of NASA astronauts and others for use during a NASA Space Shuttle mission. With the appropriate 2-line elements, STSPLUS displays the position and ground track of a variety of satellites such as the Space Shuttle, the Hubble Space Telescope, the Gamma Ray Observatory, or the Russian MIR Space Station. Accurate TDRS coverage, including times for acquisition and loss of signal, is calculated for satellites which use that satellite network for communications. Special Location and Tracking Station displays show concentric isocontours, circles of equal satellite altitude; these special maps can be especially valuable for visual or amateur radio sightings. ********************** * IMPORTANT NOTICE * ********************** After almost four years, I have discontinued support for the simple orbital model first used in my original STSORBIT program. The accuracy of that model is marginal at best and timely 2-line orbital elements for space shuttle missions and other satellites are now widely available. If you wish to use the simple orbital model, use STSORBIT or a version Program STSORBIT PLUS Satellite Orbit Simulation Page 2 of STSORBIT PLUS prior to 9240. The initial premise for STSORBIT was to attempt to duplicate the wall map in NASA's Mission Control Center in Houston, Texas. Before I started this project, I had seen several other programs which tracked satellites but each fell short of my map and display objectives for one reason or another. I therefore set out to do the job myself. STSORBIT and now STSORBIT PLUS have been the result. Since then other programs have appeared which produce similar information, most notably Paul Traufler's excellent TRAKSAT (which was inspired by STSORBIT). It may be, of course, that others will judge this effort lacking for some tasks, but no one program can do everything. One problem is that of screen size and resolution: the wall map at Mission Control Center is some twenty feet wide with an impressive pixel resolution, very different from the typical personal computer monitor. The NASA wall map shows essentially the entire globe in a cylindrical projection; STSORBIT also used a cylindrical projection and restricted the vertical display to latitudes from +85 degrees to -85 degrees in order to achieve reasonable proportions and vertical resolution while at the same time showing recognizable land features. STSORBIT PLUS now presents the Earth as a globe using an orthographic projection with zoom while still retaining the original cylindrical (rectangular) projection. STSPLUS adds many additional features and improved accuracy over the original STSORBIT. Initially, and as a consequence of a lack of accurate orbital data for Space Shuttle missions while they were in progress, I did not try to be especially precise with respect to the orbital mathematics. Additionally, mathematical complexity had to be held to a reasonable minimum if older computers not equipped with a math coprocessor were to be able to maintain the presentation in real time. My somewhat casual attitude toward mathematical precision changed with the launch of the Hubble Space Telescope (HST) and the regular availability of US Space Command 2-Line Elements via modem from TS Kelso's Celestial BBS. Until HST, I had been content to manually adjust the orbital data occasionally during the course of a typical five day mission and live with the errors inherent in my original simple orbital model. The accuracy of that model degrades rapidly after five or ten orbits and, although it could be adjusted from time to time during a mission, more accurate data are now readily available prior to a launch and during a mission. The NASA SpaceLink BBS in Huntsville, Alabama began posting 2-line orbital elements for the Space Shuttle in early 1991 due in part to my persistent and continuing requests; Bill Anderson, Jeff Ehmen, and Flint Wild, sysops of the SpaceLink BBS, are continually upgrading the services available. Beginning in mid-1990, therefore, STSORBIT was extensively modified to read orbital data from these USSPACECOM 2-line elements and thereby maintain significantly improved accuracy over long periods of time. As an incidental benefit, the ground tracks of other satellites (such as the Russian space station MIR) could also be displayed. At present, the orbital model (SGP4) used with 2-line elements is accurate only for low Earth orbits. Deep space orbits, defined as orbits having an orbital period greater than or equal to 225 minutes, require a more complex orbital model (SDP4) which takes into account solar and lunar perturbations for best accuracy. STSPLUS calculates data and displays a ground track for deep space objects but the accuracy of these data has not been validated; it is believed to be "reasonably" accurate. I plan to add the SDP4 orbital model to STSPLUS in a future release when time permits. Program STSORBIT PLUS Satellite Orbit Simulation Page 3 At about the same time, STSORBIT also found its way to the NASA Johnson Space Center in Houston, Texas. Quite a few individuals from JSC sent me comments and suggestions for further improving the program, among them Ron Parise of the STS-35/ASTRO-1 crew. Ron suggested that I make modifications to allow the display of Mission Elapsed Time (MET) for shuttle missions while using the USSPACECOM 2-line elements. This would allow both the higher accuracy of the USSPACECOM 2-line orbital data and permit following the mission timeline using MET. Since launch time and date are not included in the 2-line elements but are required to compute MET, these data must be entered independently. Another suggestion from Ron and others was to include the Sun, solar terminator (calculated at Mean Sea Level), and spacecraft lighting conditions to determine if the spacecraft is visible. Not satisfied with the somewhat rough map used with STSORBIT (a digitized EGA world map), I upgraded the maps to use a modified version of the World Data Base II. This had the desired effect, to the point where rivers and other landmarks could easily be recognized on the monitor and on downlinked orbiter television. As a side effect, however, the processor overhead increased dramatically -- some slower computers not equipped with a math coprocessor were unable to keep up. I therefore essentially "froze" the original STSORBIT program (except for minor updates) and created this new program, STSORBIT PLUS, intended for the faster, more capable processors. Since mid-1991, STSPLUS has also spread throughout the various NASA Centers and around the world. In addition to NASA and individual users all over the world, STSPLUS and STSORBIT are also being used in an educational setting. As many as 1100 high schools participated in the Inspire Project, a VLF propagation test flown on STS-45 and for which STSPLUS was one of the recommended tools. At a middle school in Kansas, the program is projected in the school auditorium from time to time during a mission to show the children graphically what is happening and to give them a sense of "real time" participation in our space program. At an Air Force training facility, STSORBIT is one of many tools used to prepare Air Force officers for their duties in the Air Force Space Command. The program was widely distributed at a recent National Association of Science Teachers convention and by radio amateurs at regional "ham fests". It is also available to educators through the NASA Teacher Resource Centers and the NASA Spacelink BBS. In perhaps its most prestigious installtion, STSPLUS is the software used by the NASA/JPL Multimission Computer Control Center in Pasadena, California, to display the ground track of Earth-orbiting satellites. The Canadian Space Agency used STSPLUS as part of their briefing government officials during the STS-52 mission in October, 1992. Intelsat used STSPLUS operationally in May of 1992 at their Launch Control Center in Washington, DC, and at five tracking stations around the world during the exciting STS- 49 mission, the maiden flight of Endeavour and the rescue/reboost of the INTELSAT-VI satellite. Intelsat was kind enough to send me a letter saying that STSORBIT PLUS was "critical to mission success"! Numerous other official and semi-official installations use STSPLUS as the primary satellite tracking software or to supplement other software. A brief biographical note: I am a retired physicist and engineer who spent all of his professional life in the world of electronics, data communications and, more recently, computers. As a young man I was actively involved in the early American space program including projects such as Ranger, Mariner, Mercury, Gemini, and Apollo. Exciting times indeed! I Program STSORBIT PLUS Satellite Orbit Simulation Page 4 spent considerable time at the Jet Propulsion Laboragory in the early 1960's as a contractor on Ranger and Mariner; my respect and admiration for JPL and its people has, if possible, increased over the intervening decades. My interest in space has continued to this day. The desire to "keep in touch" with our Space Shuttle missions was one of the incentives in the development of this software. I continue to be astonished that a relatively inexpensive personal computer is sufficient to perform calculations that pushed the limits of our best mainframe computers only a decade or so ago. If STSORBIT PLUS also serves to help spark the interest of young people in science and technology or can be a learning tool at any level, I will have more than achieved my goals. No discussion of satellite tracking would be complete without thanks to Major T. S. Kelso, USAF, who almost single handedly brought satellite tracking within the reach of "ordinary folks". TS's Celestial BBS has been providing unclassified 2-line orbital elements direct from US Space Command (formerly NORAD, the North American Air Defense Command) at Cheyenne Mountain, Colorado, since 1986 or so. For many years, Celestial BBS was the only electronic source for orbital elements in the world. The Celestial BBS may be reached at (513) 427-0674 and is located near Dayton, Ohio. TS has also written a variety of satellite tracking software and his most recent program, TRAKSTAR, may be used directly from within STSPLUS to generate tabular data on upcoming satellite passes. Special thanks to Paul Traufler for his friendship and encouragement. Our regular telephone conversations have generated many a new idea and the synergism has been beneficial to us both. Our two programs, STSORBIT and TRAKSAT, have engaged us in a friendly rivalry which has, I think, improved both programs many fold. I may have provided the initial spur to Paul to write TRAKSAT (in order to improve on my "sloppy orbital math", as Paul described it) but TRAKSAT has in turn kept my nose to the grindstone and is recognized by many as the standard against which other satellite tracking programs are judged. The emphasis of the two programs is slightly different, with STSORBIT concentrating on the graphical display and TRAKSAT on high precision analytical and predictive techniques. I highly recommend TRAKSAT for the serious satellite tracker. My thanks as well for Paul's help in upgrading STSORBIT to use the USSPACECOM 2-Line Elements and other technical assistance. Thanks also to Rob Matson and Joel Runes. Rob for offering comments and code to help me implement several of STSPLUS's more exotic features; Rob coined the phrase "isocontours" to describe the circle of equal satellite altitude around a location and his fine SKYMAP program generates high accuracy printed star maps with or without satellite tracks. And Joel for keeping us all up to date with current elements for space shuttle missions and his patience in testing innumerable beta versions of STSPLUS, thereby helping to track down some of the more subtle bugs. Finally, my thanks to all those individuals who have taken the time to write or leave a message on my BBS with comments and suggestions. While I haven't implemented every suggestion, many are now included and the feedback is most welcome. For individuals interested in our space program and who have access to a modem, I recommend NASA's SpaceLink Bulletin Board System in Huntsville, Alabama, (205) 895-0028, available twenty four hours per day, 300 to 2400 baud. NASA SpaceLink, located at the NASA Marshall Space Flight Center and with 8 lines, provides a wealth of information on NASA and its Program STSORBIT PLUS Satellite Orbit Simulation Page 5 projects. 2-line orbital elements for a Space Shuttle mission are usually available while the mission is in progress. In addition to educational materials and software (including my programs STSORBIT PLUS, STSORBIT and JPLCLOCK), general information on NASA programs and plans, news releases, and images from prior spacecraft missions such as Voyager, SpaceLink also devotes a complete section to current news and information on the Space Shuttle. I particularly appreciate the STS Mission Press Kit, posted about two weeks before each mission, which provides a great deal of information on the upcoming mission, payload and crew as well as broadcast schedules on NASA Select Television, Satellite F2-R, Transponder 13. Mission status reports are generated daily during the course of a mission. I regularly call SpaceLink and post files of interest on my own RPV ASTRONOMY BBS. For current Space Shuttle orbital information (if a mission is in progress), 2-line elements for more than 1,000 satellites, and the most recent versions of STSORBIT PLUS, STSORBIT, TRAKSTAR, TRAKSAT, and SKYMAP, call RPV ASTRONOMY BBS or RPV HOTLINE BBS (see title page for numbers and data rates available). The main system has well over 1,500 more or less regular users and is often busy, so please be patient. If you wish to receive STSORBIT PLUS (or any of my other programs) on disk, see file README for information. David H. Ransom, Jr. 7130 Avenida Altisima Rancho Palos Verdes, CA 90274 Program STSORBIT PLUS Satellite Orbit Simulation Page 6 HARDWARE AND SOFTWARE REQUIREMENTS ---------------------------------- An AT-class computer equipped with a 286 processor (running at 8 MHz) and a 287 math coprocessor chip is the minimum system used for all program testing and development. While other systems may give acceptable performance, this minimum configuration assures that most features will execute as described and in real time. Performance with 386/387 and 486DX systems will be considerably superior to 286 systems. Note that NO TESTING is performed on systems not equipped with a math coprocessor chip. The following minimum hardware is recommended: 286/386/486 IBM-compatible computer 287/387/487 math coprocessor chip VGA color display Hard disk with up to 3MB available RAM disk with at least 500K space The 287/387 (and 487 for 486SX processors) math coprocessor chip is STRONGLY RECOMMENDED and is REQUIRED for acceptable performance. The calculations relating to orbital mechanics are very complex and STSPLUS will use the coprocessor if one is equipped; performance is improved by about an order of magnitude. Other "fast" processor and coprocessor combinations may yield acceptable performance. Math coprocessor chips are now reasonably inexpensive and the performance improvement is impressive and well worth the modest cost. As an example, my vintage Zenith laptop, equipped with an 80C88 processor and an 8087 math coprocessor, is just able to keep up in real time (rectangular modes ONLY!) when running at a clock speed of 8 MHz but the map drawing times are very slow. However, an 8 MHz 286 computer without a math coprocessor does NOT provide reasonable performance; map drawing times are painfully slow. STSPLUS is intended to be used with an EGA or VGA video adapter and a color monitor; with these systems, the display is in color. Because of its improved vertical resolution, the VGA is recommended over the EGA. A monochrome display with shades of gray may also be used with the program (with the "/M" command line option). Because of hardware limitations, CGA and HGC systems can only present graphics in monochrome; although those display adapters are supported to some degree in current versions of STSPLUS, that support may NOT continue in future versions. The original STSORBIT will continue to support CGA and HGC monitors. A hard disk is required for performance reasons and for storage of the program, map databases and orbital elements files. A RAM disk with sufficient space to hold the various data files is also recommended for improved performace and to reduce wear and tear on the hard disk during periods of extended use. Although the program may execute properly on other software operating systems, STSPLUS has been designed and tested using standard configurations of Microsoft DOS 3.3 and 5.0. No optional Terminate and Stay Resident programs (TSR's) or "shell" programs have been tested except for Tom Becker's RIGHTIME. Third party memory management programs and Digital Research DRDOS may experience problems although some users report that the latest release of DRDOS 6.0 works correctly. Program STSORBIT PLUS Satellite Orbit Simulation Page 7 PROGRAM DESCRIPTION ------------------- A typical Space Shuttle orbit is nearly, but almost never exactly, circular with an altitude of approximately 160 nautical miles to a maximum of approximately 300 nautical miles and an inclination of about 28 degrees through about 57 degrees. Occasional missions, especially military missions, fly at higher altitudes and/or inclinations and often use more elliptical orbits. Prior to 1990, little of this information was known to very good accuracy by the casual listener. Initially, therefore, the interested would-be mission observer may have only the time and date of launch and intended orbital altitude and inclination to initialize a tracking program. Given the geographical coordinates of the Kennedy Space Center and assuming a circular orbit, the data is sufficient to calculate at least a rough idea of the Shuttle's position for the first several orbits. After that, additional information was required if the position was going to be very close. This was the method used in my original STSORBIT program when 2-line orbital elements were not available. Estimated 2-line elements are usually available prior to a space shuttle launch and I usually post "adjusted" 2-line elements within two hours of a launch. "Real" 2-line elements from NASA or US Space Command are usually available 8 to 12 hours after launch. 2-line elements yield a more accurate position over longer time periods (provided no orbital maneuvers are performed). Using 2-line elements for any satellite is quite simple; no adjustment of orbital parameters is necessary. An abbreviated version of the 2-line element file available at the time of this release of STSPLUS is included in the distribution files; this abbreviated file contains approximately 150 satellites while the "full" file as posted on my BBS typically has more than 700 satellites. The data for each satellite is referenced to a specific date and time, the "Epoch" of the data. As a general rule, orbital calculations will be relatively accurate for 10 to 20 days after the Epoch date; the lower the orbit, the greater the effect of factors such as atmospheric drag and the less accurate the calculations will be as time passes. STSPLUS displays a portion of the Earth using either an orthographic porjection (the Earth seen as a globe) or cylindrical projection (similar to the Mercator projection commonly used). The maps show most of the Earth's land boundaries and continental areas. Major oceans, seas, and rivers are easily recognizable. Considerable detail is shown at higher zoom factors. Automatic map generation ensures that the satellite is always displayed. The display shows the selected satellite as a small symbol or icon, the projected orbital ground track for the next three hours and the the past one and a half hours, and many other features including circles of visibility, TDRS coverage, and the solar terminator. Data is displayed which gives the current ground track position of the satellite, known as the "sub-satellite point", antenna or viewing angles, spacecraft lighting, and a variety of other information. The data are sufficiently accurate (given good 2-line orbital elements, of course!) that the program has been used operationally by NASA and Intelsat. Program STSORBIT PLUS Satellite Orbit Simulation Page 8 STSORBIT PLUS FILES ------------------- STSORBIT PLUS is normally distributed via bulletin board systems in archived form using the ZIP format by PKWare. Note that all files (except map databases) for STSORBIT PLUS are called "STSPLUS" in order to conform to DOS filename requirements and to avoid confusion with the similarly named files for the original STSORBIT. The following files are usually included (files marked with "*" are available separately): STSPLUS.EXE Main STSPLUS Program (required) STSPLUS.DOC Documentation (not required) STSPLUS.ICO Icon for WINDOWS 3 (optional) STSPLUS.KEY STSPLUS Active Keys (optional) STSPLUS.LOC Map Locations & Features (optional) STSPLUS.LTD Satellite Launch Dates (optional) STSPLUS.TRK NASA Tracking Stations (optional) STSPLUS.CTY City Coordinates (optional) STSPLUS.INI Initialization data (see below) EARTH4.MCX Level 4 Map Index (required) EARTH4.MCP Level 4 Rect Map Data (required) EARTH4.XYZ Level 4 Ortho Map Data (required) EARTH3.MCX Level 3 Map Index (optional) EARTH3.MCP Level 3 Rect Map Data (optional) EARTH3.XYZ Level 3 Ortho Map Data (optional) EARTH2.MCX Level 2 Map Index (optional) * EARTH2.MCP Level 2 Rect Map Data (optional) * EARTH2.XYZ Level 2 Ortho Map Data (optional) * EARTH1.MCX Level 1 Map Index (optional) * EARTH1.MCP Level 1 Rect Map Data (optional) * EARTH1.XYZ Level 1 Ortho Map Data (optional) * MSHERC.COM Hercules driver (required for HGC) TLEnnn.TXT 2-Line Elements (optional) NASA.TRK NASA Tracking Stations (not required) CIS.TRK Russian Tracking Stations(not required) INTELSAT.TRK INTELSAT Tracking Stns (not required) SPACENTR.TRK Other Tracking Stations (not required) README STSPLUS Confidential Questionnaire QUICK.DOC Quick Start Instructions MAK2LINE.EXE MAK2LINE Utility Program (optional) * MAK2LINE.DOC MAK2LINE Documentation (optional) * Files noted as "(required)" must be in the current default directory (or in a specified directory in some cases) for program operation. Files noted as "(optional)" are not required when STSPLUS is operated but provide additional features or information if present. In order to minimize the disk space required, all.EXE files been compressed with PKWare's PKLITE Professional; these files require additional time to begin execution since Program STSORBIT PLUS Satellite Orbit Simulation Page 9 they are decompressed "on the fly" at load time. Program MAK2LINE was written at the request of local amateur radio enthusiasts to facilitate converting Keplerian orbital elements, received by ham broadcast or via voice link, to the 2-line format. It is available separately from my bulletin board system and is included with program registration (see file README). *** IMPORTANT NOTE *** File STSPLUS.INI contains initialization data from previous runs of the program. If file STSPLUS.INI is not present it will be created. Note that if STSPLUS.INI was written by a version prior to 9242, all data will be ignored and the program must be initialized as if being run for the first time. STSPLUS can use map databases with different degrees of map detail. Level 4, required for operation, contains the minimum detail and Level 1 contains the maximum detail. As noted in the list above, three files are used for each level of map detail: MCX files contain an index of the map data; MCP files contain map coordinates for rectangular projection; and XYZ files contain map coordinates for orthographic projection. STSPLUS checks for the levels that are present and uses the level appropriate for the zoom factor in effect or, if that level is not present, the maximum level that is present. Level 1 is checked first, then Level 2, etc. Level 4 files MUST be present or an error message is displayed and the program aborts. *** IMPORTANT NOTE *** STSPLUS assumes that if a particular level of map database is found, ALL lower levels of map database are present. Missing levels of map database will cause a program error. File STSPLUS.KEY is a quick reference list of the keys that are active while the map is displayed and includes a brief description of the function of each key. It has been extracted from this documentation. File STSPLUS.LTD contains the launch date and time for selected satellites. The file may be updated when new satellite launch date and time data is entered via the program. Files with filetype .TRK are tracking station locations or other locations of interest which may be plotted on the map. These files may be created or edited with a standard ASCII editor. If you wish to use a different TRK file, use Function Key F7 from the Main Menu to select the desired file. File TLEnnn.TXT (where "nnn" will be a number such as "153") is a set of USSPACECOM 2-line elements as of the date of the file. Note that the 2- line elements should only be used for ten to twenty days after the epoch date for each satellite if reasonable accuracy is to be maintained. Current orbital elements are regularly posted on my bulletin board system and elsewhere. Other files with 2-line elements are also available; they typically have names like GSFCnnn.TXT or N2L-nnn.TXT for general satellites, and STSmmNnn.TXT for Space Shuttle missions. Space Shuttle orbital elements are usually posted at least daily during missions; because Program STSORBIT PLUS Satellite Orbit Simulation Page 10 of orbital maneuvers, Space Shuttle elements more than 24 hours old may yield inaccurate positions. File STSPLUS.LOC contains geographic coordinates and labels for selected locations and major oceans and seas. These labels may optionally be displayed on the maps. The file may be edited with a standard ASCII editor to add or delete locations and features. See the section "Location and Features Labels" for additional information. Other files, such as 2-line elements for an upcoming Space Shuttle mission or a mission in progress, may be included from time to time. Files with 2-line orbital elements normally have filetype ".TXT" or ".TLE". Some common satellite name abbreviations are: STS Space Shuttle missions HST Hubble Space Telescope GRO Compton Gamma Ray Observatory UARS Upper Atmosphere Research Satellite TOPEX Topex/Poseidon Earth Resources Satellite ROSAT Roentgen Satellite Observatory MIR Russian Space Station There are many other satellites for which data is available. US Space Command (formerly NORAD) currently tracks some 7000+ objects, of which data for more than 700 is usually included in the TLEnnn.TXT files. Program STSORBIT PLUS Satellite Orbit Simulation Page 11 STSPLUS MAP PROJECTIONS AND DATABASES ------------------------------------- Cartographers and navigators have long wrestled with the problem of map projections, the process of transferring location information from a sphere to a flat surface or map. The U.S. Geological Survey publishes "An Album of Map Projections", Professional Paper 1453, that contains some 90 basic projections in over 130 different modifications and aspects. Each projection or modification was developed to serve some specific need or to optimize certain parameters. The primary concern with any map projection is distortion. For STSPLUS, this means the accuracy with which the selected portion of the Earth's surface is displayed. Naturally, the viewer desires accuracy in area, shape, and distance; unfortunately, you can't have all three simultaneously with a single map projection. The cylindrical or rectangular projection, used here and with the original STSORBIT program, is a good compromise where drawing speed is to be minimized. The map coordinate data translate exactly to screen pixels with a minimum of computer processing. However, this projection is unable to diplay the polar regions well; the distortion increases non-linearly as the latitude increases. I have chosen to limit the latitude to plus and minus 85 degrees to avoid some of the severe problems which occur very near the poles. As the magnification is increased, the distortion inherent in this projection is reduced for the area shown but different latitudes are displayed at different scales for a given magnification. A satellite appears to move more rapidly in high latitudes than at mid or equatorial latitudes. The orthographic projection views the world as a sphere and thus only a single hemisphere can be seen at any given time. However, since the map center may be placed at any desired point, the "hemisphere" may include a pole. The projection is calculated as if the viewer were at a great distance from the Earth and therefore can see a complete hemisphere. This makes the projection ideal for viewing high inclination satellite orbits. Perspective is not included in the projection calculations for simplicity. The orthographic projection has the advantage that ANY area of the Earth may be viewed, including the poles, and the scale remains the same for any given magnification and is independent of the area viewed. At the center of the map, circles of visibility appear as true circles; however, area distortion increases toward the edge of the screen and is especially noticeable when the full hemisphere is displayed. The map databases used for STSPLUS are an adaptation of the Micro World Database II ("WDB"), generously placed in the public domain by Peter Pospeschil and Antonio Riveria, and were produced in about 1986. The original data were from the U. S. Central Intelligence Agency (CIA) as distributed by the National Technical Information Service (NTIS). There are several known errors in the database: one island in the South Pacific is missing its northwestern portion, and several islands near the North Pole are classified as "lakes" instead of "islands" and are therefore rendered in the wrong map color. There are also numerous gaps in coastlines which make color fill very difficult over the range of magnifications used here. The original map data are identified by "level of detail" with Level 1 having the greatest detail and Level 5 having the least detail. I have elected to use Levels 1 through 4 for STSPLUS; Level 5 is so coarse as to be almost useless. I have also written several utility programs to extract the map coordinate data from the original WDB files by level of detail and to build an index file for each level to speed access to the data. For the Program STSORBIT PLUS Satellite Orbit Simulation Page 12 orthographic projection, the data are also converted from latitude and longitude to geocentric Cartesian coordinates to minimize subsequent processing time. Although the resulting map database files are substantially smaller than the original data files, they are still quite large for the higher levels of detail; for example, the Level 1 files require approximately 1.5MB. STSPLUS attempts to select the map database files appropriate to a given magnification and map projection. If the selected level is not present, the program tries the next lower level until the selection process reaches Level 4, the lowest level of detail. The Level 4 map database files are required for operation of the program and are included in the standard program distribution. The Level 3 map database files are included with program registration and are available separately on my BBS. The Level 2 and Level 1 map database files are available separately to registered users. See file README for registration information. Because of the size of the map database files, and because certain third party memory managers have had problems with the dynamic memory allocation (as implemented by Microsoft BASIC) used in STSPLUS prior to Version 9240, map data are ALWAYS read directly from disk. This means that map drawing times, even for the rectangular projection, are somewhat slower than with previous versions of STSPLUS. It also means that the program uses the disk files every time the map is redrawn. Users who plan on running STSPLUS for long periods of time may wish to place the map database files on a RAM disk to minimize wear and tear on their disk drive. Use Function Keys F7+F3 from the Main Menu to set up the correct map database path. The structure of the map database files is the same for all levels of detail and the index file (filetype .MCX) is the same size in each case. STSPLUS cannot distinguish between levels except by file names. Thus, if you are using a high speed computer such as a 486DX, you may rename the files to force STSPLUS to use a higher level of detail for a given zoom or magnification factor. All three files (.MCX, .MCP, and .XYZ) for a particular level must be kept together with the same filename or chaos will result! Naturally, drawing times will be increased as the price of the improved detail. Program STSORBIT PLUS Satellite Orbit Simulation Page 13 PROGRAM SETUP AND USAGE NOTES ----------------------------- The following notes may prove helpful in setting up STSPLUS to operate most efficiently on your system or to provide hints in ways that some of the system and program features may be used to advantage. DOS 5.0 CONFIG.SYS Setup ------------------------ Users with DOS 5.0, especially those who take advantage of the high memory management capabilities and those who use add-on memory managers, should include the following line in their CONFIG.SYS file: STACKS=9,256 This command causes DOS to allocate more memory for the internal stacks used by DOS and some applications programs. DOS 5.0 seems more sensitive to the amount of allocated stack space than were prior DOS versions and programs which executed with no problems on DOS 3.3 may fail on DOS 5.0. A common symptom of insufficient internal stack space is that STSPLUS "freezes" the computer and a reboot is required. Other unpredictable errors can also result from stack errors. "9,256" creates 9 stacks of 256 bytes each; the "256" may be replaced by "384" or "512", and the "9" may be replaced by "15" if the basic STACKS command improves but does not cure the problems. See your DOS manual for additional information. The use of memory managers such as EMM386, QEMM386, and 386MAX with 386 and 486 systems will cause the processor to operate in the Virtual 8086 Mode, a "feature" which is not well documented by Microsoft. Users should be aware that this may cause considerable additional processor overhead, especially with graphics. For example, my 486DX/33 typically draws the orthographic map in almost half the time when a memory manager is NOT present but the improvement is less significant with a 386SX/20: 486DX/33 Drawing Time WITHOUT 386MAX: 3.68 seconds 486DX/33 Drawing Time WITH 386MAX: 6.70 seconds 386SX/20 Drawing Time WITHOUT QEMM386: 17.91 seconds 386SX/20 Drawing Time WITH QEMM386: 21.97 seconds As the example times illustrate, the time saving is proportionally higher with a faster computer. Note, however, that a memory manager may be required for the use of extended or expanded memory and for certain applications. The use of different CONFIG.SYS files, selected by a batch file or other methods, can optimize performance for various applications. Another method is to boot the computer from a floppy disk (suitably formatted and configured) when the "simple" CONFIG.SYS is to be used. You can still use HIMEM.SYS and load DOS in high memory when EMM386 or another memory manager is not used by just including the following lines in CONFIG.SYS: DEVICE=C:\DOS\HIMEM.SYS DOS=HIGH Program STSORBIT PLUS Satellite Orbit Simulation Page 14 Using a RAM Disk ---------------- A RAM disk is a simulated disk drive, created in the extended memory of your computer. Under most circumstances, it is much faster to read and write data to a RAM disk than to an ordinary disk drive. Remember that all data on a RAM disk is lost when the computer is shut down or power is lost. However, disk caching such as that provided by the Microsoft SMARTDRV driver or, better yet, hardware caching if it is included in your system, can perform as well as or even better than a RAM disk. Performance of disk caching varies as a function of both hardware and software, so testing may be required to determine the optimum configuration for a given computer. Because of program memory requirements, a RAM disk should be used only if your computer is equipped with expanded or extended memory. Using a RAM disk in conventional memory (the memory up to 640K) will use memory that STSPLUS (as well as most other programs) may need to operate correctly. The actual size RAM disk you can provide will depend upon how much memory is equipped in your computer and what memory may be required for other uses. The following line may be added to your CONFIG.SYS file and will create a 3000Kb RAM disk using the RAMDRIVE software provided with Microsoft DOS 5.0: DEVICE=G:\WINDOWS\RAMDRIVE.SYS 3000 /E where the file "RAMDRIVE.SYS" is located in "G:\WINDOWS\" in this example. The "3000" specifies the size of the RAM disk in Kb, and the "/E" instructs the program to use EXTENDED memory. See your DOS manual for additional information. Many of the files used by STSPLUS are read only once when the program is first started. Little gain in performance will be achieved by putting these files on a RAM disk. The map database files (EARTH*.*) and the locations and features file (STSPLUS.LOC or whatever alternate filename(s) will be used) are read each time the map is drawn. If you frequently change satellites, moving the 2-line elements file(s) to a RAM disk may also improve performance. Users with fast hard drives and/or effective disk caching software will probably notice little or no difference in performance when using a RAM disk; however, if the program is being run for extended periods of time, using a RAM disk will eliminate hard disk use (and wear and tear) during program operation. All map database files MUST be in the MAP DATABASE path displayed when F7 is pressed from the Main Menu. The size of the RAM disk must be large enough to contain all map database files used for normal operation. Once the maximum map database level has been chosen, ALL lower level map database files must also be present in the directory. For the lower zoom factors, Levels 3 and 4 are sufficient; even when using the higher zoom factors, most users will be satisfied with Levels 2, 3, and 4. Map database file sizes are shown in the following table: EARTH1.MCP 613800 08-20-92 6:44a EARTH1.MCX 11914 08-20-92 6:44a EARTH1.XYZ 920700 08-20-92 6:44a 3 files 1546414 bytes EARTH2.MCP 373948 08-06-92 1:32a EARTH2.MCX 11914 08-06-92 1:33a Program STSORBIT PLUS Satellite Orbit Simulation Page 15 EARTH2.XYZ 560922 08-06-92 1:32a 3 files 946784 bytes EARTH3.MCP 88144 08-06-92 1:04a EARTH3.MCX 11914 08-06-92 1:04a EARTH3.XYZ 132216 08-06-92 1:04a 3 files 232274 bytes EARTH4.MCP 44804 08-06-92 1:07a EARTH4.MCX 11914 08-06-92 1:07a EARTH4.XYZ 67206 08-06-92 1:07a 3 files 123924 bytes I use a batch file called "S.BAT", located in the same directory as STSPLUS.EXE, which takes care of copying the map database files to my RAM disk (drive J: in the example below) the first time the batch file is run and then starts STSPLUS: @echo off if exist j:\earth4.mcp goto Run copy /b \sop\earth4.* j: copy /b \sop\earth3.* j: copy /b \sop\earth2.* j: copy /b \sop\stsplus*.loc j: :Run stsplus /r %1 The files copied to the RAM disk in the example require somewhat less than 1.5Mb. The line which begins "if exist ..." tests to see if the files have already been copied to the RAM disk and jumps to the label ":Run" if so. The "%1" allows me to enter an additional command line option (such as "/M" or "/EGA" for testing. Depending upon where the map database files are located, the drive and/or path will have to be changed in the lines which copy the files. I also set the various paths and filenames in STSPLUS using F7 from the Main Menu to those required for use with the RAM disk. Copying Files for STSORBIT PLUS ------------------------------- STSPLUS is intended to be used on systems with a hard disk. If all files are present, up to 3MB may be required. While it is possible to operate the program from a high density floppy disk (with some files omitted), map drawing times are painfully and unacceptably slow. I recommend that a separate directory called STSPLUS be created for all of the required and optional files. If you received STSPLUS on disk with unpacked files, simply copy all files from the floppy disk(s) to your hard disk using the command: COPY /B A:*.* C:\STSPLUS where the floppy drive is assumed to be A:, the hard disk is assumed to be C:, and the subdirectory STSPLUS already exists. Use the commands C: Program STSORBIT PLUS Satellite Orbit Simulation Page 16 CD \ MD STSPLUS to create the subdirectory STSPLUS if it does not already exist. If you received the program in compressed, self-extracting .EXE format (with a filename like SOP9311A.EXE and/or SOP9311B.EXE), create the STSPLUS directory as above then log into the STSPLUS directory and unpack the files with the commands: C: CD \STSPLUS A:SOP9311A and repeat the last command for each .EXE file received, changing the command to reflect the correct filename. If you received the program in compressed format (.ZIP), copy the .ZIP file(s) to the STSPLUS directory and then enter the command: PKUNZIP <filename> where <filename" is the name of the .ZIP file to unpack. After all files have been unpacked, you may delete the .ZIP files (but keep a backup copy just in case!). You MUST use PKUNZIP Version 1.1 or later to successfully unpack .ZIP files received from my BBS or from NASA SpaceLink BBS! Slow Computers and 80x87 Math Coprocessor Chips ----------------------------------------------- STSPLUS has been designed for 80286/80287 or better computers equipped with an EGA or VGA color display. While the program can be executed on some older 8088 (XT-class) computers equipped with the 8087 math coprocessor, performance is seriously degraded. But it would seem that warnings and suggestions can NEVER convince people that the calculations required for orbital mechanics and graphics are very complex and tax even a powerful computer. The best mainframe computers we had a decade or more ago had trouble doing what I now take for granted on a personal computer! Not all personal computers are created equal. Further, the 80x87 math coprocessor chip can do many of the calculations ten or twenty times faster than the main processor. For 8088 (XT-class) and 80286 (AT-class) computers, this makes a tremendous difference AND for a very modest cost, often well under $100. Some users report problems with coprocessor chips manufactured by IIT and USLI; while the problems may be related to the computer rather than the coprocessor chip, I recommend avoiding coprocessor chips by those manufacturers. Finally, I really don't want to hear from users how slow this program can be on older machines; I recommend the original STSORBIT if you want the best performance from any computer not equipped with a math coprocessor chip. Having said that, I DO run STSPLUS on my old 8MHz 8088/8087 LCD laptop with most features enabled. STSPLUS always runs as fast as the processor will permit and, since most features are available for all computer configurations, it is the responsibility of the user to select program features and options consistent with the desired performance. For example, the solar terminator requires considerable time to perform the required calculations and to update the display and, if this feature is not required, performace will be Program STSORBIT PLUS Satellite Orbit Simulation Page 17 enhanced if it is disabled. As features have been added to STSPLUS, it has become increasingly difficult for very slow computers or computers not equipped with a math coprocessor to perform the necessary calculations in a reasonable time. STSPLUS tests to determine whether or not a math coprocessor chip is present and will automatically set the SLOW MODE if no coprocessor is detected; the SLOW MODE causes certain calculations to be made using less accurate approximations to save a little time. The following table illustrates the difference the processor and a math coprocessor chip make: Processor Speed Coprocessor Time (secs) --------------------------------------------- 486DX 33 MHz YES 6.2 386DX 20 MHz YES 12.8 386SX 20 MHZ YES 16.8 386SX 20 MHz NO 66.0 286 8 MHz YES 30.0 286 12 MHz NO 86.6 8088 8 MHz YES 65.0 8088 8 MHz NO 426.4 The tests were performed with STSPLUS by measuring the time required from the Main Menu until the satellite appeared on the world map display using the rectangular map projection. All data were resident in memory (no disk operations required). All tests were made using the same display options (most were enabled). Slightly better performance can be achieved from the slower computers if some options, such as Sun terminator, are disabled. Clearly, the 8088 without the math coprocessor chip is not acceptable, and NONE of the computers without the math coprocessor chip performs very well. When STSPLUS begins, it checks to determine the type of processor and math coprocessor. If no math coprocessor chip is detected, the following caution message is displayed. Press ENTER (or any key) to continue. ** CAUTION ** STSORBIT PLUS has detected NO MATH COPROCESSOR CHIP! CPU Type = 80386DX or 80387SX NDP Type = (not installed) STSPLUS requires a Math Coprocessor Chip for acceptable performance. Calculation and map drawing times will be VERY SLOW. There is no remedy except to add a Math Coprocessor Chip to your computer. Users without a coprocessor should consider using STSORBIT which is my original, simplified tracking program. If, in spite of everything, you insist on using STSPLUS on your old clunker, here are a few cautions and reminders. Program STSORBIT PLUS Satellite Orbit Simulation Page 18 1. Especially at startup and when drawing the maps, long time delays can be expected with no math coprocessor -- on the order of minutes in some cases. Status messages are presented on the screen during some (but not all) of these delays. Note also that STSPLUS.EXE is compressed to save disk space and is decompressed at load time; this may cause a noticeable delay on some systems. 2. Avoid using the orthographic projection with slow computers; the map drawing times are much longer than the rectangular projections. Also avoid high zoom factors since it is possible that the satellite may move during the drawing process to the point where as soon as the display is completed, it's time to redraw the map again. This process will repeat endlessly and a reboot may be required. Restart the program without the "/R" command line option and use F10+F6 from the Main Menu to select WORLD or QUAD maps. 3. If you have a monochrome monitor, experiment with the "/M" command line option to force monochrome operation. On some monochrome systems the program may otherwise fail with or without an error message. On other monochrome systems, certain colors may not be visible when simulated using shades of gray. 4. The original CGA display, even when equipped with a color monitor, can display reasonable graphics (640x320) ONLY in monochrome. Your color CGA monitor buys you nothing for graphics that are quite inferior to the EGA and VGA. Starting Program STSORBIT PLUS ------------------------------ STSPLUS uses file STSPLUS.INI to save various information required for operation. Since the format of that file may change from time to time, STSPLUS ignores the file unless it was written by a recent program version. If the file does not exist, STSPLUS will automatically create it. To start program STSPLUS, use a batch file similar to "S.BAT" in the preceeding section or enter one of the following commands: STSPLUS Automatic monitor, CGA/HGC/EGA/VGA STSPLUS /EGA Force EGA (or lower) monitor STSPLUS /CLK Use 43 or 60 lines for graphics display of data and large clock characters. NOTE: This feature available with EGA and VGA displays ONLY! It is ignored for CGA/HGC monitors. STSPLUS /CGA Force CGA monitor STSPLUS /M Force monochrome operation, EGA/VGA STSPLUS /R Resume last mission automatically Only one display option (/EGA or /CGA) may be used. Other options may Program STSORBIT PLUS Satellite Orbit Simulation Page 19 be combined and entered in any order. For example, using the following command will resume the prior mission and force EGA mode: STSPLUS /R/EGA If you are using a Hercules Graphics Card, run the program MSHERC prior to running STSPLUS. This Microsoft program works with compiled BASIC programs to enable use of the Hercules Graphics Card. Orthographic projections are NOT supported for Hercules Graphics Cards. One user reported that setting the HGC to FULL and selecting Page Zero (using software supplied with the HGC) was sufficient for proper operation. At least one HGC "clone" user reported that STSPLUS could not be run under any circumstances. If you have already run STSPLUS and simply wish to resume the prior mission, use the /R (resume) command line option: STSPLUS /R STSPLUS will sense the monitor type, enable color for EGA and VGA systems, then proceed directly to plotting the mission. The data from the last run, as saved in file STSPLUS.INI, is used to initialize the program. If 2-line elements were used, that file must also be present. Once started in this manner, pressing the ENTER key after the map is displayed will return to the Main Menu. Predicting Visible Satellite Passes ----------------------------------- One of the most popular uses for a satellite tracking program is to show when a satellite of interest will be visible from a specified location. Using STSPLUS, my wife and I have spotted four different Space Shuttle missions, the Hubble Space Telescope, the Russian MIR Space Station, and many others with the naked eye. The trick, of course, is knowing when and where to look for the satellite. During normal operation, STSPLUS displays two timers in the form of countdown clocks (Minutes:Seconds), "AOS" and "LOS", for the user's location (as well as for a number of other events). AOS, Acquisition of Signal, is the time remaining until the satellite is next within the circle of visibility. LOS, Loss of Signal, is the time remaining until the satellite next passes outside the circle of visibility. STSPLUS looks ahead four hours (240 minutes) from the time the map is drawn to determine the next AOS and LOS event; the clocks are blank if the time is greater than 240 minutes. A quick inspection of these clocks can therefore determine if a potentially visible pass is upcoming within four hours. Using its internal pass prediction feature, STSPLUS can look ahead in 48 hour blocks and list the passes when the selected satellite will be within the local circle of visibility (line of sight, no lighting constraints applied). For more extensive tabular data on upcoming visible passes, external software must be used. There are a number of satellite tracking programs, most notably Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR, which can generate tabular data for a given satellite or group of satellites listing when the satellite(s) will be visible subject to various visibility constraints. Program STSORBIT PLUS Satellite Orbit Simulation Page 20 Predicting Satellite Passes with STSPLUS ---------------------------------------- STSPLUS has a pass prediction capability (using F3 from the Main Menu) in addition to its graphics capabilities to make Line-of-Sight pass predictions for the current satellite quick and easy. Once a satellite has been selected (with F2 from the Main Menu), pressing F3 from the Main Menu, and selecting Data Format 9 (Pass Predictions ) will quickly produce a listing of the Line-of-Sight passes for that satellite over the next 48 hour period. See the section "Pass Predictions and Data Output" for additional information. Here are some comments and suggestions for satellite viewing and tracking with STSPLUS. 1. The pass predictions are listed in blocks of 48 hours beginning with the current real or simulated time, and are given an arbitrary pass number from 1 to 99. The data include the "AOS" or Acquisition of Signal when the satellite rises above the local horizon, "MAX VISIBILITY" or the time at which the satellite reaches the highest altitude above the local horizon, "LOS" or Loss of Signal when the satellite sets below the local horizon, and "Duration" or the total time the satellite is above the local horizon. Note that "local horizon" means the true horizon rather than local terrain. For either visual or electronic tracking, the altitude above the local horizon when the satellite may actually be tracked is usually at least five degrees even under optimum conditions. CAUTION: Users with slow computers, especially those without a math coprocessor, will find that pass predictions may require considerable time -- up to tens of minutes using a slow 286 without a 287! 2. Be sure to use current orbital elements for the satellite. My RPV Astronomy BBS always has current 2-line orbital elements for some 650+ satellites and these data are also available from other electronic sources. For Low Earth Orbit satellites like the Space Shuttle or MIR, orbital elements should be no more than about ten days old; for higher orbit satellites, orbital elements remain accurate for longer periods, up to about 30 days. Satellite maneuvers can radically change the orbital elements. Pass predictions can be no more accurate than the orbital elements used! 3. Examine the "Alt" (maximum altitude) given under the "MAX VISIBILITY" columns for each pass and select a suitable pass. As a general rule, the higher the maximum altitude, the better the visibility. If you wish to see a particular pass as a ground track display, enter the pass number and STSPLUS will set simulated time to about 30 seconds prior to the time of maximum visibility and prepare the display. Press "L" while the ground track is displayed to use the Location Map centered on your location with the "bulls-eye" concentric circles of equal altitude. You may stop/pause the display by pressing Function Key F6, then move the satellite forward or backward in time using the "+" and "-" keys and adjust the time step (1, 10, or 60 seconds) with Function Key F4. Press ENTER to resume normal (simulated time) operation. Program STSORBIT PLUS Satellite Orbit Simulation Page 21 4. STSPLUS lists Line-of-Sight passes, those passes where the satellite rises above the local true horizon, and all dates and times are given in Coordinated Universal Time (UTC). Remember that under most circumstances a "visible pass" means that the satellite is in full sunlight and the viewer is in darkness. Although there are exceptions in unusual situations, this generally restricts the times for visible passes to the several hours prior to dawn and the several hours after sunset. (Note, however, that "visible" to a ham radio operator or radar tracking station simply means above the horizon!) In most cases, the Space Shuttle and satellites such as MIR Space Station and Hubble Space Telescope are visible with the naked eye given favorable lighting and weather conditions. Satellites in higher altitude orbits will be visible sooner before dawn and longer after sunset. Satellites in very high orbits, no matter how large the satellite, are seldom visible without high power binoculars or a telescope. 5. The geometry of the pass and the attitude and geometry of the spacecraft are also important. The relative angles between the Sun, the satellite, and the viewer determine how light is reflected from the surfaces of the spacecraft to you, the viewer. A spacecraft passing between you and the Sun may not reflect much light to you and may therefore not be visible even at higher altitudes. On the other hand, a spacecraft nearer the horizon but on the other side of you from the Sun may appear brilliantly lighted. The kinds of surfaces on the spacecraft are important too; solar panels and flat surfaces can reflect enough light to appear the most brilliant objects in the sky while larger but rounded spacecraft may seem all but invisible. 6. Given otherwise good conditions and favorable weather, the single most important factor is spacecraft apparent altitude ("Alt") during a pass. This is the spacecraft's apparent elevation above your local horizion. Depending upon local conditions, an altitude of at least 5 to 10 degrees will generally be necessary before a spacecraft can be seen even under the best lighting conditions. In the Los Angeles area, at least 20 or 30 degrees is a better number to use because of smog, haze and light polution (except when looking out over the Pacific Ocean). 7. After altitude, the azimuth ("Azm") is the number which describes the direction from the viewer to the spacecraft at any moment. This is given in the sense NESW, North to East to South to West, in degrees. For a good pass after sunset, for example, an azimuth ranging from 60 to 150 degrees would indicate a pass moving generally from the Northeast to the Southeast, ideal lighting conditions with the Sun in the West. 8. Remember that STSPLUS automatically sets SIMULATED TIME when using the pass prediction feature to display passes. If simulated time is already in effect, pass predictions start from the current simulated time and a new simulated time is automatically set for a selected pass. Once set, simulated time remains in effect until changed by selecting another pass or until reset with F8 from the Main Menu. To return to "real time", press F8+F1 from the Main Menu. The Main Menu displays the current time with the time mode in effect labeled as Program STSORBIT PLUS Satellite Orbit Simulation Page 22 "Current Time" or "Simulated Time". Predicting Satellite Passes with TRAKSTAR ----------------------------------------- In order to generate detailed tabular predictions for satellite passes, an external program is required. I recommend two programs for this purpose: Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR. Each programs is copyrighted by the respective author and is readily available. They are both fine programs and set a standard against which other satellite tracking programs are measured for performance and accuracy. I have selected TRAKSTAR as the default external program used with STSPLUS for two reasons: first, the program quickly produces very accurate tabular data without graphics; and second, TRAKSTAR requires minimum memory and is easily configured for seamless operation with STSPLUS. TRAKSAT is a very large program with many features, and most computers will not have sufficient memory to execute TRAKSAT when STSPLUS "shells" to DOS. In order to run TRAKSAT, users must first exit STSPLUS (press "ESC" from the Main Menu). For additional information on these programs, contact the authors: TRAKSTAR: Dr. T. S. Kelso 2340 Raider Drive Fairborn, OH 45324-2001 USA BBS: Celestial BBS (513) 427-0674 300/1200/2400/4800/9600 baud TRAKSAT: Paul Traufler 111 Emerald Drive Harvest, AL 35749 USA BBS: RPV Astronomy BBS (310) 541-7299 2400/9600/14400 baud RPV Hotline BBS (310) 544-8977 1200/2400 baud As a courtesy to the author, I suggest enclosing a stamped, self-addressed envelope if you write and request a reply. The current version of each program is always posted on the indicated BBS and messages may be left there for the author. There is no "standard" filetype used for 2-line elements files; typical filetypes in regular use are ".TXT", ".TLE", ".N2L", and ".ELE"; some files also include comment lines, multi-line commentary, or additional data, some or all of which must be removed prior to use with most satellite tracking programs. As released by Dr. Kelso, TRAKSTAR expects a filetype of ".TLE" and cannot accept any other filetype without being re-compiled. STSPLUS defaults to both filetype ".TXT" and ".TLE". TRAKSAT defaults to filetype ".TXT" only. However, 2-line elements files, even on Dr. Kelso's Celestial BBS, may use either ".TLE" or ".TXT", depending upon the file. Program STSORBIT PLUS Satellite Orbit Simulation Page 23 For the past four or five years, Paul Traufler and I have been jointly releasing file TLEnnn.TXT (usually as file TLEnnn.ZIP, where "nnn" is a number like "143"). Until February, 1993, the file was named NASAnnn.TXT. This file is a sorted concantenation of files TLE.TXT and GROUP000.TLE from Celestial BBS and currently includes 2-line elements for some 700+ satellites. STSPLUS solves the filetype problem with TRAKSTAR by dynamically creating a file called STSPLUS.TLE which contains the 2-line elements for the currently selected satellite. Since STSPLUS can select 2-line elements from a file of any size, calling TRAKSTAR through STSPLUS also circumvents a minor problem in the current version of TRAKSTAR which limits the number of satellites in a 2-line elements file to 250 element sets. As a convenience, STSPLUS also dynamically creates the files STSPLUS.OBS (which contains the name, coordinates, and elevation of the current user location) and TRAKSTAR.CFG (which contains the drive and path information for TRAKSTAR). An accurate elevation (above mean sea level) for the user location is required for accurate calculations in any satellite tracking program, including STSPLUS, TRAKSTAR, and TRAKSAT. Note that the elevations of most locations in file STSPLUS.CTY are not readily available and have been set to zero. The elevation is the last parameter on each line in file STSPLUS.CTY and is given in integer meters; 1 meter equals 3.28083 feet. STSPLUS is coded to operate with TRAKSTAR Version 2.15. It may or may not operate correctly with other versions. To set up program TRAKSTAR either for independent use or for use with STSPLUS, follow the following steps: 1. Copy the TRAKSTAR files to your hard disk. Unpack the files if they are contained in an archive file such as TRAKSTR2.ZIP. I recommend using a separate directory called "TRAKSTAR". The complete TRAKSTAR package includes documentation, Pascal source, example and test files, and the program itself. The following two files are required for operation with STSPLUS: TRAKSTAR.EXE Main Program TRAKSTAR.HDR Header File Additional files are required for independent operation. Read the TRAKSTAR documentation for details. 2. Run STSPLUS and enter the drive and path information for TRAKSTAR by pressing F7+F5 (Set FILENAMES and PATHS) from the Main Menu. STSPLUS will automatically default to its own drive and directory if you omit this step. 3. Select the desired 2-line elements file and satellite by pressing F2 from the Main Menu. 4. When the map is on the screen and you have verified that the correct satellite is being tracked, press ENTER to return to the Main Menu. 5. Now press F4 from the Main Menu to run TRAKSTAR. You should immediately see TRAKSTAR's opening screen and the first selection. Make the various selections by using the up and down arrow keys to move between selections and press ENTER when you have the correct Program STSORBIT PLUS Satellite Orbit Simulation Page 24 selection. Don't forget to press SPACE to select the satellite! ************* * CAUTION * ************* TRAKSTAR Version 2.15 uses the DOS clock to determine the default start and stop times for its calculations. Not mentioned in the TRAKSTAR documentation, however, is the fact that TRAKSTAR assumes that the computer is set to Coordinated Universal Time (UTC). Be sure to take that difference, including the date, into account when entering start and stop times! 6. TRAKSTAR will now make its calculations and write the results to a file. The file is written in the TRAKSTAR directory and will overwrite an existing file of the same name. The time required will be a function of the time span and time interval requested as well as the calculation speed of your computer. Read the TRAKSTAR documentation carefully so that you will recognize the name of the file that TRAKSTAR writes. For example, requesting visible passes for the Hubble Space Telescope (NORAD #20830) will result in a filename of "VOB20830" and a filetype which is the last three digits of the element set number (such as ".866"). 7. As soon as TRAKSTAR finishes, you will return to STSPLUS's Main Menu and may continue normal operations. 8. To examine the tabular data produced by TRAKSTAR, you must either "shell to DOS" using F9 from the Main Menu or exit STSPLUS by pressing ESC at the Main Menu. Use an ASCII editor to view the file or send it to your printer for hard copy. If STSPLUS cannot find TRAKSTAR.EXE (or TRAKSTAR.BAT, see below) in the selected directory, an error message will be displayed. Press ENTER to return to the Main Menu. An alternative method is to create a file TRAKSTAR.BAT in which you place all commands required to run TRAKSTAR or the satellite tracking program of your choice. STSPLUS.TLE and TRAKSTAR.CFG will still be written to the selected directory but they need not be used. This method is only recommended for individuals who understand the use and operation of DOS batch files. Printing Graphics Screens ------------------------- Many users have requested that I add a "print" function to STSPLUS. Given the number and variety of printers available for use with these systems and the fact that I only have a couple of printers I can use for testing, this is not practical within STSPLUS. However, DOS includes the GRAPHICS command which may be used with many computers to enable printing of graphics images. Check your DOS and printer manuals for details. As an example, I use the following command on systems equipped with a Hewlett- Packard LaserJet II or III: Program STSORBIT PLUS Satellite Orbit Simulation Page 25 GRAPHICS LASERJETII There are also quite a number of screen capture and print screen programs, both commercial and shareware, which can perform this task. Note, however, that all these programs are TSR's (Terminate and Stay Resident) and some could interfere with STSPLUS's operation. Some print screen programs, inculding DOS's built-in GRAPHICS command, do not render colors very well. Certain colors may not be visible on the printed copy at all. For such programs, use the "/M" command line option to force monochrome operation when you wish to print graphics images from the screen. Known STSPLUS Problems and Bugs ------------------------------- STSPLUS is being used on thousands of computers around the world without any significant problems. However, like almost any computer program and in spite of my best efforts, there are several known problems or "bugs" with STSPLUS. Some are the result of slow computers, others are in the program itself. Hopefully, some or all of these problems, those I can reproduce at least, will be repaired in due course. Some problems are caused by other software interfering with the program's operation. Still other problems are the result of incompatible "IBM-compatible" computers for which there is no remedy. One "problem" which I frequently hear about is that the user's CGA color monitor only displays STSPLUS in monochrome. THIS IS NOT A BUG! CGA systems display "high resolution" 640 x 200 graphics in monochrome ONLY. Compared to the EGA or VGA, that resolution is barely acceptable. The color graphics mode for the CGA is 320 x 200 which is inadequate for STSPLUS. 1. STSORBIT PLUS has been run extensively on systems using Microsoft DOS 3.3 and 5.0 and there are no known problems with those operating systems EXCEPT the STACKS problem with DOS 5.0 (see the section Program Setup and Usage Notes above). Because of the many bugs reported, I do NOT recommend use of DOS 4.xx under any circumstances; upgrade ASAP to DOS 5.0! Users report memory allocation problems with some earlier versions of Digital Research DRDOS 6.0 and certain third party memory allocation programs. A typical symptom of this kind of problem is that you cannot return to DOS without either an error message or the computer freezing. 2. Note that not all computers (especially older CGA systems) will display the extended graphics characters used for the large clock characters (selected with F2 when the map is displayed). The symptom of this problem is that the lower left portion of the data block is mostly blank after pressing F2. If you have this problem and your computer is running DOS 3.x or DOS 5.0, enter the command "GRAFTABL" at the DOS prompt before running STSPLUS or include the line "GRAFTABL" in your AUTOEXEC.BAT file; this sets the "code page" to enable the computer to display the extended graphics characters. [The program GRAFTABL.COM is included as part of DOS in most cases.] 3. Some users report problems with certain Terminate and Stay Resident (TSR) programs for which the only remedy is to remove the offending Program STSORBIT PLUS Satellite Orbit Simulation Page 26 TSR. This usually requires a "trial and error" approach to pinpoint the TSR causing the problem. The best method is to remove ALL such programs from your AUTOEXEC.BAT file, including the DOS 5 "DOSSHELL", to make sure the program will work with your computer. Similarly, delete all special memory and device drivers from your CONFIG.SYS file. For DOS 5.0, add the line "STACKS=9,256" to your CONFIG.SYS file. In some cases it may be necessary to increase the number 256 to 384 or 512. One user reported a problem on an IBM PS/2 when a mouse driver was used (but I regularly execute STSPLUS on different computers with my mouse active!). 4. Several users have reported occasional "BASIC Error 11" problems; BASIC reports this error as "Division by Zero". The only way I have been able to reproduce this error is to restart the program using the command line "STSPLUS /R" after I have deleted the 2-line file used on the prior run; to avoid this error, do not use the "/R" command line option and select a new 2-line file using F2. This error may also be the result of a memory limitation (with multitasking enabled?) or it may be a BIOS problem associated with a specific computer. 5. All VGA adapter cards are not equal, in case any of you had some illusions left. In at least one case, the aspect ratio of the display is incorrect when the display is operated in the EGA simulation mode. The vertical scale is compressed by about 20% as compared to either a true EGA display or other (correct) VGA displays. So far as I know, there is no remedy. Early VGA cards (the 449 card from Zenith is an example) are not always recognized as VGA; the card is not register compatible with the IBM standard and is recognized as EGA instead. 6. There appears to be a subtle problem when changing to or from Daylight Savings Time (which recently happened and "announced" the bug). The display appears to get caught in a loop, endlessly redrawing the screen or shows the wrong time and/or time zone. To avoid the problem, change the Daylight Flag then EXIT THE PROGRAM AND RESTART. 7. Not all computers (especially older CGA systems) will display the extended graphics characters used for the large clock characters. The symptom of this problem is that the lower left portion of the data block is mostly blank after pressing F2. If you have this problem and your computer is running DOS 3.x or DOS 5.0, enter the command "GRAFTABL" at the DOS prompt before running STSPLUS or include the line "GRAFTABL" in your AUTOEXEC.BAT file; this sets the "code page" to enable the computer to display the extended graphics characters. [The program GRAFTABL.COM is included as part of DOS in most cases.] 8. Some math coprocessor chips have caused problems. In at least two reported cases, early version 386SX math coprocessor chips from IIT did not execute correctly and generated random errors; ITT replaced the suspect chips and the problems disappeared. On a 40MHz 386SX system, a USLI 387SX chip did not operate correctly; a Cyrix 387SX chip cured the problem. No problems have been reported for Intel or Cyrix chips. 9. Finally, as noted elsewhere, all computers are NOT equal. There are some computers which will not execute STSPLUS under any circumstances. Program STSORBIT PLUS Satellite Orbit Simulation Page 27 Tandy is the most common offender followed by Leading Edge. Some models from these manufacturers have BIOS problems or errors which prevent programs compiled with the Microsoft BASIC compilers from operating (sometimes only in graphics modes). There is no remedy. Other computers, Ergo for example, exhibit "strange" behavior in some graphics and text modes. There is sometimes an update or workaround for these problems; check with the manufacturer. Program STSORBIT PLUS Satellite Orbit Simulation Page 28 PROGRAM OPERATION ----------------- STSPLUS automatically checks for the presence of a VGA or EGA and will execute in color if one is found UNLESS the /M command line option is used to force monochrome operation. However, if you wish to operate STSPLUS in the EGA mode when you have a VGA monitor, you must use the /EGA option. In cases where a monochrome monitor is connected to an adapter which simulates color with gray scale, the /M command line option may be omitted but the various portions of the display may or may not be visible. STSPLUS depends upon the Microsoft BASIC Compiler to determine whether or not a particular monitor type is available. Some video adapter boards which claim to be VGA are not recognized as such by BASIC and therefore cannot be used in the higher resolution VGA display mode. Similarly, "clone" Hercules Graphics Cards do not always perform correctly. The /M option is not required for HGC and CGA graphics operation, since those adapters always render their "high resolution" graphics in monochrome. Although color CGA systems do have a 3-color mode, the limited number of colors and coarse resolution of 320x200 is not suitable for STSPLUS. Naturally, the appearance of the program is enhanced by the use of color. The vertical resolution is also adjusted depending upon the type of adapter which has been detected. Microsoft does not support SVGA adapter cards, unfortunately. Once STSPLUS has started, the display type may not be changed without exiting the program at the Main Menu with the ESC key, then restarting the program with the desired command line options. The program checks for the presence of a math coprocessor and will use it if found. Since the calculations required to determine orbital data are very complex, the use of a math coprocessor will improve the speed of operation by a very substantial amount. STSPLUS selects the icon or symbol used to graphically represent the satellite based upon the satellite name. Names which start with the letters "STS" will use an icon resembling a plan view of the space shuttle and all other missions will use an icon resembling the Hubble Space Telescope. STSPLUS reads the map coordinates from the appropriate map database files. These coordinates are converted to screen coordinates for the type of monitor detected, the current projection method, and the current magnification or zoom factor. Once the initial "housekeeping" chores have been performed, the Title Screen is displayed for 15 seconds for normal program operation or for 3 seconds if the /R command line option has been used. The Main Menu, described in a subsequent section, is then displayed. Press ENTER to proceed to the Main Menu immediately. Program STSORBIT PLUS Satellite Orbit Simulation Page 29 Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 RighTime Version 2.53 detected! Current time: 15:02:17 PST 23:02:17 UTC Current date: 02/28/1993 02/28/1993 Last Mission = Hubble Space Telescope 2-Line Elements File = F:\TLE\TLE147.TXT CPU Type = 80386DX or 80387SX NDP Type = 80387DX or 80387SX Display = VGA Color (C) Copyright David H. Ransom, Jr., 1989-1993 All rights reserved. The Title Screen displays the program version, current time and date, last mission, and 2-line elements path and filename. It also displays the type of Central Processing Unit (CPU) and Numeric Data Processor (NDP, or math coprocessor), and the type of display. The program detects 8088, 80286, 80386, and 80486 processors and the associated math coprocessor; if the math coprocessor is not present or fails a simple test, it will show as "(not installed)". The program detects CGA, HGC, EGA and VGA display systems; unless the "/M" command line option is used to force monochrome operation, EGA and VGA systems will always indicate "Color". STSPLUS is now "aware" of program RighTime by Tom Becker. If RighTime is active, the current version number will be displayed; if RighTime is not active or is not detected, no message will be displayed. STSPLUS is configured to use RighTime Version 2.5+; performance with prior versions may be unpredictable and audible alarms should NOT be enabled in that case. See the section "Accurate Time and the Personal Computer" for a further discussion of RighTime and other aspects of maintaining accurate DOS time. Program STSORBIT PLUS Satellite Orbit Simulation Page 30 STSORBIT PLUS SATELLITE TRACKING FEATURES ----------------------------------------- The principal objective of STSPLUS is to graphically display the position of the space shuttle or satellite relative to a map of the world or some relevant portion of the world along with relevant time and numerical data. Two map projections and six different map displays are available: Orthographic, World, Quadrant, Zoom, Location, Tracking Station, and Satellite Motion. Varying magnifications or zoom factors are available in most map modes. Each is discussed below. In addition to the map itself, a number of other items of interest are displayed. Some features are available only with higher resolution displays (EGA and VGA) in order to avoid cluttering the display screen. Other features may be enabled or disabled according to the user's preference. The sections which follow the map types discuss these various features. Orthographic Projection Maps ---------------------------- The orthographic projection views the Earth as a sphere as if from a great distance (perspective is not included) and is the latest addition to the map projections available in STSPLUS. This projection has the advantage that the map may be centered at any point on the Earth and may include a pole, especially helpful for high inclination satellite orbits. Unlike the world map shown with rectangular projection, only one hemisphere can be seen at a given time and therefore automatic map redrawing is always enabled. Because of the more complex calculations required to generate a map, users with slower computers may find that drawing times in the orthographic modes are unacceptably long. (A math coprocessor will improve map drawing times by almost a factor of ten!) Orbital ground tracks, especially for high inclination orbits, and the solar terminator are more readily understood using this projection. The orthographic projection displays circles of visibility as true circles near the center of the map. The default magnification for orthographic maps is 100% which displays the entire globe as a hemisphere. Using the PgUp and PgDn keys, the magnification may be selected from 100% to 4000% (2000% if Level 1 maps are not present). Each time the map is drawn, the center of the map is selected so that the satellite will remain on the map for the longest time practical. When high magnification factors are selected and the computer is not equipped with a math coprocessor, it is possible that the map drawing time will exceed the time the satellite is in view; this will cause the map to be immediately redrawn. The current map database file and map drawing time are shown near the bottom of the data block (e.g. "EARTH4 10.91"). Because only one hemisphere is shown (or a portion of a hemisphere when magnification factors greater than 100% are used), automatic map generation is ALWAYS enabled in orthographic modes. In addition, even if the satellite never leaves the current map (as is the case with geosynchronous satellites), the map will be redrawn every 2.5 hours. Users without a math coprocessor may find that map drawing times in orthographic modes are painfully slow. The only remedy is to purchase a new, more powerful computer or to add a math coprocessor chip; this will improve performance by about a factor of ten and the math coprocessor chips are now relatively inexpensive, often under $100. Program STSORBIT PLUS Satellite Orbit Simulation Page 31 The orthographic version of the Satellite Motion Map, enabled with the "M" key when the map is displayed on the screen (EGA and VGA systems ONLY) centers the satellite on the map and "moves" the map beneath the satellite using EGA graphics. The next map is started in offscreen memory as soon as a map is completed and displayed, then that map is displayed when completed and the process is repeated. Especially for slower computers, this map mode may be preferred since a map is always on the screen regardless of the drawing time required. As a footnote, the orthographic version of the Satellite Motion Map can duplicate many of the views presented on NASA Select TV during a mission. NASA frequently uses the equivalent of MAG=150 or MAG=200 for their display. STSPLUS, however, can display far greater map detail than can the NASA program, especially when the Level 3 and Level 2 map database files are present. Rectangular Projection World Maps --------------------------------- The STSPLUS rectangular projection (similar to Mercator projection) ground track display defaults to a map of the world centered on the Prime Meridian (0 degrees) and extending from approximately +85 degrees North latitude to -85 degrees South latitude using a linear cylindrical projection. Omitting the two 5 degree bands at the poles permits better detail in the mid latitudes where all space shuttle orbits and many other satellite orbits are concentrated and avoids the extreme distortion inherent in the rectangular projection near the poles. Ground track details very near the poles are therefore sacrificed for a better display in the main portion of typical orbits. The vertical resolution of the display is automatically adjusted for the type of display system in use from 200 lines (CGA) to 480 lines (VGA). Two World Maps are available: one centered on the Prime Meridian at Greenwich, England (0 degrees longitude); and, one centered on the International Date Line (180 degrees longitude). All screen maps drawn by STSPLUS use a vector database derived from the Micro World Database II. The full map of the world as used here can include up to approximately 470,000 sets of vector coordinates describing the world's coastlines, islands, lakes, and major rivers when used with the highest detail (Level 1) map database. Pressing the "W" or "0" key will switch the display to the World map. If automatic map generation is enabled, STSPLUS will select the map which most nearly centers the satellite on the map. If automatic map generation is disabled, pressing "W" or "0" will toggle between the two maps. When automatic map generation is enabled, the letter "A" appears in the upper right of the screen. Rectangular Projection Quadrant Maps ------------------------------------ The original STSORBIT program used a digitized pixel map of the world derived from an EGA display. As a consequence of the EGA source, boundaries were sometimes discontinuous on VGA displays and the display on a CGA was sometimes difficult to read. STSPLUS uses a vector map drawing method which automatically adjusts to the display type and the scale of the map. The full world map (above) is quite similar in appearance to the original display. Program STSORBIT PLUS Satellite Orbit Simulation Page 32 However, some geographic details are still difficult to distinguish, even on a VGA display. STSPLUS includes twelve quadrant maps, each overing 1/4 of the Earth's surface and using rectangular projection. These are numbered 1 to 12 and are centered on the world map roughly according to the following illustrations: 0 180 +---------------------------+ +---------------------------+ | | | | | | | 1 4 7 | | 7 10 1 | | | | | | | | | | | | | | | | | | | | 2 5 8 | | 8 11 2 | | | | | | | | | | | | | | | | | | | | 3 6 9 | | 9 12 3 | | | | | | | +---------------------------+ +---------------------------+ The center vertical quadrants in the left illustration, 4 through 6, are centered on the Prime Meridian at zero degrees longitude (Greenwich, England). The center vertical quadrants in the right illustration, 10 through 12, are centered on the International Date Line at 180/-180 degrees. The center horizontal quadrants, 2, 5, 8, and 11, are centered on the Equator. Each individual quadrant map may be selected by pressing the corresponding number key, "1" through "9"; use keys "!", "@", and "#" to select quadrants 10, 11, and 12 respectively. Pressing any of these keys for individual quadrant maps will disable automatic map generation if it is enabled (indicated by the letter "A" at the upper right of the screen). Pressing "Q" will allow STSPLUS to select the quadrant most appropriate for the satellite's current position. Rectangular Projection Zoom Maps -------------------------------- Although I was pleased with the enhanced maps using the Quadrant Mode, the map data base files contain far more information than can be effectively displayed in that mode. The next obvious step was to add the ZOOM feature, maps which yielded greater detail and which spanned as little as 30 degrees across the screen, six times better than the 180 degree quadrant maps. This approaches the practical limit for the map database files. Because of the smaller area covered, a different approach was used for map selection. There would simply be too many different possibilities for manual selection so a fully automatic Zoom Mode was implemented which calculates the optimum map center point based upon the current position of the satellite. Press the "Z" key to enable Zoom Mode. The initial map width is 75 degrees; use PgUp to widen the map width (up to 180 degrees) or PgDn to narrow the map width (down to 30 degrees. The Home key will always select 75 degrees width and the End key will return to the prior field of view. The width of the map is shown at the upper left of the map display. Press Program STSORBIT PLUS Satellite Orbit Simulation Page 33 the TAB key to enable or disable automatic map generation (the map will always be redrawn). When automatic map generation is enabled, the letter "A" appears in the upper right corner of the screen next to the map width or field of view. Zoom field of view selections are 30, 45, 60, 75, 90, 120, and 180 degrees. Location Maps with Isocontours ------------------------------ By popular request, especially from the amateur radio community, I have added the Location Map with Isocontours. (Isocontours is a term coined by Rob Matson for his SkyMap program and for which he generously supplied sample code which I adapted for STSPLUS.) Press the "L" key when the map display is present to select this display. The map will be drawn with the current magnification/zoom factor and centered on the user's location. The usual circle of visibility will be drawn and within that "circle" are seven isocontours representing viewing angles of 10 through 70 degrees in ten degree increments (five degree increments at maximum magnification factors). The projection, orthographic or rectangular, used for the Location Map is the projection in use when the "L" key is pressed. The balance of the Location Map includes the usual features. If you have entered a second location (using F10+F2 from the Main Menu), pressing the "L" key when the Location Map is already displayed will toggle between your primary location and the second location. The data related to your location (Location, Altitude, Azimuth, etc.) is calculated with respect to the indicated location. If no second location has been entered, pressing the "L" key while the Location Map is displayed will have no effect. The principal advantage of the Location Map is, of course, the isocontours -- lines of equal viewing altitude (line of sight not taking into account any refraction near the horizon) from the user's own location. The user can immediately tell by inspection whether current or upcoming passes will be "good" and what approximate maximum satellite viewing altitude can be expected. Amateur radio buffs who need to know if a pass will appear above some altitude threshold, say 20 degrees, now have that information available visually. Since this map mode uses the ZOOM map algorithms, the usual zoom map features (PgUp, PgDn, Home, End) are active. Tracking Station Maps with Isocontours -------------------------------------- The Tracking Station Maps with Isocontours are similar to the Location Maps except that they use the current TRACKING STATION file locations rather than the user's location(s). This feature was implemented at the request of folks working on the STS-49 Intelsat Reboost Mission. STSPLUS was used operationally by INTELSAT during this mission at their Launch Control Center near Washington, DC, and at their five ground tracking stations around the world. I subsequently received a letter thanking me for the use of the program and saying that it was "critical to mission success". Pressing the "T" key will select this map mode. STSPLUS calculates which of the available tracking stations is nearest to the current Program STSORBIT PLUS Satellite Orbit Simulation Page 34 satellite position and centers that tracking station on the screen. This is calculated by determining the angular difference between the sub-satellite point and each tracking station. However, this means that depending upon the Zoom factor in effect, the satellite may or may not be visible on the screen. For example, if the sub-satellite point is in South America and the only tracking station in the Western Hemisphere is in the United States, the satellite cannot be seen at narrower fields of view. The "tracking stations" may be any locations the user chooses and includes in the current TRACKING STATION file. Several different tracking station files accompany the normal STSPLUS distribution as described in the section "NASA Ground Tracking Stations" below. Use Function Key F7 from the Main Menu to select the desired file. STSPLUS contains an internal list of NASA tracking stations which will be used if the current tracking station file cannot be found. Maps in this mode are displayed using rectangular projection. Since this map mode uses the ZOOM map algorithms, the usual zoom map features (PgUp, PgDn, Home, End) are active. Location and Features Labels ---------------------------- Beginning with Version 9240, STSPLUS can add labels for locations and features to all maps. Enable or disable location and features labels using Function Keys F10+F3+F9 from the Main Menu. By default, STSPLUS expects the geographic location and features data to be in file STSPLUS.LOC. If you have created your own .LOC file or the file is not in the current directory, use F7 from the Main Menu to specify an alternate file and/or path. The supplied file includes 350+ locations (cities) and features (oceans and seas), their coordinates, and certain information required by the program. The file is standard ASCII "comma-delimited" data. The following is a typical data line in the file: "London",-.1167,51.5,7,100 ---+-- ---+-- --+- + -+- | | | | | | | | | +--- Minimum magnification to display | | | | | | | +------ Color to display label (1 to 15) | | | | | +--------- Latitude in degrees | | | +--------------- Longitude in degrees | +----------------------- Location or feature name The label will be displayed if the current magnification is equal to or greater than the minimum magnification value specified for that label. All label names are converted to upper case for display; avoid the use of punctuation other than the period (".") or comma (","). The minimum magnification factors in file STSPLUS.LOC have been carefully selected so that the display is not too "cluttered" at a given magnification and so that location or feature names near to each other do not usually overlap each other. Some care is required when adding new locations to avoid this problem! If you wish to add your own locations Program STSORBIT PLUS Satellite Orbit Simulation Page 35 and/or features, use the supplied STSPLUS.LOC file as a guide and template for your changes. Use a standard ASCII editor; word processor users must use the "non-document" mode. Magnifications are calculated automatically and ranges from 50% to 4000%, depending upon the map mode in effect. In orthographic map mode the magnification factor is displayed as "MAG". In rectangular map modes, the displayed ZOOM factor is the approximate field of view and may be converted to magnification according to the following table: ZOOM MAG ----------- 360 50 World maps 180 100 Quadrant and Zoom maps 120 150 ) 90 200 ) 75 240 ) Zoom maps 60 300 ) 45 400 ) 30 600 ) The "color" is a number from 1 to 15 according to the following table: Black = 0 Gray = 8 Blue = 1 LtBlue = 9 Green = 2 LtGreen = 10 Cyan = 3 LtCyan = 11 Red = 4 LtRed = 12 Magenta = 5 LtMagenta = 13 Brown = 6 Yellow = 14 White = 7 LtWhite = 15 The color Black is ignored and is only shown for completeness. If the color is a NEGATIVE number, the small circle marking the location of the city or feature will NOT be displayed and the label will be displayed centered on the coordinates specified. Thus, if the a mountain range, lake, or river is to be labeled, you may wish to set the color negative. The latitude and longitude are expressed in degrees and decimal fractions of a degree; West longitudes and South latitudes must be negative. Note that many atlases show a number such as "24.45" which is actually 24 degrees and 45 minutes (NOT 24.45 degrees!) and should be entered as "24.75" (24 + 45/60). When using multi-line feature labels (see file STSPLUS.LOC for examples), labels should be spaced approximately one degree apart in latitude for display at a magnification of 100%, less for higher magnitudes. All labels are automatically centered with respect to longitude. There is no restriction on the length of the location name. However, avoid long names if possible so as to avoid location names displaying on top of one another or "cluttering" the display. IMPORTANT NOTE: The program performs no error checking on the contents of file STSPLUS.LOC. Avoid the use of punctuation other than the period or comma. Be sure to use a simple ASCII editor or use your word processor in the "Non-Document" mode when editing file STSPLUS.LOC. Very strange results can appear if the wrong data are present or the wrong number of items is in a data line! Program STSORBIT PLUS Satellite Orbit Simulation Page 36 Big Clock Options ----------------- In rectangular map projections, STSPLUS defaults to a standard display with a text block shown on the lower five lines of the display; three different times are shown at the lower left of this display: Launch/Epoch date and time, UTC date and time, and local date and time. Pressing Function Key F2 while the map is displayed switches between this default mode and three Big Clock modes: UTC date and time, local date and time, and MET/T+Epoch. Because of display space limitations, big clock options are NOT available in orthographic projections. For EGA and VGA users, an additional command line option, "/CLK", is available which changes the number of lines per screen to 43 and 60 lines respectively for rectangular projections. The big clocks are then placed below the standard data instead of replacing a portion of the regular data area. In orthographic modes, VGA monitors ONLY, F2 will display the time at the bottom of the data block at the right of the screen. Note that for all magnification factors above 100%, the time is shortened to hours and minutes because of display space limitations. Satellite Motion Maps --------------------- It is sometimes instructive and interesting to see the ground track from the satellite point of view. The Satellite Motion Map, available ONLY with EGA and VGA displays, centers the satellite in the display and draws the map accordingly. Unlike all other map displays, this mode takes advantage of the dual-page capability of the EGA display and the VGA display (operating in EGA emulation mode); the current map is always displayed and the new map is drawn "off screen" and updated as frequently as the capability of the processor will permit. For VGA users, the vertical map resolution in this mode is reduced from 400 lines to 280 lines (rectangular projections) and from 480 lines to 350 lines (orthographic projection). Users with slow computers may prefer this display because, once the map has been drawn the first time (however long that may take), a complete map is always displayed. This is especially true at higher zoom or magnification factors where the map is redrawn more frequently. The Satellite Motion Map is enabled by pressing the "M" key when the map is displayed. The Motion Map will be displayed using the same projection as is presently in effect, rectangular (automatically switches to zoom) or orthographic. When switching to this map mode, the message Switching to EGA Dual-Page Mode ... is displayed on the screen while the initial map is being drawn offscreen. Thereafter, the map is drawn off-screen and will require the "usual" time during which the screen will be unchanged. (My 386DX systems update every 10 seconds but my 286 systems can only manage every 20 or 30 seconds -- and they all have math coprocessors!) The following keys are active when the Satellite Motion Map is displayed: Program STSORBIT PLUS Satellite Orbit Simulation Page 37 Home Zoom=75 (rect) or Mag=100 (ortho) End Return to last zoom/mag PgDn Decrease field of view (zoom in) PgUp Increase field of view (zoom out) M Return to normal map mode (rect or ortho) ENTER Return to Main Menu Satellite Position and Orbit Projections ---------------------------------------- The focus of the display, and the reason for program STSPLUS, is to show the position of the spacecraft or satellite. For the space shuttle (and provided the mission name begins with the letters "STS"), a symbol has been chosen which resembles that spacecraft. For all other satellites, a symbol has been chosen which resembles the Hubble Space Telescope. In either case, the symbol is shown in the following colors (EGA and VGA displays only): Satellite is sunlit Bright White Satellite is in penumbra Yellow Satellite is in umbra Dim White In addition, an asterisk ("*") is shown to the right of "Orbit #" when the satellite is sunlit or in penumbra; this will assist users of monochrome monitors where colors cannot be distinguished. For better visibility, the satellite symbol will normally "blink" on CGA monitors; the symbol may be made to blink on any system if desired by pressing the letter "B" while the ground track is displayed. Note however that for very slow computers, the blink may appear erratic if most of the time is spent performing calculations. Just seeing the spacecraft or satellite on the map display yields information as to its present position. However, for satellite viewing and planning purposes, STSPLUS calculates the predicted ground track for approximately three hours in the future and the past ground track for approximately one and a half hours in the past. The ground track may be selected to display as a series of light green dots (future track) or light red dots (past track), as a solid light green line, or as a solid light green line with yellow dots(future track) and light red dots (past track). The dots are plotted at one minute intervals. To select the desired ground track display, press Function Key F10 and then press Function Key F5 until the desired mode is displayed; the available selections are: OFF, DOTS, LINE, and BOTH. Note that for satellites in high Earth orbits, the ground track may appear as a solid line if the dots are very close together. Unlike prior versions of STSPLUS, the ground track is NOT updated (except to re-color dots for past track). With automatic map generation off, the map will be automatically redrawn every 2.5 hours. User's Circle of Visibility --------------------------- Centered around the user's geographic location, and marked with a Program STSORBIT PLUS Satellite Orbit Simulation Page 38 small circle on EGA and VGA systems, is a magenta circle of the approximate line of sight visibility for the mission in progress. For rectangular projections, the "circle" appears on the display as a circle near the Equator and as a distorted circle at higher latitudes. In near-polar regions, the circle takes on a very strange shape. The shape is entirely an artifact of the map projection; when displayed using the orthographic projection, it appear as a true circle near the center of the map. The radius of this circle of visibility is calculated for each satellite based upon its altitude at the instant the map is first drawn as well as the user's elevation above mean sea level and corresponds to "line of sight" visibility for that satellite. When a second location has been selected using F10+F2, a second circle of visibility will also be drawn for that location. When audible alarms are enabled (F10+F3+F8 from the Main Menu), tones sound 2 minutes before the satellite enters the circle of visibility and again 30 seconds before the satellite leaves the circle of visibility. Both the primary and secondary locations are monitored, with slightly different tones for each. And "up-down" sequence of tones is used prior to entry into the circles and a series of tones prior to leaving the circles. When a satellite is within the circle, direct visual, radio or radar communications with the satellite should be practical. Actual visibility, of course, depends upon more than simply whether or not the satellite is above the viewer's horizon. Most important is the sun to satellite to viewer geometry; the satellite must be in sunlight and the viewer in darkness for reasonable visibility. Almost as important is the size and geometry of the satellite itself; a large, bright-metal satellite with huge solar arrays reflects far more sunlight than a small dark satellite. In addition to the satellites themselves, many booster rockets and other "spare parts" are orbiting the Earth. Since they are not attitude stabilized, booster rockets often are tumbling and may therefore appear to flash on and off as they pass over. For the Space Shuttle as well as most other satellites with near circular orbits, the circle of visibility calculations are reasonably accurate; however, the position of the sun and the effect of atmospheric refraction are not taken into account, only whether or not the satellite is in line of sight view from the observing location. For highly eliptical orbits, however, the accuracy is substantially degraded since the radius of the circle of visibility changes dramatically depending upon whether the satellite is nearer apogee or perigee at the time the calculation is made, and the period of the orbit. In the course of a single orbit, the altitude of such a satellite may change by thousands of miles. Satellite "DE 1", usually included in the TLEnnn.TXT 2-line elements file, is in a highly elliptical orbit with long period and illustrates the problem. Spacecraft Circle of Visibility ------------------------------- The spacecraft circle of visibility is calculated dynamically using the same alrorithm as for the user's circle of visibility. Like the user's circle, the spacecraft circle may appear on rectangular projections as an odd shape because of the scaling factors used by the map projection. The difference is that the spacecraft circle moves with the spacecraft and illustrates the approximate area visible from the spacecraft at any given moment. The circle is updated every ten seconds (or as frequently as the Program STSORBIT PLUS Satellite Orbit Simulation Page 39 processor will permit). Comparisons using a VGA display system during the STS-35/ASTRO-1 mission in December, 1990 confirmed that the circle shown is quite close to that shown by one of the special graphics displays occasionally seen on NASA Select Television as well as the actual horizon view seen from the payload bay television cameras. SUN and Solar Features ---------------------- Many types of observations, especially Earth observations, often require that the target or terrain be in sunlight. The performance of solar panels and certain other instruments on a spacecraft is dependent upon whether or not the Sun is in view. Also, it is usually impossible to visually see a spacecraft which is not in sunlight. The solar terminator is a series of yellow points on the display which represent the line at which the center of the Sun is at an observer's horizon for Mean Sea Level. Although a quick glance at the clock should suffice to determine which side of the terminator line is in sunlight and which in darkness, EGA and VGA systems also display the Sun as a small yellow circle. The terminator as displayed by STSPLUS is sometimes confused with a line denoting sunrise and sunset. Two factors make the terminator only an approximation: first, the terminator is based upon the center of the Sun, while actual sunrise and sunset are calculated using the upper limb of the Sun; and second, the terminator is calculated for Mean Sea Level rather than a specific local elevation. These two factors combined can result in a difference of up to ten minutes when the times are compared against published values or those calculated by my program ASTROCLK, sunrise being earlier and sunset being later. The Sun and solar features are enabled and disabled using F10+F3+F8 from the Main Menu. Since these features -- especially the terminator -- require some calculation and drawing time, users with slower computers may wish to disable these features for faster screen updates. The following features are included: Sun: A yellow circle is plotted at the sub-solar point, the geographic coordinates directly beneath the current position of the Sun. The position of the Sun is recalculated every 10 seconds and the display is updated every 60 seconds. (Not shown on CGA and HGC displays.) Terminator: A dotted yellow line is plotted for the solar terminator, that point on the Earth at which the center of the Sun is at the horizon. The terminator is partially updated every 10 seconds and is fully updated every 60 seconds.The terminator is shown for Mean Sea Level and does NOT take into account the non-spherical shape of the Earth. Lighting: The current spacecraft lighting is shown using color for the satellite icon, and in the data block (to the right of "Orbit #:") and displayed using the following symbols and colors: * Bright White Full sunlight + Yellow Partial sunlight (penumbra) Program STSORBIT PLUS Satellite Orbit Simulation Page 40 - Light Red Refracted sunlight White Full shadow (umbra), no symbol Solar lighting conditions are updated every second or as rapidly as the speed of the processor will permit. In order to minimize calculation delays during ground track plotting, the event times for orbital sunrise and sunset are approximated. The dynamic lighting calculations, used to plot the color of the spacecraft icon, are more precise. Typical errors due to the simplified algorithm, are on the order of 10 seconds. Note that Yellow and Light Red will display as Bright White on most monochrome monitors. TDRS Satellite Features ----------------------- TDRS Satellite features are shown only on HGC, EGA and VGA monitors. When TDRS coverage is enabled (F10+F3+F2), the three active TDRS satellites (Tracking and Data Relay Satellites), used for most communications to and from the Space Shuttle, the Hubble Space Telescope, and other active spacecraft, are each shown as a dot inside a small yellow circle on the Equator. There are three TDRS satellites in geosynchronous orbit, TDRS East at approximately 41 degrees West longitude and the TDRS West Cluster consisting of two satellites (TDRS West and TDRS Spare) at approximately 170 and 174 degrees West longitude respectively. The TDRS Spare satellite has partially failed but is used occasionally as a backup. Each TDRS location provides communications coverage for almost half of the Earth for low Earth orbits and essentially full time coverage for higher orbits. However, since the NASA Ground Terminal is at White Sands, New Mexico, the coverage has been slightly overlaped to provide good ground communications. This, in turn, means that there is a narrow band, known by NASA as the Zone of Exclusion (marked "ZOE" on the screen), off the East coast of Africa which is not covered by either TDRS for low Earth orbits. Two red "circles" on the display show the limits of coverage for each TDRS location. Each circle, whose shape may be quite distorted when using rectangular projection, encloses an area where a TDRS satellite is out of range of the satellite and is centered on the opposite side of the Earth from the TDRS satellite's position. While the ground track is being calculated, STSPLUS also calculates the times for acquisition of signal (AOS) and loss of signal (LOS). When TDRS coverage is enabled, these times are displayed in minutes for TDRS East and TDRS West. The method used for the calculation of the TDRS coverage normally accurate to about 10 seconds (assuming accurate 2-line elements for the satellite and for the TDRS). However, spacecraft attitude can cause loss of TDRS communications at unexpected times. STSPLUS calculates AOS and LOS for four hours (240 minutes) from the time the map is drawn. If a time is beyond that limit (or if the condition does not occur), the time is left blank. Each time is presented in the form of a countdown clock, minutes and seconds, until the next occurence of the condition: TDRE AOS/LOS 72:42 50:42 (for rectangular projections) Program STSORBIT PLUS Satellite Orbit Simulation Page 41 TDRW AOS/LOS 45:42 22:42 AOS LOS TDRE: 72:42 50:42 (for orthographic projections) TDRW: 45:42 22:42 For rectangular projections, these data are displayed in the lower right portion of the map. For EGA and VGA users, however, the data may be displayed in the lower section of the data block by pressing F2 while the map is displayed until MET/T+E is displayed. For orthographic projections, the data are part of the standard data block at the right of the screen. The clocks for each TDRS are color coded to indicate the current status: GREEN when the satellite is in communication, and RED when the satellite is out of range of the TDRS. Two minutes prior to a change in status, the appropriate clock color changes to YELLOW. Users with monochrome monitors must make a quick mental calculation to determine the status; if the AOS time is larger than the LOS time, the satellite is in communication. STSPLUS can sound an audible alarm (three beeps) 30 seconds prior to TDRS AOS or LOS. Use F10+F3+F8 to enable or disable the audible alarms. Most satellites which utilize the TDRS system for communications are in low Earth orbits (generally below 1500 km). However, other satellites may also use the TDRS system for regular or backup communications. The Global Positioning Satellites (GPS), with orbital altitudes of about 11,000 nautical miles (20,000 kilometers), are an example. For such high orbits, the coverage by each TDRS satellite is nearly continuous. There are actually four TDRS satellites in orbit as of late 1992, TDRS 1 and TDRS 3 through TDRS 5. (TDRS 2 was lost in the Challenger accident.) TDRS 6 is scheduled for launch in early 1993. The current assignments are: TDRS# NORAD# Long Description -------------------------------------------------------------- TDRS 1 13969 -170W TDRS West Spare, used occasionally TDRS 3 19548 -62W On orbit spare TDRS 4 19883 -41W TDRS East (STSPLUS default) TDRS 5 21639 -174W TDRS West (STSPLUS default) STSPLUS will use TDRS 4 and TDRS 5 by default and approximate positions as of 1 OCT 1992 are automatically saved in file STSPLUS.INI. Note that some 2-line element files (including TLEnnn.TXT) often refer to the TDRS satellites using numbers 1 through 4 or letters A through D or E. Use the NORAD numbers to be certain that you display the correct satellite. TDRS satellites do change position and/or assignment periodically for one reason or another. Users who wish the most accurate TDRS positions and AOS/LOS data should periodically update the default positions by successively displaying the two satellites. To do this, press F2 from the Main Menu, select a 2-line elements file which includes the TDRS satellites (the TLEnnn.TXT file from my BBS is one such file), then for each TDRS satellite enter the NORAD number and display the satellite. The new position data will be used for subsequent AOS/LOS calculations and saved in file STSPLUS.INI. If you wish to change the default TDRS satellites, you must edit file STSPLUS.INI. Use a standard ASCII editor; if you use a word processor, use the "non-document" mode. CAUTION: STSPLUS does no error checking on file STSPLUS.INI and errors may cause unpredictable performance; if that Program STSORBIT PLUS Satellite Orbit Simulation Page 42 happens, delete file STSPLUS.INI, run the program, and start over. The TDRS information is included in lines 6 and 7 of the file: 19883,"TDRE",-2.87065876318583D-02,-40.9568653303904 21639,"TDRW",1.11188496191951D-02,-174.185413704575 For each line, the data are NORAD#, TDRS abbreviation, and the latitude and longitude of the sub-satellite point. If you wish to use a different TDRS satellite, changing the NORAD number in file STSPLUS.INI to the number desired is sufficient; run STSPLUS, select the new TDRS satellite (by NORAD number) for display, and all data will be updated. If you wish to change the TDRS abbreviation, remember that STSPLUS performs NO ERROR CHECKING on file STSPLUS.INI on the assumption that it wrote the file itself. The TDRS abbreviation MUST be exactly 4 characters long and be enclosed in double quotation marks as shown above! In theory, any satellite could be substituted for one or both of the TDRS satellites; in practice, since STSPLUS assumes the "TDRS" satellite is "stationary" in geosynchronous orbit, this makes little sense except in a few cases. For example, substituting MIR (NORAD #16609) for one of the TDRS satellites would indicate in the AOS/LOS data when direct, line-of-sight communications was possible between MIR and the active satellite (such as a Space Shuttle) but the data would be reasonably accurate for only a few minutes at most since MIR is in motion. Ground Tracking Stations and .TRK files --------------------------------------- NASA maintains a number of ground tracking stations around the world. Some of these tracking stations are essential for the ascent or landing phases of a space shuttle flight; others are used for in-flight communications. File STSPLUS.TRK contains the information for these ground tracking stations. Other files with filetype .TRK contain the information for other launch and/or tracking stations. Each ground tracking station is shown as a small symbol surrounded by a brown or light yellow "circle of visibility" which gives the approximate area of antenna coverage and shows how small a proportion of each orbit can be monitored without the TDRS system. When for some reason the TDRS system is down (as has occurred during infrequent computer failures at White Sands, New Mexico, the TDRS Ground Station), these ground tracking stations become the only means of communication with the Space Shuttle. (Another unexpected method was demonstrated during a 1992 space shuttle mission when the SAREX, Shuttle Amateur Radio EXperiment, was used during a complete loss of normal communications!) Because of budget constraints, many of these ground tracking stations may be (or have already been) shut down. Some, such as MIL and BDA (see list below) will be retained because they are required for the ascent phase of a space shuttle mission. Others, such as HAW, CTS and GWM, are operated jointly with, or independently by, the U.S. Air Force. NASA is not always consistent as to the abbreviations used for these tracking stations; on NASA Select TV, Gwan, Hawaii, and Vandenbert are usually shown as GTS, HTS, and VTS respectively. When using rectangular map projections, the shape of the antenna range "circle of visibility" varies as a function of the latitude and is an artifact of the map projection; when projected on a sphere, as is the case with orthographic projection, they are true circles. In order to avoid Program STSORBIT PLUS Satellite Orbit Simulation Page 43 cluttering the display with countless meaningless lines, tracking station circles of visibility are shown only if that circle has an angular diameter of 90 degrees or less. The following table lists the internal ground tracking stations as of early 1989 which are shown along with their abbreviations and approximate map coordinates (longitude, latitude): MIL -81,28 Merritt Island, FL BDA -64,32 Bermuda DKR -17,14 Dakar, Senegal ACN -14,-8 Ascension Island MAD -5,41 Madrid, Spain IOS 56,-5 Indian Ocean HAW -156,20 Hawaii GWM 143.33,14 Gwam VAN -120.57,34.73 Vandenberg, CA YAR 115,-29 Yargidy, Australia CAN 149,-36 Canberra, Australia GDS -116.88,35.93 Goldstone, CA CTS -105,38 Colorado Springs, CO AGO -71,-34 Santiago, Chile NGT -106,33 White Sands, NM STSPLUS first checks for the presence of file STSPLUS.TRK for its ground tracking station information. This is the default TRACKING STATION filename used if no other selection has been made using F7 from the Main Menu. If that file is present, its data is used instead of the internal data above. The supplied STSPLUS.TRK has the following format: "Maui, Hawaii",-156.7,20.9,0,"HAW" "Vandenberg, CA",-120.5667,34.7333,112,"VAN" "White Sands, NM",-106,33,0,"NGT" "Colorado Springs, CO",-105,38,0,"CTS" "Merritt Island, FL",-81,28,0,"MIL" "Santiago, Chile",-71,-34,0,"AGO" "Bermuda",-64,32,0,"BDA" "Dakar, Senegal",-17,14,0,"DKR" "Ascension Island",-14,-8,0,"ACN" "Madrid, Spain",-5,41,0,"MAD" "Indian Ocean Stn",56,-5,0,"IOS" "Yargidy, Australia",115,-29,0,"YAR" "Guam",143.3333,14,0,"GWM" "Canberra, Australia",149,-36,0,"CAN" These files are ASCII and may be prepared or edited with any standard ASCII editor; if using a word processor, select the "non-document" mode. Five items are required for each location; the longitude and latatude are expressed in degrees and fraction of a degree, elevations above Mean Sea Level are expressed in meters, and names or abbreviations are included in double quotation marks. The following example illustrates the .TRK file format: Program STSORBIT PLUS Satellite Orbit Simulation Page 44 "Merritt Island, FL",-81.0,28.0,0,"MIL" --------+----------- --+-- --+- + --+-- | | | | | | | | | +--- 3-Letter Abbreviation | | | +------- Elevation (meters) | | +---------- Latitude (degrees) | +---------------- Longitude (degrees) +------------------------------- Location Name For those interested in the Russian space program, a list of Russian ground tracking stations is provided in file CIS.TRK (data courtesy Ellwood Marshall). With the breakup of the Soviet Union, some of these installations may no longer be active or the name may have changed. "Tyuratam Cosmodrome",63.3392,45.9235,0,"TYR" "Kaliningrad Cntrl Ctr",37.816,55.916,0,"KAL" "Plesetsk Cosmodrome",40.7,62.75,0,"PLS" "Petropavlovsk Russia",158.933,53.216,0,"PTR" "Tbilisi Georgia",44.75,41.66,0,"TBL" "Ulan Ude Russia",107.683,51.983,0,"ULN" "Ussuriysk Russia",132.15,43.8,0,"USS" "Yevpatoria Ukraine",33.3666,45.2166,0,"YEV" Other nations also have facilities for satellite launches. As of early 1993, file SPACENTR.TRK includes the following locations: "Alcantara LC Brazil",-44.3999,-2.3999,0,"ALC" "Esrange,Kiruna Sweden",21.067,67.883,0,"ESR" "Jiuquan Space LC China",100.033,40.83,0,"JIU" "Kagoshima Center Japan",131.083,31.25,0,"KAG" "Kourou Space Ctr Fr.Gu",-52.7669,5.23,0,"KOU" "San Marco Platform",40.2,-2.9329,0,"SMP" "Sriharikota Ctr India",80.25,13.78,0,"SRI" "Tanegashima SC Japan",130.967,30.4,0,"TAN" "Xichang Space LC China",102.217,27.967,0,"XUC" The first mission of Endeavour, STS-49, was in May, 1992. This dramatic and exciting mission captured the INTELSAT VI (F3) satellite, stranded in a useless orbit by its booster rocket failure since January, 1990, and attached a new booster rocket which placed the satellite in its proper orbit. STSPLUS was used operationally during the mission by Intelsat, another "first" for the program. Intelsat used its own ground tracking stations for communications with INTELSAT VI (F3); the ground stations which participated in the mission are listed in file INTELSAT.TRK (information courtesy Dee Smith): "Paumalu, Hawaii",-158.0342,21.6711,157.86,"PAU" "Tangua, Brazil",-42.7845,-22.7442,35.38,"TAN" "Jatiluhur, Indonesia",107,-6.5213,161.49,"JAT" "Perth, Australia",115.25,-31.8,0,"PER" "Gandoul, Senegal",-17.4745,14.43,0,"GAN" These TRK files are standard ASCII files and may be edited with any editor; word processor users be sure to use the ASCII or non-document mode. The files use a standard comma-delimited format as shown; positions are Program STSORBIT PLUS Satellite Orbit Simulation Page 45 given in longitude (degrees) and latitude (degrees), rounded to the nearest degree. A maximum of 25 ground stations is permitted. The use of TRK files is not restricted to tracking stations, of course. So long as the correct data format is observed, any desired location may be included in the tracking station file up to the maximum of 25 locations. Event Timers and Audible Alarms ------------------------------- STSPLUS is often operated for long periods of time with minimum operator attention or intervention. Users may perform other tasks while the satellite display is active and while awaiting some subsequent event of interest. Event timers are displayed for the selected events if they will occur within approximately four hours of the time that the map is drawn; if an event will not occur within that time, the event is blank. Audible alarms serve to alert the user to upcoming selected events. The event timers are enabled with F10+F7 from the Main Menu. Audible alarms are enabled with F10+F8 from the Main Menu and require also that the event timers be enabled. All events are termed "AOS" (Acquisition of Signal or Source) or "LOS" (Loss of Signal or Source) and are generally calculated for line of sight conditions. Each phenomena which may be timed has an associated AOS and LOS timer which displays the hours and minutes ("HHH:MM") remaining until the next event if that event will occur within the next four hours (240 minutes), one hour past the last time for which the ground track is plotted. The current status of the signal or source is indicated by the color of the timer digits: GREEN indicates signal or source acquisition, and RED indicates signal or source loss. Two minutes prior to an event, the timer for that event will change from the signal status color (GREEN or RED) to YELLOW to visually alert the user. Users with monochrome monitors will be unable to distinguish these color changes, of course, but can determine the signal status by comparing the AOS and LOS times; if the AOS time is less than the LOS time, the signal is currently out of contact and vice versa. All calculations for upcoming events are made each time the ground track is drawn on the display and will affect the time required to prepare the display, especially on slower computers. In order to minimize these calculation delays, the event calculations for orbital sunrise and sunset use a simplified algorithm which does not take into account the non- spherical shape of the earth (unlike the dynamically calculated spacecraft lighting features which are more accurate). Orbital sunrise and sunset are the times that the spacecraft transitions between refracted sunlight (sunlight refracted through the Earth's atmosphere) to partial sunlight (illumination from only a portion of the solar disk); this corresponds to the transitions between RED and YELLOW color on the satellite icon and illumination symbols respectively. The errors resulting from the simplified algorithm are usually less than plus or minus 10 seconds; because of the more oblique angles and geometry involved, higher errors are usually associated with higher inclination orbits. When no secondary location is selected, the headings "AOS" and "LOS" will appear in orthographic modes; the headings do not appear in rectangular modes or in orthographic modes when a secondary location is selected in order to make room for the additional line of data. A typical event timer will appear as: Program STSORBIT PLUS Satellite Orbit Simulation Page 46 STN: 23:47 45:18 (orthographic projections) or TDRW AOS/LOS: 14:21 57:32 (rectangular projections) The following events may be timed and will cause an audible alarm if the events themselves are appropriately enabled: Local Visibility For the primary location: three sets of up/down tones two minutes prior to AOS and five tones thirty seconds prior to LOS. For the secondary location (if enabled): two sets of up/down tones two minutes prior to AOS and four tones thirty seconds prior to LOS. Refers to the times the satellite enters or leaves the local circle of visibility. TDRS Acquisition Three short tones thirty seconds prior to AOS or LOS. Refers to the times the satellite acquires or loses the ability to communicate with either of the programmed Tracking and Data Relay Satellites. Orbital Sunrise/set Two tones thirty seconds prior to approximate orbital sunrise or sunset. Refers to actual line of sight solar contact; refracted sunlight is not included. The characteristics of the audible tones have been selected to allow the user to uniquely identify the kind of AOS or LOS event that is about to happen. STSPLUS is now "aware" of program RighTime by Tom Becker and its use is recommended for accurate timekeeping. Audible alarms in prior versions would perform unpredictably when RighTime was active because they use the hardware clock's timer functions (which RighTime also uses). STSPLUS now detects RighTime and temporarily disables RighTime while an audible alarm is being generated and then re-enables RighTime after the alarm has completed, restoring precise timekeeping. With RighTime active, alarms are generated in foreground, which may cause a slight delay in screen updating. ************* * CAUTION * ************* STSPLUS expects RighTime Version 2.5+; performance with prior versions of RighTime may yield unpredictable results. If using a prior version of RighTime, do NOT enable audible alarms! If RighTime is not present or is not detected, the audible alarms are generated in background as in prior versions. This usually causes the loss of several clock ticks in the DOS software clock for each audible alarm. Although the time loss per audible alarm is very small, the cumulative error may become significant over extended time periods. Program STSORBIT PLUS Satellite Orbit Simulation Page 47 Pausing the Ground Track Display -------------------------------- Pressing F6 will cause the ground track display to "freeze" at the current time. This is called PAUSE mode. This permits closer examination of the data and/or display at any given time and to "move" the display forward and backward in time. Note that the pause takes effect AFTER the next second tick on the system clock; thus, if you wish to pause at 01:00 (one minute exactly on one of the clocks), press F5 when the display reads 00:59. After pressing F6, the following message will appear near the lower right of the screen: PAUSE...Press ENTER This reminds the user that PAUSE is in effect and to press ENTER to resume normal operation. When normal operation is resumed, the time continues from its present value, as if you had set SIMULATED TIME using F8+F3 or F8+F4 from the Main Menu. To return to REAL TIME, use F8+F1 from the Main Menu. While PAUSE is in effect, the "+" and "-" keys may be used to advance or retard the current time by the amount of the current time step. You may also use the "=" key instead of the "+" key to avoid pressing the SHIFT key. The only other key active in PAUSE mode is F4, which may be used to adjust the "time step" by pressing the key until the desired time multiplier is displayed at the upper right of the screen. Time multipliers of "X1" (no message displayed), "X10", and "X60" are selected in succession. The default time step is 1 second. Note that the automatic map generation feature is also used in PAUSE mode; automatic map generation may be enabled or disabled in the rectangular projections (use the TAB key) and is ALWAYS enabled in orthographic projections. Thus, when the satellite is moved near the edge of the display, the map may be redrawn if the appropriate point is reached. If you wish to synchronize the time used by STSPLUS to some other source (such as the slightly delayed orthographic displays presented from time to time on NASA Select TV), you may also use PAUSE mode for this purpose. Simply pause the display, use the "+" or "-" keys to adjust the time slightly ahead of the time to which you wish to synchronize. Then press ENTER when the times agree. Time can only be synchronized in this manner to plus or minus one second. If you need higher precision, set SIMULATED TIME using F8+F3 or F8+F4 from the Main Menu. Using FAST Time --------------- Press F4 while the map is displayed to use FAST time. FAST TIME is a variation of SIMULATED TIME which automatically advances the time displayed by 10 or 60 seconds, as indicated at the upper left of the screen. Press F4 again to change the time step; when "(X10)" or "(X60)" is NOT displayed, the time step is one second. The actual time increment is a function of the computer's speed. For fast computers, the time increment will usually be 10 or 60 seconds but may vary by a second occasionally; for slower computers, Program STSORBIT PLUS Satellite Orbit Simulation Page 48 the time increment may be somewhat longer. FAST time is disabled when PAUSE mode is in effect and for the Satellite Motion Map. FAST time may be used to advance the display to a future time and for demonstration purposes. Once the desired time has been reached, simply press F4 until no time step is displayed at the upper left of the screen and time will advance normally. Note that FAST time sets the program to SIMULATED TIME; to restore "real time", press F8+F1 from the Main Menu. The Main Menu also indicates when SIMULATED TIME is in effect: the words "Current Time" will appear at the left of the times at the top of the screen when real time (the time your DOS clock is using) is in effect; the words "Simulated Time" appear when a simulated time is in effect. On-line Help ------------ An on-line Help Screen is available during the ground track display (rectangular map modes ONLY) to remind the user of the available functions and which keys to press to trigger those functions. When the ground track display is active, press Function Key F1 to display the Help Screen in the lower portion of the display: F1=Resume Data F6=Pause (+,-) TAB=Auto Maps On/Off L=Location Maps F2=Select Clocks F7=Circle of Vis W=World Maps T=Tracking Maps F3=Printer Log F8=SUN and Term Q=Quadrant Maps M=Motion Map F4=Time Step F9=Units (nm/km) Z=Zoom Maps: O=Orthographic F5=MET/T+Epoch F10=Sat Coordinates Home,PgUp,PgDn STSPLUS Ver 9311 The ground track display will continue to be updated in real time while the help screen is displayed. If only the graphical display of the ground track is of interest, the help screen may be kept on the display continuously. Press Function Key F1 again to return to the normal data display in the lower portion of the screen. Note that the Help Screen is disabled when the Motion Map is displayed. Program STSORBIT PLUS Satellite Orbit Simulation Page 49 ACTIVE KEYS DURING GROUND TRACK DISPLAY --------------------------------------- The following table lists the various keys which are active when the tracking display is shown on the screen. Some of these features are more fully described elsewhere. ENTER Return to Main Menu (cancel the simulation). F1 On-line HELP. Press F1 to display a help screen in the lower portion of the screen. Press F1 again to resume normal data display. F2 Selects the Big Clock mode. These modes are selected in the following order: 0 No clock displayed 1 UTC date and time 2 Local date and time 3 STN/TDRS AOS/LOS and MET or T+Epoch (select with F5) Note that not all computers (especially older CGA systems) will display the extended graphics characters used for the large clock characters. The symptom of this problem is that the lower left portion of the data block is mostly blank after pressing F2. If you have this problem and your computer is running DOS 3.x or DOS 5.0, enter the command "GRAFTABL" at the DOS prompt before running STSPLUS or include the line "GRAFTABL" in your AUTOEXEC.BAT file; this sets the "code page" to enable the computer to display the extended graphics characters. [The program GRAFTABL.COM is included as part of DOS in most cases.] F3 Enable or disable printer logging. If logging is enabled, the word LOG appears in the lower right of the screen. Be sure the printer is turned on BEFORE using the L command. The "L" command automatically enables the display of ascending and descending node information. F4 Toggle FAST mode from x1 to x10 to x60 to x1, etc. When either of the fast modes is enabled, "(x10)" or "(x60)" will appear at the upper right of the data block in red. This feature operates in both the normal (real or simulated time) and PAUSE modes. When x10 or x60 fast modes are used, automatic map generation is disabled; use the TAB key to restore automatic map generation. F5 When using 2-line elements, the elapsed time may be switched between "T+Epoch" and "MET" by using the "T" command. If no launch time and date have been entered, this command will have no effect. F6 Enable PAUSE mode. The plot is frozen at the current position and the "+" and "-" keys are enabled. (The "=" key may be used instead of the "+" key to avoid use of the SHIFT KEY.) Press ENTER to resume normal operation. Program STSORBIT PLUS Satellite Orbit Simulation Page 50 F7 Enable or disable the spacecraft circle of visibility. F8 Enable or disable the SUN, solar terminator, and spacecraft lighting feature. NOTE: The SUN and spacecraft lighting are not available on CGA systems. F9 Change units of distance between kilometers (km) and nautical miles (NM). F10 Change satellite coordinates between Altitude and Azimuth, Right Ascension and Declination, and Geocentric Rectangular (XYZ) systems. + During PAUSE mode only, moves the satellite to the NEXT calculated position based upon the FAST mode then in effect: simulated time is advanced 1, 10, or 60 seconds. (NOTE: The "=" key may be used instead of "+" to avoid the SHIFT KEY.) - During PAUSE mode only, moves the satellite to the PREVIOUS calculated position based upon the FAST mode then in effect: simulated time is backed up 1, 10, or 60 seconds. NOTE: Since this "-" or reverse feature was implemented primarily for testing and demonstration, the ground track logic does not recognize these reverse movements and may become slightly confused. To restore the ground track properly, press ENTER TWICE to stop the display and then to resume the mission. TAB Enable or disable automatic map generation. Automatic map generation is ALWAYS enabled in orthographic modes. When automatic map generation is enabled in rectangular map modes, the letter "A" will appear in the upper right of the display screen. Pressing the TAB key will always cause the map to be redrawn. PgUp When in one of the zoom modes, increases the field of view up to a maximum of 180 degrees. Press rapidly to execute multiple zoom steps without redrawing the map for each keypress. PgDn When in one of the zoom modes, decreases the field of view down to a minimum of 45 degrees. Press rapidly to execute multiple zoom steps without redrawing the map for each keypress. Home When in one of the zoom modes, returns the field of view to 75 degrees. End When in one of the zoom modes, returns the field of view to the last zoom factor used prior to pressing the HOME key. B Toggle the BLINK mode of the satellite symbol between blinking and steady. O Select Orthographic Projection (the LETTER "O" not the digit zero). PgUp, PgDn, Home, and End are active to select the magnification. Program STSORBIT PLUS Satellite Orbit Simulation Page 51 W,0 Select World Map display, showing the full world from +85 degrees North latitude to -85 degrees South latitude using rectangular projection. If automatic map generation is disabled, pressing "W" or "0" will toggle between the two world map displays. Q Select Quadrant Map display, showing 180 degrees field of view (rectangular projection) and selected so as to approximately center the satellite. 1-9 Select the indicated Quadrant Map. Automatic map generation is !@# disabled when a specific quadrant map is selected. See the chart in the section Quadrant Maps for the map numbers. Z Select Zoom Map display, showing from 180 to 45 degrees field of view (rectangular projection) and selected so as to approximately center the satellite. The default is 75 degrees. L Select Location Map display, showing concentric isocontours for your location. If a second location has been enabled, press "L" again for that location. T Tracking Station Map display, showing concentric isocontours for the tracking station closest to the current ground track position of the satellite (rectangular projection). Uses the data in the current TRACKING STATION file to select the tracking station(s); if the file is not found, STSPLUS defaults to an internal set of tracking stations. Use F7 from the Main Menu to select the TRACKING STATION filename. M Satellite Motion Map display, available on EGA and VGA systems only. Displays a map with the satellite centered using the map projection in effect when the key is pressed. In rectangular modes, the map is shown in zoom. Maps are drawn "off screen" and a complete map is always displayed. The map is updated every 10 seconds or as rapidly as the computer processor will permit. While the Satellite Motion Map is displayed, the following keys are active: ENTER, "M", "Home", "End", "PgUp", and "PgDn"; these keys perform the same functions as during the normal display except that the "M" key cancels the Satellite Motion Map and returns to normal display. Program STSORBIT PLUS Satellite Orbit Simulation Page 52 STSORBIT PLUS MAIN MENU ----------------------- Once the map coordinates have been stored internally, STSORBIT PLUS presents its Main Menu: Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 15:47:28 PST 23:47:28 UTC Current date: 03/11/1993 03/11/1993 F1 Convert Keplerian Data to 2-Line Format F2 Read NASA/NORAD 2-Line Elements (.TXT/.TLE Files) F3 Pass Predictions and Data Output F4 Tabular Satellite Positions (TRAKSTAR by TS Kelso) F5 Set Launch Time and/or Launch Date F6 Display MET & Launch Times (now 2-Line Epoch Times) F7 Set FILENAMES and Paths F8 Set program TIME and/or DATE F9 DOS Shell (CAUTION: DOS Version 3.x+ ONLY!) F10 Set STSORBIT PLUS Program Options and Features ENTER Resume Mission (MIR Space Station) ESC Quit STSORBIT PLUS and Save Current Mission Select desired function: During operation of STSPLUS, data are displayed by STSPLUS in several standard formats: 4/05/1990 Date in month/day/year 14:33:00 UTC Coordinated Universal Time in hours:mins:secs 06:33:00 PST Local Time in hours:mins:secs (abbr. may vary) 3/09:23:15 MET in days/hours:minutes:seconds 320.50 nm Distance in nautical miles 551.37 km Distance in kilometers -69.34 Angles in degrees; WEST longitude and SOUTH latitude are negative Note that latitudes and longitudes also include "N" and "E" for positive values respectively, and "S" and "W" for negative values respectively. This convention, which may seem redundant, has been used to avoid possible confusion; there are a number of representations for latitude and longitude in common use which use different sign conventions. Azimuth (heading) is given in the sense North-East-South-West where North is 0 degrees, East is 90 degrees, and so forth. The degree symbol is shown on the display for all angles but has been omitted from this documentation because it may not print correctly on all printers. Program STSORBIT PLUS Satellite Orbit Simulation Page 53 F1 Convert Keplerian Data to 2-Line Format ---------------------------------------------- This function provides a means to individuals without modems to receive the so-called "Keplerian Orbital Elements" and reliably convert those data to "2-Line Orbital Elements" as required by STSPLUS as well as other programs such as Paul Traufler's excellent TRAKSAT. However, more information is included in the 2-line orbital element set than is usually distributed as the Keplerian orbital elements; this means that the "missing" information must either be obtained from other sources or be set to a specified value or zero. These instructions and the example and sample form which follows will help the unskilled user to do these tasks. This conversion function has but a single purpose: to prepare 2-line orbital elements from Keplerian orbital elements by means of user keyboard input. Since the program is designed only to transcribe valid data from one format to another, no error checking is performed and the program makes no tests of the "reasonableness" of the various data and parameters. The user is therefore cautioned to check his data before using this program, or to use the resulting data with caution until it has been verified. The information shown below is usually included in the Keplerian orbital elements as received via modem or via voice (amateur radio or telephone). This sample is an actual file for Space Shuttle Flight STS-55 scheduled for early 1993 and received via modem direct from the NASA Johnson Space Center: Satellite: STS-55 Catalog number: 00055 Epoch time: 93073.67556033 =====> (14 MAR 93 16:12:48.41 UTC) Element set: JSC-003 Inclination: 28.4697 deg RA of node: 228.7025 deg Space Shuttle Flight STS-55 Eccentricity: .0003812 Prelaunch Keplerian Elements Arg of perigee: 314.2100 deg Launch: 14 MAR 93 15:00 UTC Mean anomaly: 45.8202 deg Mean motion: 15.90487610 rev/day G. L. Carman Decay rate: 1.2020e-03 rev/day~2 NASA Johnson Space Center Epoch rev: 2 If you compare the information requested here (as shown on the example on the following page) with that above, several items are missing or may be in a slightly different format. Here are some suggestions. 1. A sample form is included in this documentation which will assist you when receiving Keplerian orbital information by voice line or when it is transmitted by amateur radio link. Note that the form includes lines for "IAU Designation" and "BSTAR Drag"; these items are frequently omitted from voice transmissions. 2. The NORAD Number is assigned by the U. S. Space Command at Cheyenne Mountain after a satellite has been successfully launched. Initial or pre-launch Keplerian elements may use the mission number or some other convenient number for this item. Most tracking programs will accept any number here. 3. The IAU (International Astronomical Union) Designation is often not Program STSORBIT PLUS Satellite Orbit Simulation Page 54 assigned until well after a flight is in progress; press ENTER to use all spaces for this item. 4. For the 2-line orbital element set, the element set number (shown as "JSC-003" in the example above) MUST be numeric. For this example, enter "3" or "003". Most tracking programs will accept any number for this item, up to a maximum of FOUR DIGITS. 5. The "Epoch Rev/Orbit" is the orbit number at the epoch (the instant when the data is taken). Up to FOUR DIGITS may be entered here but except for the orbit number on displays, this number has no effect on the propagated orbit. 6. When the program asks for "NDOT2 Drag/Decay", the information being requested is the "Decay rate" in the Keplerian elements. It may be entered in the form shown in the example or as a decimal fraction such as ".002102" (which is identical to the "2.10200e-03" in scientific notation as used in the example). 7. When the program asks for "NDDOT6 Drag", press ENTER to insert a value of zero. This should be satisfactory for most tracking programs. 8. When the program asks for "BSTAR", you may press ENTER to insert a value of zero. This will be satisfactory for times very close to the Epoch Time for the elements. However, as time progresses the satellite may lag behind the propagated (projected) ground track if no value is avaialble for BSTAR. It may be satisfactory to use a value from a similar satellite or a prior set of 2-line elements in order to achieve more accurate long term results. 9. After the last data item has been entered, STSPLUS will request the filename to which the 2-line orbital data is to be written. Enter the full file name such as "TESTSAT.TXT". The file will be written to the current drive and directory set using F7 from the Main Menu. DO NOT INCLUDE A DRIVE OR DIRECTORY; THAT INFORMATION IS ADDED AUTOMATICALLY! Any prior file by the same name will be overwritten. 10. If you make a mistake during the data entry process, you may use the BACKSPACE key until ENTER has been pressed. If you wish to cancel the program without writing the data to a file, press ENTER when asked for the filename and the data will be discarded. Finally, a word about the NDOT2 and BSTAR parameters. Both the U. S. Space Command (formerly NORAD) and Johnson Space Center have been known to "tweak" these values for a variety of reasons. Usually it is because the orbit is in a state of change due, perhaps, to maneuvers or excessive drag. A positive value for BSTAR, which indicates positive acceleration and is somewhat unusual (and often also an indication of "tweaking"), is NOT handled correctly at this point and must be manually edited. Program STSORBIT PLUS Satellite Orbit Simulation Page 55 EXAMPLE DATA INPUT ------------------ Enter 2-LINE ELEMENTS Enter the required data as prompted. Most essential data is so-called Keplerian Orbital Data available to amateur radio enthusiasts. Other data may be inserted if available or may be omitted if not. Accuracy may be affected, see documentation. Enter Satellite Name (15 chars max): sts-55 Enter NORAD Number (NNNNN): 55 Enter IAU Designation (8 chars max): Enter Epoch Time (YYDDD.TTTTTTTT): 93073.67556033 Enter Element Set Number (NNN): 3 Enter Inclination (DDD.DDDD): 28.4697 Enter RA of Ascend Node (DDD.DDDD): 228.7025 Enter Eccentricity (.NNNNNNN): .0003812 Enter Arg of Perigee (DDD.DDDD): 314.21 Enter Mean Anomaly (DDD.DDDD): 45.8202 Enter Mean Motion (NN.NNNNNNNN): 15.9048761 Enter Epoch Rev/Orbit (NNN): 2 Enter NDOT2 Drag/Decay (.NNNNNNNN): .001202 Enter NDDOT6 Drag (NNNNN-N): 00000-0 Enter BSTAR (NNNNN-N): 36300-3 EXAMPLE DATA OUTPUT ------------------- Satellite Data has been entered as: Satellite Name (15 chars max): Sts-55 NORAD Number (NNNNN): 00055 IAU Designation (8 chars max): Epoch Time (YYDDD.TTTTTTTT): 93073.67556033 Element Set Number (NNN): 3 Inclination (DDD.DDDD): 28.4697 RA of Ascend Node (DDD.DDDD): 228.7025 Eccentricity (.NNNNNNN): .0003812 Arg of Perigee (DDD.DDDD): 314.2100 Mean Anomaly (DDD.DDDD): 45.8202 Mean Motion (NN.NNNNNNNN): 15.90487610 Epoch Rev/Orbit (NNN): 2 NDOT2 Drag/Decay (.NNNNNNNN): .00120200 NDDOT6 Drag (NNNNN-N): 00000-0 BSTAR (NNNNN-N): 36300-3 Sts-55 1 00055U 93073.67556033 .00120200 00000-0 36300-3 0 33 2 00055 28.4697 228.7025 0003812 314.2100 45.8202 15.90487610 23 Enter FILENAME for 2-Line Elements: Program STSORBIT PLUS Satellite Orbit Simulation Page 56 RECEIVED KEPLERIAN ORBITAL DATA FORM ------------------------------------ This form is provided as a convenience to users receiving Keplerian orbital data via voice link (amateur radio or telephone). Each set of underline characters indicates an expected character; the decimal point is shown where expected (if appropriate for the item). Make multiple copies of this form prior to a mission. Satellite: __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ Catalog Number: __ __ __ __ __ IAU Designation: __ __ __ __ __ __ __ __ Epoch Time: __ __ __ __ __ . __ __ __ __ __ __ __ __ Element Set: __ __ __ __ Inclination: __ __ __ . __ __ __ __ RA of Node: __ __ __ . __ __ __ __ Eccentricity: . __ __ __ __ __ __ __ Arg of Perigee: __ __ __ . __ __ __ __ Mean Anomaly: __ __ __ . __ __ __ __ Mean Motion: __ __ . __ __ __ __ __ __ __ __ Decay Rate: . __ __ __ __ __ __ __ __ BSTAR Drag: __ __ __ __ __ - __ Epoch Rev: __ __ __ __ Program STSORBIT PLUS Satellite Orbit Simulation Page 57 F2 Read NASA/NORAD 2-Line Elements from *.TXT/*.TLE Files ------------------------------------------------------------- In order to read the NASA/NORAD 2-line elements, you must have a file with that data. A current file is included in the standard distribution of STSPLUS. These files have names such as "TLE147.TXT" where the "147" corresponds to the particular US Space Command Prediction Bulletin number from T. S. Kelso's Celestial BBS and may change several times per week. Pressing F2 will display a list of all available files with default filetypes ".TXT" and ".TLE". The following example has been edited to show only 8 files: Select NASA/NORAD 2-Line Elements File Enter 2-Line Filename [TLE147.TXT]: Use ARROW KEYS, press ENTER to use the current default file shown in square brackets [...], or press ESC to CANCEL. 8 matching files in directory F:\TLE GPS.TXT GROUP000.TLE GSFC198.TXT GSFC199.TXT MIR.TLE TLE141.TXT TLE146.TXT TLE147.TXT The list of files is sorted in alphabetical order by filename then displayed using up to five columns. The display mode is adjusted for the maximum number of lines permissible for the active monitor type: 25 lines for CGA and HGC, 43 lines for EGA, and 50 lines for VGA. The maximum number of files which may be displayed for each monitor type is shown in the following table: Screen File Max Monitor Lines Lines Files ---------------------------------- VGA 50 42 210 EGA 43 35 175 CGA/HGC 25 17 85 To accept the default file shown in the square brackets, TLE147.TXT in the example, press ENTER. To manually enter a filename, type the name (the filetype .TXT will be appended if no filetype is typed) and press ENTER. To select one of the displayed files, use the ARROW KEYS (UP, DOWN, LEFT, RIGHT), Home, End, PgUp, or PgDn to move through the list until the desired file is highlighted and shown in the square brackets, then press ENTER. To cancel the function and return to the Main Menu, press ESC. STSPLUS defaults the drive and directory to the current directory, the one from which STSPLUS is being executed. However, some users prefer to use a separate directory for 2-line elements files. To specify a different drive and/or directory, enter the drive (followed by a colon) and the desired directory (followed by a trailing backslash, "\"). The specified Program STSORBIT PLUS Satellite Orbit Simulation Page 58 drive, directory, and filename are saved in file STSPLUS.INI and will be used the next time STSPLUS is executed. The following examples illustrate this method: D:\ Use the root directory on drive D: \ELEMENTS\ Use the current drive and directory \ELEMENTS\ C:\TLE\ Use drive C: and directory \TLE\ Failing to include the trailing backslash will cause STSPLUS to interpret what you intended as a directory to be a filename! The complete path with filename and filetype mask may also be entered: C:\TLE\*.TXT Use .TXT files on Drive C: and directory TLE D:\TLE\*.* Display all files on drive D: and directory \TLE\ F:\TLE\TLE*.TXT Use drive F:, directory \TLE\ and all files matching "TLE*.TXT" Although STSPLUS defaults to filetypes "*.TXT" and "*.TLE", you may use this command to temporarily specify a different filename and filetype mask if desired. If no files with filetype .TXT or .TLE (or files corresponding to the current filename and filetype mask) are found in the specified directory, the following error message will be displayed: No matching files found in specified drive/directory: E:\JUNK Press any key to continue ... To specify NO fileltype, enter the filename followed by a period, i.e. "ELEMENTS.". Any desired filetype may be used, but the program will always default to ".TXT" and ".TLE" each time F2 is used. If you include a drive (such as "D:") and/or directory (the directory MUST be followed by a trailing backslash, "\"), and the drive or directory cannot be found, the following error message will be displayed: Drive or path error: E:\JUNK Press any key to continue ... Once the file has been selected, a default satellite name will appear in the next prompt: Enter 2-Line Filename [STS50N38.TXT]: STS50N38.TXT Enter Satellite Name/#nnnnn [STS...]: (Enter '*' to match any satellite name) STSPLUS will normally display the first three characters of a satellite name or the full NORAD number, enclosed in square brackets, as the default choice. If no prior satellite has been selected, the satellite name will default to "STS..." for space shuttle missions (provided the filename begins with "STS") and to "HST..." for all other satellites; Program STSORBIT PLUS Satellite Orbit Simulation Page 59 otherwise, it will be the first three letters or full five digit NORAD number of the currently selected satellite. NORAD numbers are always prefixed with the "#" character. If you wish to change the information (or if no default is shown), enter the required information followed by ENTER. For the satellite name, only sufficient letters to unambiguously identify the desired satellite, upper or lower case, are required. For example, "Alou" would select "Alouette 1". However, note that entering "MIR" could select "MIRANDA" before it finds "MIR" depending upon the ordering of the 2-line elements within the file. Alternatively, you may enter the NORAD number for the desired satellite by entering "#" followed by the number; leading zeroes may be omitted. Once the information has been entered, STSPLUS will attempt to locate the data for the requested satellite. If a satellite matching the requested name is found, the data for that satellite are displayed. Certain non- essential data are not always included in the 2-line elements and may be replaced by spaces, indicated by "(n/a)". Satellite Name: STS-50 Satellite NORAD Number: #22000 Elements File: STS50N38.TXT Elements File Record#: 1 (*) Element Set Number: 38 Elements Epoch: 92187.57342677 05 JUL 1992 @ 13:45:44 UTC Orbit # at Epoch: 159 Launch Year: 1992 Launch Number: 34 Launch Piece: A Inclination: 28.467 RA of Ascend Node: 275.07 Eccentricity: .0007237 Arg of Perigee: 340.7929 Mean Anomaly: 19.153 Mean Motion: 15.91359642 Acceleration/Drag: -.00032668 BSTAR Drag: -.000097874 Press ENTER to ACCEPT this satellite, OR Press any other key to REJECT and continue searching: (*) This line is normally blank. However, one of the following messages will appear here if a checksum error is detected in the element set: BAD CHECKSUM in line 1 ignored! BAD CHECKSUM in line 2 ignored! BAD CHECKSUM in both lines ignored! In all three cases, STSPLUS will accept the data and attempt to use it. Be advised, however, that the checksums are included to help detect errors that might otherwise yield an incorrect position! Program STSORBIT PLUS Satellite Orbit Simulation Page 60 If this is the satellite you wish, press ENTER and the data will be entered into STSPLUS. If, on the other hand, a different satellite is desired, press any other key (such as the SPACE BAR) and STSPLUS will search for another name matching the requested satellite. For example, there are a number of NAVSTAR Global Positioning Satellites usually included in the file with official names such as "GPS-0001", "GPS-0002", "GPS BII-01" and so forth; requesting "GPS" will allow you to cycle through all the available choices. The file TLEnnn.TXT is an ASCII file; it may be helpful to view or print the file to see the available satellite names. Once the satellite has been selected, STSPLUS will require a brief time to calculate certain required orbital parameters, then will proceed directly to the display of the ground track. As a point of interest, the 2-line elements for the Space Shuttle Mission STS-50 used in the example above are as follows: STS-50 1 22000U 92 34 A 92187.57342677 -.00032668 00000-0 -97874-4 0 380 2 22000 28.4670 275.0700 0007237 340.7929 19.1530 15.91359642 1596 F3 Data Output and Pass Prediction Selections ------------------------------------------------- By popular request, STSPLUS has been enhanced to send selected data for the current satellite to other equipment via a serial port (COM1 or COM2), to a file (STSPLUS.LOG), or to the printer (LPT1). Validation of the serial port output has been accomplished using two computers and a "Null Modem" cable. Two classes of data may be selected for output: current position data in four formats, and predicted Line-of-Sight passes in the future. The current position data is generated while the ground track map is displayed; the predicted pass data is calculated "off-line" and is displayed on the screen as well as being sent to the selected output destination. Current position data include the UTC date/time and are generated for local horizon coordinates (altitude and azimuth), geographic coordinates (geocentric latitude, longitude, and orbital altitude), topocentric equatorial coordinates (right ascension and declination), and X-Y-Z inertial state vector (position and velocity components). Potential applications for these data include automatic antenna pointing systems, off-line high precision plotting, and widespread distribution of the data within a large facility or via modem. Users who develop applications to utilize these data are invited to contribute their programs and documentation for general use. Since this is a new and relatively untried feature for STSPLUS, comments and suggestions are welcome. Although STSPLUS retains the capability of performing off-line pass predictions with TS Kelso's TRAKSTAR or other satellite tracking software, many users have requested that a similar feature be incorporated directly into STSPLUS. Pass predictions may only be calculated for satellites having a mean motion greater than 1.5; this eliminates satellites in near geosynchronous or higher orbits, but since such satellites don't move much that does not represent a significant constraint. The satellite's orbit is examined for the next 48 hours (using the current real or simulated time) with a sampling interval which ranges from 10 to 60 seconds depending upon the orbit. Because of this "granularity" in the search algorithm, it is possible to skip passes whose duration is less than the sampling interval. Program STSORBIT PLUS Satellite Orbit Simulation Page 61 Since those brief passes would barely peek above the user's horizon, they are thus not significant. Pass predictions may be continued in 48 hour segments until 99 visible passes have been displayed. Since a typical satellite may have from about two to seven passes in a 24 hour period, the passes may be examined for a considerable time into the future. Predicted pass data are calculated using the current satellite for Line-of-Sight visibility; that is, when the satellite is in line of sight to the user's location and without consideration of lighting effects. Since STSPLUS users are about equally divided between those who track satellites visually and those who use electronic equipment, this method provides data for all users. Passes which occur near local sunrise or sunset may be tested for lighting constraints and/or ground visibility by displaying the ground track for the pass or other means. Note that all dates and times are given in Coordinated Universal Time (UTC) and that the date for each pass is given only for AOS (Acquisition of Signal); it is possible for the pass to span 00:00 UTC with a consequent date change during the pass. Prediction calculations may require some time; calculation delays are noted with the message "calculating ...". Using a processor equipped with a math coprocessor chip, each 48 hour block may require from less than 10 seconds to a minute or more. However, users without math coprocessor chips will experience significant delays -- minutes or even tens of minutes! The following table lists typical calculation times for various processors (all with math coprocessors!) using the Russian MIR Space Station: 286/287 386SX/387SX 486DX 8 MHz 20 MHz 33 MHz --------------------------------------------------- MIR 60 sec 30 sec 6 sec The data output feature MUST be enabled with F3 each time STSPLUS is run; it is NOT automatically restarted when the "/R" (RESUME) command line option is used. STSPLUS sets up certain initial default parameters for data output and displays the current parameters each time F3 is pressed: STSORBIT PLUS Data Output Parameters: Data Output: STSPLUS.LOG Data Format: 1 = Azimuth, Elevation, Range Data Interval: 10 seconds Accept Parameters [Y,n]: The selected Data Interval is not shown if Data Format 9 (Line-of-Sight Predictions) has been selected; predictions are always performed for blocks of 48 hours. If the current parameters are correct, press "Y" (or ENTER) to accept them. If the parameters are to be changed, press "N" to be prompted for new parameters. In each case, the default value which will be used if ENTER is pressed will be shown in square brackets; if more than one choice is shown, separated by commas, the first choice will be used if ENTER is pressed. The user must first select the data output device or destination by pressing the indicated key: Program STSORBIT PLUS Satellite Orbit Simulation Page 62 Select Output [F,p,1,2]: F = File STSPLUS.LOG P = Printer LPT1: 1 = Serial Port COM1: 2 = Serial Port COM2: Pressing ENTER or the letter "F" (upper or lower case) will select the FILE output and the data will be sent to the file STSPLUS.LOG. If the file does not exist, it will be created; if the file already exists, the data will be appended to the existing data. Press the letter "P" to direct the data to the printer on LPT1. Press "1" or "2" to direct the data to one of the two serial ports. When a serial port (COM1: or COM2:) is selected, the user next selects the data rate to be used for communications with the external equipment. Only the four data rates shown below the prompt are supported. Use the first character of the desired rate to select it, or press ENTER to use the data rate shown in the square brackets: Select DATA RATE [9600]: (300, 1200, 2400, 9600) STSPLUS automatically sets the communications parameters to "8,N,1"; these are fixed and may not be altered. These communications parameters select 8 data bits per transmitted byte, NO parity, and 1 stop bit. Most external equipment will operate satisfactorily with these parameters. STSPLUS requires several additional items of information before it can send data to the external equipment, file or printer. The first is the data format to be used. Five different data formats are available. The next prompt lists the formats and shows the current default in square brackets: Select Data to Output [1]: 1 = Azimuth, Elevation, Range 2 = Latitude, Longitude, Orbit Altitude 3 = Right Ascension, Declination 4 = X-Y-Z State Vector (km) Press the number key corresponding to the desired Data Mode or press ENTER to select the choice shown in square brackets. See the Data Mode Formats in the following sections for specific details on the data included in each data mode. For current position formats ( 1 through 4), the desired time interval between successive sets of data must be also selected. Any interval between 1 and 900 seconds (that is, up to 15 minutes maximum) may be selected. Note also that this is the DESIRED time interval; if your computer is too slow to complete its calculations in that time, the interval will be longer. In other words, STSPLUS will generate the requested data no more frequently than the interval requested but may take longer, depending upon what has to be done each time. In response to the prompt, press ENTER to accept the default value shown in square brackets or type the desired numerical value (in seconds) followed by ENTER: Data Interval (secs) [10]: (Min = 1 sec, Max = 900 secs) If a value less than 1 second is entered, 1 second will be substituted; if Program STSORBIT PLUS Satellite Orbit Simulation Page 63 a value greater than 900 seconds is entered, 900 will be substituted. STSPLUS now returns to the initial parameter display and again asks if the parameters are correct. In the following example, the output has been changed to COM1: STSORBIT PLUS Data Output Parameters: Data Output: COM1: COM Speed: 9600 (8,N,1) Data Format: 1 = Azimuth, Elevation, Range Data Interval: 10 seconds Accept Parameters [Y,n]: As before, press "Y" (or ENTER) to accept the current parameters, or press "N" to repeat the change process. When the parameters are accepted, STSPLUS asks if the data output process should be initiated now: Setup Data Output Now [Y,n]: Press "N" to save the parameters for use at a subsequent time or, in the case of Line-of-Sight predictions (Data Mode = 9), to send the output to the display screen ONLY; the selected parameters will appear as the default choices. Press "Y" (or ENTER) to setup the data output immediately. The following message will be sent to the selected destination: STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 1 where "Data = 1" will indicate the code for the Data Mode in effect. This completes the setup of the data output. NOTE: Users are reminded that when data output is sent to the file STSPLUS.LOG, a considerable volume of data may be accumulated over long periods of time. It is possible to completely fill a disk with this data! The file should be periodically copied to other media or deleted to avoid this problem. For current position data modes, STSPLUS will automatically send data to the specified destination after the ground track map is displayed. All data is sent in standard ASCII format and each data line is terminated with CR+LF. The following sample illustrates typical data: STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 1 02/10/1993 13:58:09 20580 -2.472 248.222 1675 02/10/1993 13:58:20 20580 -1.896 247.880 1637 02/10/1993 13:58:34 20580 -1.147 247.420 1589 02/10/1993 13:58:40 20580 -0.819 247.213 1569 02/10/1993 13:58:09 20580 -2.472 248.222 1675 02/10/1993 13:58:20 20580 -1.896 247.880 1637 02/10/1993 13:58:30 20580 -1.363 247.554 1603 02/10/1993 13:58:40 20580 -0.819 247.213 1569 02/10/1993 13:58:50 20580 -0.265 246.857 1535 02/10/1993 13:59:00 20580 0.300 246.484 1501 02/10/1993 13:59:10 20580 0.878 246.092 1467 02/10/1993 13:59:20 20580 1.468 245.681 1433 Program STSORBIT PLUS Satellite Orbit Simulation Page 64 02/10/1993 13:59:30 20580 2.072 245.249 1399 02/10/1993 13:59:40 20580 2.691 244.794 1365 The first line of the sample is the setup line. The second line is the first data line; note that it is generated as soon as possible after the ground track display has been drawn and the time is more or less random. Subsequent lines are generated at the specified time interval except when required calculations require a longer time to complete or when the map is being redrawn; unless the computer is able to complete its calculations and redraw the map in less than the specified time interval, a break in the data stream will occur at these times. Selecting the full world (with rectangular projection, "W") or MAG=100 (with orthographic projection, "O" plus HOME) will reduce the frequency that the map is redrawn. STSPLUS saves the data output configuration information in file STSPLUS.INI, but the data output feature must be enabled with F3 each time STSPLUS is started from the DOS prompt. However, the ground track display may be stopped (by pressing ENTER) to return to the Main Menu and, as long as the program is not exited (by pressing ESC), the data output remains enabled and will resume sending data when the ground track display is restarted regardless of any other changes (such as simulated time or the selection of a different satellite). For Line-of-Sight predictions, the data are displayed on the screen as calculated and optionally sent to the selected destination device. The following is an edited sample of the screen display: ---------16609 AOS-------- ---MAX VISIBILITY-- ------LOS------ # UTC Date UTC Time Azm UTC Time Alt Azm UTC Time Azm Duration 1 02/23/1993 03:05:56 171.5 03:09:39 7 125.1 03:13:23 78.4 0:07:27 2 02/23/1993 04:40:12 230.2 04:45:23 70 318.8 04:50:32 44.9 0:10:20 3 02/23/1993 06:17:58 281.3 06:22:02 9 333.9 06:26:07 26.7 0:08:09 4 02/23/1993 07:57:27 328.5 07:59:40 2 354.4 08:01:53 20.3 0:04:26 5 02/23/1993 09:34:31 339.1 09:37:34 4 15.9 09:40:38 52.7 0:06:07 6 02/23/1993 11:09:57 325.6 11:14:46 21 34.8 11:19:35 103.4 0:09:38 7 02/23/1993 12:46:00 302.3 12:50:56 29 229.0 12:55:55 155.6 0:09:55 8 02/24/1993 02:12:22 131.7 02:13:17 0 121.3 02:14:12 110.9 0:01:50 9 02/24/1993 03:43:39 212.0 03:48:44 42 132.6 03:53:48 53.7 0:10:09 10 02/24/1993 05:20:25 263.7 05:25:02 16 327.6 05:29:40 31.9 0:09:15 11 02/24/1993 06:59:36 314.0 07:02:22 3 347.0 07:05:09 20.0 0:05:33 12 02/24/1993 08:37:54 340.4 08:40:18 2 8.7 08:42:43 37.0 0:04:49 13 02/24/1993 10:13:30 331.3 10:17:49 12 28.7 10:22:09 85.8 0:08:39 14 02/24/1993 11:49:11 311.8 11:54:20 79 224.7 11:59:31 137.0 0:10:20 15 02/24/1993 13:26:53 273.2 13:29:57 4 236.4 13:33:01 199.8 0:06:08 Elapsed time = 27 seconds Repeat for NEXT 48 HOURS or DISPLAY PASS [N,y,pass#]: The column headings indicate the data displayed. "16609" indicates that the data is for NORAD number 16609, the MIR Space Station. "AOS" is Acquisition of Signal or when the satellite rises above the user's true horizon. "MAX VISIBILITY" is the maximum altitude above the user's true horizon that the satellite reaches during the pass. "LOS" is Loss of Signal or when the satellite sets below the user's true horizon. "#" is an arbitrary pass number for this set of calculations. The format for the data sent to the destination device is slightly different from that displayed; see the Data Mode 9 format description below. Program STSORBIT PLUS Satellite Orbit Simulation Page 65 The UTC date given is for AOS; since passes may span 00:00 UTC, the actual UTC date for MAX VISIBILITY or LOS may have to be incremented. Times are calculated to the nearest second, altitudes are rounded to the nearest degree, and azimuths are rounded to the nearest tenth of a degree. Azimuth is always calculated in the sense NESW where North = 0 degrees, West = 90 degrees, etc. Note that the degree symbol will appear on the display for all "Azm" and "Alt" data but has been deleted in the sample above in order to maintain compatibility with various printers; the actual display is thus four columns wider than the example above. Press ENTER while the passes are being calculated to stop the calculations. When all calculations for the current 48 hour block have been completed, the time elapsed for the calculations is displayed and the user is asked if another set of calculations is desired of if a particular pass should be displayed. Press "N" or ENTER to return to the Main Menu, or press "Y" to perform the next 48 hour block of calculations. The calculations will be stopped when 99 passes have been listed. Typically, from four to sixteen passes are listed for each 48 hour block, the number being related to the characteristics of the current satellite's orbit. If additional passes beyond that time are desired, set simulated time (F8+F3 from the Main Menu) to the desired start time and repeat the predictions. To display a particular pass, enter the listed pass number. Passes are assigned arbitrary numbers from 1 to 99 beginning with the first pass which occurs during or subsequent to the current real or simulated time. Any pass number may be selected, from pass #1 to the last listed pass shown on the screen. (Attempting to enter a pass number larger than the last one shown will cause the computer to "beep" and the prompt will be repeated.) STSPLUS will set simulated time to approximately 30 seconds prior to the mid-point of the selected pass and prepare the display. The pass may then be examined for details of lighting, ground track, and so forth. If desired, use F6 to PAUSE the display, then use the "+" or "-" keys to adjust the simulated time forward or backward. The default time step is one second; press F4 to select a different time step: 1, 10, or 60 seconds. Press ENTER to return to normal operation from the PAUSE mode. Note that STSPLUS automatically sets simulated time to display a predicted pass, and that new simulated time remains in effect until set by another predicted pass or until reset using F8 from the Main Menu. Each time predicted passes are requested, the list begins with the first pass which occurs at or subsequent to the current real or simulated time. If predicted passes are requested and displayed with real time in effect and the same list is then desired again, it is necessary to reset STSPLUS to real time (using F8+F1) or to the original simulated time (F8+F3 for simulated time or F8+F4 for MET). Otherwise, the list of predicted passes will be generated beginning with the simulated time then in effect and the pass numbers may be different. Program STSORBIT PLUS Satellite Orbit Simulation Page 66 Data Mode 1: Azimuth/Elevation Data Format ------------------------------------------ 1 2 3 4 5 0123456789012345678901234567890123456789012345678901234 ------------------------------------------------------- 02/10/1993 13:58:09 20580 -2.472 248.222 1675 [CR/LF] -----+---- ----+--- --+-- ----+--- ----+--- ---+--- | | | | | | | | | | | +--- Range | | | | | | | | | +----------- Aximuth | | | | | | | +--------------------- Elevation | | | | | +------------------------------ NORAD # | | | +-------------------------------------- UTC Time | +------------------------------------------------- UTC Date UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy UTC Time: Current time in Universal Coordinated Time, hh:mm:ss NORAD #: Satellite NORAD Number Azimuth: Azimuth in degrees to satellite in the sense NESW Elevation: Elevation to satellite in degrees above true horizon Range: Range from User Location to Satellite in km [CR/LF]: Each data line is terminated with a CR and LF in addition to the 54 printing characters shown, for a total of 56 characters per data line. Program STSORBIT PLUS Satellite Orbit Simulation Page 67 Data Mode 2: Latitude/Longitude Data Format ------------------------------------------- 1 2 3 4 5 0123456789012345678901234567890123456789012345678901234 ------------------------------------------------------- 02/11/1993 13:46:40 20580 -5.182 155.667 593 [CR/LF] -----+---- ----+--- --+-- ----+--- ----+--- ---+--- | | | | | | | | | | | +--- Orbit Altitude | | | | | | | | | +----------- Longitude | | | | | | | +--------------------- Latitude | | | | | +------------------------------ NORAD # | | | +-------------------------------------- UTC Time | +------------------------------------------------- UTC Date UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy UTC Time: Current time in Universal Coordinated Time, hh:mm:ss NORAD #: Satellite NORAD Number Latitude: Geodetic Latitude in degrees of sub-satellite point (satellite ground track) Longitude: Geodetic Longitude in degrees of sub-satellite point (satellite ground track) Orbit Alt: Altitude in kilometers of the satellite above the Earth's surface [CR/LF]: Each data line is terminated with a CR and LF in addition to the 54 printing characters shown, for a total of 56 characters per data line. Program STSORBIT PLUS Satellite Orbit Simulation Page 68 Data Mode 3: Topocentric RA/DEC Data Format ------------------------------------------- 1 2 3 4 01234567890123456789012345678901234567890123456 ----------------------------------------------- 02/11/1993 13:47:20 20580 7.111 -25.941 [CR/LF] -----+---- ----+--- --+-- ----+--- ----+--- | | | | | | | | | +----------- DEC | | | | | | | +--------------------- RA | | | | | +------------------------------ NORAD # | | | +-------------------------------------- UTC Time | +------------------------------------------------- UTC Date UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy UTC Time: Current time in Universal Coordinated Time, hh:mm:ss NORAD #: Satellite NORAD Number RA: Topocentric Right Ascension in hours DEC: Topocentric Declination in degrees [CR/LF]: Each data line is terminated with a CR and LF in addition to the 46 printing characters shown, for a total of 48 characters per data line. NOTES: 1. Topocentric coordinates give the right ascension and declination as seen from the current user's location on the surface of the Earth. Program STSORBIT PLUS Satellite Orbit Simulation Page 69 Data Mode 4: X-Y-Z Cartesian State Vector ----------------------------------------- 1 2 3 4 5 6 7 0123456789012345678901234567890123456789012345678901234567890123456789012345 ---------------------------------------------------------------------------- 93051.850694 20580 5705.34 -2656.38 -2988.02 2.432 6.991 -1.571 -----+------ --+-- -----+---- -----+---- -----+---- ---+--- ---+--- ---+--- | | | | | | | | | | | | | | | | NASA-DOY NORAD# X Y Z X-Dot Y-Dot Z-Dot -------------------------------- ----------------------- Position Velocity NASA-DOY: NASA Day-of-Year time of data (yyddd.dddddd) NORAD #: Satellite NORAD Number X, Y, Z: Cartesion coordinates (km) X-, Y-, Z-Dot: Cartesian velocity components (km/sec) [CR/LF]: Each data line is terminated with a CR and LF in addition to the 75 printing characters shown, for a total of 77 characters per data line. NOTES: 1. The X-Y-Z Cartesian State Vector is given as a standard inertial cartesian 6-dimensional state vector where the X-Axis is pointing toward the vernal equinox, the Z-Axis is pointing toward the North Pole, and the Y-Axis is mutually orthogonal to the other axes. 2. For convenience, all position coordinates are given in kilometers (km) and all velocity components are given in kilometers per second (km/s). 3. State vectors for the space shuttle as issued by Johnson Space Center (JSC) are usually given in feet (ft) and feet per second (fps or ft/sec). To convert the values given here to the units used by JSC, multiply each value by 3280.8336. 4. The NASA Day-of-Year format is used here for date and time since that is the format used by JSC for X-Y-Z state vectors and also in 2-line elements. In the DOY format, time is counted from midnight (00:00 UTC) each day. Some calculations require instead the Julian Date format which counts time from noon (12:00 UTC) each day. Program STSORBIT PLUS Satellite Orbit Simulation Page 70 Data Mode 9: Pass Predictions ----------------------------- --------#20580 AOS-------- --MAX VISIBILITY-- ------LOS------ # UTC Date UTC Time Azm UTC Time Alt Azm UTC Time Azm Duration 1 02/27/1993 03:58:09 205.1 04:03:00 9 157.9 04:07:52 110.8 0:09:43 -+ ---------+--------- --+-- ----+--- -+ --+-- ----+--- --+-- ----+--- | | | | | | | | | Pass # | | | | | | | | | | | | | | | | +----------+ | | | | | | | | | | | | | | | | +---------------------+ | | | | | | | | | | | | | | | +----- AOS Azimuth (degrees) | | | | | | | | | | | | | +-------- AOS UTC Date/Time | | | | | | (mm/dd/yyy hh:mm:ss) | | | | | | | | | | | | +---------------------------------+ | | | | | | | | | | | | +-------------------------------------+ | | | | | | | | | | | | +--------------------------------------+ | | | | | | | | | | | +-- MAX Azimuth (degrees) | | | | | | | | | +----- MAX Altitude (degrees) | | | | | | | +-------- MAX UTC Time (hh:mm:ss) | | | | | | +-----------------------------------------------------+ | | | | | | +----------------------------------------------------------+ | | | | | +----- LOS Azimuth (degrees) | | | +-------- LOS UTC Time (hh:mm:ss) | | Total Pass Duration (hh:mm:ss) --+ NOTES: 1. The Pass # is an arbitrary number assigned by STSPLUS during the pass calculations and is a function of the real or simulated time at which the calculations are performed. 2. The satellite NORAD number is included in the heading, "20580" in the sample above. 3. The UTC Date is given only for AOS. Since a pass may span 00:00:00 UTC, the date for MAX VISIBILITY or LOS may have to be incremented. 4. All azimuths have been rounded to the nearest 0.1 degree; the MAX altitude has been rounded to the nearest degree. Program STSORBIT PLUS Satellite Orbit Simulation Page 71 F4 Calculate Satellite Positions with TRAKSTAR -------------------------------------------------- Tabular predictions for the currently selected satellite may be made by using TRAKSTAR by Dr. TS Kelso. STSPLUS has been arranged to operate seamlessly with TRAKSTAR by simply pressing Function Key F4 from the Main Menu. All data required by TRAKSTAR is automatically supplied by STSPLUS. See the section above "Predicting Satellite Passes with TRAKSTAR" and the TRAKSTAR documentation for full information. F5 Set Launch Time and Date ------------------------------- Orbital data for the satellite must be loaded using the F2 command on the Main Menu before the launch date and time may be set or changed. Once saved in file STSPLUS.LTD, the launch date and time will be automatically read from that file each time the satellite is selected (see below). ******************** * IMPORTANT NOTE * ******************** LAUNCH TIME AND DATE MUST EITHER BE INCLUDED IN FILE STSPLUS.LTD OR BE MANUALLY ENTERED FOR EACH SATELLITE OR MISSION SINCE THAT INFORMATION IS NOT INCLUDED IN 2-LINE ELEMENTS. Launch date and time are most important for manned missions such as the Space Shuttle since the mission timeline is reckoned using Mission Elapsed Time. However, MET may be used whenever actual launch date and time are known. The only requirement is that 2-line orbital elements must be available for the satellite. Since launch date and time are NOT included in the 2-line orbital elements, this means that you obtain the launch date and launch time independently and manually enter that data. Pressing F5 to enter launch date and time begins with the prompt: Enter Launch Time (HH:MM:SS): [Add 'U'or 'G' for UTC/GMT] Enter the time in the format shown using 24-hour notation. Add the letter "U" to signify UTC (Coordinated Universal Time) or the letter "G" to signify GMT (Greenwich Mean Time, essentially identical to UTC for the purposes of this program). Use no suffix for local time; it will be internally converted to UTC/GMT. If you enter "U" or "G", the abbreviation used in the menus will be set to "UTC" or "GMT" respectively. One or two digit numbers may be used as required. [The comma is also acceptable as a separator in place of the colon.] You may omit seconds [or minutes and seconds] if desired. For example, an entry of "16" will be entered as 16:00:00 or 4:00 PM. Press ENTER to leave the entry unchanged. Enter Launch Date (MM/DD/YYYY): [Enter '*' to clear LAUNCH DATE] Enter the date in the format shown. Note that if you requested UTC or GMT when entering the time, the date is interpreted as the UTC/GMT date. The Program STSORBIT PLUS Satellite Orbit Simulation Page 72 full four digit year may be used OR two digits as in "92". Be sure to use the SLASH "/" rather than the MINUS "-" as the separator; STSPLUS's internal date algorithms will interpret the minus sign as just that and some rather strange dates can result! You may also use relative dates: -1 will use the prior day, +2 will use two days hence, and so forth. Press ENTER to leave the date unchanged. Press "*" (followed by ENTER) to clear the launch date and time; this does NOT remove it from file STSPLUS.LTD. Press ENTER to accept, SPACE BAR to repeat: When all data have been entered, the program pauses for your approval. If all data are correct, press ENTER. Press the SPACE BAR to start over. You are next asked if you wish to save this data: Add/Update this data in file STSPLUS.LTD [Y,n]: Press "Y", "y" or ENTER to add or update the data in file STSPLUS.LTD (see below). Press "N" or "n" to use the data but not add or update it in file STSPLUS.LTD. Adding or updating the data to file STSPLUS.LTD makes sure that the launch date and time data will be available the next time this particular satellite is selected. Using File STSPLUS.LTD for Launch Date & Time --------------------------------------------- An alternative and automatic method to set launch date and time is to use file STSPLUS.LTD. This file contains the NORAD number and launch date and time (UTC Julian date) for selected satellites. A sample entry appears as: 22194,2448918.21503472,0 --+-- -------+-------- + | | | | | +--- (Reserved, must be present) | | | +------------- Launch Date (UTC Julian date) | +------------------------ NORAD Number The Sample above shows the data for Space Shuttle mission STS-52 (NORAD #22194) and corresponds to a launch date and time of 22 OCT 1992 @ 17:09:39 UTC. The file is in standard ASCII format and may be edited with any standard editor; word processor users use the "non-document" mode. Use care when manually editing the file as STSPLUS performs NO ERROR CHECKING! Estimated 2-line orbital elements are usually available prior to a Space Shuttle launch, and actual 2-line orbital elements within about 8 to 12 hours after a launch. Note, however, that the NORAD number is not assigned until actual launch and a "dummy" NORAD number is used for estimated pre-launch elements; for example, "00052" for STS-52. Once the launch has taken place, the permanent NORAD number is assigned. This change in NORAD number will require either that file STSPLUS.LTD be edited OR that a new entry be made. Note that there are still a few satellites around with low NORAD numbers! Program STSORBIT PLUS Satellite Orbit Simulation Page 73 If file STSPLUS.LTD is present and if the selected satellite is found, the launch time and date will be set and Mission Elapsed Time (MET) will be used automatically; otherwise, T+Epoch (T+E) will be used. When MET is displayed, it may be changed to T+E by pressing F6 from the Main Menu (below) or F5 while the map is displayed. File STSPLUS.LTD is read each time a new satellite is selected using F2 from the Main Menu. If file STSPLUS.LTD is NOT present, the launch date and time will be saved in file STSPLUS.INI and must be MANUALLY MAINTAINED as in versions prior to 9245! If you wish to use the old method, rename or delete file STSPLUS.LTD. F6 Select Time Since Epoch or Mission Elapsed Time ------------------------------------------------------ STSPLUS by default displays the time elapsed since the epoch date of the elements in the upper right portion of the data block unless the launch date and time are included in file STSPLUS.LTD, in which case Mission Elapsed Time (MET) is the default. This marked on the display as "T+Epoch" or "MET" respectively. While T+Epoch is not of particular value for satellite viewing purposes, it does indicate the relative age of the orbital data. As a general rule, especially for lower Earth orbits, the effects of orbit decay make position predictions less accurate as time passes. Data which are more than 10 or 20 days old may produce less accurate positions. For a space shuttle mission, however, all mission events are scheduled against the mission timeline and are reckoned in Mission Elapsed Time (MET), the time elapsed since launch. It is therefore useful to be able to display MET during the course of a mission or to review the flight post- mission. Unfortunately, the standard NASA/NORAD 2-line element format does not include the launch time and launch date and therefore this information must be secured independently and manually entered into STSPLUS. Once entered, STSPLUS saves the information in file STPLUS.LTD. The F6 command may be used to switch the display between Time Since Epoch ("T+Epoch") and Mission Elapsed Time ("MET"). The command description on the Main Menu indicates which mode will be selected if Function Key F6 is pressed: F6 Display MET & Launch Times (now 2-Line Epoch Times) F6 Display 2-Line Epoch Times (now MET & Launch Times) The first example (the default) indicates that MET will be displayed if the function key is pressed; the second example indicates that the display will return to Time Since Epoch if the function key is pressed. (The elapsed time option may also be switched at any time during the tracking display by pressing Function Key F5.) The F6 command checks that you have already entered the launch time and launch date or that it has been read from file STSPLUS.LTD. If no launch time and date are present, you will be prompted for the information as if you had pressed function key F5 (see above). The F6 command is inactive unless you have read in 2-line elements using function key F2. Program STSORBIT PLUS Satellite Orbit Simulation Page 74 F7 Set FILENAMES and PATHS ------------------------------ Function Key F7 allows the user to select the paths and/or filenames for the various files that STSPLUS uses to select satellites, tracking stations, and other features: Select path or filename to set, press ENTER when done: F1 Set 2-LINE ELEMENTS path: [F:\TLE\] F2 Set TRACKING STATION filename: [STSPLUS.TRK] F3 Set MAP DATABASE FILES path: [F:\STSPLUS\] F4 Set FEATURES LABEL filename: [F:\STSPLUS\STSPLUS.LOC] F5 Set TRAKSTAR path: [F:\STSPLUS\] Enter selection or ENTER: Press the indicated function key for the item you wish to change. The current path or filename is shown in square brackets for each selection. Press ENTER to leave a path or filename unchanged. The following is a typical prompt for filename: Enter TRACKING STATION filename: _ (Press ENTER to leave unchanged) For filenames, enter the full filename including filetype. If no filetype is entered, STSPLUS will automatically supply ".TRK" for tracking station files, and ".LOC" for features label files. If the desired file has no filetype, include the period in the filename entered (for example: "STATION.") to prevent the automatic addition of a filetype. For the path selections, enter the desired drive and subdirectory. The trailing backslash will automatically be added if it is omitted. If the path cannot be found, an error message will be displayed and the path will default to the current drive and directory. For best performance, use a RAM disk for Map Database Files; see the section "Using a RAM Disk" for further information. After each entry, the Path and Filenames Menu is again displayed with the current selections. Press ENTER when done to return to the STSPLUS Main Menu. F8 Set Program TIME and DATE -------------------------------- This menu provides a number of time and date functions for use with STSPLUS. The program clock may be set to real or simulated time using several methods, current clock corrections applied by program RIGHTIME may be displayed, and the UTC OFFSET and DAYLIGHT Flag may be adjusted. It is often convenient to set the TIME and DATE within STSPLUS to something other than the current system time and date, or to return to the current system time and date if the program time and date have been changed. Press F8 to go to the TIME and DATE Menu: Program STSORBIT PLUS Satellite Orbit Simulation Page 75 Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 14:52:24 PST 22:52:24 UTC Current date: 03/10/1993 03/10/1993 ACTUAL SYSTEM DATE AND TIME SHOWN ABOVE (Assisted by RIGHTIME) F1 Restore SYSTEM date and time (use "real time") F2 Set DOS SYSTEM CLOCK using calendar date and time F3 Set SIMULATED date and time using calendar date and time F4 Set SIMULATED date and time using Mission Elapsed Time F9 Display Current RIGHTIME Corrections F10 Set UTC OFFSET and DAYLIGHT Flag ENTER Return to MAIN MENU Select desired function: The Date and Time Menu, shown above, displays the available time setting functions along with the actual system date and time as determined by the DOS software clock in your computer (even if simulated time is in effect). If program RIGHTIME Version 2.5+ is currently enabled, the message "(Assisted by RIGHTIME)" will also appear. Both your local date and time, "PDT" or Pacific Daylight Time in the example, and "UTC" (Coordinated Universal Time) date and time are displayed. If times have been set using the letter "G", the abbreviation at the right will be "GMT" (Greenwich Mean Time). Press ENTER to return to the Main Menu with the date and time as displayed on the screen (Current or Simulated). If you wish to execute STSPLUS in "real time", cancelling any simulated time that may be in effect, use the F1 command. This will restore the time and date used for the tracking display to that shown at the top of the menu. If the actual system date or time displayed is incorrect, use program TIMESET (if available) or the F2 command to correctly set your system clock. Some organizations, NASA for example, continue to use the wording "Greenwich Mean Time" or "GMT" for what is now usually referred to as "Coordinated Universal Time" or "UTC" (and sometimes, depending upon the application, as "UT", "UT1" or "UT2"). STSPLUS uses Coordinated Universal Time or "UTC", the time used for civil timekeeping and broadcast by radio stations such as WWV and the BBC. Although technically these different time standards are not exactly the same, the difference is only a maximum of 0.9 seconds and the program treats them all as identical. STSPLUS defaults to the abbreviation "UTC" but if you prefer to use "GMT", enter any simulated time using F3 and include the letter "G" (upper or lower case) at the end. The time abbreviation at the top of the screen will change from "UTC" to "GMT" and will continue using that abbreviation until a time is entered suffixed with "U". Times are always entered as "HH:MM:SS" where HH is HOURS, MM is Program STSORBIT PLUS Satellite Orbit Simulation Page 76 MINUTES, and SS is SECONDS. The time entry format is very flexible. Leading zeroes are not required. The comma (",") may be used in place of the colon (":") as a separator if desired. SECONDS or MINUTES and SECONDS may be omitted if desired. Time entries are assumed to be local time; to enter UTC or GMT times, add the letter "U" or "G" (upper or lower case) respectively following the entry. For example, the following are valid time entries: Entry Interpreted as ------ -------------------------- 12 12:00:00 (LOCAL TIME ZONE) 13,1 13:01:00 (LOCAL TIME ZONE) 4:1:15 04:01:15 (LOCAL TIME ZONE) 1,1,1 01:01:01 (LOCAL TIME ZONE) 13,45U 13:45:00 UTC 1:20g 01:20:00 GMT Dates are entered as "MM/DD/YYYY" or "MM/DD/YY" where MM is MONTHS (as a number from 1 to 12), DD is DAYS, and YYYY is the full four-digit YEAR or YY is the last two digits of the YEAR. Except for the two digit year option, the full date must always be entered; leading zeroes are not required. The date entered is assumed to be for the same time zone as the time entered. If local time is entered, the date will be treated as the local date; if UTC (or GMT) time is entered, the date will be treated as the UTC/GMT date. After a time or date entry has been accepted (after you press the ENTER key), STSPLUS reformats the entry to its standard format, clears the characters you entered, and replaces them by the standard format in both local and UTC/GMT time zones. This provides a double check that the program has interpreted your entry as you wished. F1 Restore System Date and Time ----------------------------------- Press F1 to restore the program date and time to the system date and time. This command reads the DOS clock and restores the program to "real time" operation. If the program date and time have not been changed with the F3 or F4 commands, this command will have no effect. F2 Set DOS System Clock --------------------------- Press F2 to set the DOS system clock. Use this command if you wish to change the actual date and time on your system. Note that on many systems using DOS 3.3 or higher, this command will set BOTH the software clock AND the hardware clock. ************* * CAUTION * ************* This function should NOT be used when program RIGHTIME is regulating the DOS clocks UNLESS no other method is available. Use program TIMESET to set the DOS clocks accurately instead! Program STSORBIT PLUS Satellite Orbit Simulation Page 77 Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 19:59:10 PST 03:59:10 UTC Current date: 02/24/1993 02/25/1993 CAUTION: This function will change the computer's SYSTEM CLOCK! Press ENTER to leave an item unchanged Enter TIME (HH:MM:SS): 16:34:24 PST Enter DATE (MM/DD/YYYY): 4/08/1992 Press ENTER to accept, SPACE BAR to repeat: _ The sample above shows the screen after the time and date entries have been completed. The current ACTUAL system date and time are displayed for approval. Press ENTER to accept the time and date displayed, or press the SPACE BAR to repeat the entries. F3 Set Simulated Date and Time using Calendar Method -------------------------------------------------------- Press F3 to set a simulated date and time. The date and time may be either in the past or in the future. This command does NOT affect the DOS clock in your system! Use the F1 command above to restore the date and time to "real time". Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 19:59:10 PST 03:59:10 UTC Current date: 02/24/1993 02/25/1993 Press ENTER to leave an item unchanged Enter SIMULATED TIME [12:05:06]: 13:00:00 PST 21:00:00 UTC Enter SIMULATED DATE [11/11/1991]: 11/09/1991 11/09/1991 Press ENTER to accept, SPACE BAR to repeat: _ The sample above shows the screen after the time and date entries have been completed. The new SIMULATED date and time are displayed (and counting) for approval. Press ENTER to accept the time and date displayed, or press the SPACE BAR to repeat the entries. Program STSORBIT PLUS Satellite Orbit Simulation Page 78 F4 Set Simulated Date and Time using MET -------------------------------------------- Press F4 to set a simulated date and time using MET (Mission Elapsed Time). Note that this command will appear ONLY if the mission name begins with the letters "STS", signifying a Space Transportation System (Space Shuttle) mission AND if a launch time and date have previously been entered. Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Simulated time: 00:17:18 PST 08:17:18 UTC Simulated date: 10/09/1992 10/09/1992 Enter desired Mission Elapsed Time (MET) Enter MET DAY (NN): 3 day(s) Enter MET TIME (HH:MM:SS): 04:30:00 MET Press ENTER to accept, SPACE BAR to repeat: _ The sample above shows the screen after the day and time entries have been completed. The Mission Elapsed Time is immediately converted to actual date and time and the current SIMULATED date and time, based upon the MET just entered, are then displayed (and counting) for approval. Press ENTER to accept the time and date displayed, or press the SPACE BAR to repeat the entries. F9 Display Current RIGHTIME Corrections ------------------------------------------- If program RIGHTIME has been detected, the "F9" menu item will be displayed and you may press F9 to display the time since the last TIMESET, the current WARM correction, and the current COOL correction: RighTime Version 2.53 detected! Time Since Last TIMESET: 0 days 08:58:20 Current WARM Correction: -0.01 seconds Current COOL Correction: -0.35 seconds Press any key to continue ... _ The version of RIGHTIME is displayed. The time since the last TIMESET is saved by program RIGHTIME to the nearest 200 seconds and will therefore not change until that increment is reached. The time is shown as days followed by hours:minutes:seconds. If more than 7 days has elapsed since the last TIMESET, an additional message "(TIMESET suggested!)" will also appear. The Program STSORBIT PLUS Satellite Orbit Simulation Page 79 WARM and COOL corrections are shown and are updated when the system time is set using Function Key F1 from this menu, by program TIMESET, or by other means. Press any key, such as ENTER, to return to the Time and Date Menu. F10 Set UTC OFFSET and DAYLIGHT Flag --------------------------------------- You may change the UTC Offset and/or the setting of the Daylight Flag using F10. The prompts are self-explanatory; see the section "Program Options and Features, Set UTC Offset and Daylight Flag" for a detailed description of the UTC Offset and Daylight flag. F9 DOS Shell (CAUTION: DOS Version 3.x+ ONLY!) ------------------------------------------------- If a system function is desired at the Main Menu, press F9 to execute BASIC's DOS SHELL function. This will return you to a DOS prompt and most DOS commands may be executed immediately. When the Shell is executed, STSPLUS remains in memory and the map data will not be re-read when you return. However, this means that a substantial amount of memory is in use and not available to DOS during the shell operations. Enter "EXIT" (without the quotation marks and followed by ENTER) at the DOS prompt when you wish to return to STSORBIT. CAUTION: The BASIC SHELL function is only reliable for versions of DOS of 3.0 or higher! Systems with less than 640K memory may fail to execute the shell and applications requiring large amounts of memory may also fail. F10 Set STSORBIT PLUS Program Options and Features ----------------------------------------------------- A number of program features and display options are set using the F10 Program Options Menu. These selections are further described in the section "Program Options Menu" below. ENTER Resume Mission --------------------- Pressing ENTER resumes the current mission shown in parentheses to the right of the command on the Main Menu. The 2-line elements file from which the data was read is shown in square brackets. ENTER Resume Mission (STS-41 [STS41F]) Any manually entered data is retained. "ENTER" means the key marked ENTER, RETURN, or with a left pointing arrow -- but not the backspace or cursor position keys which may also be marked with arrows! (I am afflicted with too long a memory; once upon a time this function was known as Carriage Return and was often shortened to RETURN or even CR. With the advent of electronic typewriters, video terminals, dot matrix printers and all the rest, "carriages" have long since disappeared but old habits die hard! Most PC keyboards are now marked with "ENTER".) Use ENTER to resume plotting a mission in progress after returning to Program STSORBIT PLUS Satellite Orbit Simulation Page 80 the Main Menu to perform some change (such as enabling the node display, enabling the NASA tracking stations, or adjusting the time or date). ESC Quit STSORBIT PLUS and Save Current Mission -------------------------------------------------- Press ESC (the key marked "ESC" or "Esc", not the letters E+S+C) to quit program STSORBIT PLUS. If you press ESC to quit the program and have manually entered orbital data, STSPLUS will save all required mission data in file STSPLUS.INI prior to terminating. This will be the data available with the ENTER key the next time you execute the program. The demonstration data will not be saved, preserving any previously saved mission data. When you have finished with STSPLUS, press ESC at the Main Menu to return to DOS. The data (and any adjustments you have made) for the current mission are saved in file STSPLUS.INI, but the map data is lost and will be re-read when you next use program STSPLUS. Program STSORBIT PLUS Satellite Orbit Simulation Page 81 PROGRAM OPTIONS AND FEATURES MENU --------------------------------- A number of program features and display options are set using the F10 Program Options Menu. When used with CGA displays, the features shown below as selected by function keys F3 and F4 are not available because of the low resolution of the CGA display. The following Options Menu is displayed when the F10 command is entered from the Main Menu: Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 19:59:10 PST 03:59:10 UTC Current date: 02/24/1993 02/25/1993 F1 Program STSORBIT PLUS Information F2 Set New Local Coordinates (Rancho Palos Verdes, CA) F3 Select Display Features F4 A/A Select Satellite Coordinates: RA/DEC, Alt/Az or XYZ F5 OFF Show Ascending & Descending Node Data F6 ORTHO Set Map Projection and Size F7 OFF Enable/Disable EVENT TIMERS F8 ON Enable/Disable Audible ALARMS F9 -7.00 Set UTC Time Offset and Daylight Flag F10 OFF Enable/Disable Printer Logging ENTER Return to MAIN MENU Select desired function: F1 Program STSORBIT PLUS Information ---------------------------------------- Function Key F1 displays information about program STSORBIT PLUS including the copyright notice, version number, my name and address, and the telephone number of my RPV ASTRONOMY BBS (Bulletin Board System). The current version of STSORBIT PLUS is always posted on the BBS. The BBS has a power controller; if it hasn't answered after the THIRD RING, hang up and call back in two minutes. The BBS is available 24 hours per day at 9600, 2400 and 1200 baud. F2 Set New Local Coordinates -------------------------------- In order to perform the calculations related to satellite visibility and altitude/azimuth, STSPLUS must know the geographic coordinates for the user's location. The name of the current location is shown in parentheses. When STSPLUS is first started, the default coordinates are set to Rancho Palos Verdes, California, near Los Angeles. The current location is Program STSORBIT PLUS Satellite Orbit Simulation Page 82 indicated by the name in parentheses on the Options Menu. The program provides two methods for setting your own coordinates: reading a file of city names and coordinates (STSPLUS.CTY); or manually entering the information. Pressing F2 will display the following reminder: STSPLUS searchs STSPLUS.CTY for the CITYNAME you enter anywhere in the city names. 'SAN' appears in 'SAN DIEGO', 'SANTA ANA', 'THOUSAND OAKS. Press ENTER to delete SECOND LOCATION, or enter '*' to manually enter a city name and coordinates (and optionally add it to STSPLUS.CTY). In other words, when you enter a name or partial name, STSPLUS will attempt to match that group of characters anywhere in the names which appear in the city file. For example, 'SAN' matches 'SAN diego' as well as 'SAN jose' and 'thouSANd oaks'. To get 'SAN FRANCISCO' on the first try, enter 'SAN F' with a space between the 'N' and 'F'. Case is not significant; upper and lower case letters are treated identically. If you change your mind and wish to cancel the operation, simply press ENTER by itself. Use BACKSPACE to make corrections. To begin the search, enter the desired name after the prompt. In the example which follows, the name 'ran' was entered for the search. Enter CITYNAME to match: ran Processing record 1 City Name: Rancho Palos Verdes CA Latitude: 33.7675 Longitude: -118.4033 Elevation: 186 meters Press ENTER to ACCEPT this city as your location, OR Press TAB to also display this city's location, OR Press SPACE to search for next city: _ If the city displayed is the one you wish to use as your local coordinates, press ENTER. If you wish to display this city as a second location on the display, press TAB. The data will be entered into STSPLUS and subsequently saved in file STSPLUS.INI. If you wish to search further in the file, press the SPACE BAR. NOTE: The elevations contained in file STSPLUS.CTY are almost all zero except for Rancho Palos Verdes, CA for which I have accurate elevation above mean sea level. If you know the correct elevation for your location, edit the file using any ASCII text editor and change the last number on the line. STSPLUS.CTY contains over 800 cities. If users send me their correct elevations (or additional cities they wish added), I will incorporate that data into subsequent versions of file STSPLUS.CTY. To enter location data manually, press "*" (without the quotation marks) followed by ENTER. You will be prompted for the city name, latitude, longitude, and elevation. Latitude and longitude may be entered using three different formats for convenience (note the use of comma and decimal point): Program STSORBIT PLUS Satellite Orbit Simulation Page 83 DDD.DDDDD Degrees and decimal fraction DD,MM.MMM Degrees, minutes and decimal fraction DD,MM,SS.SS Degrees, minutes, seconds and fraction Note that SOUTH latitude and WEST longitude must be entered as NEGATIVE numbers as measured south of the Equator or west of the Prime Meridian at Greenwich, respectively. The default unit for elevations is meters above mean sea level; add "F" (upper or lower case without the quotation marks) if you wish to use feet. After the elevation has been entered, the data will be displayed for approval. All data are converted to degrees or meters as appropriate, regardless of the units used on input. City Name: Rancho Palos Verdes CA Latitude: 33.7675 Longitude: -118.4033 Elevation: 186 meters Press ENTER to ACCEPT this city, OR Press SPACE to cancel this data: _ Press ENTER to accept the data as shown or SPACE to cancel the data and return to the Options Menu. If the data is accepted, STSPLUS will ask if you wish to append (add) this city/location to the existing file STSORBIT.CTY so that it will be automatically available thereafter. Do you with to append this data to file STSPLUS.CTY (Y/n): _ Press "Y" or ENTER to append the data to the file, or press "N" to not modify the STSPLUS.CTY file. F3 Set Display Features --------------------------- A number of display features may be enabled or disabled using a separate sub-menu. See the section SET DISPLAY FEATURES below for a full description. F4 Select Satellite Coordinates ----------------------------------- The F4 command may be used to select the units used to display the current coordinates for the satellite. The choices are: RA/DEC Right Ascension and Declination (Equator and Equinox of Date). Alt/Az Altitude and Azimuth. Altitude is the elevation above the horizon (assuming mean sea level), and azimuth is the direction in the sense NESW (North to East to South to West). Program STSORBIT PLUS Satellite Orbit Simulation Page 84 XYZ Geocentric Cartesion Coordinates. The X-Axis and Y-Axis are aligned with the Equator with the X-Axis pointing in the direction of the Vernal Equinox. The Z-Axis points toward the North Pole. F5 Show Ascending & Descending Node Data -------------------------------------------- The nodes of an Earth orbit are the points on the ground track where the path crosses the Equator. The ascending node crosses from South to North and the descending node crosses from North to South. Orbit numbers normally increment at the ascending node. This command adds two additional lines of data at the lower left of the screen giving the time (MET or time since epoch) and longitude of the most recent ascending and descending nodes. This information is useful when comparing STSPLUS's data against other sources such as the wall map in Mission Control. F6 Set Map Projection and Size ---------------------------------- The F6 command selects the size and field of view of the displayed map. By default, the map is displayed using the orthographic projection, "ORTHO", shows one complete hemisphere, and is centered so that the selected satellite is visible. This corresponds to a magnification factor of 100%. Pressing F6 will select between WORLD, QUAD, ZOOM, and ORTHO maps. Selecting WORLD will display the full world using rectangular projection centered on the Prime Meridian at Greenwich, England at 0 degrees longitude or at the International Date Line at 180 degrees longitude. Selecting QUAD will select one of twelve Quadrant Maps showing a field of view (horizontal size) of 180 degrees using rectangular projection. Selecting ZOOM will select a Zoom Map with field of view adjustable from 45 degrees to 180 degrees; the default field of view is 75 degrees; the Zoom Map is approximately centered on the current ground track position of the satellite. Selecting ORTHO will select the orthographic projection. See the sections ORTHOGRAPHIC MAPS, QUADRANT MAPS, ZOOM MAPS, and AUTOMATIC MAP GENERATION for additional information. F7 Enable/Disable EVENT TIMERS ---------------------------------- Press F7 to enable or disable all event timers. Event timers are enabled by default if file STSPLUS.INI is present. Especially while the map is being drawn, the calculations associated with the event times require appreciable time. If the event timers are disabled, the audible alarms will also be disabled. See the section "Event Timers and Audible Alarms" for a full discussion of the event timers. Program STSORBIT PLUS Satellite Orbit Simulation Page 85 F8 Enable/Disable Audible ALARMS ------------------------------------ Provided event timers are enabled (above), you may press F8 to enable or disable audible alarms. Many users allow their computer to run STSPLUS while performing other tasks and the audible alarm will alert them to an imminent AOS (Acquisition of Signal) or LOS (Loss of Signal) event associated with either their local circle of visibility or the TDRS communications satellites. For the local circle of visibility, an "up/down" tone sounds six times two minutes prior to AOS and five tones sound thirty seconds prior to LOS. Provided TDRS coverage is enabled (F10+F3+F2 from the Main Menu), three brief tones sound thirty seconds prior to AOS or LOS. Provided Sun features are enabled (F10+F3+F8), two tones will sound approximately thirty seconds before orbital sunrise and sunset. The characteristics of the audible tones will thus allow the user to identify what kind of AOS or LOS event is about to happen. Depending upon the computer and the version of DOS being used, "music" such as these audible alarms may cause the DOS clock to lose a small amount of time each time an alarm sounds. The amount of time loss is quite small but may accumulate over long periods of time. (The DOS clock may also run either fast or slow and effectively mask the time loss due to sound effects.) F9 Set UTC Time Offset and Daylight Flag -------------------------------------------- STSPLUS uses UTC or Coordinated Universal Time, an adjusted version of Universal Time (which STSPLUS considers the same as GMT or Greenwich Mean Time), for certain functions such as launch time. The difference between UT, UT1, UT2 and UTC is never more than 0.9 seconds. UTC is used because it is the standard for civil timekeeping and agrees with standard atomic time, TDB or Terrestrial Barycentric Time, used by astronomers. However, NASA continues to use the GMT designation, a holdover from earlier days before the introduction of UTC. Using UTC permits critical data to be used across many time zones without conversion. However, it also means that STSORBIT must know what number of hours to add to UTC in order to obtain your local time, and whether or not you are currently using daylight savings time (summer time in the UK). When prompted, enter the time offset in hours from your local time to Coordinated Universal Time. Examples are shown for most time zones in North America. STSPLUS then asks if you are using daylight savings time; enter "0" if not, and "1" if so. The sum of these two values is shown on the Main Menu; for example, if the computer is set to Pacific Daylight Time (UTC offset is -8.00 hours and Daylight Flag = 1), the sum will be -7.00. For most time zones in North America, the correct zone abbreviation will be shown on the ground track display for Local date and time. When you change your computer from/to daylight savings time, use this command to update STSPLUS. The following shows the display when using the F9 command: Set UTC TIME ZONE OFFSET and DAYLIGHT FLAG STSPLUS must know the difference between your local time zone and Program STSORBIT PLUS Satellite Orbit Simulation Page 86 Coordinated Universal Time (UTC), also sometimes known as Greenwich Mean Time (GMT). With this information, STSPLUS can automatically adjust launch or Epoch times and dates for your local time zone. In addition, STSPLUS must know if your computer is now set to STANDARD or DAYLIGHT time. First, enter the difference between your STANDARD time zone and UTC in hours. Do NOT include the hour for daylight time if you are now on DAYLIGHT time; it will be entered separately. For most time zones in the United States and Canada, the entries required are: Eastern Standard Time EST -5.0 Central Standard Time CST -6.0 Mountain Standard Time MST -7.0 Pacific Standard Time PST -8.0 Enter UTC Offset (hours): -8 Enter DAYLIGHT Flag (0=OFF, 1=ON): 1 Once this information has been entered, it will be saved in file STSPLUS.INI and will not be requested again. If you change from Standard to Daylight Time or vice versa, use the F10+F9 command to update the Daylight Flag. If you change the setting of the Daylight Flag, STSPLUS will ask if you wish to adjust your DOS software clock: You have changed the setting of the Daylight Flag. Do you wish to adjust your DOS clock to reflect the change [y/N]: If you have already made the change at the DOS prompt (or using some other software) or do not wish to change the DOS clock, press ENTER (or type "N" followed by ENTER). If you wish to adjust the DOS clock to correspond to the new setting of the Daylight Flag, press "Y" followed by ENTER. When STSPLUS changes the DOS clock, it synchronizes the time change to the nearest second but there may be a small error introduced; only if your computer is precisely set would the error be detectable. ************* * CAUTION * ************* For computers equipped with 80286 or higher processors AND using DOS 3.2 or higher, changing the DOS clock will ALSO change the hardware clock. 8088- based computers may or may not have a hardware clock installed and, even if a hardware clock is present, it may or may not be compatible with the DOS time setting commands. F10 Enable/Disable Printer Logging ------------------------------------- I have found it interesting to log the orbital data and the ascending and descending node information on my printer when analyzing the mission data over long periods of time. The F10 command toggles the printer logging function on and off. The first page of the log includes the current orbital Program STSORBIT PLUS Satellite Orbit Simulation Page 87 data and subsequent pages contain only node information. In addition to the information presented on the display, the printer log also calculates the current orbital time, the time from one ascending (descending) node to the next, for the third and subsequent nodes. A typical log is shown below. IMPORTANT: BE SURE THE PRINTER IS TURNED ON PRIOR TO ENTERING THE F10 COMMAND. STSORBIT: Space Shuttle Tracking Program, Version 9311 Page 1 ORBITAL DATA for STS-31 Discovery/HST NORAD Number: 20580 Launch Date: 04/24/1990 Launch Time: 05:33:52 Orbit Inclination: 28.4695 Orbit Altitude: 329.50 nm Adjust Longitude: 9.80 Adjust Orbit Time: 8.40 min ORBIT UT DATE UT TIME ORBIT LONG MET TIME Ascend Node: 04/28/1990 20:32:52 70 -69.95 4/14:58:07 Dscend Node: 04/28/1990 21:20:52 70 97.64 4/15:46:35 Ascend Node: 04/28/1990 22:09:52 71 -94.77 4/16:35:02 1:36:55 When printer logging is enabled and the ground track is displayed, the word "LOG" will appear in red at the right of the text area. Enabling printer logging also automatically enagles the display of ascending and descending node information. When a printer log is prepared for a satellite using 2-line elements, the Adjust Longitude and Adjust Orbit Time entries will not be shown in the header data. The Launch Date and Launch Time entries are given if that information has been entered indepentently. The Epoch Date and Epoch Time are always shown for 2-line element simulations. Note also that the orbit altitude shown is the altitude at the time the log was started and will not be correct for subsequent entries, especially if the satellite has an elliptical orbit (high eccentricity). A printer log may be prepared in advance of a mission by enabling printer logging from the Set Options Menu (with the F10+F10 command), setting the desired simulation time (F8+F3 command), then starting the ground track display with ENTER; once the ground track has appeared on the screen, pressing the F key twice to set STSPLUS in the X60 fast time mode will generate the date relatively quickly (although the UT TIME printed may be off by as much as one minute in the X60 mode). Allow the simulation to run for the desired length of time, then press ENTER to return to the Main Menu. While the ground track is active Function Key F3 performs the same function as the F10+F10 command to enable or disable printer logging. Program STSORBIT PLUS Satellite Orbit Simulation Page 88 SET DISPLAY FEATURES -------------------- Depending upon the satellite and personal preferences, a variety of display features may be enabled or disabled. Not all features are available with monochrome or CGA monitors. Pressing F3 on the Set Program Options and Features Menu will display the following menu: Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9311 Current time: 19:59:10 PST 03:59:10 UTC Current date: 02/24/1993 02/25/1993 F1 ON Display LOCAL Circles of Visibility F2 ON Display TDRS Coverage F3 ON Display Additional Map Grid Lines F4 OFF Display Tracking Stations F5 BOTH Display Ground Track: DOTS/LINE F6 ON Display Spacecraft Circle of Visibility F7 OFF Display South Atlantic Anomaly Zone F8 ON Display Terminator, SUN, and Spacecraft Lighting F9 ON Display Map Locations and Features F10 ON Display Lakes and Rivers ENTER Return to MAIN MENU Select desired function: F1 Display LOCAL Circles of Visibility ------------------------------------------ Function Key F1 enables and disables the local circles of visibility, centered on your location and a second location (if enabled), and shows the approximate area within which direct line of sight communication with the satellite is possible. The circle is calculated at the instant the map is drawn and may not be accurate over long periods of time for satellites with highly eccentric orbits. In some situations (geosynchronous satellites, for example), these circles of visibility cover so large an area that they simply confuse and clutter the display. Use this command to disable the circles. F2 Display TDRS Coverage ---------------------------- This command will display the communications coverage for the Tracking and Data Relay Satellites (TDRS) EAST and WEST. The coverage boundaries overlap between the East and West TDRS satellites and Mission Control may select either satellite during the overlap period. STSPLUS Program STSORBIT PLUS Satellite Orbit Simulation Page 89 displays the areas covered by each satellite and the times for acquisition and loss of signal (AOS and LOS). See the section "TDRS Satellite Features" above for a full discussion of the TDRS coverage features. F3 Display Additional Map Grid Lines ---------------------------------------- This command is not available for CGA systems. The basic world map includes the Equator and the meridians at 0 degrees (Prime Meridian) and 108 degrees (International Date Line) shown in bright blue on color monitors. Turning on the map grid adds additional lines of longitude and latitude. Displaying the additional grid lines on some monochrome monitors, especially CGA, may make the screen too "busy". In the Orthographic, Quadrant and Zoom Map modes, the spacing of the additional grid lines is adjusted for the map field of view. In rectangular map modes (EGA and VGA systems only), each grid line is labeled at the left or bottom of the display screen. F4 Display Tracking Stations -------------------------------- The F4 command enables/disables the display of the tracking stations included in file STSPLUS.TRK or the current TRACKING STATION filename as set by Function Key F7 on the Main Menu. If that file is not found, internal data are used for NASA's 14 original ground tracking stations plus the NASA Ground Terminal at White Sands, NM. Each tracking station is located with a small red circle. The circle of visibility is also shown if that circle has an angular diameter of 90 degrees or less. The circles of visibility are calculated at the instant the map is drawn and may not be accurate over long periods of time for satellites with highly eccentric orbits. For all map modes EXCEPT the World Maps, each tracking station is also labeled with its 3-character abbreviation. This command is not available for CGA monitors. F5 Display Ground Track: DOTS/LINE -------------------------------------- STSPLUS calculates the ground track for the satellite for a period from one and one half hours in the past to three hours in the future. Press F5 to change from one mode to the next. Depending upon the user's preferences, this function may be used to set the displayed ground track to any of the following modes: NONE The ground track is not displayed. DOTS The ground track is displayed using RED dots for the past ground track and GREEN dots for the future ground track. The dots are spaced at one minute intervals. As time passes, the GREEN dots will change to RED. LINE The ground grack is displayed using a GREEN line. Program STSORBIT PLUS Satellite Orbit Simulation Page 90 BOTH The ground track is displayed using a GREEN line with RED dots for past ground track minute marks and YELLOW dots for future ground track minute marks. As time passes, the YELLOW dots will change to RED. F5 Display Spacecraft Circle of Visibility ---------------------------------------------- STSPLUS can calculate the approximate circle of visibility from the spacecraft, the area of the Earth's surface which is visible from the cockpit windows and television cameras or, for unmanned spacecraft, the direct line of sight visibility from the ground. Note that the shape of the "circle" varies depending upon the magnification or zoom factor and map projection being used. With rectangular projection, the shape is approximately a circle near the Equator and more like a rounded triangle at higher latitudes; near the poles, the "circle" spreads out across the map. This is an artifact of the rectangular map projection. When enabled, the circle of visibility is recalculated every 10 seconds based upon the spacecraft's current altitude. This means that orbits with a high eccentricity (that is, a highly elliptical orbit whose apogee and perigee are very different) will exhibit a constantly changing circle of visibility. F7 Display South Atlantic Anomoly Zone ------------------------------------------ The South Atlantic Anamoly (SAA) is an area in the southern hemisphere lying between southern tip of Africa and South America which can cause severe electromagnetic disturbances on spacecraft. For example, the semiconductor memory on the Hubble Space Telescope (which regularly passes through the SAA) was being changed by this phenomenon until a patch was uplinked to work around the problem. The area is shown on the ground track as an ellipse for simplicity; its actual outline is more nearly shaped like a kidney bean. Using NASA Mission Charts for various Space Shuttle missions as a reference, the SAA is adjusted for spacecraft altitudes from 160 nm to 350 nm (although it extends out to geosynchronous orbits). SAA coverage is disabled in orthographic modes pending better data and the development of a mathematical model for use in those modes. F8 Display Terminator, Sun, and SpaceCraft Lighting ------------------------------------------------------- This function enables and disables the Sun and related solar features. See the section "Sun and Solar Features" for a full discussion. STSPLUS calculates whether the spacecraft is in full sun, penumbra (partial shadow) or refracted sunlight, or umbra (full shadow) and adjusts the color of the spacecraft icon accordingly: bright white, yellow, and dim white respectively. This feature is not available on CGA and HGC monitors. The current spacecraft solar lighting is indicated in the data block (next to "Orbit #:") by the following symbols: Program STSORBIT PLUS Satellite Orbit Simulation Page 91 * Full sunlight + Partial sunlight (penumbra) - Refracted sunlight Full shadow (umbra) F9 Display Map Locations and Features ----------------------------------------- This feature enables or disables the display of the map locations and features contained in file STSPLUS.LOC if present. See the section "Location and Features Labels" above for a full discussion. F10 Display Lakes and Rivers ------------------------------- This feature enables or disables the display of lakes and rivers on the map. Removing the lakes and rivers will lessen the time required to draw a map and can improve screen legibility especially for CGA systems. (The lakes and rivers are always disabled on the rectangular world map to avoid cluttering an already busy display!) Program STSORBIT PLUS Satellite Orbit Simulation Page 92 STSORBIT PLUS's Orbital Model ----------------------------- The original version of STSORBIT was first prepared without reference materials of any kind and the simplest possible orbital model was therefore selected. The primary objective was to duplicate the NASA wall map at the Mission Control Center in Houston, Texas. This "simple" model assumed that the orbit was perfectly circular at a specified altitude and inclination which never degraded due to other factors such as drag or perturbation. Some simplifying assumptions were incorporated to handle the initial ascent portion of a mission and the launch site was hard coded to Cape Canaveral, Florida. With only minor modifications, the program was essentially unchanged for the next year. The launch of STS-31 and the Hubble Space Telescope highlighted the need for improved accuracy because of public interest and the length of the mission. The orbital calculations were modified (STSORBIT Version 9015) to include the J2 factor, the perturbation of low Earth orbits due to variations in the gravitational field related to the non-spherical shape of the Earth (among other factors); omission of the J2 factor caused errors in longitude of approximately -5 to -7 degrees per day. That is, the orbital track drifted Westward from its true position by that amount. More accurate models of low orbits also include the J3 and J4 perturbation factors, atmospheric drag, and a host of other less significant items. Although reasonably accurate for the first day or so of a space shuttle mission, the "simple" model is by no means ideal. In calculating the current orbital longitude, for example, the "simple" model assumes a circular orbit. For orbits with low inclinations, as is typical for launches from Kennedy Space Center, the errors are not particularly significant and are probably overshadowed by the fundamental uncertainties in orbital parameters and by the limitations imposed by display resolution. Orbits with higher inclinations, as would be the case if near-polar launches from Vandenburg AFB in California are ever initiated, would have much larger periodic errors which would be both noticeable and objectionable. More important for longer missions and for general satellite tracking is the fact that due to the method used, errors in the orbital calculations tend to be cumulative. After a day or two, the errors become unacceptably large. The real problem with the simple method, of course, is that the Earth is not a perfect sphere and actual satellite orbits are never perfectly circular. Satellite orbits are significantly perturbed by the non-spherical gravitational field of the Earth, by the Sun and Moon, atmospheric drag, and other factors. Accurate satellite tracking over longer periods of time therefore demands more accurate data and a more rigorous treatment of satellite orbits. The only practical alternative is to use the NASA/NORAD 2-line orbital element sets. Not only are these data readily available publicly, but they are relatively accurate and are updated regularly. Therefore, STSORBIT PLUS relies on the NORAD SGP4 prediction model and the 2-line orbital element sets for orbit predictions. 2-line element sets for non-military space shuttle missions are typically available on the same day as the launch. Amateur astronomers and satellite tracking experts often generate "unofficial" 2-line element sets even for military missions. Six quantities are required by classical gravitational theory to completely characterize the orbit of one body about another in time and space, the "Two Body Problem". These six quantities, often referred to as Keplerian orbital elements, are included in the NASA/NORAD 2-line element Program STSORBIT PLUS Satellite Orbit Simulation Page 93 sets along with other numerical and statistical data. The U.S Space Command, (formerly NORAD, the North American Air Defense Command) headquartered in Cheyenne Mountain, Colorado, developed the SGP4 and SDP4 orbital models and the 2-line element format many years ago as part of their satellite tracking efforts and NASA subsequently adopted the same format -- more or less. NASA and NORAD do not always use the same definition for revolution (orbit) numbers; NASA frequently gives a number one (or two) greater than NORAD, calling the first partial orbit number one while NORAD calls that same partial orbit number zero. Except for short duration missions, such as the Space Shuttle, revolution numbers are of no practical importance. Having timely and accurate orbital data is of little help without a computer model or program which can use those data. NORAD has rather arbitrarily divided satellite orbits into two categories: near Earth orbits and deep space orbits. Near Earth orbits are defined as those with orbital periods of 225 minutes or less and deep space orbits are all others. Computer models are described in the literature for each category. STSORBIT PLUS employs the SGP4 Near Earth Model only, using a composite of code of my own combined with translated Fortran and Basic source supplied by Paul Traufler and C source by Paul Hirose. I plan to add the SDP4 deep space model in early 1993. Not only are the near Earth orbits generally of more interest to observers, but the errors associated with deep space orbits processed with the SGP4 model (rather than the correct SDP4 model) are not particularly significant for the purposes of a program such as STSORBIT PLUS. Further, watching a geostationary satellite orbit on the screen is not unlike watching grass grow and is about as exciting. Program STSORBIT PLUS Satellite Orbit Simulation Page 94 Accurate Time and the Personal Computer --------------------------------------- For a program like STSPLUS, accuracy and precision of the timekeeping functions are essential. There is a tendency these days to accept whatever a computer says as the absolute truth without regard for whether or not the information is even "reasonable". For something as basic as time, even an experienced computer user may assume that it is correct. This discussion attempts to compare reality with that expectation. Given the clock drift and accuracy problems inherent in the design of the typical IBM-compatible personal computer, frequent time setting and/or adjustments are required. Accurate time setting would not be practical for most people without the various time services provided by the National Institute of Standards and Technology (NIST) and the U.S. Naval Observatory (USNO). The NIST radio stations WWV and WWVH provide an inexpensive and convenient means for "ordinary folks" to synchronize clocks and other equipment. The NIST and USNO Telephone Time Services offer a high precision standard time calibration source when such accuracy is required. Similar radio and telephone services are available in Candad and Europe. Once a computer clock has been set with reasonable accuracy, the accuracy of the computer's clock will indeed be sufficient for many applications; if you are using a word processing or spreadsheet program, knowing the time to within a minute or two is probably adequate. For programs such as STSPLUS and other time-dependent applications, however, this level of accuracy simply will not suffice; when used for satellite tracking, the time should be accurate to within a second. Unless steps are taken to both set the clock and to maintain its accuracy, this will not be the case. No matter how accurately the clock on a typical personal computer is set, it will only be a matter of hours before the time will have drifted by some seconds. Measured over a number of days, the accumulated errors can easily amount to a minute or more. The timekeeping operations of an IBM-compatible computer are actually performed by two separate and independent functions: a clock-calendar CMOS integrated circuit and lithium battery combination which maintains the current time and date in hardware; and, a section of the DOS operating system software which maintains the current time and date in software. When computer power is off, the hardware chip continues to operate using its battery; when the computer is started ("booted"), the operating system software reads the hardware clock and sets its internal software clock. Absent special software, the DOS time thereafter relies entirely on the software clock until the next time the computer is restarted. Unfortunately, neither of these clocks was designed for accuracy; early versions of the PC did not even include the hardware/battery arrangement. Even the typical electric clock, which uses the power line frequency for its timekeeping reference, is usually far more accurate. The accuracy of the DOS time at any instant is the result of the accumulated errors in both clocks. The hardware clock will drift as a function of time, temperature, voltage, and crystal aging; the software clock will gain or lose time depending upon the skill with which its software was written and how well that software "cooperates" with the balance of the computer's hardware and software. Some software, especially network and high speed communications software, can prevent the DOS clock software from incrementing when it should, usually resulting in the DOS clock losing time. The problem was compounded with the release of DOS Version 3.3; beginning with that version, the DOS TIME and DATE commands Program STSORBIT PLUS Satellite Orbit Simulation Page 95 adjust BOTH the hardware and software clocks and thereby potentially eliminate the hardware clock as even a modestly reliable reference. Methods for Setting DOS Time ---------------------------- Bearing these considerations in mind, there are a number of approaches to the DOS time question. The most obvious approach, used by the vast majority of computer users, is to either ignore the computer clock entirely or to say "It's close enough". Regardless of the application, I strongly recommend that the DOS clock be REGULARLY set to the correct time if only to assure that files are more or less correctly date and time stamped. If the accuracy of DOS time is important, the computer clock may be set or synchronized in a number of ways, some of which are described below. In this context, "ACCURACY" means the accuracy of the time setting operation and NOT the longer term accuracy and stability of the DOS time. 1. TELEPHONE: Many local telephone companies offer a telephone time service, usually with a message such as "When you hear the signal the time will be ... (beep)". I am not aware of any hardware or software which uses this signal for time setting purposes. ACCURACY: Generally plus or minus 5 seconds. With the advent of digital voice response equipment in recent years, the accuracy has improved to perhaps plus or minus 1 second. 2. COMMERCIAL RADIO: Hourly time signals broadcast on commercial radio may be used to manually set the time. My experience suggests that the CBS network time signal is usually reliable. ACCURACY: Usually within plus or minus 2 seconds, depending upon the source. Satellite distribution of network feeds add a time delay of approximately 0.25 seconds per "hop" but some stations, including some network stations, generate time signals locally. 3. SHORTWAVE RADIO: Time signals are broadcast on shortwave radio stations WWV and WWVH by the National Institute of Standards and Technology. These time signals may be used to manually set the time. WWV and WWVH broadcast on several frequencies: 2.5MHz, 5MHz, 10MHz, 15MHz, and 20 MHz (WWV only). Reception will vary according to your distance from the transmitter, time of day, and atmospheric conditions. These time signals are very precise; the only major variable is the propagation delay, the time it takes the radio signal to travel from the transmitter to your receiver. The typical propagation delay is approximately 5 microseconds per mile. Outside North America, other national radio services such as the British Broadcasting Company's BBC World Service offer accurate hourly shortwave time signals. ACCURACY: Time setting using WWV or WWVH can usually be performed to within about plus or minus 250 milliseconds, of which up to 25 milliseconds is transmission time and the balance is user response time. With practice, plus or minus about 100 milliseconds is practical. Program STSORBIT PLUS Satellite Orbit Simulation Page 96 4. HEATH GC-1000 MOST ACCURATE CLOCK: The GC-1000 is a combination digital clock and scanning shortwave radio receiver which may be equipped with an RS-232 communications port for use with computers and other electronic equipment. Operation with DC power is available to maintain accurate time during periods of AC power loss. This is the only method which provides more or less continuous accurate time information without telephone toll charges. ACCURACY: When properly configured for your location, equipped with an external antenna, used with appropriate computer software, and when the receiver is locked to one of the WWV (or WWVH) time signals, the GC-1000 can provide time information and a standard calibration frequency to an accuracy of plus or minus 10 milliseconds. When signal lock is lost, the receiver scans the 5MHz, 10MHZ, and 15MHz broadcasts to reacquire signal and lock. Even after signal lock is lost, the receiver maintains an accuracy of plus or minus 100 milliseconds for some hours. 5. NIST/USNO TELEPHONE TIME SERVICE: When real precision and accuracy are required, the computer clock may be set remotely using the telephone time service of either the National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards or NBS) in Boulder, Colorado, or the U.S. Naval Observatory (USNO) in Washington, D.C. This method requires a modem connected to a telephone line and is available for systems using DOS version 3.3 or higher AND equipped with 80286 processor or higher; some 8088-equipped systems may also use this method depending upon the type of clock hardware installed and the version of DOS being used. The recommended method uses the programs TIMESET and RIGHTIME (see below) although other commercial and shareware programs may be available. ACCURACY: This is the most accurate method available for setting and maintaining the DOS clocks. Depending upon which service is used, NIST or USNO, whether or not line delay compensation ("lag") is employed, and the frequency of time setting, the DOS time can be set to within plus or minus 2 milliseconds. However, since the "time ticks" of the DOS software clock occur every 55 milliseconds, or 18.2 times per second, this "granularity" may limit the accuracy of reading the DOS clocks. See the documentation for programs TIMESET and RIGHTIME for additional discussion. Choose one of the methods suggested or a suitable alternative based upon your precision and accuracy requirements. Other methods of maintaining an accurate time standard such as atomic clocks, Global Positioning Satellite (GPS) time receivers, and NIST time code equipment, are also available -- for a price. Those methods are beyond the scope of this documentation. Maintaining Accurate DOS Time ----------------------------- Just in case you missed the point earlier, accurately setting DOS time is only half the battle. Even if the DOS time is set very precisely as Program STSORBIT PLUS Satellite Orbit Simulation Page 97 discussed above, all that assures is that the time is correct to the required accuracy at that instant. The problem then becomes one of knowing how the DOS clocks change or drift with time and how to compensate for those changes or, alternatively, checking the DOS time frequently enough that any drift on the part of the DOS clocks is acceptable for the intended application. Of the two clocks in a typical personal computer, the hardware clock is considerably more consistent and reliable. I have checked perhaps a dozen PC hardware clocks in recent years, and almost all kept reasonably good time over a period of several days; as expected, none kept "perfect" time. Typical drift rates ranged from about 3 seconds per day to near zero seconds per day, with the magnitude and direction of the drift more or less constant over the period of measurement. The hardware clock is typically sensitive to both voltage and temperature, both of which undergo significant change when the computer is turned on or off. Complete calibration of the hardware clock requires knowledge of its performance under both circumstances. Once a hardware clock has been calibrated, its performance may be predicted with reasonable accuracy over periods of some weeks or more. Crystal aging rates suggest that calibration should be performed at least monthly. The hardware clock is normally interrogated only when the computer is first started or rebooted. The correct time can therefore be predicted at that moment for a calibrated hardware clock, given the last time that clock was synchronized with an appropriate time standard. Microsoft provides no standard software tools for interrogating the hardware clock at other times except for low level interrupt services. Quite the contrary; beginning with DOS Version 3.3, using the DOS TIME and DATE commands to set the DOS software clock will also set the hardware clock and effectively destroy its usefulness as a calibrated time reference. I am at a complete loss to understand the reasoning behind this change in DOS; I presume that users were being "confused" by differences between the hardware and software clocks; instead of either explaining or fixing the problem, Microsoft elected to "legislate" the problem away -- a process any politician would recognize instantly. The only mitigating consideration is that any really effective solution would probably require hardware as well as software changes. Blame IBM, I guess. The software clock provides the only time information readily accessible to DOS using standard software. Since this clock is maintained entirely in software, with no reference to the hardware clock except at bootup, it is at the mercy of other software which may execute from time to time. The software clock increments its time using "interrupts", a technique which stops a software process in progress just long enough to do the required tasks and then resumes the interrupted process. These interrupts occur every 55 milliseconds. So long as none is missed, the software clock should keep accurate time -- if the software is written correctly and if the computer's crystal controlled oscillator is in turn accurate. It may be that neither of these conditions is true; certainly the crystal controlled oscillator (quite similar to the one which runs the hardware clock) was not designed for accuracy or stability. It's original purpose was solely to generate the necessary timing signals for the operation of the computer. Cost, not accurate time, was the primary consideration in its design. Other software designers have contributed to the problem by writing software which, deliberately or inadvertently, prevents the software clock from being updated. Off-brand BIOS firmware can present occasional Program STSORBIT PLUS Satellite Orbit Simulation Page 98 problems. Local Area Network (LAN) and high speed communications software are also frequent culprits in this respect. For example, a casual check of the clock while using a high speed computer-to-computer file transfer program indicated that the clock was effectively suspended when data transfers were in progress. In one relatively brief test, the DOS clock lost about 30 seconds. As a result of all of these factors, the accuracy of the DOS software clock can vary wildly from one computer to the next and from one situation to another. One inexpensive "clone" computer that I'd rather forget couldn't manage to keep time to better than about 30 seconds per HOUR! Before planning to use a particular computer as a time reference with programs like STSPLUS, check the computer hardware and software you intend to use very carefully. Programs TIMESET and RIGHTIME ----------------------------- Two fine programs, TIMESET by Peter Petrakis and RIGHTIME by Tom Becker, provide all the features required to accurately set and maintain the computer's hardware and software clocks. Development efforts on these programs have been carefully coordinated so that they cooperate with each other. Both programs are copyrighted commercial software distributed as "shareware" and require registration after an initial evaluation period. I highly recommend these programs and encourage users to support the authors and their work. So far as I know, there are no other comparable programs available at any price! TIMESET, Version 7.10, uses the telephone time services of NIST, USNO, and three European services to precisely set the computer clocks. The standard distribution also includes several additional time-related utility programs. It is available on many computer bulletin board systems or direct from: Peter Petrakis Life Sciences Software 8925 271st N.W., Suite 112 Box 1560 Stanwood, Washington 98292 USA Telephone: (206) 387-9788 RIGHTIME, Version 2.5+, is a program to compensate for the various drift factors in a computer's hardware and software clocks. When used in conjunction with TIMESET and properly calibrated, RIGHTIME "learns" the warm and cool drift factors for a specific computer. As a result, the clock's can be maintained with an accuracy of a fraction of a second over long periods of time. It is available on many computer bulletin board systems or direct from: Tom Becker Air System Technologies, Inc. 14232 Marsh Lane, Suite 339 Dallas, Texas 75234 USA Program STSORBIT PLUS Satellite Orbit Simulation Page 99 Telephone: (214) 402-9660 Tom Becker and Peter Petrakis may be also contacted directly on the Air Systems Technologies computer bulletin board system in Dallas, Texas. The BBS always has the latest versions of TIMESET and RIGHTIME available for download: Air Systems Technologies BBS (214) 869-2780 STSPLUS is now "aware" of program RighTime and its use is recommended for accurate timekeeping. Audible alarms in prior versions would perform unpredictably when RighTime was active because they use the hardware clock's timer functions (which RighTime also uses). STSPLUS now detects RighTime and temporarily disables RighTime while an audible alarm is being generated and then re-enables RighTime after the alarm has completed, restoring precise timekeeping. With RighTime active, alarms are generated in foreground, which may cause a slight delay in screen updating. ************* * CAUTION * ************* STSPLUS expects RighTime Version 2.5+; performance with prior versions of RighTime may yield unpredictable results. If using a prior version of RighTime, do NOT enable audible alarms! If RighTime is not present or is not detected, the audible alarms are generated in background as in prior versions. This usually causes the loss of several clock ticks in the DOS software clock for each audible alarm. Although the time loss per audible alarm is very small, the cumulative error may become significant over extended time periods. The following descriptive text is extracted with permission from the documentation for the current versions of TIMESET and RIGHTIME; please consult the documentation for each program for full details. Although future versions of both programs are expected to remain compatible with STSPLUS, they should be tested carefully before regular use. FEATURES OF TIMESET 7.10 ------------------------ TimeSet has been evolving steadily ever since the first version was released in the summer of 1987. That version and several subsequent ones could only set a computer's clock from the U.S. Naval Observatory (USNO) in Washington, D.C. Version 6.00, released in 1990, added ability to use telephone time signals from the National Institute of Standards and Technology (NIST) in Boulder, Colorado, making it the first program of its kind able to address more than one atomic time service. This made it possible for computer users in the eastern and western United States to keep down long distance bills by choosing the time service closest to them. Version 7.10 continues that evolution with a number of new features Program STSORBIT PLUS Satellite Orbit Simulation Page 100 and supporting utilities: o TimeSet can now access five atomic clock-based telephone time services on two continents: the USNO and the NIST in the United States, as before, and atomic time services in Sweden (National Time and Frequency Laboratory), Austria (Technical University of Graz), and Italy (National Electrotechnical Institute). People in European countries who want to set their computers to an atomic clock no longer need to make a trans-Atlantic phone call. o TimeSet 7.10 is designed to interact closely with version 2.5+ of RighTime (tm), the excellent memory-resident regulator for computer clocks developed by Tom Becker of Air System Technologies, Inc., Dallas. RighTime learns the drift rate in the computer's clock and continuously applies a correction to compensate for it, and it refines the correction each time the computer clock is set. A computer with RighTime installed and trained can maintain system clock accuracy within a second for at least a week. Furthermore, version 2.46 provides true 0.01-sec resolution in the DOS clock, in contrast to the normal 0.055-sec resolution. This allows greater accuracy in timesetting than ever before, indeed the maximum accuracy that can be obtained with a computer clock. Life Sciences Software and Air System Technologies cooperated closely during the development of TimeSet 7.10 and RighTime 2.46, with the result that TimeSet can access several RighTime functions directly. "TIMESET" is a trademark of Life Sciences Software (TM) The following is a screen dump of the data displayed by TIMESET: +------------------- From NIST. Connect time: 11.97 sec. --------------------+ | DATA FOR TIME CALCULATIONS (all data pertain to Coordinated Universal Time) | | Time data string: 49051 93-03-05 14:07:20 81 0 -.1 051.1 UTC(NIST) | | Date: 03-05-1993 | | Julian date: 2449051 | | Day of year: 064 | | Hour: 14 Minute: 07 Second: 20 | | The United States mainland is on standard time. | | U.S. daylight time begins on 04-04-1993 at 02:00:00 local time. | +-----------------------------------------------------------------------------+ System clock set: 06:07:20.01 +-----------------------------------------------------------------------------+ | ACTION SUMMARY (at instant of timesetting) | | Internal delay adjustment: .01 sec. (added to set time) | | Line delay adjustment: .0511 sec. (precompensated by time service) | | | | Universal Time Coordinated: 14:07:20.01 (time at 0x longitude) | | UTC Date: 03-05-1993, Friday (date at 0x longitude) | | | | Local computer time was: 06:07:20.01 (RighTime-assisted) | | Set to: 06:07:20.01 Pacific Standard | | Local computer date was: 03-05-1993 | | Set to: 03-05-1993, Friday, Day 064 of 1993 | +-----------------------------------------------------------------------------+ Program STSORBIT PLUS Satellite Orbit Simulation Page 101 FEATURES OF RIGHTIME 2.5+ ------------------------- RighTime brings exceptional system time of day clock performance to the DOS-based AT-class-compatible PC computer with no additional hardware. With RighTime installed, the standard real time clock system becomes an Adaptive Mathematically Compensated Crystal-controlled Oscillator based clock. Under stable conditions, RighTime can produce a system clock that keeps time within one half second per week or better (some testers have reported accuracy of 0.07 second per week); this is about 0.8 parts per million error, or more than 100 times better than an unconditioned crystal time base alone, or 30 times better than a moderately conditioned one like a modern watch of quality. o True one hundredth second DOS clock resolution: the 55-millisecond barrier is broken! The standard DOS clock resolves to only about 1/18 second; under RighTime v2, the new high resolution DOS clock resolves to, and increments in, hundredths while the Int 08h and 1Ch tick rate remains standard. o RighTime intrinsically sets the hardware clock and solves the midnight rollover date bug that exists in some DOS versions; this eliminates the need for other utility programs or drivers that perform these functions. Unlike DOS alone, the hardware clock seconds transition will be properly set by RighTime and the time will be set to hundredths of a second resolution, and these qualities will survive through rebooting. o Each time you set the time, RighTime will improve the accuracy of the clock error corrections and will subsequently improve the accuracy of the clocks. It should be easy to achieve a worst-case error of less than 0.5 second per day and under good conditions, less than 0.5 second per week; typical results are much better. Command line options are provided that allow fine tuning the correction process to your system. A trimming option provides for offset adjustments in hundredths of a second. The following is a screen dump of the data displayed by RIGHTIME: RighTime: Indicated DOS clock date and time is 1993/03/05 06:04:45.66. RighTime: Warm correction rate is +2.83 seconds per day. RighTime: Cool correction rate is +4.27 seconds per day. RighTime: Current applied DOS-CMOS RTC offset is +0.46 second. RighTime: Last CMOS RTC adjustment was 0.00 hours ago. RighTime: Last timeset was 23.33 hours ago. RighTime: System has been warm 17% of the time since the last timeset. RighTime: Stack A headroom is 92 bytes; Stack space used is 68 bytes. Stack D headroom is 100 bytes; Stack space used is 60 bytes. RighTime: /?=Help; Version 2.53 RighTime: Copyright 1991-93 GTBecker, Dallas 214/402-9660. All Rights Reserved. RighTime: Resident and enabled. RighTime: Selftest passed. Program STSORBIT PLUS Satellite Orbit Simulation Page 102 Computer Bulletin Board Systems ------------------------------- Timely 2-line orbital elements are essential for accurate satellite tracking. In addition to my own bulletin board systems (see title page for numbers), four other bulletin board systems provide authoritatve data for the general public. Most files on these systems are compressed to reduce downloading time and must be decompressed before use. For the past several years, Major T. S. Kelso, USAF, has been making the US Space Command (formerly NORAD) orbital data available as a public service on his Celestial BBS at (513) 427-0674, 1 line at 1200 to 14400 baud. The 2-line element sets are prepared by Kelso using data received directly from U.S. Space Command (formerly NORAD) by special arrangement. I regularly post a concantenated and sorted version of the current element sets on my own RPV ASTRONOMY BBS as file TLEnnn.ZIP, where "nnn" is the current Prediction Bulletin number. Kelso provides data for several categories of satellites: Amateur Radio, Earth Resources, Manned Spacecraft, Navigation, Weather, and NASA's 30 Day Specials (which contain objects launched within the last 30 days and are often easy to spot visually). More specifically, these include the following satellites or satellite series: OSCAR, Radio Sputnik, UOSAT, Cosmos, LandSat, SeaSat 1, SPOT, Mir, Salyut 7, Soyuz, Space Shuttle, NAVSTAR (GPS), GOES, Meteor, and NOAA. The Canadian Space Society BBS, (416) 458-5907, 1 line at 1200 and 2400 baud, also regularly posts NORAD 2-line elements. Much of the orbital data is obtained from Celestial BBS but additional data is generated by Ted Molczan and his worldwide team of observers. Note that the CSS format is slightly non-standard, having additional information on the first (title) line for each satellite, and may have to be edited for use with some tracking programs. The CSS files also have considerable additional text material (including current satellite news) before and after the actual 2- line elements data. The U.S. Space Command sends all unclassified 2-line elements to the Orbital Information Group at Goddard Space Flight Center. These elements are available on the GSFC OIG RBBS, (301) 306-0010, 4 lines @ 1200 and 2400 baud. The OIG database contains elements for some 7000+ satellites and is updated every weekday morning except holidays. Elements for popular satellites are posted in seven ".DAT" files (with the NORAD number only in the first line of data rather than the more usual satellite name or IAU identification) and all other satellites are available on a query basis. I regularly post a combined and sorted set of the .DAT data as file GSFCnnn.ZIP on my own RPV ASTRONOMY BBS where "nnn" is a number like "170". Individuals who wish access to the RBBS must write (include full name and address): NASA Goddard Space Flight Center Project Operations Branch/513 Attn: Orbital Information Group Greenbelt, MD 20771 USA The OIG RBBS began operation in September, 1991. Until that time, the only method for obtaining the OIG data was by mail. OIG now plans to discontinue all mail services in early 1993 and thereafter the only method for obtaining the OIG data will be via the RBBS. The NASA SpaceLink BBS in Huntsville, Alabama, (205) 895-0028, 8 lines Program STSORBIT PLUS Satellite Orbit Simulation Page 103 @ 300-2400 baud, provides mission information for all space shuttle missions and (usually) 2-line orbital elements both pre-mission and while a mission is in progress. In addition, SpaceLink has a wealth of other NASA information, computer programs, teaching materials, and image files. In January of 1993 the Public Affairs Office at the NASA Jet Propulsion Laboratory began BBS service related to JPL-supported missions. Mission status reports and high quality GIF images are the principal files currently available. The number is (818) 354-1333, two lines at 1200 to 9600 baud. Program STSORBIT PLUS Satellite Orbit Simulation Page 104 STSORBIT PLUS Revision History ------------------------------ Each released version of STSPLUS uses a four digit revision code such as 9311. The first two digits indicate the year and the second two digits indicate the week of the year. In some cases, an additional letter suffix is added to distinguish changes occurring within the same week or to identify special versions. A partial week at the beginning or end of the year is counted as a full week. Using this method, a year will typically have 53 weeks although it is possible to have 54 weeks in a leap year (1972 is an example). The current year-week revision code is shown on the Julian Date display, Display Mode 7, in my program ASTROCLK. This file records the revision history of program STSPLUS through all of the minor twists and turns that usually accompany the evolution of such a complex program. It illustrates the tortuous process of maintaining and refining a program as ideas and problems are reported from every quarter. These notes may also be helpful to users who are upgrading from one version to another to find out what has changed. David H. Ransom, Jr. Version 9311 -- March 1993 -------------------------- -This is a FULL RELEASE with updated documentation, and includes all changes listed here as well as those made in Preliminary Versions 9307 through 9310. Please see the update notes below for details. -Added F1 to the Main Menu, Convert Keplerian Elements to 2-Line Format, which incorporates the features formerly provided separately in my program MAK2LINE. See new text for discussion and for a form which may be used to transcribe data received by voice or modem. -Repaired a bug which caused the Location Map isocontours to be drawn at the wrong location when a second location was enabled in orthographic mode. Thanks to Paul Ferrante for reporting the problem! -Added Function Key F9 to the Time and Date Menu (F8 from the Main Menu) to show the last system TIMESET and the current RIGHTIME corrections. This menu item will not appear if program RIGHTIME is not detected. -Added additional code to maintain the prior state of RIGHTIME per Tom Becker. Thanks, Tom! -Various minor cosmetic changes. -Documentation updated. Version 9310 -- March 1993 -------------------------- -This is a MAINTENANCE UPDATE and also includes several improvements to Version 9309. Users updating from Version 9250 should also read the notes for Version 9309 below. -In my rush to release Version 9309 of STSPLUS prior to STS-55, I neglected to finish updating the code for F2 (Read 2-line elements). Hopefully, that code has now been repaired correctly ... sorry! -STSPLUS is now "aware" of program RighTime by Tom Becker. Audible alarms in prior versions would perform unpredictably when RighTime was active because MS BASIC uses the hardware clock's timer functions for "music" (which RighTime also uses). STSPLUS now detects RighTime and temporarily Program STSORBIT PLUS Satellite Orbit Simulation Page 105 disables RighTime while an audible alarm is being generated and then re- enables RighTime after the alarm has completed, restoring precise timekeeping. With RighTime active, alarms are generated in foreground, which may cause a slight delay in screen updating. -CAUTION: STSPLUS expects RighTime Version 2.5+; performance with prior versions of RighTime may yield unpredictable results. If using a prior version of RighTime, do NOT enable audible alarms! -If RighTime is not present or is not detected, the audible alarms are generated in background as in prior versions. This usually causes the loss of several clock ticks in the DOS software clock for each audible alarm. Although the time loss per audible alarm is very small, the cumulative error may become significant over extended time periods. -Added the flashing message "calculating ..." during Pass Prediction calculations so that users with slow computers (especially those without a math coprocessor) will know that the process is continuing. Users with 286 computers and no math coprocessor report delays up to tens of minutes for satellites with low mean motions! Version 9309 -- February 1993 ----------------------------- -This is a PRELIMINARY RELEASE of a major update for STSPLUS and the first public release since Version 9250. This version is being released as an UPDATE ONLY for Versions 9250 and 9307; the full version will be released shortly, complete with full documentation, pending the results of testing for this preliminary release. See also the update notes for Version 9307 below. Comments and suggestions are invited, particularly with respect to the new Data Output and Pass Prediction features. -Function Key F3 on the Main Menu, Pass Predictions and Data Output, has been rewritten and improved. -Added Line-of-Sight Pass Predictions for the current satellite. Use F3 from the Main Menu and select Data Format 9. Pass predictions are made for 48-hour blocks and for up to 99 passes. Users may immediately display a listed pass by entering the pass number. STSPLUS then automatically sets SIMULATED TIME to the middle of the pass and switches to the ground track display. See the section "Pass Predictions and Data Output" for additional information. The capability to use TRAKSTAR or other external tabular pass prediction software has been retained for those who prefer that technique. -Improved and refined the Data Output capabilities introduced in Beta Version 9307. Added FILE Data Output to file STSPLUS.LOG, and PRINTER Data Output to printer LPT1:. -Modified F2 on the Main Menu (Read 2-line Elements) to require the "#" symbol when entering the NORAD number; enter the NORAD number as "#20580". This now permits satellite names such as "1993 012A" to be found correctly; prior versions would treat such an entry as a NORAD number and the search would fail. -Entering a full drive and path specification in addition to a filename with F2 on the Main Menu (Read 2-line Elements) will now correctly set the path without the need to use F7 (Set Paths and Filenames). Root directories ("C:\") are now processed correctly. Press ESC to cancel. -Added text section titled "Time and the Personal Computer" which offers information on setting and maintaining the PC clocks over long periods of time. Includes information on programs TIMESET and RIGHTIME. Program STSORBIT PLUS Satellite Orbit Simulation Page 106 Version 9307 -- February 1993 ----------------------------- -This is a BETA TEST VERSION, not released publicly. -Added Function Key F3 to the Main Menu. This provides data output on the selected COM port with specified data items. Three different data formats have been implemented so far. -Removed the original Function Key F3 (Read .INI file) from the Main Menu. Use F2 to read 2-line elements and/or set file names. In Version 9250, the satellite data was not being read when the .INI file was changed. This was caused by logic changes to speed up initialization of the program. Also, reading "foreign" .INI files sometimes caused problems. -Corrected a bug which caused a new launch time/date NOT to be added to file STSPLUS.LTD if the curret satellite's NORAD number was less than the last NORAD number in the file. -In response to a request by Maj. T.S. Kelso, USAF, who prepares the 2-line orbital elements which I post on my RPV ASTRONOMY BBS, I have changed the name of that file from "NASAnnn.TXT" to "TLEnnn.TXT". The default file which STSPLUS looks for has been similarly changed. Since the orbital data in the file does NOT come from NASA but from US Space Command, the use of "NASA" in the filename was confusing and did not give credit where it was due. -Corrected a minor bug which caused five pixels to be restored incorrectly under the starbord (right) wing of the space shuttle icon. -Modified the operation of Function Key F5 from the Main Menu to ADD or UPDATE new launch time and date in file STSPLUS.LTD rather than to append the new data at the end of the file. This assures that the satellite is included only once in the file and that the new or updated information is always read correctly. Prior versions required the user to manually edit the file to remove multiple entries. -Adjusted the maximum angle displayed for the isocontours (concentric circles of satellite visibility) on the Location Map in orthographic mode to take satellite altitude into account. -Corrected the STSPLUS.OBS file format for use with TRAKSTAR. The data was correct but the spacing caused TRAKSTAR to sometimes read the data incorrectly. Thanks to Michael Simmons for reporting the problem! -Corrected the latitude of Sao Paulo, Brazil in file STSPLUS.LOC. It was one degree off to the South and wound up in the Atlantic Ocean ... Version 9250 -- December 1992 ----------------------------- -This is a MAINTENANCE AND FEATURES UPDATE. -In response to numerous suggestions, I have redesigned and enlarged the space shuttle icon and switched from a profile to a plan view to make the icon easier to find on the screen. The new icon has almost three times as many pixels and takes more time to draw. Comments are invited! -In response to many user requests, I have improved file selection logic for 2-line elements using F7 from the Main Menu to "remember" the path and save it in file STSPLUS.INI. Users may now keep all 2-line elements files for STSPLUS and other tracking programs in a separate directory. -While the default filetype for 2-line elements is still ".TXT", the program now also searches for filetype ".TLE". -Event timers (showing AOS and LOS for the local station, TDRS, etc.) are now enabled by F10+F7 from the Main Menu. -I have added the Location Map in orthographic mode; press "L" while an Program STSORBIT PLUS Satellite Orbit Simulation Page 107 orthographic map is displayed. The projection used for the Location Map is now based upon the current projection, rectangular or orthographic, when "L" is pressed. -Improved resolution of spacecraft lighting from 10 seconds to 1 second and the Sun's position is now calculated every 10 seconds instead of every 60 seconds. -Spacecraft lighting icon and symbol (to the right of "Orbit #:" in the data block) now indicate the full range of solar illumination: * Bright White Full sunlight + Yellow Partial sunlight (penumbra) - Light Red Refracted sunlight White Full shadow (umbra) Note that LIGHT RED and the "+" and "-" symbols have been added to distinguish refracted sunlight from partial sunlight. -In response to several user requests, I have added AOS and LOS event timers for orbital sunrise and sunset, displayed when the solar features are enabled. In order to avoid excessive delays during the ground track plotting (when the timers are set up), I have used a simpler algorithm for orbital sunrise and sunset than that used during program operation. The simpler algorithm is usually accurate to about plus or minus 15 seconds. The actual spacecraft lighting is calculated dynamically and is both more accurate and takes into account the non-spherical shape of the Earth. -After several user comments about the "big clocks", I have again tweaked the shape of the large digit "5" (back to what I started with) and modified the "6" to better distinguish it from the "5". -In order to free a display line in orthographic mode, the map drawing time and map database file information have been combined on a single line (e.g. "EARTH4 10.91") at the bottom of the display block. -STSPLUS now automatically detects the type of processor and math coprocessor; if no math coprocessor chip is detected, the program displays a caution message at startup. The SLOW MODE is now automatically set or reset depending upon the presence or absence of the math coprocessor and the menu selection for the SLOW MODE has been removed. -Performance may be improved if a memory manager such as EMM386, QEMM386 or 386MAX is NOT used! See the section "PROGRAM SETUP AND USAGE NOTES" for specific information. -Changed the grid spacing in orthographic mode, MAG=200, to 10 degrees from 5 degrees to make the display a bit less cluttered. -STSPLUS is now compiled using Microsoft Visual Basic for DOS. -Updated this documentation. Added the sections "SUN and Solar Features", "Event Timers and Audible Alarms", and "F5 Display Ground Track: DOTS/LINE". Moved the section "F5 Show Ascending & Descending Node Data" to the proper place in the text. -Corrected a bug which caused a minus sign (if present on Y or Z) to persist when changing from XYZ to Alt/Az or RA/DEC satellite coordinates. -Various minor cosmetic changes. -Version 9249 was a limited release beta version. Version 9245 -- October, 1992 ----------------------------- -This is a MAINTENANCE UPDATE, correcting several bugs and adds the launch date and time capability. -Added file STSPLUS.LTD which contains the NORAD number and launch date (Julian date, UTC) for selected satellites. A sample entry appears as: Program STSORBIT PLUS Satellite Orbit Simulation Page 108 22194,2448918.21503472,0 This example is the data for Space Shuttle mission STS-52 (NORAD #22194) and corresponds to a launch date and time of 22 OCT 1992 @ 17:09:39 UTC. The last parameter is reserved and should be set to zero. Launch date and time may be appended to file STSPLUS.LTD when entered using F5 from the Main Menu. See the section "Using File STSPLUS.LTD for Launch Date & Time" for a complete discussion. -Corrected a misplaced statement which caused "BASIC PDS Error = 5" when the Satellite Motion Map was requested from rectangular modes. -Changed future dots on ground track to LIGHT GREEN when only dots are shown to avoid confusion with solar terminator. (That's what it was supposed to be but I messed up ...) -Changed satellite circle of visibility on the Satellite Motion Map to solid white (from light white dots) for greater clarity. -Added a default magnification of 200 for the End key. -Corrected the coordinates for Shanghi, China, in STSPLUS.LOC. Version 9244A -- October, 1992 ------------------------------ -On rectangular projections, the LAUNCH TIME and LAUNCH DATE were shown incorrectly. The calculations for MET were correct. Version 9244 -- October, 1992 ----------------------------- -Version 9244 is a MAINTENANCE UPDATE which adds several new features in addition to repairing a number of bugs which have been discovered as a result of the addition of the orthographic map mode and other new features such as enhanced TDRS coverage. This is still "early in the game" following the major rework associated with the addition of orthographic projection. Comments, suggestions, and bug reports will be appreciated. -Added EGA dual-page Satellite Motion Map to orthographic modes, available ONLY for EGA and VGA systems. Press "M" while the orthographic map is displayed. Press "M" or ENTER to return to normal map modes. PgUp, PgDn, Home, and End are the only other keys which are active with the Satellite Motion Map. -In response to MANY requests, I have restored the "red dots" for past orbital ground track. (My original method no longer worked when I added the orthographic projection.) -AOS/LOS for secondary location now available in orthographic mode and in rectangular mode with "/CLK" command line option AND when large clock is selected for MET/T+Epoch (using F2 when the map is displayed). Finding display space is getting very difficult, particularly in normal rectangular modes! Primary location is labeled "STN1" and secondary location is labeled "STN2". -The PAUSE mode has FINALLY been repaired so that it operates correctly. Press F6 while the map is displayed to enter PAUSE, press ENTER to resume normal operation. Use the "+" and "-" keys to advance or retard the time, and use F4 to set the time step. See the section "Pausing the Ground Track Display" for a full description. -The FAST mode has also been repaired so that it works more or less in the manner intended. Press F4 while the map is displayed to enter FAST mode. Note that the actual time increment is a function of the computer's speed. Program STSORBIT PLUS Satellite Orbit Simulation Page 109 For fast computers, the time increment will usually be 10 or 60 seconds but may vary by a second occasionally; for slower computers, the time increment may be somewhat longer. See the section "Using FAST Time" for a full description. -Corrected a problem with TDRS coverage when updating from one version to another. The TDRS AOS/LOS labels read ":" instead of "TDRE:" and "TDRW:" and the AOS/LOS calculations could be incorrect or blanked out. (The TDRS data were not being set up correctly.) As a work-around, the problem could be corrected by deleting file STSPLUS.INI and restarting the program. -Corrected a crash with "BASIC PDS Error 5" which occurred under certain circumstances when drawing circles of visibility in orthographic mode. (An array index was being overrun.) -Corrected a minor bug in the AOS/LOS logic that limited the time resolution to 2 seconds instead of 1 second (4 seconds instead of 2 seconds when the SLOW flag is set). Thanks to Joel Runes for spotting the problem! -Various minor cosmetic bugs. NOTE: Version 9243 was a beta version released on a limited basis to individuals who had problems and/or registered the program immediately before and during Mission STS-52. Version 9243 included some of the changes noted above for Version 9244. Version 9242 -- October, 1992 ----------------------------- -Version 9242 is primarily a Maintenance Update, correcting a number of minor bugs and documentation errors. However, several "new and improved" features have also been added as a result of continued testing and user requests. Thanks to everyone who sent in encouragement and suggestions! -In response to MANY user requests, I have added an interface (via F4 from the Main Menu) to TS Kelso's new satellite prediction program TRAKSTAR. Download TRAKSTR2.ZIP (filename for Version 2.15) from RPV ASTRONOMY BBS or from Celestial BBS (see text for telephone number). CAUTION: TRAKSTAR uses UTC time rather than LOCAL time! See text for full description and setup instructions. -By popular request, I've added an audible warning for AOS and LOS at the user's location. The AOS warning occurs 2 minutes prior to AOS, and the LOS warning occurs 30 seconds prior to LOS. Audible warnings are enabled and disabled using F10+F8 from the Main Menu. Past versions of Microsoft's compilers have caused the system clock to lose time when "music" was played; I would appreciate feedback from users if this feature causes problems. -A similar (but shorter) audible warning has also been added for TDRS coverage. The TDRS warnings occur 30 seconds before AOS or LOS if TDRS coverage and audible alarms are both enabled. -AOS and LOS clocks now change to YELLOW if the time is 2 minutes or less, as stated in the documentation. A minor bug has been repaired that caused the AOS or LOS clocks to sometimes "freeze" at 00:00 or 00:01 when no future event was detected. -AOS and LOS calculations have been improved in precision by a factor of two and the average time required for the calculations has decreased by about 5:1 using a binary search algorithm. This may be just an exercise in performance improvement since factors such as antenna pointing errors and atmospheric conditions may introduce errors of up to tens of seconds! -When launch time and data have been entered and Mission Elapsed Time is Program STSORBIT PLUS Satellite Orbit Simulation Page 110 selected for display, the HOURS:MINUTES for MET will appear at the bottom of the data block in large digits for orthographic modes. (When MAG is greather than 100, seconds are not displayed because of space limitations. The full MET, including days, is always displayed near the top of the data block in normal characters.) -Corrected error when changing to/from DAYLIGHT TIME using F8+F10 from the Main Menu. If the Daylight setting is changed, STSPLUS now asks if you wish to adjust your DOS clock. CAUTION: Setting the DOS clock may NOT execute correctly for 8088 computers! (Prior versions required exit from the program and restart before the time was shown correctly.) -Corrected the satellite coordinates when orthographic mode was selected with the second city displayed. (V9240 displayed the primary location name but the data for the secondary location.) -Corrected a problem (which left the screen black most of the time and then was redrawn immediately) when Motion Map was requested (by pressing "M") from other than Zoom Mode. -Corrected TDRS AOS/LOS title placement error with "/CLK" command line option. -Meridian drawing algorithm adjusted to (hopefully) always draw the lines of equal longitude to the bottom or top of the map in orthographic mode. -Added a test for field overflow in the first derivative of mean motion (dx/dt, the parameter following the epoch on Line 1). Field overflow is indicated by a numeric field of ".********" and it is now set to a value of 1 or -1 depending upon the leading sign. This is often an indication that the satellite has decayed or soon will decay. -Corrected the default directory upon return from DOS using F9 on the Main Menu. (Default directory was left where the user last logged and file STSPLUS.INI was written there instead of where it belonged.) -Corrected file list to show CIS.TRK instead of USSR.TRK and updated the distribution files accordingly. -Description of TDRS satellite locations in the text corrected. -Description of MCX, MCP, and XYZ map database files corrected to restore a line of text that was dropped by my word processor. Version 9241 was released for beta testing only. Version 9240 -- October, 1992 ----------------------------- ********************* * IMPORTANT NOTES * ********************* After almost four years, I have at last discontinued support for the simple orbital model in STSORBIT PLUS. Users who wish to continue using the simple orbital model must use prior versions of STSPLUS or use the original STSORBIT program. I plan to add manual generation of estimated 2-line orbital elements for the Space Shuttle in the next release of STSPLUS. Motion maps are available only with rectangular projection. The FAST modes are still not really repaired. Maybe I'll get around to that in the next release ... Program STSORBIT PLUS Satellite Orbit Simulation Page 111 The South Atlantic Anomaly (SAA) is disabled for orthographic modes until I digitize a better model from NASA's Mission Charts. -Version 9240 is a MAJOR UPGRADE and is the initial public release with the orthographic projection techniques used in my program ORTHOGRAPHIC EARTH VIEW. -While the principal new feature is the orthographic projection, that addition affected almost all parts of the program and many different routines have been updated or modified. I have also rewritten the AOS/LOS code for TDRS and the user's location. Although considerable beta testing has been performed, there are surely a few bugs that have not yet been discovered. Special thanks to Joel Runes for his help with the beta versions! Comments and bug reports are welcome. -Added Orthographic Projection maps and new map databases. Orthographic maps are selected using the letter "O" when the map is displayed or by selecting "ORTHO" using F10+F6 from the Main Menu. PgUp, PgDn, Home, and End may be used to select the magnification factor. See the text for a full description. -A math coprocessor is REQUIRED for the orthographic maps. Orthographic maps require MUCH more computation time. Most computers not equipped with a math coprocessor chip, even 386 systems, will yield poor or unacceptable performance in orthographic modes. Typical orthographic map drawing times range from 5 or 10 seconds for a 486DX/33 to 600 seconds or more for an 8088 without a math coprocessor! -All rectangular projection map routines have been rewritten to use the new indexed map database files and the maximum zoom factor has been increased to a field of view of 30 degrees. This yields much improved map detail at higher zoom factors and decreases the map drawing time in most cases. The old map database file, STSPLUS.MVF, may be deleted. -Because of their size, the high detail map database files cannot be downloaded from the RPV ASTRONOMY BBS except for callers with 9600 or faster baud modems. See file README for additional information on these files. -The TDRS sub-satellite coordinates are now included in STSPLUS.INI and may be updated by displaying the appropriate satellite. For TDRS East display NORAD #19883, and for TDRS West display NORAD# 21639. See the section "TDRS Satellite Features" for additional information. Thanks to Jim Henderson of NASA White Sands (and others) for the suggestion. -Changed TDRS coverage algorithm to reflect actual coverage as a function of satellite altitude above the Earth's surface. Provided current TDRS position data is used, accuracy should now be on the order of tens of seconds. Prior versions assumed a "customer" satellite orbital altitude of approximately 160 miles. -Added location and features labels to all maps, enabled or disabled by F10+F3+F9 from the Main Menu. Labels are contained in file STSPLUS.LOC. See the section "Location and Features Labels" for additional information. -Rewrote the time base algorithms to better accomodate slower computers and the longer calculation times required in orthographic modes. The program now operates correctly even when the map drawing and updating times are longer than ten seconds. Updating of the spacecraft circle of visibility, for example, will occur at ten second intervals if the necessary calculations and screen operations can be performed in less than one second; if not, the update interval will be adjusted as necessary. Program STSORBIT PLUS Satellite Orbit Simulation Page 112 -Partly because of the new timebase algorithms, the ground track has been changed. The "minute marker" dots are now yellow when DOTS+LINES are enabled and the dots no longer change color. (A synchronization problem.) -Changed the algorithm for the Circle of Visibility to correctly calculate near the poles. The new algorithm is now used in all map projections. Users who complained about the circles of visibility for high inclination orbits will find them now correct -- although somewhat slower. The algorithm was adapted from FORTRAN code generously supplied by Paul Traufler. Thanks yet again, Paul! -Changed most circle of visibility plotting routines from double to single precision and used in-line code to improve performance. -Added a black dot on the satellite icons to show the center of the icon. -Corrected a fatal error if the map data files were missing. This problem was frequently caused by using an old version of PKUNZIP (earlier than Version 1.10) which could not unpack the map data file, the only file which used the most recent compression algorithm. No error message was displayed and the computer had to be rebooted. (Users who downloaded the program from NASA SpaceLink BBS often had this problem since NASA had the wrong version of PKUNZIP posted -- which they corrected at my request!) -Corrected an error in the internal tracking station data which caused a fatal Basic PDS Error 3 ("Syntax Error") if file STSPLUS.TRK was missing. -Changed "current file" display to use inverse video when selecting 2-line elements files. The color change used in prior versions did not show on monochrome systems! -Corrected a bug in the 2-line file selection logic that prevented entry of a specific filename and improved the error trapping. -Corrected the longitude of Cape Canaveral in STSPLUS.CTY so that it was not out in the Atlantic Ocean. (Thanks to all of you who reported it!) -Increased internal STACK size to 6144 bytes (vs. 3072) in the hope of eliminating some reported memory problems (which I can't duplicate). -Corrected a minor bug in the (25 line modes only) large character display of MET/T+Epoch if the days were four characters; the time was shifted left one digit. Days may now range from -999 to +9999. Also eliminated a double minus sign if MET or T+Epoch was negative. -Corrected a minor bug in satellite coordinates if a distance was greater than -99999.99 km/nm. The display wrapped because of field overflow. The distance is now shown as -NNNNNN.N (one less digit to the right of the decimal point) for large distances. Most folks won't notice this one! -Corrected a minor bug in large character negative MET/T+Epoch that caused the time to be green for one second before turning red under certain circumstances. -Corrected an occasional bug which caused the colors to go awry or to monochrome. -Various minor cosmetic bugs. (Intermediate update notes deleted to save space, available on request.) Beta Version 9137 -- September, 1991 ------------------------------------ -Initial public beta version.