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Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation With Multi-Satellite Tracking (Enhanced Version for 386/486 Computers) (C) Copyright David H. Ransom, Jr., 1989-1994 All rights reserved. Version 9435A August 25, 1994 David H. Ransom, Jr. 7130 Avenida Altisima Rancho Palos Verdes, California, 90275 USA CompuServe: 75240,176 Bulletin Board System --------------------- RPV ASTRONOMY BBS (310) 541-7299 @ 2400-14400 Baud Program STSORBIT PLUS Satellite Orbit Simulation Page ii TABLE OF CONTENTS INTRODUCTION ......................................................1 HARDWARE AND SOFTWARE REQUIREMENTS ................................6 PROGRAM DESCRIPTION ...............................................7 STSORBIT PLUS FILES ...............................................9 STSPLUS MAP PROJECTIONS AND DATABASES .............................12 PROGRAM SETUP AND USAGE NOTES .....................................14 DOS 5.0 CONFIG.SYS Setup ........................................14 Using a RAM Disk ................................................15 Copying Files for STSORBIT PLUS .................................16 Slow Computers and 80x87 Math Coprocessor Chips .................17 Starting Program STSORBIT PLUS and Command Line Options .........20 Predicting Visible Satellite Passes .............................22 Predicting Satellite Passes with STSPLUS ......................23 Predicting Satellite Passes with TRAKSTAR .....................25 Printing Graphics Screens .......................................27 Known STSPLUS Problems and Bugs .................................28 Satellite Name Cross-Reference using STSPLUS.XRF ..................31 Preparing 2-Line Elements using VEC2TLE by Ken Ernandes ...........32 PROGRAM OPERATION .................................................34 STSORBIT PLUS SATELLITE TRACKING FEATURES .........................36 Orthographic Projection Maps ....................................36 Rectangular Projection World Maps ...............................37 Rectangular Projection Quadrant Maps ............................37 Rectangular Projection Zoom Maps ................................38 Location Maps with Isocontours ..................................39 Tracking Station Maps with Isocontours ..........................39 Location and Features Labels ....................................40 Big Clock Options ...............................................42 Satellite Motion Maps ...........................................42 Satellite Position and Orbit Projections ........................43 Satellite Visibility ............................................44 User's Circle of Visibility .....................................44 Spacecraft Circle of Visibility .................................45 SUN and Solar Features ..........................................46 TDRS and Real Time Satellite Features ...........................48 Ground Tracking Stations and .TRK Files..........................50 Event Timers and Audible Alarms .................................52 Pausing the Ground Track Display (F6 Key) .......................55 Switching between MET and T+Epoch ...............................56 Using FAST Time (F4 Key) ........................................56 On-line Help (F1 Key) ...........................................57 Satellite Communications and Amateur Radio ........................58 STSPLUS Doppler Shift Mode ......................................59 Satellite Phase (Mean Anomaly) ..................................61 Satellite Communications Technique and Cautions .................62 Preparing File STSPLUS.FRQ for Amateur Radio Use ................64 ACTIVE KEYS DURING GROUND TRACK DISPLAY ...........................68 STSORBIT PLUS MAIN MENU ...........................................72 F1 Convert Keplerian Data to 2-Line Format .....................73 Program STSORBIT PLUS Satellite Orbit Simulation Page ii Example Data Input and Output ...............................75 Received Keplerian Orbital Data Form ........................77 F2 Read/Update NASA/NORAD 2-Line Elements ......................78 Select/Update Preset Frequency Selections ...................78 Update Current TDRS and Real Time Satellites ................78 Read NASA/NORAD 2-Line Elements from a File .................80 F3 Data Output and Pass Prediction Selections ..................84 Setting up Position and State Vector Data Output ............86 Setting up Tabular Pass Predictions .........................89 Data Mode 1: Azimuth/Elevation Data Format ..................94 Data Mode 2: Latitude/Longitude Data Format .................95 Data Mode 3: Topocentric RA/DEC Data Format .................96 Data Mode 4: Ascending Node X-Y-Z State Vector ..............97 Data Mode 5: X-Y-Z Cartesian State Vector, 2 Data Lines .....99 Data Mode 6: X-Y-Z Cartesian State Vector, Comma Delim ......101 Data Mode 7: X-Y-Z Cartesian State Vector, Labeled Data .....103 Data Mode 8: Doppler Shift Predictions ......................105 Data Mode 9: Pass Predictions ...............................106 F4 Calculate Satellite Positions with TRAKSTAR .................108 F5 Set Launch Time and Date ....................................108 Using File STSPLUS.LTD for Launch Date & Time ...............109 F6 Set/Read/Save TDRS and Real Time Satellites .................110 F1 Display/Modify Satellite Assignments ....................110 F2 Save SCF Satellite Configuration File ...................114 F3 Read SCF Satellite Configuration File ...................115 F4 Select New PRIMARY Satellite ............................115 F5 Select New TARGET Satellite .............................116 F6 Clear Static and Real Time Satellites ...................117 F7 Set FILENAMES and PATHS .....................................117 F8 Set Program TIME and DATE....................................118 F1 Restore System Date and Time ............................120 F2 Set DOS System Clock ....................................120 F3 Set Simulated Date and Time using Calendar Method .......121 F4 Set Simulated Date and Time using MET ...................121 F9 Display Current RIGHTIME Corrections ....................122 F10 Set UTC OFFSET and DAYLIGHT Flag ........................123 F9 DOS Shell ...................................................124 F10 Set STSORBIT PLUS Program Options and Features ..............124 ENTER Resume Mission ...........................................125 ESC Quit STSORBIT PLUS and Save Current Mission ..............125 PROGRAM OPTIONS AND FEATURES MENU .................................126 F1 Program STSORBIT PLUS Information ...........................126 F2 Set New Local Coordinates ...................................126 F1/F2 Search CITYFILE for location ..........................127 F3/F4 Enter New Coordinates for Location ....................128 F5 Clear (disable) Secondary Location ......................129 F3 Set Display Features (see separate section below) ...........129 F4 Set Satellite Coordinates ...................................130 F5 Show Ascending & Descending Node Data .......................130 F6 Set Map Projection and Size .................................131 F7 Enable/Disable EVENT TIMERS .................................131 F8 Enable/Disable Audible ALARMS ...............................131 F9 Set User-Definable Map Colors ...............................132 F10 Enable/Disable Printer Logging ..............................133 SET DISPLAY FEATURES ..............................................134 Program STSORBIT PLUS Satellite Orbit Simulation Page iii F1 Display LOCAL Circles of Visibility .........................134 F2 Display TDRS and Real Time Satellites .......................134 F3 Display Additional Map Grid Lines ...........................135 F4 Display Tracking Stations ...................................135 F5 Display Ground Track: DOTS/LINE .............................135 F6 Display Spacecraft Circle of Visibility .....................136 F7 Display South Atlantic Anomaly Zone .........................136 F8 Display Terminator, Sun and Spacecraft Lighting .............136 F9 Display Map Locations and Features ..........................137 F10 Display Lakes and Rivers ....................................137 STSORBIT PLUS's Orbital Model .....................................138 Accurate Time and the Personal Computer ...........................140 Methods for Setting DOS Time ....................................141 Maintaining Accurate DOS Time ...................................142 Programs TIMESET and RIGHTIME ...................................144 Program PRECISION TIME ..........................................148 Computer Bulletin Board Systems ...................................150 STSORBIT PLUS Revision History ....................................152 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 386 or better (IBM compatible) computer is required. A math coprocessor chip is STRONGLY RECOMMENDED and will dramatically improve performance; the math coprocessor chip is REQUIRED for acceptable performance when using the orthographic projection. (Some users have reported acceptable performance using a 286/287 system but some operations are quite slow. Other users report "usable" performance on an XT-class machine with a math coprocessor (8088/8087) but the performance is marginal at best.) 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. One primary satellite and up to 32 additional "static" or "real time" satellites may be simultaneously tracked in real time on most computers. 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 very accurate when used with current (and accurate) 2-line elements. The program has been qualified by the USAF and meets the requirement of placing a satellite within 0.5 km over a 24-hour time span from the epoch time of the 2-line elements. It is used daily at the USAF Central Computer Complex at Cape Canaveral, by the DOD C-Band Radar Network at their worldwide radar sites, and at half a dozen NASA and aerosapce control centers around the country. The program is made available to schools through the NASA Spacelink BBS and the NASA Teacher Resource Centers. Numerous schools and amateur radio enthusiasts have made contact with the space shuttle via SAREX amateur radio while using STSORBIT PLUS. 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. Additional higher detail map database files are available to registered users by mail. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 2 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 of STSORBIT PLUS prior to 9240. Users who wish to convert space shuttle or satellite state vectors to 2-line format should see the section "Preparing 2-Line Elements using VEC2TLE" for a description of a program by Kenneth Ernandes written specifically for this purpose. VEC2TLE has been validated during several space shuttle missions and is highly recommended. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 3 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. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 4 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 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 5 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 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 (see title page for telephone number 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 90275 Program STSORBIT PLUS Satellite Orbit Simulation Page 6 HARDWARE AND SOFTWARE REQUIREMENTS ---------------------------------- A 386SX-class computer running at 20MHz and equipped with a 387 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 386DX/387 and 486DX or higher systems will be considerably superior to 386SX systems. Note that NO TESTING is performed on systems not equipped with a math coprocessor chip. The following minimum hardware is recommended: 386 or higher IBM-compatible computer 387/487 math coprocessor chip (if not included in main processor) VGA color display Hard disk with up to 3MB available RAM disk with at least 500K space The 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, TDRS communications coverage (when applicable), and a variety of other information. A selection of map modes and display features allow users to configure the program to meet their requirements. STSPLUS has been validated by the USAF and is approved for use on the Eastern and Western Ranges. It is sufficiently accurate (given current and accurate 2-line orbital elements, of course!) that the program is being used operationally by NASA, USAF, and Intelsat. Among the current users are: Program STSORBIT PLUS Satellite Orbit Simulation Page 8 NASA/JPL Multimission Computer Control Center, Pasadena, CA NASA/Lewis User Operations Facility, Cleveland, OH Rockwell Mission Control & Support, Downey, CA Aerojet Emergency Control Center, Sacramento, CA USAF Central Computer Complex, Cape Canaveral, FL DOD C-Band Radar Network, worldwide radar sites In addition to these official or semi-official users, thousands of amateur radio operators and "just plain folks" all over the world use STSPLUS to track the space shuttle and other satellites. Program STSORBIT PLUS Satellite Orbit Simulation Page 9 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.FRQ Preset Frequencies (optional) STSPLUS.ICO Icon for WINDOWS 3.x (optional) STSPLUS.KEY STSPLUS Active Keys (optional) STSPLUS.LOC Map Locations & Features (optional) STSPLUS.LTD Satellite Launch Dates (optional) STSPLUS.SCF Satellite Config File (optional) STSPLUS.TRK NASA Tracking Stations (optional) STSPLUS.CTY City Coordinates (optional) STSPLUS.XRF Sat Name Cross Reference (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 (required) NASA.TRK NASA Tracking Stations (not required) CIS.TRK Russian Tracking Stations(not required) INTELSAT.TRK INTELSAT Tracking Stns (not required) SPACENTR.TRK Other Tracking Stations (not required) STSLNDG.TRK Orbiter Landing Sites (not required) README STSPLUS Registration and Questionnaire SETUP.DOC Quick Setup Instructions SOP9311.ICO Alternate STSPLUS Icon (not required) Files noted as "(required)" must be in the current default directory (or in a specified directory in some cases) for program operation. Files noted as "(optional)" are not required when STSPLUS is operated but provide Program STSORBIT PLUS Satellite Orbit Simulation Page 10 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 they are decompressed "on the fly" at load time. *** IMPORTANT NOTE *** File STSPLUS.INI contains initialization data from previous runs of the program. If file STSPLUS.INI is not present it will be created. Note that if STSPLUS.INI was written by a version prior to 9332, 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.FRQ contains a list of preset frequencies for amateur radio satellites and is not required except when STSPLUS is operated in the Doppler Shift Mode. See the section "Satellite Communications and Amateur Radio" for additional information. 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 STSPLUS.SCF is a sample multiple satellite configuration file which may be used to display multiple TDRS and real time satellites. Up to 16 additional satellites may be tracked using this feature. File STSPLUS.XRF is a satellite name cross-reference file (NORAD Number to Satellite Name) which may be used to substitute a preferred name for that found in a TLE file. STSPLUS.XRF must be in the same directory as the main program. See the section Satellite Cross-Reference for additional Program STSORBIT PLUS Satellite Orbit Simulation Page 11 information. File TLEnnn.TXT (where "nnn" will be a number such as "153") is a set of USSPACECOM 2-line elements as of the date of the file. Note that the 2- line elements should only be used for ten to twenty days after the epoch date for each satellite if reasonable accuracy is to be maintained. Current orbital elements are regularly posted on my bulletin board system and elsewhere. Other files with 2-line elements are also available; they typically have names like GSFCnnn.TXT or N2L-nnn.TXT for general satellites, and STSmmNnn.TXT for Space Shuttle missions. Space Shuttle orbital elements are usually posted at least daily during missions; because of orbital maneuvers, Space Shuttle elements more than 24 hours old may yield inaccurate positions. File STSPLUS.LOC contains geographic coordinates and labels for selected locations and major oceans and seas. These labels may optionally be displayed on the maps. The file may be edited with a standard ASCII 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 full TLEnnn.TXT files posted on my bulletin board system. Program STSORBIT PLUS Satellite Orbit Simulation Page 12 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 13 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 14 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: Pentium 90 Drawing Time WITHOUT EMM386: 1.05 seconds Pentium 90 Drawing Time WITH EMM386: 2.80 seconds 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 Times will vary as a function of the satellite position and other program features. As the example times above 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 configuration files, selected by a batch file or other methods, can optimize performance for various applications. DOS 6.2 and higher includes a multiple boot configuration facility. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 15 CONFIG.SYS: DEVICE=C:\DOS\HIMEM.SYS DOS=HIGH Change the "C:\DOS\" portion of the first line to correspond to the actual drive and directory where HIMEM.SYS is located in your system. 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. The hardware and software caching I use on one of my 486DX laptops is sufficiently large that even with Level 2 Map Database files, no disk reads are performed as the map is being redrawn. 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*.MCP and EARTH*.XYZ) 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 16 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 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: :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 Program STSORBIT PLUS Satellite Orbit Simulation Page 17 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: 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 SOP9435A.EXE and/or SOP9435B.EXE), create the STSPLUS directory as above then log into the STSPLUS directory and unpack the files with the commands: C: CD \STSPLUS A:SOP9435A 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 2.04G or later to successfully unpack .ZIP files received from my BBS or from NASA SpaceLink BBS! ******************** * IMPORTANT NOTE * ******************** If you are upgrading from a prior version of STSPLUS and experience problems, delete the file STSPLUS.INI to force the program to recreate its initialization parameters! This will resolve most path and filename problems. Use Function Keys F7 and F10+F3 from the Main Menu to set all program paths, filenames, and options. Slow Computers and 80x87 Math Coprocessor Chips ----------------------------------------------- STSPLUS has been designed for 80386/80387 or better computers equipped with an EGA or VGA color display. While the program can be executed on some older 8088/8087 (XT-class) or 80286/80287 (AT-class) computers, performance is seriously degraded. But it would seem that warnings and suggestions can NEVER convince people that their old clunker is past its prime or that the Program STSORBIT PLUS Satellite Orbit Simulation Page 18 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 486DX 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 80386 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 ULSI; while the problems may be related to the computer rather than the coprocessor chip, I recommend avoiding coprocessor chips by those manufacturers. Finally, I really don't want to hear from users how slow this program runs on older machines; I recommend the original STSORBIT if you want the best performance from any computer not equipped with a math coprocessor chip. Having said that, I DO occasionally run STSPLUS on my old 8MHz 8088/8087 LCD laptop with most features enabled. STSPLUS always runs as fast as the processor will permit and, since most features are available for all computer configurations, it is the responsibility of the user to select program features and options consistent with the desired performance. For example, the solar terminator requires considerable time to perform the required calculations and to update the display and, if this feature is not required, performace will be enhanced if it is disabled. As features have been added to STSPLUS, it has become increasingly difficult for very slow computers or computers not equipped with a math coprocessor to perform the necessary calculations in a reasonable time. STSPLUS tests to determine whether or not a math coprocessor chip is present and will use it if so. The following table illustrates the difference the processor and a math coprocessor chip make: Processor Speed Coprocessor Time (secs) --------------------------------------------- Pentium 90 MHz YES 2.5 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 All systems used MS-DOS in the "typical" configuration for the machine under test; a memory manager was present in 386 and higher systems. 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. (Not all tests were performed with the same version of STSPLUS!) 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. The Title Screen displays the processor type, coprocessor Program STSORBIT PLUS Satellite Orbit Simulation Page 19 type (if present, otherwise "(not installed)") and display type. Since STSPLUS cannot distinguish between 486DX and Pentium processors, it displays "486DX+" for those processors. 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 80386SX 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. 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 Color Graphics Adapter, 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. Support for CGA and Hercules monitors may be discontinued for future versions of STSPLUS. Program STSORBIT PLUS Satellite Orbit Simulation Page 20 Starting Program STSORBIT PLUS and Command Line Options ------------------------------------------------------- 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 STSPLUS /R/SS Force "screen saver" mode Only one display option (/EGA or /CGA) may be used. Other options may be combined and entered in any order. For example, using the following command will resume the prior mission and force EGA mode: STSPLUS /R/EGA If you are using a Hercules Graphics Card, run the program MSHERC prior to running STSPLUS. This Microsoft program works with compiled BASIC programs to enable use of the Hercules Graphics Card. Orthographic projections are NOT supported for Hercules Graphics Cards. One user reported that setting the HGC to FULL and selecting Page Zero (using software supplied with the HGC) was sufficient for proper operation. At least one HGC "clone" user reported that STSPLUS could not be run under any circumstances. If you have already run STSPLUS and simply wish to resume the prior mission, use the /R (resume) command line option: STSPLUS /R STSPLUS will sense the monitor type, enable color for EGA and VGA systems, then proceed directly to plotting the mission. The data from the last run, as saved in file STSPLUS.INI, is used to initialize the program. Once started in this manner, pressing the ENTER key after the map is displayed will return to the Main Menu. The special command line option "/R/SS", used after you have already run STSPLUS, forces the "screen saver" mode: Program STSORBIT PLUS Satellite Orbit Simulation Page 21 STSPLUS /R/SS In this mode, available only with EGA and VGA monitors, the program displays the orthographic globe with ground track and other selected display features but NO DATA. Using the orthographic globe, the screen changes frequently EXCEPT that the satellite icon remains always centered on the map and the circle outlining the globe is always drawn (which may eventually cause phosphor burns in those areas). To return to DOS, press ENTER or ESC. Several additional command line options are available to control certain map display features. These may be included in addition to the command line options above. +L Include Location and Feature Labels -L Exculde Location and Feature Labels +R Include Rivers and Lakes -R Exclude Rivers and Lakes +T Include Tracking Stations -T Exclude Tracking Stations +V Include Local Circle of Visibility -V Exclude Local Circle of Visibility These command line options are useful in the "screen saver" mode, with batch files, and for operations when no operator is present. When a feature is enabled or disabled with these command line options, the new status of the feature is saved for subsequent uses. For example, the following command line could be used in "screen saver" mode for a "minimum" display: STSPLUS /R/SS-L-R-V and normal use would be invoked with: STSPLUS /R+L+R+V The following sequence of operations is recommended when STSPLUS is run for the first time: 1. Make sure all required STSPLUS files are in subdirectory \STSPLUS (or whatever you named it). In addition to the program files, check that 2-line elements are also available; the file TLEnnn.TXT (where "nnn" is a number like "440" is usually supplied with STSPLUS) and similar files are available via BBS or the Internet. 2. STSPLUS will first request that the user enter the time offset from Universal Coordinated Time ("UTC") and whether or not Daylight Savings Time is in effect. Enter the appropriate responses. Examples are shown on the screen. 3. After a short delay, the Main Menu will be displayed. Press Function Key F7 and set all paths and filenames. If all files have been copied to the subdirectory from which the program was executed, the default values shown should be correct. Press ENTER to return to the Main Menu when all changes have been completed. Program STSORBIT PLUS Satellite Orbit Simulation Page 22 4. Press Function Key F10 followed by Function Key F2 to set your local coordinates. STSPLUS defaults to Palos Verdes, CA, near Los Angeles and some program functions require your coordinates for accuracy. Press Function Key F1 to set the primary location and follow the instructions. If your location is not included in STSPLUS file of city names (STSPLUS.CTY), select a large nearby city. If you know your local coordinates, you may enter them manually using Function Key F3 and append them to file STSPLUS.CTY. When your local coordinates have been set, press ENTER twice to return to the Main Menu. 5. Press Function Key F2 to select the primary satellite you wish to track with STSPLUS. You will be asked to select a filename (the available files whose filetype is ".TXT" or ".TLE" are displayed and may be selected using the arrow keys). Type the filename or press ENTER after selecting a filename. You will then be asked to select a satellite by name or NORAD number. If you do not know a specific satellite name, enter "HST" for the Hubble Space Telescope. (Caution: some TLE files also include "HST Array"; press the SPACE BAR to continue searching for HST.) The data for the satellite is displayed; press ENTER to accept the data. STSPLUS will immediately begin drawing the map. 6. While the map is displayed you may press ENTER to return to the Main Menu. Press ESC at the Main Menu to return to the DOS prompt. 7. STSPLUS is a complex program. Only the most basic and essential features have been covered in this brief startup list. Please take time to read the manual with your favorite editor or print the text as reference material. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 23 software must be used. There are a number of satellite tracking programs, most notably Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR, which can generate tabular data for a given satellite or group of satellites listing when the satellite(s) will be visible subject to various visibility constraints. Predicting Satellite Passes with STSPLUS ---------------------------------------- STSPLUS has a pass prediction capability (using F3 from the Main Menu) in addition to its graphics capabilities to make Line-of-Sight pass predictions for the current satellite quick and easy. Once a satellite has been selected (with F2 from the Main Menu), pressing F3 from the Main Menu, and selecting Data Format 9 (Pass Predictions ) will quickly produce a listing of the Line-of-Sight passes for that satellite over the next 48 hour period. See the section "Pass Predictions and Data Output" for additional information. Here are some comments and suggestions for satellite viewing and tracking with STSPLUS. 1. The pass predictions are listed in blocks of 48 hours beginning with the current real or simulated time, and are given an arbitrary pass number from 1 to 99. The data include the "AOS" or Acquisition of Signal when the satellite rises above the local horizon, "MAX VISIBILITY" or the time at which the satellite reaches the highest altitude above the local horizon, "LOS" or Loss of Signal when the satellite sets below the local horizon, and "Duration" or the total time the satellite is above the local horizon. Note that "local horizon" means the true horizon rather than local terrain. For either visual or electronic tracking, the altitude above the local horizon when the satellite may actually be tracked is usually at least five degrees even under optimum conditions. CAUTION: Users with slow computers, especially those without a math coprocessor, will find that pass predictions may require considerable time -- up to tens of minutes using a slow 286 without a 287! 2. Be sure to use current orbital elements for the satellite. My RPV Astronomy BBS always has current 2-line orbital elements for some 650+ satellites and these data are also available from other electronic sources. For Low Earth Orbit satellites like the Space Shuttle or MIR, orbital elements should be no more than about ten days old; for higher orbit satellites, orbital elements remain accurate for longer periods, up to about 30 days. Satellite maneuvers can radically change the orbital elements. Pass predictions can be no more accurate than the orbital elements used! 3. Examine the "Alt" (maximum altitude) given under the "MAX VISIBILITY" columns for each pass and select a suitable pass. As a general rule, the higher the maximum altitude, the better the visibility. If you 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 24 equal altitude. You may stop/pause the display by pressing Function Key F6, then move the satellite forward or backward in time using the "+" and "-" keys and adjust the time step (1, 10, or 60 seconds) with Function Key F4. Press ENTER to resume normal (simulated time) operation. 4. STSPLUS lists Line-of-Sight passes, those passes where the satellite rises above the local true horizon, and all dates and times are given in Coordinated Universal Time (UTC). Remember that under most circumstances a "visible pass" means that the satellite is in full sunlight and the viewer is in darkness. Although there are exceptions in unusual situations, this generally restricts the times for visible passes to the several hours prior to dawn and the several hours after sunset. (Note, however, that "visible" to a ham radio operator or radar tracking station simply means above the horizon!) In most cases, the Space Shuttle and satellites such as MIR Space Station and Hubble Space Telescope are visible with the naked eye given favorable lighting and weather conditions. Satellites in higher altitude orbits will be visible sooner before dawn and longer after sunset. Satellites in very high orbits, no matter how large the satellite, are seldom visible without high power binoculars or a telescope. 5. The geometry of the pass and the attitude and geometry of the spacecraft are also important. The relative angles between the Sun, the satellite, and the viewer determine how light is reflected from the surfaces of the spacecraft to you, the viewer. A spacecraft passing between you and the Sun may not reflect much light to you and may therefore not be visible even at higher altitudes. On the other hand, a spacecraft nearer the horizon but on the other side of you from the Sun may appear brilliantly lighted. The kinds of surfaces on the spacecraft are important too; solar panels and flat surfaces can reflect enough light to appear the most brilliant objects in the sky while larger but rounded spacecraft may seem all but invisible. 6. Given otherwise good conditions and favorable weather, the single most important factor is spacecraft apparent altitude ("Alt") during a pass. This is the spacecraft's apparent elevation above your local horizion. Depending upon local conditions, an altitude of at least 5 to 10 degrees will generally be necessary before a spacecraft can be seen even under the best lighting conditions. In the Los Angeles area, at least 20 or 30 degrees is a better number to use because of smog, haze and light polution (except when looking out over the Pacific Ocean). 7. After altitude, the azimuth ("Azm") is the number which describes the direction from the viewer to the spacecraft at any moment. This is given in the sense NESW, North to East to South to West, in degrees. For a good pass after sunset, for example, an azimuth ranging from 60 to 150 degrees would indicate a pass moving generally from the Northeast to the Southeast, ideal lighting conditions with the Sun in 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 25 time and a new simulated time is automatically set for a selected pass. Once set, simulated time remains in effect until changed by selecting another pass or until reset with F8 from the Main Menu. To return to "real time", press F8+F1 from the Main Menu. The Main Menu displays the current time with the time mode in effect labeled as "Current Time" or "Simulated Time". Predicting Satellite Passes with TRAKSTAR ----------------------------------------- In order to generate detailed tabular predictions for satellite passes, an external program is required. I recommend two programs for this purpose: Paul Traufler's TRAKSAT and TS Kelso's TRAKSTAR. Each programs is copyrighted by the respective author and is readily available. They are both fine programs and set a standard against which other satellite tracking programs are measured for performance and accuracy. I have selected TRAKSTAR as the default external program used with STSPLUS for two reasons: first, the program quickly produces very accurate tabular data without graphics; and second, TRAKSTAR requires minimum memory and is easily configured for seamless operation with STSPLUS. TRAKSAT is a very large program with many features, and most computers will not have sufficient memory to execute TRAKSAT when STSPLUS "shells" to DOS. In order to run TRAKSAT, users must first exit STSPLUS (press "ESC" from the Main Menu). For additional information on these programs, contact the authors: TRAKSTAR: Dr. T. S. Kelso 2340 Raider Drive Fairborn, OH 45324-2001 USA BBS: Celestial BBS (513) 427-0674 300/1200/2400/4800/9600 baud TRAKSAT: Paul Traufler 111 Emerald Drive Harvest, AL 35749 USA BBS: RPV Astronomy BBS (310) 541-7299 2400/9600/14400 baud 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 26 Celestial BBS, may use either ".TLE" or ".TXT", depending upon the file. For the past four or five years, Paul Traufler and I have been jointly releasing file TLEnnn.TXT (usually as file TLEnnn.ZIP, where "nnn" is a number like "143"). Until February, 1993, the file was named NASAnnn.TXT. This file is a sorted concantenation of files TLE.TXT and GROUP000.TLE from Celestial BBS and currently includes 2-line elements for some 700+ satellites. STSPLUS solves the filetype problem with TRAKSTAR by dynamically creating a file called STSPLUS.TLE which contains the 2-line elements for the currently selected satellite. Since STSPLUS can select 2-line elements from a file of any size, calling TRAKSTAR through STSPLUS also circumvents a minor problem in the current version of TRAKSTAR which limits the number of satellites in a 2-line elements file to 250 element sets. As a convenience, STSPLUS also dynamically creates the files STSPLUS.OBS (which contains the name, coordinates, and elevation of the current user location) and TRAKSTAR.CFG (which contains the drive and path information for TRAKSTAR). An accurate elevation (above mean sea level) for the user location is required for accurate calculations in any satellite tracking program, including STSPLUS, TRAKSTAR, and TRAKSAT. Note that the elevations of most locations in file STSPLUS.CTY are not readily available and have been set to zero. The elevation is the last parameter on each line in file STSPLUS.CTY and is given in integer meters; 1 meter equals 3.28083 feet. STSPLUS is coded to operate with TRAKSTAR Version 2.15. It may or may not operate correctly with other versions. To set up program TRAKSTAR either for independent use or for use with STSPLUS, follow the following steps: 1. Copy the TRAKSTAR files to your hard disk. Unpack the files if they are contained in an archive file such as TRAKSTR2.ZIP. I recommend using a separate directory called "TRAKSTAR". The complete TRAKSTAR package includes documentation, Pascal source, example and test files, and the program itself. The following two files are required for operation with STSPLUS: TRAKSTAR.EXE Main Program TRAKSTAR.HDR Header File Additional files are required for independent operation. Read the TRAKSTAR documentation for details. 2. Run STSPLUS and enter the drive and path information for TRAKSTAR by pressing F7+F5 (Set FILENAMES and PATHS) from the Main Menu. STSPLUS will automatically default to its own drive and directory if you omit this step. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 27 move between selections and press ENTER when you have the correct selection. Don't forget to press SPACE to select the satellite! ************* * CAUTION * ************* TRAKSTAR Version 2.15 uses the DOS clock to determine the default start and stop times for its calculations. Not mentioned in the TRAKSTAR documentation, however, is the fact that TRAKSTAR assumes that the computer is set to Coordinated Universal Time (UTC). Be sure to take that difference, including the date, into account when entering start and stop times! 6. TRAKSTAR will now make its calculations and write the results to a file. The file is written in the TRAKSTAR directory and will overwrite an existing file of the same name. The time required will be a function of the time span and time interval requested as well as the calculation speed of your computer. Read the TRAKSTAR documentation carefully so that you will recognize the name of the file that TRAKSTAR writes. For example, requesting visible passes for the Hubble Space Telescope (NORAD #20830) will result in a filename of "VOB20830" and a filetype which is the last three digits of the element set number (such as ".866"). 7. As soon as TRAKSTAR finishes, you will return to STSPLUS's Main Menu and may continue normal operations. 8. To examine the tabular data produced by TRAKSTAR, you must either "shell to DOS" using F9 from the Main Menu or exit STSPLUS by pressing ESC at the Main Menu. Use an ASCII editor to view the file or send it to your printer for hard copy. If STSPLUS cannot find TRAKSTAR.EXE (or TRAKSTAR.BAT, see below) in the selected directory, an error message will be displayed. Press ENTER to return to the Main Menu. An alternative method is to create a file TRAKSTAR.BAT in which you place all commands required to run TRAKSTAR or the satellite tracking program of your choice. STSPLUS.TLE and TRAKSTAR.CFG will still be written to the selected directory but they need not be used. This method is only recommended for individuals who understand the use and operation of DOS batch files. 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 28 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 occasionally still hear about is that a 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. Because of the poor performance of the CGA display, some program features are NOT available. Support for the CGA and HGC display may be discontinued completely in the future. 1. STSORBIT PLUS has been run extensively on systems using Microsoft DOS 3.3 through 6.2 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 6.2! Many users report good performance using IBM OS/2, Version 2.1; earlier versions of OS/2 are NOT recommended. Users report memory allocation problems with some early versions of Digital Research DRDOS 6.0 and certain third party memory allocation programs. A typical symptom of this kind of problem is that when you attempt to return to DOS, you receive an error message or the computer freezes. 2. Some math coprocessor chips fail to execute STSPLUS and similar programs correctly. In at least two reported cases, early 387SX math coprocessor chips from IIT generated random errors; when notified of the problem, ITT replaced the suspect chips and the problems disappeared. Reports indicate that USLI 387SX chips do not operate correctly with STSPLUS or TRAKSAT; Intel or Cyrix 387SX chips have always cured the problems. No problems have been reported for Intel or Cyrix chips. Program STSORBIT PLUS Satellite Orbit Simulation Page 29 3. 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 higher, 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 usually included as part of DOS.] 4. Some users report problems with certain Terminate and Stay Resident (TSR) programs for which the only remedy is to remove the offending TSR. This usually requires a "trial and error" approach to pinpoint the TSR causing the problem. The best method is to remove ALL such programs from your AUTOEXEC.BAT file, including "DOSSHELL", to make sure the program will work with your computer in the simplest possible configuration. Similarly, delete all special memory and device drivers from your CONFIG.SYS file. For DOS 5.0 and higher, include 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 with my mouse active!). 5. LCD VGA displays, such as are found on newer laptops, have 480 fixed scan line positions (unlike the variable scan modes available with CRT displays). This means that the EGA emulation used in the STSPLUS Motion Maps may use only 350 of the available 480 scan lines and the image will be compressed vertically. An alternate solution to EGA emulation is to repeat (double) some scan lines; this can result in peculiar display artifacts such as double-thick horizontal lines at certain screen locations. The solution to this dilemma varies by laptop manufacturer. 6. Even with CRT monitors, all VGA adapter cards are not equal -- just in case any of you had some illusions left. In at least one case, the aspect ratio of the CRT 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 adapter cards. So far as I know, there is no remedy. Some early VGA cards (the 449 card from Zenith is an example) are not always recognized as VGA; the card may not be register-compatible with the IBM standard and is recognized only as EGA instead. 7. 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. 8. Several users have reported "bugs" with the local Circle of Visibility and the ZOE (Zone of Exclusion) when displaying satellites with relatively high eccentricity. This is NOT a bug, rather it's a problem with the orbit. STSPLUS determines the local coverage and ZOE based Program STSORBIT PLUS Satellite Orbit Simulation Page 30 upon the satellite altitude at the instant the map is drawn and these map features are updated only when the map is redrawn. For a satellite with a high eccentricity (such as RS-10, NORAD #18129, a popular amateur radio satellite), the diameter of the local Circle of Visibility can change considerably over relatively short time periods especially when the satellite is near perigee. Likewise, TDRS coverage will be continuous near apogee and hence no ZOE. When the map is redrawn nearer perigee, coverage will not be continuous and a ZOE will be shown. To minimize this effect, press ENTER twice as the satellite approaches a point or time of interest; this will cause the map to be redrawn with current data. As an aside, the TDRS system is NOT used with such satellites! 9. The map database used with STSPLUS originated with the CIA quite some years ago (early 1980's). Certain islands in Northern Canada are shown instead as lakes, and several islands in the South Pacific are misdrawn or are missing entirely; Fiji and Western Samoa are examples respectively. Most very small islands were intentionally omitted. I have a more recent version of the map database but the current files are large and distribution is so widespread that changing the database presents major problems. For the present, I plan to continue with the current database files, errors notwithstanding. 10. Finally, as noted elsewhere, all computers are NOT equal. There are a few (usually older) computers which will not execute STSPLUS under any circumstances. Tandy is the most common offender followed by Leading Edge. Some models from these and other 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 may be an update or workaround available for these problems; check with the computer manufacturer. Program STSORBIT PLUS Satellite Orbit Simulation Page 31 Satellite Name Cross-Reference using STSPLUS.XRF ------------------------------------------------ STSPLUS can perform satellite name cross-references using file STSPLUS.XRF. Each time TLEs are read and accepted, STSPLUS checks for the cross-reference file and, if the file is present in the current directory, checks for the NORAD Number of the satellite and a cross-reference name. If found, the new name is substituted for that in the TLE file. The XRF file is standard ASCII and may be created and/or edited with a standard ASCII editor. Word processor users must use the "non-document" mode. Each entry consists of a SPACE, the five-digit NORAD Number, a SPACE, and then the satellite name. A sample file: 22920 HST Solar Array 22076 Topex/Poseidon 21225 Gamma Ray Observ 20638 Rosat Observatory 20580 Hubble Telescope 16609 MIR Space Station NOTE: The leading space shown above is required for file compatibility with XRF files used with my program ORBITEL (but is optional for STSPLUS). The NORAD Number MUST be 5 digits; pad with leading zeroes if necessary. Only one entry is read per satellite; the search stops with the first match of NORAD Numbers. There is no limit on the number of entries, but larger files with many entries may introduce a slight delay as the file is read. If the satellite name is longer than 19 characters, only the first 19 characters of the name will be used because of space restrictions on the display. Since the name substitution is unconditional, care should be taken to enter the correct NORAD Number for the named satellite; if in doubt, use F2 from the Main Menu to request orbital data by the NORAD Number (enter "#nnnnn" for the satellite name) to inspect the data and to verify that it is the correct satellite. This feature may be used to substitute a preferred name for that given in a TLE file (which may not always be consistent from source to source) or to specify the name of a payload piggy-backed on another satellite (as is frequently the case with amateur radio transponders). In the example above, "Hubble Telescope" is substituted for "HST", the satellite name usually present in TLE files for NORAD Number 20580. A number of XRF files are posted on my RPV Astronomy BBS; such files must be renamed STSPLUS.XRF before use with STSPLUS. Program STSORBIT PLUS Satellite Orbit Simulation Page 32 Preparing 2-Line Elements using VEC2TLE by Ken Ernandes ------------------------------------------------------- Especially for Space Shuttle missions, Earth-Centered Inertial ("ECI") cartesian state vectors may be the only orbital information available in near real time. Such a state vector, consisting of position and velocity data at a specified time, is sufficient to determine the instantaneous orbit of a satellite. NASA and other agencies may provide state vectors referenced to the mean equator and equinox of the Besselian year 1950 ("M50", "Mean of 1950", or "B1950") with units of measure in feet and feet per second. Data may also be available for the true equator and equinox of date (such as the state vectors generated by STSPLUS), the mean equator and equinox of the Julian year 2000 ("J2000"), or in the time-independent Earth-Fixed Greenwich ("EFG") coordinate systems. Kilometers or nautical miles or variations may also be used as the units of measure. However, STSPLUS and most other satellite tracking programs require orbital data in the "2-Line Elements" or "TLE" format and state vectors must be converted to that format before the data may be used. The 2-Line format originated as 2-Card Elements back in the days of IBM punched cards at NORAD (North American Aerospace Defense Command, now US Space Command), and has become the de facto standard format for orbital data used with satellite tracking software. Mr. Kenneth J. Ernandes has written program VEC2TLE, Vector to Two Line Elements, specifically to convert state vectors to the 2-line format. VEC2TLE is copyrighted software distributed as shareware, and registration is required prior to regular use. Mr. Ernandes has extensive experience in orbital mechanics with US Space Command and in industry, and has used his expertise to create a precision conversion program. For additional information and registration details, write: Mr. Kenneth J. Ernandes 16 Freshman Lane Stony Brook, NY 11790-2712 CompuServe: 70511,3107 Internet: 70511.3107@cis.com When writing Mr. Ernandes for information, I suggest including a stamped self-addressed envelope as a courtesy. The current version of VEC2TLE is usually posted on the RPV ASTRONNOMY BBS and on the CompuServe Astronomy and Space Forum. Note that although 2-line elements can be generated using only the data in an ECI state vector and these elements will yield an accurate position at the specified time, the "epoch" of the data, additional data (in particular, Drag and B-Star parameters) are required to generate 2-line elements which propagate accurately over time. Certain additional parameters, such as element set number and orbit number, do NOT affect the accuracy of the propagated position; these data may be obtained from other sources or default values may be used. US Space Command assigns a Catalog Number, often referred to as the "NORAD Number", some time after launch; pre-launch elements for Space Shuttle missions may have a temporary Catalog Number (corresponding to the mission number) until the actual Catalog Number is assigned. The International Designation is assigned by COSPAS at the time a launch is registered by the launching country and may be blank. Element set ("ElSet") numbers are assigned arbitrarily by the originating Program STSORBIT PLUS Satellite Orbit Simulation Page 33 individual or agency and have no effect on the orbital data. Orbit (or revolution or "REV") numbers are incremented on each revolution at the ascending node, the point at which a orbit crosses the equator heading North. Note that US Space Command does not usually use the same reference for orbit numbers as does NASA; NASA defines the first partial orbit as "Rev 1" whereas US Space Command may call that "Rev 0" or some other arbitrary number. At least for Space Shuttle missions, it is common practice to adjust USSPACECOM orbit numbers to conform to the NASA convention. VEC2TLE accepts all data required to form a complete 2-line orbital element set, either as manually entered data or from a properly formatted vector input file, performs limited error checking on these data, then displays and writes the generated 2-line elements file. VEC2TLE supports STSPLUS Data Mode 5 through 7 state vector formats. The program also supports a variety of coordinate systems, units of measure, and time formats as well as offering many other useful features. Care must be taken when using VEC2TLE that the proper units of measure (kilometers, feet, or nautical miles), coordinate system (ECI or EFG), and epoch (True of Date, Mean of 1950, etc.) are used. See the VEC2TLE documentation for additional information on the available options. STSPLUS generates ECI X-Y-Z state vectors for the true equator and equinox of date and may use any of three units of measure. NASA, on the other hand, usually generates their state vectors for the mean equinox and equator of 1950 ("M50") and uses feet and feet/second units of measure. Obviously, using the wrong units of measure or coordinate system will yield invalid results! VEC2TLE has been extensively validated and tested in conjunction with STSPLUS using NASA ECI state vectors (provided courtesy Willie Musty, Mission Support, Rockwell International, Downey, CA) heginning with Space Shuttle missions STS-56 and STS-55 in early 1993. The resulting 2-line elements yielded orbiter positions which corresponded exactly with those shown live on NASA Select TV, and the 2-line elements were in close agreement with 2-line elements subsequently released by US Space Command for a comparable epoch. In fact, during mission STS-56, Rockwell used 2- line elements at their Mission Control Center which I generated using VEC2TLE when USSPACECOM and NASA 2-line elements were not forthcoming in a timely manner. In addition to simply converting state vectors to 2-line elements, the primary purpose of the program, VEC2TLE may be used in conjunction with STSPLUS or other sources of state vectors to model orbit adjust burns and similar maneuvers. STSPLUS is used to generate a state vector at the midpoint of the burn, the appropriate delta velocities (obtained independently) are added to the state vector quantities Xdot, Ydot, and Zdot, then new, post-burn 2-line elements are generated with VEC2TLE. More complex maneuvers may also be calculated or modeled although these more complicated exercises are not recommended for the novice. VEC2TLE may also be used to precess a set of 2-line elements to the next Ascending Node, required by some software. My thanks to Ken Ernandes for writing VEC2TLE, for making it available to the satellite tracking community, and for his assistance in validating the precision state vector output data from STSPLUS. Thanks also to Willie Musty (for providing state vectors) and to Joel Runes (for validation and testing). As with any complex program, considerable effort has been expended in writing, testing, and documenting the program. If you use VEC2TLE, please register your copy so as to encourage Ken and others to continue writing such useful software. Program STSORBIT PLUS Satellite Orbit Simulation Page 34 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 35 Press ENTER to ACCEPT this city as your PRIMARY location, OR Press ESC or SPACE to cancel this data: Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9435 Current time: 19:01:32 PDT 02:01:32 UTC Current date: 26 JUL 1994 27 JUL 1994 Last Mission = Mir 2-Line Elements File = C:\STSPLUS\TLE431.TXT CPU Type = 80486DX+ or 80486SX NDP Type = 80486DX+ or 80487SX Display = VGA Color (C) Copyright David H. Ransom, Jr., 1989-1994 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 36 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 37 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 38 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 39 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 40 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 current map projection. Since this map mode uses the ZOOM map algorithms, the usual zoom map features (PgUp, PgDn, Home, End) may be used to adjust the field of view (zoom or magnification). 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 ("."), dash ("-"), 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 41 locations to avoid this problem! If you wish to add your own locations 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 magnifications. All labels are automatically centered with respect to longitude. IMPORTANT NOTE: The program performs no error checking on the contents of the location and features file. 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 or creating a location and features file. Illegal characters will be replaced by a SPACE. 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 42 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 43 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 in refracted sunlight Red Satellite is in umbra Dim White In addition, an asterisk ("*") is shown to the right of "Orbit #" when the satellite is sunlit or in penumbra; this will assist users of monochrome monitors where colors cannot be distinguished. For better visibility, the satellite symbol will normally "blink" on CGA monitors; the symbol may be made to blink on any system if desired by pressing the letter "B" while the ground track is displayed. Note however that for very slow computers, the blink may appear erratic if most of the time is spent performing calculations. Just seeing the spacecraft or satellite on the map display yields information as to its present position. However, for satellite viewing and planning purposes, STSPLUS calculates the predicted ground track for approximately three hours in the future and the past ground track for approximately one and a half hours in the past. The ground track may be selected to display as a series of light green dots (future track) or light red dots (past track), as a solid light green line, or as a solid light green line with yellow dots(future track) and light red dots (past track). The dots are plotted at one minute intervals. To select the desired ground track display, press Function Key F10 and then press Function Key F5 until the desired mode is displayed; the available selections are: OFF, DOTS, LINE, and BOTH. Note that for satellites in high Earth orbits, the ground track may appear as a solid line if the dots are very close together. Unlike prior versions of STSPLUS, the ground track is NOT updated (except to re-color dots for past track). With automatic map generation off, the map will be automatically redrawn every 2.5 hours. Program STSORBIT PLUS Satellite Orbit Simulation Page 44 Satellite Visibility -------------------- Satellite visibility, or the ability to see a satellite with the naked eye (or binoculars for the truly dedicated), attracts the novice and expert alike. It can be a great thrill to point out the Space Shuttle or MIR Space Station to a child or a friend as it streaks across the sky where and when predicted. Unfortunately, predicting that visibility is more complicated than "simple" orbital mechanics and trigonometry; spacecraft altitude, position, physical geometry, reflectivity, and attitude with respect to both the viewer and the Sun, as well as local atmospheric clarity not to mention weather, all contribute to whether or not a satellite may actually be seen. Some of these factors are beyond the capabilities of a program like STSPLUS. All that can be done is to indicate when conditions are such that the satellite MIGHT be sighted visually. STSPLUS estimates viewer visibility by calculating that: a) The satellite is at least partially lighted by the Sun; b) The Sun is 1.7 degrees or more below the viewer's horizon so that the viewer is in at least partial darkness; and, c) The satellite is within the viewer's local circle of visibility and is four degrees or more above the horizon. If all these conditions are met, STSPLUS displays the word "VIS" in the data block next to the orbit inclination. To these calculations must be added the uncertainties described above. In my experience, the best satellite sightings have usually occured when I am between the satellite and the Sun, enabling flat surfaces such as solar panels to reflect the sunlight back to me. Although STSPLUS makes the visibility calculations for any satellite, as a general rule only satellites in low Earth orbit, say under 1000 km (600 miles) altitude, are likely to be seen with the naked eye. Binoculars can extend that range somewhat. Satellites in very high or geosynchronous orbits can be seen only with precision optical or radar equipment. Last but not least, current 2-line elements must be used for reliable predictions. ********** * NOTE * ********** SATELLITE VISIBILITY IS ONLY ACTIVE WHEN THE SOLAR FEATURES ARE ENABLED WITH F10+F3+F8. User's Circle of Visibility --------------------------- Centered around the user's geographic location, and marked with a small circle on EGA and VGA systems, is a magenta circle of the approximate line of sight visibility for the mission in progress. For rectangular projections, the "circle" appears on the display as a circle near the Equator and as a distorted circle at higher latitudes. In near-polar regions, the circle takes on a very strange shape. The shape is entirely an Program STSORBIT PLUS Satellite Orbit Simulation Page 45 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+F8 from the Main Menu), tones sound 2 minutes before the satellite enters the circle of visibility and again 30 seconds before the satellite leaves the circle of visibility. Both the primary and secondary locations are monitored, with slightly different tones for each. And "up-down" sequence of tones is used prior to entry into the circles and a series of tones prior to leaving the circles. When a satellite is within the circle, direct visual, radio or radar communications with the satellite should be practical. Actual visibility, of course, depends upon more than simply whether or not the satellite is above the viewer's horizon. Most important is the sun to satellite to viewer geometry; the satellite must be in sunlight and the viewer in darkness for reasonable visibility. Almost as important is the size and geometry of the satellite itself; a large, bright-metal satellite with huge solar arrays reflects far more sunlight than a small dark satellite. In addition to the satellites themselves, many booster rockets and other "spare parts" are orbiting the Earth. Since they are not attitude stabilized, booster rockets often are tumbling and may therefore appear to flash on and off as they pass over. For the Space Shuttle as well as most other satellites with near circular orbits, the circle of visibility calculations are reasonably accurate; however, the position of the sun and the effect of atmospheric refraction are not taken into account, only whether or not the satellite is in line of sight view from the observing location. For highly eliptical orbits, however, the accuracy is substantially degraded since the radius of the circle of visibility changes dramatically depending upon whether the satellite is nearer apogee or perigee at the time the calculation is made, and the period of the orbit. In the course of a single orbit, the altitude of such a satellite may change by thousands of miles. Satellite "DE 1", usually included in the TLEnnn.TXT 2-line elements file, is in a highly elliptical orbit with long period and illustrates the problem. Spacecraft Circle of Visibility ------------------------------- The spacecraft circle of visibility is calculated dynamically using the same alrorithm as for the user's circle of visibility. Like the user's circle, the spacecraft circle may appear on rectangular projections as an odd shape because of the scaling factors used by the map projection. The difference is that the spacecraft circle moves with the spacecraft and illustrates the approximate area visible from the spacecraft at any given moment. The circle is updated every ten seconds (or as frequently as the processor will permit). Comparisons using a VGA display system during the STS-35/ASTRO-1 mission in December, 1990 confirmed that the circle shown is quite close to that shown by one of the special graphics displays occasionally seen on NASA Select Television as well as the actual horizon view seen from the payload bay television cameras. Program STSORBIT PLUS Satellite Orbit Simulation Page 46 SUN and Solar Features ---------------------- Many types of observations, especially Earth observations, often require that the target or terrain be in sunlight. The performance of solar panels and certain other instruments on a spacecraft is dependent upon whether or not the Sun is in view. Also, it is usually impossible to visually see a spacecraft which is not in sunlight. The solar terminator is a series of yellow points on the display which represent the line at which the center of the Sun is at an observer's horizon for Mean Sea Level. Although a quick glance at the clock should suffice to determine which side of the terminator line is in sunlight and which in darkness, EGA and VGA systems also display the Sun as a small yellow circle. The terminator as displayed by STSPLUS is sometimes confused with a line denoting sunrise and sunset. Two factors make the terminator only an approximation: first, the terminator is based upon the center of the Sun, while actual sunrise and sunset are calculated using the upper limb of the Sun; and second, the terminator is calculated for Mean Sea Level rather than a specific local elevation. These two factors combined can result in a difference of up to ten minutes when the times are compared against published values or those calculated by my program ASTROCLK, sunrise being earlier and sunset being later. The Sun and solar features are enabled and disabled using F10+F3+F8 from the Main Menu. Since these features -- especially the terminator -- require some calculation and drawing time, users with slower computers may wish to disable these features for faster screen updates. The following features are included: Sun: A yellow circle is plotted at the sub-solar point, the geographic coordinates directly beneath the current position of the Sun. The position of the Sun is recalculated every 10 seconds and the display is updated every 60 seconds. (Not shown on CGA and HGC displays.) Terminator: A dotted yellow line is plotted for the solar terminator, that point on the Earth at which the center of the Sun is at the horizon. The terminator is partially updated every 10 seconds and is fully updated every 60 seconds.The terminator is shown for Mean Sea Level and does NOT take into account the non-spherical shape of the Earth. Lighting: The current spacecraft lighting is shown using color for the satellite icon, and in the data block (to the right of "Orbit #:") and displayed using the following symbols and colors: * Bright White Full sunlight + Yellow Partial sunlight (penumbra) - Light Red Refracted sunlight White Full shadow (umbra), no symbol Note that Yellow and Light Red will display as Bright White or shades of gray on monochrome monitors. Program STSORBIT PLUS Satellite Orbit Simulation Page 47 Solar lighting conditions are updated every second or as rapidly as the speed of the processor will permit. In order to minimize calculation delays during ground track plotting, the event times for orbital sunrise and sunset are approximated. The dynamic lighting calculations, used to plot the color of the spacecraft icon, are more precise. Typical errors due to the simplified algorithm, are on the order of 10 seconds. SUN Timer: When Event Timers are enabled, the orbital sunrise (AOS) and sunset (LOS) times are shown. A blank AOS or LOS timer indicates the event will not occur within the next four hours. An asterisk ("*") to the left of "SUN" indicates sunlight is on the satellite: AOS LOS *SUN 73:20 37:40 In this example, the satellite is in sunlight. Orbital sunset will occur in 37:40 and the next orbital sunrise will occur in 73:20. Program STSORBIT PLUS Satellite Orbit Simulation Page 48 TDRS and Real Time Satellite Features ------------------------------------- TDRS and Real Time Satellite features are available only on EGA and VGA monitors. These features permit up to thirty two additional satellites to be tracked in real time. Satellites to be tracked are designated by the user as "static" (geosynchronous or geostationary) and "real time" (satellites whose sub-satellite point changes substantially with time). Static satellites are only plotted when the map is redrawn; real time satellites are updated every second with 386/387 or better computers, every ten seconds for older computers, or as often as the processor can complete the required calculations. When using X10 or X60, the update occurs at the display rate (10 or 60 seconds). When TDRS and Real Time Satellite coverage is enabled (F10+F3+F2), all 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 shown as a dot inside a small circle near the Equator (provided they have been included in the current TDRS and Real Time Satellite configuration). Use F6 from the Main Menu to display and/or modify that configuration. See the text section on Function Key F6 for a complete description of Static and Real Time satellites. As of August, 1993, there are five TDRS satellites in geosynchronous orbit. The primary satellites consist of TDRS East ("TDRS 3") at approximately 41 degrees West longitude and the TDRS West Cluster consisting of two satellites, TDRS West ("TDRS 4") and TDRS Spare ("TDRS 1") at approximately 174 and 170 degrees West longitude respectively. The TDRS Spare satellite has partially failed but is used occasionally as a backup; this satellite is also low on propellant and is allowed to drift considerably with an inclination of about 7 degrees. "TDRS 2" has also partially failed and is currently parked at approximately 62 degrees West longitude and is presently dedicated to downlinking data from GRO, the Gamma Ray Observatory, whose tape recorders have failed. "TDRS 5" is the most recent satellite launched, is fully operational, and is parked at about 138 degrees West longitude as an on-orbit spare. Users should check the current positions of the TDRS satellites since they are periodically moved or reassigned. Each TDRS location provides communications coverage for almost half of the Earth for low Earth orbits and essentially full time coverage for higher orbits. However, since the NASA Ground Terminals are located at White Sands, New Mexico, the coverage has been slightly overlaped to provide good ground communications at White Sands. 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 primary TDRS for low Earth orbits. Two red "circles" on the display show the limits of coverage for each primary TDRS satellite. Each circle, whose shape may be quite distorted when using rectangular projection, encloses an area where the TDRS satellite is out of range of the primary satellite being tracked 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 for TDRS East and TDRS West. The method used for the calculation of the TDRS coverage is usually accurate to about 10 seconds (assuming accurate 2-line elements for the satellite and for the TDRS). However, spacecraft attitude can cause loss of Program STSORBIT PLUS Satellite Orbit Simulation Page 49 TDRS communications at unexpected times. When Event Timers are enabled, STSPLUS calculates AOS and LOS for four hours (240 minutes) from the time the map is drawn. If a time is beyond that limit (or if the condition does not occur), the time is left blank. Each time is presented in the form of a countdown clock, minutes and seconds, until the next occurence of the condition: *TDRE AOS/LOS 72:42 50:42 (for rectangular projections) *TDRW AOS/LOS 45:42 22:42 AOS LOS *TDRE: 72:42 50:42 (for orthographic projections) *TDRW: 45:42 22:42 An asterisk ("*") is shown to the left of the satellite name if AOS is in effect. For rectangular projections, these data are displayed in the lower right portion of the map. For EGA and VGA users, however, the data may be displayed in the lower section of the data block by pressing F2 while the map is displayed until MET/T+E is displayed. For orthographic projections, the data are part of the standard data block at the right of the screen. The clocks for each TDRS are color coded to indicate the current status: GREEN when the satellite is in communication, and RED when the satellite is out of range of the TDRS. Two minutes prior to a change in status, the appropriate clock color changes to YELLOW. Users with monochrome monitors must observe the presence or absence of the asterisk to determine the status. STSPLUS can sound an audible alarm (three beeps) 30 seconds prior to TDRS AOS or LOS. Use F10+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 NAVSTAR Global Positioning Satellites (GPS), with orbital altitudes of about 11,000 nautical miles (20,000 kilometers), are an example. For such high orbits, the coverage by each TDRS satellite is nearly continuous. As noted above, there are currently five TDRS satellites in orbit as of mid 1993, TDRS 1 through TDRS 5. (These numbers are those currently used by US Space Command in their 2-line elements. NASA sometimes uses different numbers corresponding to the original launch letters as shown in the following chart. TDRS "B", which should have become "TDRS 2", was lost in the Challenger accident.) As of July, 1993, the TDRS assignments are: TDRS# * NORAD# Long Description ----------------------------------------------------------------- TDRS 1 (A) 13969 -170W TDRS West Spare, used occasionally TDRS 2 (C) 19548 -62W Dedicated to Gamma Ray Observatory TDRS 3 (D) 19883 -41W TDRS East (STSPLUS default) TDRS 4 (E) 21639 -174W TDRS West (STSPLUS default) TDRS 5 (F) 22314 -138W On-orbit spare * Original NASA letter designation at launch STSPLUS will use TDRS 3 and TDRS 4 by default and approximate positions as of July, 1993 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 5 or letters A through D or E. Use the Program STSORBIT PLUS Satellite Orbit Simulation Page 50 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 using the automatic update feature with F2 from the Main Menu to read and update the 2-line elements. Ground Tracking Stations and .TRK files --------------------------------------- NASA maintains a number of ground tracking stations around the world. Some of these tracking stations are essential for the ascent or landing phases of a space shuttle flight; others are used for in-flight communications. File STSPLUS.TRK contains the information for these ground tracking stations. Other files with filetype .TRK contain the information for other launch and/or tracking stations. Each ground tracking station is shown as a small symbol surrounded by a brown or light yellow "circle of visibility" which gives the approximate area of antenna coverage and shows how small a proportion of each orbit can be monitored without the TDRS system. When for some reason the TDRS system is down (as has occurred during infrequent computer failures at White Sands, New Mexico, the TDRS Ground Station), these ground tracking stations become the only means of communication with the Space Shuttle. (Another unexpected method was demonstrated during a 1992 space shuttle mission when the SAREX, Shuttle Amateur Radio EXperiment, was used during a complete loss of normal communications!) Because of budget constraints, many of these ground tracking stations may be (or have already been) shut down. Some, such as MIL and BDA (see list below) will be retained because they are required for the ascent phase of a space shuttle mission. Others, such as HAW, CTS and GWM, are operated jointly with, or independently by, the U.S. Air Force. NASA is not always consistent as to the abbreviations used for these tracking stations; on NASA Select TV, Gwan, Hawaii, and Vandenbert are usually shown as GTS, HTS, and VTS respectively. When using rectangular map projections, the shape of the antenna range "circle of visibility" varies as a function of the latitude and is an artifact of the map projection; when projected on a sphere, as is the case with orthographic projection, they are true circles. In order to avoid cluttering the display with countless meaningless lines, tracking station circles of visibility are shown only if that circle has an angular diameter of 90 degrees or less. The following table lists the internal ground tracking stations as of early 1989 which are shown along with their abbreviations and approximate map coordinates (longitude, latitude): MIL -81,28 Merritt Island, FL BDA -64,32 Bermuda DKR -17,14 Dakar, Senegal ACN -14,-8 Ascension Island MAD -5,41 Madrid, Spain IOS 56,-5 Indian Ocean HAW -156,20 Hawaii GWM 143.33,14 Guam VAN -120.57,34.73 Vandenberg, CA YAR 115,-29 Yarragadee, Australia Program STSORBIT PLUS Satellite Orbit Simulation Page 51 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" "Yarragadee, Australia",115,-29,0,"YAR" "Guam",143.3333,14,0,"GWM" "Canberra, Australia",149,-36,0,"CAN" These files are ASCII and may be prepared or edited with any standard ASCII editor; if using a word processor, select the "non-document" mode. Five items are required for each location; the longitude and latatude are expressed in degrees and fraction of a degree, elevations above Mean Sea Level are expressed in meters, and names or abbreviations are included in double quotation marks. The following example illustrates the .TRK file format: "Merritt Island, FL",-81.0,28.0,0,"MIL" --------+----------- --+-- --+- + --+-- | | | | | | | | | +--- 3-Letter Abbreviation | | | +------- Elevation (meters) | | +---------- Latitude (degrees) | +---------------- Longitude (degrees) +------------------------------- Location Name For those interested in the Russian space program, a list of Russian ground tracking stations is provided in file CIS.TRK (data courtesy Ellwood Marshall). With the breakup of the Soviet Union, some of these installations may no longer be active or the name may have changed. "Tyuratam Cosmodrome",63.3392,45.9235,0,"TYR" "Kaliningrad Cntrl Ctr",37.816,55.916,0,"KAL" "Plesetsk Cosmodrome",40.7,62.75,0,"PLS" "Petropavlovsk Russia",158.933,53.216,0,"PTR" "Tbilisi Georgia",44.75,41.66,0,"TBL" "Ulan Ude Russia",107.683,51.983,0,"ULN" Program STSORBIT PLUS Satellite Orbit Simulation Page 52 "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 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 53 Source) or "LOS" (Loss of Signal or Source) and are generally calculated for line of sight conditions. Each phenomena which may be timed has an associated AOS and LOS timer which displays the hours and minutes ("HHH:MM") remaining until the next event if that event will occur within the next four hours (240 minutes), one hour past the last time for which the ground track is plotted. The current status of the signal or source is indicated by the color of the timer digits and the presence or absence of an asterisk ("*") to the left of the event name: GREEN indicates signal or source acquisition, and RED indicates signal or source loss. Two minutes prior to an event, the timer for that event will change from the signal status color (GREEN or RED) to YELLOW to visually alert the user. Users with monochrome monitors will be unable to distinguish these color changes, of course, but can determine the current signal status using the asterisk indicator. All calculations for upcoming events are made each time the ground track is drawn on the display and will affect the time required to prepare the display, especially on slower computers. In order to minimize these calculation delays, the event calculations for orbital sunrise and sunset use a simplified algorithm which does not take into account the non- spherical shape of the earth (unlike the dynamically calculated spacecraft lighting features which are more accurate). Orbital sunrise and sunset are the times that the spacecraft transitions between refracted sunlight (sunlight refracted through the Earth's atmosphere) to partial sunlight (illumination from only a portion of the solar disk); this corresponds to the transitions between RED and YELLOW color on the satellite icon and illumination symbols respectively. The errors resulting from the simplified algorithm are usually less than plus or minus 10 seconds; because of the more oblique angles and geometry involved, higher errors are usually associated with higher inclination orbits. When no secondary location is selected, the headings "AOS" and "LOS" will appear in orthographic modes; the headings do not appear in rectangular modes or in orthographic modes when a secondary location is selected in order to make room for the additional line of data. Typical Event Timers are shown in the following examples. For orthographic projections: *STN 95:15 6:21 AOS now in effect AOS will next occur in 95:15 LOS will occur in 6:21 STN 23:47 45:18 LOS now in effect AOS will occur in 23:47 LOS will next occur in 45:18 and similarly for rectangular projections: *TDRW AOS/LOS 85:14 33:43 AOS now in effect AOS will next occur in 85:14 LOS will occur in 33:43 TDRW AOS/LOS 14:21 57:32 LOS now in effect AOS will occur in 14:21 LOS will next occur in 57:32 Program STSORBIT PLUS Satellite Orbit Simulation Page 54 except the primary location AOS/LOS, which is unlabeled in rectangular projections and appears at the upper right of the data block (immediately to the right of MET/T+E): * 89:39 1:27 AOS now in effect AOS will next occur in 89:39 LOS will occur in 1:27 70:15 76:38 LOS now in effect AOS will occur in 70:15 LOS will next occur in 76:38 The following events may be timed and will cause an audible alarm if audible alarms are enabled and the appropriate events are enabled: Local Visibility For the primary location ("STN" or "STN1"): three sets of up/down tones two minutes prior to AOS and five tones thirty seconds prior to LOS. For the secondary location ("STN2" if enabled): two sets of up/down tones two minutes prior to AOS and four tones thirty seconds prior to LOS. Refers to the times the satellite enters or leaves the local circle of visibility. TDRS Acquisition ("TDRE" or "TDRW" if enabled) Three short tones thirty seconds prior to AOS or LOS. Refers to the times the satellite acquires or loses the ability to communicate with either of the programmed Tracking and Data Relay Satellites. Orbital Sunrise/set ("SUN" if enabled) Two tones thirty seconds prior to approximate orbital sunrise or sunset. Refers to actual line of sight solar contact; refracted sunlight is not included. The characteristics of the audible tones have been selected to allow the user to uniquely identify the AOS or LOS event that is about to happen. STSPLUS is now "aware" of program RighTime by Tom Becker and its use is recommended for accurate timekeeping. Audible alarms in prior versions would perform unpredictably when RighTime was active because they use the hardware clock's timer functions (which RighTime also uses). STSPLUS now detects RighTime and temporarily disables RighTime while an audible alarm is being generated and then re-enables RighTime after the alarm has completed, restoring precise timekeeping. With RighTime active, alarms are generated in foreground, which may cause a slight delay in screen updating. ************* * CAUTION * ************* STSPLUS expects RighTime Version 2.5+; performance with prior versions of RighTime may yield unpredictable results. If using a prior version of RighTime, do NOT enable audible alarms! Program STSORBIT PLUS Satellite Orbit Simulation Page 55 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. 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 56 Switching between MET and T+Epoch --------------------------------- 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 "T+E" and "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. Once the ground track map is displayed, the F5 command may be used to switch the display between Time Since Epoch ("T+Epoch" or "T+E") and Mission Elapsed Time ("MET"). The F5 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, the command will have no effect. Press ENTER to return to the Main Menu and press F5 to enter launch time and launch date. Using FAST Time --------------- Press F4 while the map is displayed to use FAST time. FAST TIME is a variation of SIMULATED TIME which automatically advances the time displayed by 10 or 60 seconds, as indicated at the upper left of the screen. Press F4 again to change the time step; when "(X10)" or "(X60)" is NOT displayed, the time step is one second. The actual time increment is a function of the computer's speed. For fast computers, the time increment will usually be 10 or 60 seconds but may vary by a second occasionally; for slower computers, the time increment may be somewhat longer. FAST time is disabled when PAUSE mode is in effect and for the Satellite Motion Map. 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 57 On-line Help ------------ An on-line Help Screen is available during the ground track display to remind the user of the available functions and which keys to press to trigger those functions. When the ground track display is active, press Function Key F1 to display the Help Screen in the lower portion of the display. The following help screen will appear in rectangular modes: F1=Resume Data F6=Pause (+,-) TAB=Auto Maps On/Off L=Location Maps F2=Select Clocks F7=Circle of Vis W=World Maps T=Tracking Maps F3=Printer Log 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 9435 The help screen in orthographic modes is similar but in a vertical format at the right side of the screen. The ground track display will continue to be updated in real time while the help screen is displayed. If only the graphical display of the ground track is of interest, the help screen may be kept on the display continuously. Press Function Key F1 again to return to the normal data display in the lower portion of the screen. Note that the Help Screen is disabled when the Motion Map is displayed. Program STSORBIT PLUS Satellite Orbit Simulation Page 58 Satellite Communications and Amateur Radio ------------------------------------------ By now, everyone is familiar with communications satellites. They provide almost instant communications, particularly television, around the globe from their assigned geostationary "parking slots" some 22,300 miles above the surface of the Earth. The concept of the geostationary communications satellite was originated by the science fiction writer Arthur C, Clarke some thirty-odd years ago. Novel and revolutionary at the time, they have become an accepted part of global communications, all but taken for granted by the millions of people who see the images they transmit over vast distances. Glossing over some of the "minor technological details" that make these miracles possible, the communications satellite is relatively easy to use. Because of its geostationary orbit (which matches its orbital velocity with the Earth's rate of rotation), it appears to remain at the same point in the sky. Once properly located, ground terminals may be more or less permanently aimed and that's that. Reliable communications are routine except during the semi-annual Sun blockage periods when the Sun, satellite, and ground terminal are in a direct line with each other and the Sun's powerful radiation overwhelms the signals from the satellite. However, geostationary communications satellites are but one example of the uses for satellite communications. Except for a relatively few passive satellites, each satellite has on board radio transmitters and receivers so that its ground control centers may send commands and receive data; these commands and data provide for the operational control and orbital position and stability of the satellite. Unlike the geostationary communications satellites, these satellites are in orbits which cause them to appear to move rapidly across the sky when viewed from the ground. The typical effective ground speed of the space shuttle, for example, is some 17,500 miles per hour; other satellites in higher orbits move more slowly. Viewed from afar, both the ground station and the satellite are moving rapidly, sometimes toward each other and sometimes away, as a result of the rotation of the Earth and orbital direction/velocity respectively. Since the typical satellite's receiver(s) and transmitter(s) are usually set for fixed frequencies, these high relative velocities cause a problem on the ground known as Doppler Shift. Almost everyone has heard a train whistle as it speeds past; the whistle's pitch is high when first heard, then drops steadily as the train passes. The "true" pitch of the whistle is heard when the train is opposite the listener. While the train is approaching the pitch is shifted to a higher frequency, and as the train recedes the pitch is shifted to a lower frequency. For satellite communications, this effect is increased by the much higher relative velocities involved and it is usually necessary to adjust the transmit and receive frequencies on the ground to compensate for the shift. Stated simply, the ground station must adjust its transmitting frequency such that the shifted frequency as received by the satellite is the exact frequency for which the satellite receiver is set. Similarly, the ground station must adjust its receiver frequency to the shifted frequency at which the satellite's signal will be received. Like the train whistle, the ground station's transmit and receive frequencies are constantly changing as the satellite approaches and then departs from the ground station. As a general rule, no two satellite passes over a ground station have exactly the same geometry and therefore these frequency shift adjustments must be calculated dynamically for each pass. In the special Program STSORBIT PLUS Satellite Orbit Simulation Page 59 case of Frequency Modulation (FM) transmissions using a receiver with Automatic Frequency Control (AFC) and a sufficiently wide receiver AFC bandwidth, no adjustments may be necessary. Given a satellite's orbital paramaters and the appropriate computer software, these data can be calculated in advance of an upcoming pass as well as in real time. Most of the required data are already calculated in satellite tracking software such as STSPLUS. Ken Ernandes, N2WWD, offered his expertise and amateur radio equipment to assist in the implementation and test of Doppler Shift calculations in STSPLUS. The necessary changes and additions to the software were implemented in mid-March 1994 and Ken made a preliminary test using Radio Sputnik 10 (RS-10, a piggybacked transponder on the Russian COSMOS 1861 satellite, NORAD #18129). To our considerable surprise and delight, the very first test was a complete success; although the satellite only reached a maximum of 7 degrees above the ground station's horizon, the transponder signal was heard (rather weak and noisy) on the predicted frequency. Although we both were confident in our mathematical solution to the Doppler shift problem, it is seldom that such calculations turn out to be correct on the first try! Testing and validation continue. STSPLUS Doppler Shift Mode -------------------------- STSPLUS' Doppler Shift Mode of operation may be used for real time communications with any satellite, not just amateur radio transponders, for which orbital data ("2-line elements" or "TLE") are available. For each satellite, the user prepares a preset frequency list in file STSPLUS.FRQ which includes the satellite's NORAD Number, the transmit (XMIT) and receive (RECV) center frequencies, and a special code which is used to select NORMAL or INVERTED satellite transmitter transponders (see below). For satellites with fixed transmit and receive frequencies, that is all that is required; for satellites which receive and transmit over a band of frequencies, such as the passbands of the typical amateur radio repeater transponder, the receive and transmit frequencies may be quickly "tuned" in tandem by fine increments of 100 Hz or coarse increments of 1 KHz over the entire passband. For those who may be interested, the solution of the Doppler shift computations required that the ground station position vector and the satellite position and velocity vectors be calculated using standard transformation algorithms (and the SGP4 Orbital Model for determining the satellite data), then converted to Earth-Fixed Greenwich ("EFG") coordinates, a geocentric intertial coordinate system using the WGS-72 Geodetic Model. From these data the relative velocity and frequency shift ratios are next calculated. These ratios are then applied to the preset transmit and receive center frequencies to yield the shifted frequencies, all of which are then displayed to the user. Provided the computer is equipped with a math coprocessor chip, all data are updated each second. The following is an example of the frequency data displayed as a satellite (RS-10 in the example) approaches the ground station: UpLink: 145.8900 Uplink frequency received by satellite XMIT: 145.8880 TRANSMIT frequency at ground station DnLink: 29.3900 Downlink frequency xmitted by satellite RECV: 29.3904 RECEIVE frequency at ground station Program STSORBIT PLUS Satellite Orbit Simulation Page 60 The shifted transmit frequency (XMIT) and receive frequency (RECV) are also color coded to indicate the signal status: RED The satellite is below the receiver horizon; communications are normally not possible. YELLOW The satellite is from zero to five degrees above the receiver horizon; transmissons MAY be possible. GREEN The satellite is five degrees or more above the receiver horizon; transmissions should be practical if the receiver horizon is clear in the direction of the satellite. The altitude (or elevation) of the satellite above the receiver horizon is usually a good indicator of communications capability. However, transmitter power, receiver sensitivity, antenna structure and orientation, and atmospheric conditions all play a role in making reliable full duplex communications practical. For example, the large antennas used by the DOD C-Band Radar Network, used to track the orbiter and other satellites during ascent and critical maneuvers, typically acquire signal lock when the satellite is between 3 and 4 degrees above the local horizon. A low power amateur radio rig may require that the satellite be from 5 to 8 degrees above the local horizon for reliable communications. To illustrate the role atmospheric conditions may play, the space-based geostationary TDRS (Tracking and Data Relay Satellite) typically acquires signal lock with a target satellite at or near Earth limb (what passes for the "horizon" at the satellite). In addition to the frequency data, the ground station ("STN") times for Acquisition of Signal ("AOS") and Loss of Signal ("LOS"), calculated for the true ground station horizon, are displayed so that the user may quickly determine how soon a pass will begin or how much time remains in a current pass. For ground station to satellite communications, operation is straightforward. The user simply adjusts his transmit ("XMIT") and receive ("RECV") frequencies to those shown by STSPLUS as the satellite passes his location. Since the frequencies required at the satellite are known and do not change, there are no "fine tuning" adjustments required. Compared to a satellite with fixed receive and transmit frequencies, the typical amateur radio satellite transponder (also referred to as a "crossband repeater") presents a slightly more complex situation. The transponder receives signals across a passband of frequencies (20 to 80 KHz are typical bandwidths), then retransmits the received signals across a passband of the same width but centered at a different frequency. The center frequency of the receive and transmit passbands are known in advance but may change from time to time depending upon the transponder mode (CW, voice, digital packet, etc.). The transmit side of the transponder may also operate in either NORMAL or INVERTED mode. That is, for NORMAL mode the transmitted signal is the same frequency above or below the center frequency as is the received signal; for INVERTED mode, the transmitted signal is the same frequency above (below) the transmit center frequency as the received signal is below (above) the receive center frequency. STSPLUS addresses this situation in two ways. First, once the user has received a signal of interest, he uses the PgUp, PgDn, UP, and DOWN keys to "fine tune" the downlink frequency shown by STSPLUS ("RECV") until it matches the actual received frequency. PgUp and PgDn perform "coarse tuning" in increments of 1 KHz, and UP and DOWN perform "fine tuning" in Program STSORBIT PLUS Satellite Orbit Simulation Page 61 increments of 100 Hz. The response is quite rapid and the fine tuning may usually be performed in no more than several seconds. STSPLUS then makes the necessary calculations to show the required uplink frequency ("XMIT") to permit full duplex communications. The second part of the problem is the transponder mode; STSPLUS selects NORMAL or INVERTED transponder mode based upon the mode parameter supplied by the user in file STSPLUS.FRQ: 1 = NORMAL, -1 = INVERTED. Satellite Phase (Mean Anomaly) ------------------------------ Some amateur satellite transponders (an example is AO-13) change their mode of operation based upon a parameter called "phase". Data is published by AmSat and/or others for these transponders giving the mode of operation for specific ranges of Phase. Phase is the Mean Anomaly, one of the six parameters of orbital data, normalized to the range from 0 to 255. Phase = 0 (Mean Anomaly = 0 degrees) corresponds to perigee, the point at which the satellite's orbit makes its closest approach to the center of the Earth (NOT the surface!); Phase = 128 (Mean Anomaly = 180 degrees) corresponds to apogee, the point in the orbit at which the satellite is most distant from the center of the Earth. When the Doppler Shift Mode is enabled in orthographic projection (by pressing F8 while the map is displayed), the Phase is displayed PROVIDED that the Eccentricity is greater than or equal to 0.005: Phase: 123.9 When the conditions for the display of Phase data are met, it replaces the orbital period data ("Per'd") in the Doppler Shift Mode; if not, the orbital period data will be displayed. Technically, Phase is defined as an integer in the range 0 to 255. However, in order to give the user some advance warning when the Phase will step from one number to the next, STSPLUS also displays the first decimal digit. Phase is NOT displayed in rectangular projections due to insufficient display space. TECHNICAL NOTES REGARDING PHASE: 1. The Mean Anomaly is dynamically calculated by the SGP4 algorithm within STSPLUS. This value (in radians) is divided by (2 * PI) and the result multiplied by 256 to obtain Phase. The Phase is then displayed as a number ranging from 0.0 to 255.9. The technical definition of Phase is as an integer ranging from 0 to 255 (so as to fit in a single 8-bit byte of computer data). 2. Phase is calculated based upon geocentric (center of the Earth) data rather than geodetic (surface of the Earth taking into account the shape of the Earth) data. What may appear as an apogee or perigee based upon "Elv", the distance above Mean Sea Level, may NOT be the actual apogee or perigee when calculated using geocentric data. Because of the shape of the Earth, these distances may vary up to 21 kilometers from the Equator to a pole. 3. Mean Anomaly (and therefore Phase) is undefined for a perfectly circular orbit; there is no perigee or apogee in this situation. In addition, some uncertainties are also introduced by gravitational Program STSORBIT PLUS Satellite Orbit Simulation Page 62 variations which can make accurate dynamic determination of apogee or perigee difficult for low Earth orbits. These variations and inaccuracies become significant for orbits with an Eccentricity of 0.005 or less, a situation which is typical for most low Earth orbits. For this and other reasons, amateur satellites in low Earth orbits do not use Phase to determine operating modes. 4. The following conditions are required for the Phase data to be displayed: a) The orthographic projection has been selected by pressing "O" while the map is displayed. b) The Doppler Shift Mode has been selected using F8 while the map is displayed. c) The Eccentricity of the satellite's orbit is 0.005 or greater. If any of these three conditions is not satisfied, the orbital period data ("Per'd") will be displayed. Satellite Communications Technique and Cautions ----------------------------------------------- Once full duplex communications have been established, remaining "in lock" throughout a pass requires that both parties continually adjust their transmit and receive frequencies to the values displayed by STSPLUS to the extent practical and consistent with the bandwith capabilities of their receivers. Although this may seem a bit daunting at first, the actual rate of change of the frequencies is sufficiently slow that it can easily be managed by the relative novice with a little practice. Equally important in the relatively new area of communications with or via manned and unmanned satellites is that all participants recognize that the available bandwidth and communications opportunities are a "scarce resource" that must be used with care and shared. This is in keeping with long standing amateur radio tradition. The problem can be particularly difficult with the manned spacecraft, MIR and the Space Shuttle. Careful attention to doppler shift can be of considerable help in completing the call by using the correct frequency or frequencies. ******************** * IMPORTANT NOTE * ******************** Experience with communications via amateur ratio satellites such as RS-10 has shown that careful test and calibration of the receiver and transmitter are essential to successful communications. For example, an error or bias of 2 or 3 KHz on the receiver frequency can make the difference between a successful call and a failure. If the receiver or transmitter has a consistent bias, it may be possible to temporarily adjust the values of the center frequencies to compensate for the problem but the best solution, of course, is to have the equipment calibrated and operating correctly. Equally important, the computer clock must be accurately set. Radio time signals such as those broadcast by the National Institute of Standards Program STSORBIT PLUS Satellite Orbit Simulation Page 63 and Technology (NIST) on WWV are sufficiently accurate for this purpose. The program TIMESET by Peter Petrakis is highly recommended to automatically set the computer clock via the telephone time services of NIST or the U.S. Naval Observatory (USNO). Finally, the frequencies calculated by STSPLUS are no more accurate than the orbital data used. For the typical amateur radio satellite, the orbital data should be no more than a week old for reasonable results. If the satellite is performing orbital maneuvers (as MIR does from time to time), only the most current elements will yield satisfactory results. Sources such as Internet, Celestial BBS, NASA Spacelink BBS, NASA GSFC RBBS, and my own RPV Astronomy BBS offer up-to-date 2-line elements for all or most of the common amateur radio satellites. See the section "Computer Bulletin Board Systems" near the end of this document for current BBS telephone numbers and related information. Since the amateur radio transponders are often "piggybacked" on a primary satellite, the name of the satellite used by these sources may be different from the amateur radio designation. Use the example file STSPLUS.FRQ to check for the NORAD numbers of common amateur radio satellites and use the NORAD number rather than a satellite name or designation when searching for TLEs. Program STSORBIT PLUS Satellite Orbit Simulation Page 64 Preparing File STSPLUS.FRQ for Amateur Radio Use ------------------------------------------------ File STSPLUS.FRQ contains the parameters required for STSPLUS to operate in the Doppler Shift Mode. Each entry (line) in the file includes the satellite NORAD Number, UPLINK and DOWNLINK center freqencies, and the transponder mode, specified in in that order, separated by commas and without any leading or trailing spaces. The following format is used for each entry: 00000,100,100,1 (Default values if sat not included) 18129,145.8900,29.3900,1 (Parameters for NORAD #18129) --+-- ----+--- ---+--- + | | | | | | | +-- Transponder Mode: 1 = NORMAL | | | -1 = INVERTED | | | | | +------- DownLink Center Frequency (MHz) | | | +--------------- UpLink Center Frequency (MHz) | +----------------------- Satellite NORAD Number The first sample line shows the "00000" entry which determines the default values if the satellite is NOT included in file STSPLUS.FRQ. This should be the FIRST LINE in file STSPLUS.FRQ. The second line gives real parameters for a specific satellite; the frequencies shown select the Mode A voice passband for Radio Sputnik 10 (RS-10, piggybacked on COSMOS 1861, NORAD #18129). Preset frequencies may range from 1.0000 MHz to 99000.0000 MHz. Neither the uplink nor downlink frequency should exceed approximately 99000.0000 MHz to avoid an overflow condition on the display. Although the center frequencies are shown above in MHz, any desired units may be used since STSPLUS simply calculates a ratio and displays the results with four digits to the right of the decimal point. File STSPLUS.FRQ may be created or edited with any ASCII editor; word processor users, use the "non-document" mode. Note that only minimum error checking is performed and the user must observe the required format exactly for each line in the file. Up to ten entries may be included for a given satellite (using the same NORAD Number) in order of preference. If more than one entry is present for the current satellite, the user is presented with a list and asked to make a choice. Ken Ernandes, N2WWD, in conjunction with his tests of STSPLUS' Doppler Shift Mode, has prepared a preliminary STSPLUS.FRQ file with the current (as of March, 1994) center frequencies of fourteen amateur radio satellites. Note that several satellites have more than one entry, corresponding to different modes of operation: 00000,100,100,1 (Default values) 14129,435.1025,145.9025,-1 (AO-10) 16609,145.5500,145.5500,1 (MIR) 18129,145.8850,29.3800,1 (RS-10) 18129,21.1800,145.8800,1 18129,21.1800,29.3800,1 19216,435.4950,145.9000,-1 (AO-13) Program STSORBIT PLUS Satellite Orbit Simulation Page 65 19216,144.4500,435.9650,-1 19216,1269.4750,435.8600,-1 19216,435.6190,2400.7290,-1 20437,145.9750,435.0700,1 (UO-14) 20439,145.9000,437.02625,1 (PACSAT) 20441,1265.0000,437.0751,1 (WO-18) 20441,1265.0000,437.1258,1 20442,145.8400,437.15355,1 (LO-19) 20480,145.9550,435.8500,-1 (FO-20) 21087,435.0160,145.9870,1 (AO-21) 21087,435.0620,145.8920,-1 21087,435.0830,145.9060,-1 21089,21.2400,29.4400,1 (RS-12/13) 21089,21.2400,145.9400,1 21089,145.4400,29.4400,1 21575,145.9000,435.1200,1 (UO-22) 22077,145.9000,435.1670,1 (KO-23) 22077,145.9000,435.1200,1 22825,145.8500,436.8000,1 (AO-27) NOTE: The center frequencies listed above are preliminary, based upon available information. For example, the uplink frequencies for the first entry for RS-10 and the entry for FO-20 have been adjusted up by 5KHz to compensate for an apparent transponder bias. These data will be coordinated by Ken Ernandes, N2WWD. Ken may be contacted through my RPV Astronomy BBS at (310) 541-7299 or on CompuServe at 70511,3107. Users who have carefully calibrated their receivers and transmitters and who have updated information are encouraged to contact Ken. SAREX, the Shuttle Amateur Radio EXperiment, is frequently assigned to Space Shuggle flights. The following uplink and downlink frequencies have been assigned for that flight (data as of April 1994): UPLINK DOWNLINK NOTES ------------------------------------------- VOICE: 144.91 MHz 145.55 MHz EXCEPT EUROPE 144.93 144.95 144.97 144.99 144.70 MHz 144.55 MHz EUROPE ONLY 144.75 144.80 PACKET: 144.49 MHz 145.55 MHz WORLDWIDE NASA adds the following note with respect to the voice uplink: "The astronauts will not favor any one of the above frequencies. Therefore, the ability to talk with an astronaut depends on selecting one of the above frequencies chosen by the astronaut." (Information courtesy NASA Spacelink BBS as of April, 1994) Thus, for a station in North America, the user may add the following entries to file STSPLUS.FRQ: Program STSORBIT PLUS Satellite Orbit Simulation Page 66 00059,144.91,145.55,1 00059,144.93,145.55,1 00059,144.95,145.55,1 00059,144.97,145.55,1 00059,144.99,145.55,1 00059,144.49,145.55,1 where "00059" must be replaced by the actual NORAD number assigned to the flight. A temporary NORAD number corresponding to the flight number, illustrated by "00059" in the example above, is usually used until the permanent NORAD number is assigned (although some sources use a different method to assign a temporary NORAD number -- check the TLEs). However, if a temporary NORAD number is used during the initial portion of the flight, the data in file STSPLUS.FRQ must later be updated to the permanent NORAD number when that number is used in the TLEs in order for STSPLUS to recognize the flight's frequency list. A typical set of TLEs for a Space Shuttle are shown with the NORAD number and Eccentricity noted: STS-65 1 23173U 94039A 94203.67836573 .00310904 40043-6 28999-3 0 371 2 23173 28.4640 263.1143 0006121 89.0653 314.1440 16.10872029 2244 --+-- ---+--- | | | +----- Eccentricity (=0.0006121) | +------------------------------ NORAD Number Because different sources of 2-line elements (TLEs) may use different names for the same satellite, numerous satellites may have similar names, and some payloads (especially amateur radio transponders) are "piggybacked" on a primary satellite with a different name, always use the NORAD Number if possible when searching a file for the TLEs. The MIR Space Station, NORAD Number #16609, can be mistaken for numerous MIR debris objects ("DEB" or "D" appears in the first line of the TLEs). For AO-13, for example, press F2, select the desired TLE filename, then enter "#19216" (without the quotation marks but WITH the pound sign) as the satellite name. This method will ALWAYS find the data if they are present in the file. Once the data are found, STSPLUS displays them as usual. If there is only one entry in file STSPLUS.FRQ for the satellite, STSPLUS will immediately draw the map after ENTER is pressed to approve the satellite and its data. However, if more than one entry for the satellite is present, and STSPLUS is currently in the Doppler Shift Mode, STSPLUS will display a list of the available preset frequencies and request the user to select one: Preset Frequency Selections for 19216 # UpLink DnLink Mode --------------------------------- 1 435.4950 145.9000 -1 2 144.4500 435.9650 -1 3 1269.4750 435.8600 -1 4 435.6190 2400.7290 -1 Enter Desired Preset Frequency Selection Number [1]: Program STSORBIT PLUS Satellite Orbit Simulation Page 67 Enter the desired preset frequency selection number followed by ENTER. If you wish selection #1, you may simply press ENTER. Entering a number less than 1 or greater than the highest selection number will also pick selection #1. Note that when STSPLUS is NOT in the Doppler Shift Mode, no list of preset frequency selections is displayed and STSPLUS automatically picks selection #1 (to avoid bothering folks who are not interested in the Doppler Shift Mode). Program STSORBIT PLUS Satellite Orbit Simulation Page 68 ACTIVE KEYS DURING GROUND TRACK DISPLAY --------------------------------------- The following table lists the various keys which are active when the ground track display is shown on the screen. Some of these features are more fully described elsewhere. ENTER Return to Main Menu (cancel the simulation). F1 On-line HELP. Press F1 to display a help screen in the lower portion of the screen. Press F1 again to resume normal data display. F2 Selects the Big Clock mode. These modes are selected in the following order: 0 No clock displayed 1 UTC date and time 2 Local date and time 3 STN/TDRS AOS/LOS and MET or T+Epoch (select with F5) Note that not all computers (especially older CGA systems) will display the extended graphics characters used for the large clock characters. The symptom of this problem is that the lower left portion of the data block is mostly blank after pressing F2. If you have this problem and your computer is running DOS 3.x or DOS 5.0, enter the command "GRAFTABL" at the DOS prompt before running STSPLUS or include the line "GRAFTABL" in your AUTOEXEC.BAT file; this sets the "code page" to enable the computer to display the extended graphics characters. [The program GRAFTABL.COM is included as part of DOS in most cases.] F3 Enable or disable printer logging. If logging is enabled, the word LOG appears in the lower right of the screen. Be sure the printer is turned on BEFORE using the L command. The "L" command automatically enables the display of ascending and descending node information. F4 Toggle FAST mode from x1 to x10 to x60 to x1, etc. When either of the fast modes is enabled, "(x10)" or "(x60)" will appear at the upper right of the data block in red. This feature operates in both the normal (real or simulated time) and PAUSE modes. When x10 or x60 fast modes are used, automatic map generation is disabled in rectangular projections; use the TAB key to restore automatic map generation. F5 Switches the elapsed time between "T+Epoch" and "MET". If no launch time and date have been entered, this command will have no effect. F6 Enable PAUSE mode. The plot is frozen at the current position and the "+" and "-" keys are enabled. The "=" key may be used instead of the "+" key to avoid use of the SHIFT KEY. Press ENTER to resume normal operation using the current simulated time. (NOTE: To return to REAL TIME after the PAUSE mode, press ENTER after Program STSORBIT PLUS Satellite Orbit Simulation Page 69 leaving PAUSE to return to the Main Menu, then press F8+F1.) F7 Enable or disable the spacecraft circle of visibility. F8 Switches program operation between NORMAL and DOPPLER SHIFT modes. (Orthographic projection only; see text for details.) F9 Change units of distance between kilometers (km) and nautical miles (nm). F10 Change satellite coordinates between Altitude/Elevation and Azimuth (Topocentric), Right Ascension and Declination (Equatorial), and X-Y-Z (Geocentric Rectangular, also known as ECI or Earth-Centered Inertial) coordinate systems. If a Target Satellite has been selected, F10 may also be used to display Relative Range and Velocity between the Primary and Target Satellites. +/= 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. The "=" key may be used instead of "+" to avoid use of the SHIFT KEY. - During PAUSE mode only, "-" moves the satellite to the PREVIOUS calculated position based upon the FAST mode then in effect: simulated time is backed up 1, 10, or 60 seconds. TAB In rectangular map modes only, 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 NORMAL OPERATION: 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. DOPPLER SHIFT MODE: Increases the "RECV" frequency by 1 KHz. Hold down or press rapidly for large frequency changes. PgDn NORMAL OPERATION: When in one of the zoom modes, decreases the field of view down to a minimum of 30 degrees. Press rapidly to execute multiple zoom steps without redrawing the map for each keypress. DOPPLER SHIFT MODE: Decreases the "RECV" frequency by 1 KHz. Hold down or press rapidly for large frequency changes. Home NORMAL OPERATION: When in one of the zoom modes, returns the field of view to 75 degrees (rectangular projections) or the full globe (orthographic projections). DOPPLER SHIFT MODE: Restores the UpLink and DnLink center Program STSORBIT PLUS Satellite Orbit Simulation Page 70 frequencies to the original values read from file STSPLUS.FRQ. End NORMAL OPERATION: When in one of the zoom modes, returns the field of view to the last zoom factor used prior to pressing the HOME key. DOPPLER SHIFT MODE: (not used and inactive) UP NORMAL OPERATION: (not used and inactive) DOPPLER SHIFT MODE: Increases the "RECV" frequency by 100 Hz. Hold down or press rapidly for larger frequency changes. DOWN NORMAL OPERATION: (not used and inactive) DOPPLER SHIFT MODE: Decreases the "RECV" frequency by 100 Hz. Hold down or press rapidly for larger frequency changes. B Toggle the BLINK mode of the satellite symbol between blinking and steady. NOTE: On most systems, the satellite symbol will appear to blink very briefly as it is erased and redrawn even when BLINK is OFF. O Select Orthographic Projection (the LETTER "O" not the digit zero). PgUp, PgDn, Home, and End are active to select the magnification. W,0 Select World Map display, showing the full world from +85 degrees North latitude to -85 degrees South latitude using rectangular projection. If automatic map generation is disabled, pressing "W" or "0" will toggle between the two world map displays. 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 30 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 using the current 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 71 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 72 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 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 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 Set/Read/Save TDRS and Real Time Satellites F7 Set FILENAMES and Paths F8 Set program TIME and/or DATE F9 DOS Shell (CAUTION: DOS 3.x or higher ONLY!) F10 Set STSORBIT PLUS Program Options and Features ENTER Resume Mission (Mir) ESC Quit STSORBIT PLUS and Save Current Mission Select desired function: WHILE MAP IS DISPLAYED: F1 = HELP ENTER = Main Menu During operation of STSPLUS, data are displayed by STSPLUS in several standard formats: 26 JUL 1994 Date in day/month/year format 02:01:57 UTC Coordinated Universal Time in hours:mins:secs 19:01:57 PDT 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 73 F1 Convert Keplerian Data to 2-Line Format ---------------------------------------------- This function provides a means to individuals without modems to receive the so-called "Keplerian Orbital Elements" by voice or other means and reliably convert those data to the "2-Line Element" format as required by STSPLUS and other satellite tracking programs. However, more data is included in the 2-line orbital element set than is usually distributed as the Keplerian orbital elements; this means that the missing data must either be obtained from other sources or be set to a specified value or zero. These instructions and the example and sample form which follows will help the unskilled user to do these tasks. This conversion function has but a single purpose: to prepare 2-line orbital elements from Keplerian orbital elements by means of user keyboard input. Since the program is designed only to transcribe valid data from one format to another, no error checking is performed and the program makes no tests of the "reasonableness" of the various data and parameters. The user is therefore cautioned to check his data before using this program, or to use the resulting data with caution until it has been verified. The information shown below is usually included in the Keplerian orbital elements as received via modem or voice (amateur radio or telephone). This sample is an actual file for Space Shuttle Flight STS-55 launched in early 1993 as received via modem direct from the NASA Johnson Space Center prior to launch: Satellite: STS-55 Catalog number: 00055 Epoch time: 93073.67556033 =====> (14 MAR 93 16:12:48.41 UTC) Element set: JSC-003 Inclination: 28.4697 deg RA of node: 228.7025 deg Space Shuttle Flight STS-55 Eccentricity: .0003812 Prelaunch Keplerian Elements Arg of perigee: 314.2100 deg Launch: 14 MAR 93 15:00 UTC Mean anomaly: 45.8202 deg Mean motion: 15.90487610 rev/day G. L. Carman Decay rate: 1.2020e-03 rev/day~2 NASA Johnson Space Center Epoch rev: 2 If you compare the information required by STSPLUS (as shown in the example on the following page) with that above, several items are missing or may be in a slightly different format. Here are some suggestions. 1. A sample form is included in this documentation which will assist you when receiving Keplerian orbital information by voice or by amateur radio link. Note that the form includes lines for "Int'l Designation" and "BSTAR Drag"; these items are frequently omitted and must be determined independently (see below). 2. The Catalog Number (often referred to as the NORAD Number) is assigned by US Space Command at Cheyenne Mountain after a satellite has been successfully launched. Initial or pre-launch Keplerian elements may use the mission number or some other convenient number for this item. Most tracking programs will accept any number here. STSPLUS uses the Catalog number to keep track of launch date and time; if the Catalog number used for a mission changes, the launch date and time must be Program STSORBIT PLUS Satellite Orbit Simulation Page 74 entered again. 3. The Epoch time is the instant for which the Keplerial elements have been calculated and is NOT the same as the launch date and time. Launch date and time is shown separately, is NOT part of the 2-line elements, and must be entered in STSPLUS using F5 from the Main Menu. 4. The International Designation is often not assigned until well after a flight is in progress; press ENTER to use all spaces for this item. 5. For the 2-line orbital element set, the element set number (shown as "JSC-003" in the example above) MUST be numeric. For this example, enter "3" or "003". Most tracking programs will accept any number for this item, up to a maximum of FOUR DIGITS. 6. The "Epoch Rev/Orbit" is the orbit number at the epoch (the instant when the data is taken). Up to FOUR DIGITS may be entered here but except for the orbit number on displays, this number has no effect on the propagated orbit. NASA assigns Orbit/Rev 1 to the first partial orbit following launch; US Space Command usually (but not always) assigns Orbit/Rev 0 to the first partial orbit and the orbit number for space shuttle missions must usually be adjusted to conform to NASA convention. 7. When the program asks for "NDOT2 Drag/Decay", the information being requested is the "Decay rate" in the Keplerian elements. It may be entered in the form shown in the example or as a decimal fraction such as ".002102" (which is identical to the "2.10200e-03" in scientific notation as used in the example). 8. When the program asks for "NDDOT6 Drag", press ENTER to insert a value of zero. This should be satisfactory for most satellites and most tracking programs. 9. When the program asks for "BSTAR", you may press ENTER to insert a value of zero. This will be satisfactory for times very close to the Epoch Time for the elements. However, as time progresses the satellite may lag behind the propagated (projected) ground track if no value is avaialble for BSTAR. For space shuttle missions, NASA often assigns a default value of "25599-3" or ".00025599". A value from a prior set of 2-line elements may also be used. 10. After all data have been entered, STSPLUS will request the filename to which the 2-line orbital data is to be written. Enter the full filename and filetype, such as "TESTSAT.TXT". The file will be written to the drive and directory set using F7+F3 from the Main Menu. DO NOT INCLUDE A DRIVE OR DIRECTORY; THAT IS ADDED AUTOMATICALLY! An existing file with the same name will be overwritten. 11. If you make a mistake during the data entry process, you may use the BACKSPACE key until ENTER has been pressed. If you wish to cancel the program without writing the data to a file, press ENTER when asked for the filename and the data will be discarded. As noted elsewhere, orbital elements have a limited lifetime. How long Program STSORBIT PLUS Satellite Orbit Simulation Page 75 that lifetime may be depends primarily upon the orbital altitude. Low Earth orbit (LEO) satellites, especially those such as the space shuttle and Russian space station, are frequently maneuvered to maintain the desired orbit. Orbital elements for these satellites may be valid for only days or sometimes even hours. Orbital elements for higher orbital altitudes, say above 1,500 km, tend to be valid for much longer -- up to weeks. Satellites in very high or geosynchronous orbits exhibit usually long term orbital stability. The Bottom Line: The accuracy with which any tracking program can determine a satellite's position is primarily dependent upon having accurate orbital elements! Finally, a word about the NDOT2 and BSTAR parameters. A satellite's orbit is completely and accurately determined at the epoch time without NDOT2 and BSTAR. These two parameters determine various adjustments as the orbit is propagated in time and are a function of such things as orbital altitude, spacecraft attitude and cross-sectional area, atmospheric density changes due to sunspot activity, and so on. Both US Space Command and Johnson Space Center have been known to "tweak" these values for a variety of reasons, usually because the orbit is in a state of change due to maneuvers and/or excessive drag. NOTE: A positive exponent for BSTAR, which indicates high acceleration and is somewhat unusual (and often an indication of "tweaking"), is NOT handled correctly and must be manually edited. The resulting elements may not propagate accurately for more than a few hours. EXAMPLE DATA INPUT ------------------ Enter 2-LINE ELEMENTS Enter the required data as prompted. Most essential data is included in the Kelplerian Orbital Data available to amateur radio enthusiasts. Other data may be inserted if available or may be omitted if not. Accuracy may be affected, see documentation. Enter Satellite Name (15 chars max): sts-55 Enter NORAD Number (NNNNN): 55 Enter Int'l Designation (8 chars max): Enter Epoch Time (YYDDD.TTTTTTTT): 93073.67556033 Enter Element Set Number (NNN): 3 Enter Inclination (DDD.DDDD): 28.4697 Enter RA of Ascend Node (DDD.DDDD): 228.7025 Enter Eccentricity (.NNNNNNN): .0003812 Enter Arg of Perigee (DDD.DDDD): 314.21 Enter Mean Anomaly (DDD.DDDD): 45.8202 Enter Mean Motion (NN.NNNNNNNN): 15.9048761 Enter Epoch Rev/Orbit (NNN): 2 Enter NDOT2 Drag/Decay (.NNNNNNNN): .001202 Enter NDDOT6 Drag (NNNNN-N): 00000-0 Enter BSTAR (NNNNN-N): 36300-3 Program STSORBIT PLUS Satellite Orbit Simulation Page 76 EXAMPLE DATA OUTPUT ------------------- Satellite Data has been entered as: Satellite Name (15 chars max): Sts-55 NORAD Number (NNNNN): 00055 Int'l 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 77 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: __ __ __ __ __ Int'l 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 78 F2 Read/Update NASA/NORAD 2-Line Elements from *.TXT/*.TLE Files -------------------------------------------------------------------- In order to read or update the NASA/NORAD 2-line elements, you must have a file with data for the appropriate satellites. A current file is included in the standard distribution of STSPLUS. These files have names such as "TLE360.TXT" where the "360" corresponds to the particular US Space Command Prediction Bulletin number from T. S. Kelso's Celestial BBS and are usually updated several times per week. This and other TLE files are available from my BBS and from various other sources including CompuServe and INTERNET. Select/Update Preset Frequency Selections ----------------------------------------- STSPLUS reads file STSPLUS.FRQ for preset frequency selections for the current satellite each time the program is started. STSPLUS will re-read file STSPLUS.FRQ each time F2 is used to select or update the current primary satellite. When the Doppler Shift Mode is active (selected using F8 while the map is displayed) and more than one preset frequency selection is available for the satellite, STSPLUS will present a list of available selections and the user may choose the desired selection. The following is a sample list of preset frequency selections for AO-13, NORAD #19216: Preset Frequency Selections for 19216 # UpLink DnLink Mode --------------------------------- 1 435.5325 145.9375 1 2 144.4625 435.9275 1 3 1269.5475 435.9325 1 4 435.6280 2400.7380 1 Enter Desired Preset Frequency Selection Number [1]: Enter the desired preset frequency selection number followed by ENTER. If you wish selection #1, you may simply press ENTER. Entering a number less than 1 or greater than the highest selection number will also pick selection #1. If you wish to change your preset frequency selection, you must be in the Doppler Shift Mode -- press F8 while the map is displayed. Return to F2 on the Main Menu, re-select the desired satellite, then choose the desired preset frequency selection. See the section "Satellite Communications and Amateur Radio" for additional information on the Doppler Shift Mode. NOTE: When STSPLUS is NOT in the Doppler Shift Mode, no list of preset frequency selections is displayed and STSPLUS automatically picks selection #1 to avoid bothering folks who are not interested in the Doppler Shift Mode. Update Current TDRS and Real Time Satellites -------------------------------------------- Program STSORBIT PLUS Satellite Orbit Simulation Page 79 Once Secondary Satelliets (TDRS, Static, and Real Time) have been selected (using F6+F1 from the Main Menu), it is necessary to periodically update the 2-line elements ("TLEs") for these satellites so that the calculated positions are accurate. Naturally, this is also true for the primary satellite being tracked. TLEs have a limited lifetime. For higher altitude satellites such as geosynchronous satellites, 4 to 8 weeks is probably sufficient unless the satellite is being maneuvered (although I usually do this task at least weekly since I have the data). For low Earth orbit satellites, even when the satellite is not being maneuvered, I recommend a maximum interval of about two weeks; if the satellite is being maneuvered, such as is usually the case with the Space Shuttle, daily updates may be required. The Secondary Satellite display (F6+F1) flags real time satellites whose elements are more than 10 days old, and static satellites whose elements are more than 60 days old. To update 2-line elements for the primary satellite and all Secondary Satellites, press F2 from the Main Menu and select the desired file as described in the following section. Then enter the satellite name as "&" to request TLE update mode. The TLE file will be scanned and all satellite TLEs will be updated if their Epoch Time is later than those presently stored. The entire process takes only a few seconds. The following prompt illustrates the "Update" selection: Select NASA/NORAD 2-Line Elements File Enter 2-Line Filename [GSFC315.TXT]: GSFC315.TXT Enter Satellite Name/#nnnnn [#20638]: & (Enter '*' to match any satellite name, '&' for AUTO UPDATE) As STSPLUS updates TLEs, a list of the satellites for which new TLEs have been loaded is displayed: Automatic TLE updates for: Satellite 8: Norad# 22920 HST Solar Array @ 93355.87870989 Satellite 10: Norad# 22076 TOPEX @ 93357.21248411 Satellite 12: Norad# 21987 EUVE @ 93356.85536486 Satellite 7: Norad# 21701 UARS @ 93353.94360770 Satellite 11: Norad# 21225 GRO @ 93356.46954065 Satellite 9: Norad# 20638 ROSAT @ 93353.77650216 Satellite 13: Norad# 20580 HST @ 93357.18124168 Satellite 6: Norad# 16609 MIR @ 93356.89342327 Press any key to continue ... The satellite number indicates the "slot" in the Secondary Satellite configuration, or "P" for the Primary Satellite. In the example shown, the TLEs for eight satellites were updated to the Epoch Times (YYDDD.DDDDDDDD) indicated. The satellites are listed in the order found in the TLE file. The updated TLEs will be saved in file STSPLUS.INI. Press ENTER to return to the Main Menu. Program STSORBIT PLUS Satellite Orbit Simulation Page 80 Read NASA/NORAD 2-Line Elements from a File ------------------------------------------- For both "Read" and "Update" functions, 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 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: Program STSORBIT PLUS Satellite Orbit Simulation Page 81 \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, '&' for AUTO UPDATE) 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; 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 82 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: Mir Satellite NORAD Number: #16609 Elements File: TLE233.TXT Elements File Record#: 315 (*) Element Set Number: 201 Elements Epoch: 93206.84472440 25 JUL 1993 @ 20:16:24.188 UTC Orbit # at Epoch: 42516 Launch Year: 1986 Launch Number: 17 Launch Piece: A Inclination: 51.6213 RA of Ascend Node: 25.384 Eccentricity: .0004375 Arg of Perigee: 244.4461 Mean Anomaly: 115.6366 Mean Motion: 15.58931226 Acceleration/Drag: .00007676 BSTAR Drag: .000099999 Press ENTER to ACCEPT this satellite, OR Press any other key to REJECT and continue searching: (*) This line is normally blank. However, one of the following messages will appear here if a checksum error is detected in the element set: BAD CHECKSUM in line 1 ignored! BAD CHECKSUM in line 2 ignored! BAD CHECKSUM in both lines ignored! In all three cases, STSPLUS will accept the data and attempt to use it. Be advised, however, that the checksums are included to help detect data errors that might otherwise yield an incorrect position! Serious errors may even cause STSPLUS to abort with an error message. For convenience, the Elements Epoch (the instant at which these orbital elements were calculated) is shown in two formats: the first format is that used in the 2-line elements, YYDDD.DDDDDDDD; and the second format is the same time converted into conventional date and time notation. You Program STSORBIT PLUS Satellite Orbit Simulation Page 83 may thus see immediately how old the elements are and take this into account when evaluating the satellite's projected position. If this is the satellite you wish, press ENTER and the data will be entered into STSPLUS. If, on the other hand, a different satellite is desired, press any other key (such as the SPACE BAR) and STSPLUS will search for another name matching the requested satellite. For example, there are a number of NAVSTAR Global Positioning Satellites usually included in the file with official names such as "GPS-0001", "GPS-0002", "GPS BII-01" and so forth; requesting "GPS" will allow you to cycle through all the available choices. The file TLEnnn.TXT is an ASCII file; it may be helpful to view or print the file to see the available satellite names. Once the satellite has been selected, STSPLUS will require a brief time to calculate certain required orbital parameters, then will proceed directly to the display of the ground track. However, if the current calculated altitude of the satellite is less than 75 nautical miles, the satellite has probably decayed. STSPLUS will display the following message before returning to the Main Menu: Satellite MIR DEB (#22209) indicates a current altitude less than 75 nautical miles and has probably decayed. STSORBIT PLUS can NOT process the orbital data for this satellite! Use Function Key F2 from the Main Menu to select another satellite and verify the satellite NAME and NORAD NUMBER. Press any key to return to the Main Menu ... As a point of interest, the 2-line elements for the Space Shuttle Mission STS-50 used in the example above are as follows: STS-50 1 22000U 92 34 A 92187.57342677 -.00032668 00000-0 -97874-4 0 380 2 22000 28.4670 275.0700 0007237 340.7929 19.1530 15.91359642 1596 Program STSORBIT PLUS Satellite Orbit Simulation Page 84 F3 Data Output and Pass Prediction Selections ------------------------------------------------- By popular request, STSPLUS has been enhanced to send selected data for the current satellite to other equipment via a serial port (COM1 or COM2), to a file (STSPLUS.LOG), or to the printer (LPT1). Validation of the serial port output has been accomplished using two computers and a "Null Modem" cable. Three classes of data may be selected for output: current position data in three formats, precision Earth-centered inertial ("ECI") state vectors in four formats, and tabular Line-of-Sight pass predictions (which are also displayed on the screen). The precision state vector outputs have been carefully coordinated with Ken Ernandes so that they may be used as input to his program VEC2TLE, Version 9331 or later. Using these state vectors and VEC2TLE, the user may generate 2-line elements at any desired time (including just after the ascending node) for use with STSPLUS or other satellite tracking programs. With these programs, the user has a very powerful set of tools which can be used for a variety of analytical and display purposes. Cross validation of the two programs during Space Shuttle missions STS-56 and STS-55, as well as comparison with US Space Command data of comparable epoch, demonstrated high accuracy and excellent correlation. Each Data Output function is assigned a "Data Mode" number: 1 = Azimuth, Elevation, Range 2 = Latitude, Longitude, Orbit Altitude 3 = Right Ascension, Declination 4 = Ascending Node Data with State Vector 5 = Precision X-Y-Z State Vector (2-Line Data) 6 = Precision X-Y-Z State Vector (Comma Delimited) 7 = Precision X-Y-X State Vector (Labeled Data) 8 = Doppler Shift Frequency Predictions 9 = Tabular Line-of-Sight Predictions The current position data and precision state vectors are generated while the ground track map is displayed; for all Data Modes EXCEPT #4, data output may be logged continuously, for a specified time (UTC/GMT or local time), or for a specified time span (UTC/GMT or local time). Data Mode 4 records data ONLY at the Ascending Node, e.g. when the Northbound equator crossing is detected. The predicted pass data is calculated "off-line" using UTC/GMT or local time, and is displayed on the screen as well as being sent to the selected output destination. Current position data include the UTC date/time and are generated for local horizon coordinates (altitude and azimuth), geographic coordinates (geocentric latitude, longitude, and orbital altitude), and topocentric equatorial coordinates (right ascension and declination calculated for the user's location). Precision X-Y-Z Earth-centered inertial state vectors (ECI position and velocity components) are generated as two numeric data lines, single line comma delimited, and multi-line labeled data. The details for each data output format are given in following sections. The precision ECI X-Y-Z state vectors, generated by STSPLUS for the true equator and equinox of date, have been extensively tested and validated in conjunction with Ken Ernandes' program VEC2TLE during Space Shuttle missions STS-56 and STS-55 in early 1993. For example, the combination of the two programs, STSPLUS and VEC2TLE, may be used to Program STSORBIT PLUS Satellite Orbit Simulation Page 85 convert data between 2-line and ECI formats with very high accuracy. State vectors from STSPLUS may be read by VEC2TLE and converted into 2-line elements, then in turn read again by STSPLUS with essentially exact conversions. VEC2TLE has also been used during STS-56 and STS-55 to convert real time state vectors ("M50" or Mean of 1950) supplied courtesy Willie Musty of Mission Support, Rockwell International, into 2-line elements equal in accuracy to those generated by US Space Command (and made available four to eight hours sooner!). See the separate text section describing VEC2TLE. Note that the timing accuracy for Data Mode 4 is a fixed at 0.01 seconds, regardless of the time step (X1, X10, or X60) then in effect. STSPLUS detects the Ascending Node data when the latitude switches from negative to positive on the Northbound crossing of the Equator. An iterative process is then used to refine the time to the nearest 0.01 seconds and the data at that time are recorded. Potential applications for the position data include automatic antenna pointing systems, off-line high precision plotting, and widespread distribution of the data within a large facility or via modem. ECI state vectors may be used in real time to create 2-line elements for a specified epoch to full precision. Users who develop applications to utilize these data are invited to contribute their programs and documentation for general use. Since these are new features for STSPLUS, comments and suggestions are welcome. Although STSPLUS retains the capability of performing off-line pass predictions with TS Kelso's TRAKSTAR or other satellite tracking software, many users have requested that a similar feature be incorporated directly into STSPLUS. Pass predictions may only be calculated for satellites having a mean motion greater than 1.5; this eliminates satellites in near geosynchronous or higher orbits, but since such satellites don't move much that does not represent a significant constraint. The satellite's orbit is examined for 48 hours, starting at the current real or simulated time, with a sampling interval which ranges from 10 to 60 seconds depending upon the orbit. Because of this "granularity" in the search algorithm, it is possible to skip passes whose duration is less than the sampling interval. Since those brief passes would barely peek above the user's horizon, they are thus not significant. Pass predictions may be continued in 48 hour segments until 99 passes have been displayed. Since a typical satellite may have from about two to seven passes in a 24 hour period, the passes may be examined for a considerable time into the future. Predicted pass data are calculated using the current satellite for Line-of-Sight visibility; that is, when the satellite is in line of sight to the user's location and without consideration of lighting effects. Since STSPLUS users are about equally divided between those who track satellites visually and those who use electronic equipment such as amateur radio, this method provides data for all users. Passes which occur near local sunrise or sunset may be tested for lighting constraints and/or ground visibility by displaying the ground track for the pass or other means. Dates and times may be displayed in Coordinated Universal Time (UTC/GMT) or in local time. Note that the date for each pass is given only for AOS (Acquisition of Signal); it is possible for the pass to span 00:00:00 hours (midnight) for the time scale in use with a consequent date change during the pass for MAX VISIBILITY and/or LOS (Loss of Signal). Prediction calculations may require some time; calculation delays are noted with the message "calculating ...". Using a processor equipped with a Program STSORBIT PLUS Satellite Orbit Simulation Page 86 math coprocessor chip, each 48 hour block may require from less than 10 seconds to a minute or more. However, users without math coprocessor chips will experience significant delays -- minutes or even tens of minutes! The following table lists typical calculation times for various processors (all with math coprocessors!) using the Russian MIR Space Station: 286/287 386SX/387SX 486DX 8 MHz 20 MHz 33 MHz --------------------------------------------------- MIR 60 sec 30 sec 6 sec The data output feature MUST be enabled with F3 each time STSPLUS is run; it is NOT automatically restarted when the "/R" (RESUME) command line option is used. ********** * NOTE * ********** Users are reminded that when data output is sent to the file STSPLUS.LOG, a considerable volume of data may be accumulated over long periods of time. It is possible to completely fill a disk with this data! The file should be periodically copied to other media or deleted to avoid this problem. Setting Up Position and State Vector Data Output ------------------------------------------------ Data output of position and state vectors ONLY occurs while the ground track is displayed; no data are generated until the ground track is actually in progress! The appropriate data are sent to the destination device at the selected data interval (continuous), at a specified time, or at the selected data interval over a specified time span covering no more than 24 hours. ************************ * IMPORTANT REMINDER * ************************ STSPLUS generates Earth-Centered Inertial ("ECI") state vectors for the true equator and equinox of date. Other software and various agencies may use different coordinate systems. In particular, NASA uses the mean equator and equinox of the Besselian year 1950 ("Mean of 1950", "M50" or "B1950"). Astronomers and other agencies may use the mean equator and equinox of the Julian year 2000 ("Mean of 2000" or "J2000"). Other agencies, such as the DOD C-Band Radar Network, use a time- independent coordinate system ("Earth-fixed Greenwich" or "EFG") for predicted state vectors prior to a launch. Users must take care that the appropriate coordinate system is used for each application and/or perform the required conversions. Program STSORBIT PLUS Satellite Orbit Simulation Page 87 STSPLUS sets up certain initial default parameters for data output and displays the current parameters each time F3 is pressed, as shown in the following example: STSORBIT PLUS Data Output Parameters: Data Output: STSPLUS.LOG Data Format: 7 = Precision X-Y-Z State Vector Data Interval: 60 seconds (continuous) Data Units: Kilometers, Multi-Line Labeled Accept Parameters [Y,n,x]: For Data Modes 8 and 9, the final prompt includes the option to display the data on the screen: Accept Parameters [Y,n,s,x]: To cancel data output and return to the Main Menu, press "X". If the current parameters are correct, press "Y" (or ENTER) to accept them. If the parameters are to be changed or if a specified time or time span is desired, press "N" to be prompted for new parameters. In each case, the default value which will be used if ENTER is pressed will be shown in square brackets; if more than one choice is shown, separated by commas, the first choice will be used if ENTER is pressed. The user must first select the data output device or destination by pressing the indicated key: Select Output [F,p,1,2]: F = File STSPLUS.LOG P = Printer LPT1: 1 = Serial Port COM1: 2 = Serial Port COM2: Pressing ENTER or the letter "F" (upper or lower case) will select the FILE output and the data will be sent to the file STSPLUS.LOG. If the file does not exist, it will be created; if the file already exists, the data will be appended to the existing data. Press the letter "P" to direct the data to the printer on LPT1. Press "1" or "2" to direct the data to one of the two serial ports. When a serial port (COM1: or COM2:) is selected, the user next selects the data rate to be used for communications with the external equipment. Only the four data rates shown below the prompt are supported. Use the first character of the desired rate to select it, or press ENTER to use the data rate shown in the square brackets: Select DATA RATE [9600]: (300, 1200, 2400, 9600) STSPLUS automatically sets the communications parameters to "8,N,1"; these are fixed and may not be altered. These communications parameters select 8 data bits per transmitted byte, NO parity, and 1 stop bit. Most external equipment will operate satisfactorily with these parameters. STSPLUS requires several additional items of information before it can send data to the external equipment, file or printer. The first is the data format to be used. Eight different data formats are available. The next Program STSORBIT PLUS Satellite Orbit Simulation Page 88 prompt lists the formats and shows the current default in square brackets: Select Data to Output [7]: 1 = Azimuth, Elevation, Range 2 = Latitude, Longitude, Orbit Altitude 3 = Right Ascension, Declination 4 = Ascending Node X-Y-Z State Vector 5 = Precision X-Y-Z State Vector (2-Line Data) 6 = Precision X-Y-Z State Vector (Comma Delimited) 7 = Precision X-Y-X State Vector (Labeled Data) 8 = Doppler Shift Frequency Predictions 9 = Tabular Line-of-Sight Predictions Press the number key corresponding to the desired Data Mode or press ENTER to select the choice shown in square brackets. See the Data Mode Formats in the following sections for specific details on the data included in each data mode. For current position and state vector formats except Data Mode 4, the desired time interval between successive sets of data must be also selected. (Data Mode 4 records data immediately after the Ascending Node and does not use the time interval parameter.) Any interval between 1 and 900 seconds may be selected (that is, up to 15 minutes maximum). Add the letter "T" or "t" if you wish the data to be logged for a specific time or time span. Note also that this is the DESIRED time interval; if your computer is too slow to complete its calculations in that time, the interval will be longer. In other words, STSPLUS will generate the requested data no more frequently than the interval requested but may take longer, depending upon what has to be done each time. In response to the prompt, press ENTER to accept the default value shown in square brackets or type the desired numerical value (in seconds) followed by ENTER: Data Interval (secs) [60]: (Min = 1 sec, Max = 900 secs; Add 'T' for timer) If a value less than 1 second is entered, 1 second will be substituted; if a value greater than 900 seconds is entered, 900 will be substituted. If "T" is entered by itself, the default value shown in square brackets will be used for the Data Interval. If "T" is appended to the desired interval or is entered by itself, STSPLUS requests the Start Time for logging: Start Time (HH:MM:SS): (Add 'U' or 'G' for UTC/GMT) Enter the desired LOCAL Start Time or add the letter "U" or "G" for UTC/GMT time. STSPLUS will reformat the entered time and add the appropriate time zone designation, then prompt for the Stop Time: Start Time (HH:MM:SS): 08:45:00 PDT Stop Time (HH:MM:SS): (Press ENTER for Stop Time = Start Time) Enter the desired Stop Time using the SAME time scale used for Start Time, or press ENTER to use the Start Time. STSPLUS will reformat the entered time and add the appropriate time zone designation. Program STSORBIT PLUS Satellite Orbit Simulation Page 89 Stop Time (HH:MM:SS): 08:50:00 PDT When Start Time equals Stop Time, only one set of data will be recorded. Reasonable care is required when setting up these times. If the current time (real or simulated) is past the Start Time, data will be recorded immediately. Times may be set to less than 24 hours into the future. When state vectors are requested (Data Modes 5 through 7), STSPLUS must also know the desired units of measure, kilometers ("km" or "KM"), feet ("ft" or "FT"), or nautical miles ("nm" or "NM"): Data Units [KM,ft,nm]: (Press 1st letter to select) Press the first letter of the desired units of measure or press ENTER for the current default units of measure (shown in capital letters in the prompt, "KM" in the example above). STSPLUS now displays the new parameters for approval: STSORBIT PLUS Data Output Parameters: Data Output: STSPLUS.LOG Data Format: 7 = Precision X-Y-Z State Vector Data Interval: 60 seconds, 08:45:00-08:50:00 PDT Data Units: Kilometers, Multi-Line Labeled Accept Parameters [Y,n,x]: If no Start and Stop Times have been entered, "(continuous)" will appear in place of the Start and Stop Times. As before, press "Y" (or ENTER) to accept the parameters and enable data output, "N" to re-enter the parameters, or "X" to cancel data output and return to the Main Menu. Setting Up Tabular Pass Predictions ----------------------------------- STSPLUS provides two Data Modes, 8 and 9, to generate tabular pass prediction data. These two Data Modes may also be used simply to display passes of interest (with the generated data not used or discarded). 8 = Doppler Shift Frequency Predictions --------------------------------------- Data Mode 8, Doppler Shift Frequency Predictions, displays upcoming satellite passes over the user's primary location for 48-hour periods. When a pass is selected and displayed, the map is drawn with simulated time set to just before the beginning of the pass. As the pass proceeds, the Doppler Shift information is calculated and sent to the selected output device. Program STSORBIT PLUS Satellite Orbit Simulation Page 90 9 = Tabular Line-of-Sight Predictions ------------------------------------- Data Mode 9, Tabular Line-of-Sight Predictions, displays (and optionally sends to an output device) data for upcoming satellite passes over the user's primary location during 48-hour periods. The user may select a particular pass and cause simulated time to be set to the middle of the pass. The map is drawn and the user may view the pass to determine any additional information of interest. The appropriate data are displayed and sent to the destination device at the selected data interval (continuous), at a specified time, or over a specified time span covering no more than 24 hours. The user may simply view the tabular pass information or he may select a specific pass to view on the map. Data Mode 8, the Doppler Shift Frequency Predictions, can be particularly helpful in preparing for a satellite amateur radio contact by printing the resulting frequency predictions for use during the contact. In this data mode, the tabular data are generated as a selected pass is displayed; the data include date and time, satellite geodetic coordinates (latitude and longitude), horizon coordinates (elevation and azimuth), and the frequency differences from the specified uplink and downlink center frequencies. See the format description for Data Mode 8 below for additional details. The pass selection list is NOT sent to the output device in this Data Mode. STSPLUS sets up certain initial default parameters for tabular pass predictions and displays the current parameters each time F3 is pressed, as shown in the following example: STSORBIT PLUS Data Output Parameters: Data Output: STSPLUS.LOG Data Format: 9 = Tabular Line-of-Sight Predictions (Using PDT for times) Accept Parameters [Y,n,s,x]: To cancel data output and generate pass predictions on the screen ONLY, press "X". If the current parameters are correct, press "Y" (or ENTER) to accept them or press "S" if output to the screen only is desired. If the parameters are to be changed or if a specified time is desired, press "N" to be prompted for new parameters. In each case, the default value which will be used if ENTER is pressed will be shown in square brackets; if more than one choice is shown, separated by commas, the first choice will be used if ENTER is pressed. The user must first select the data output device or destination by pressing the indicated key: Select Output [F,p,1,2]: F = File STSPLUS.LOG P = Printer LPT1: 1 = Serial Port COM1: 2 = Serial Port COM2: Pressing ENTER or the letter "F" (upper or lower case) will select the FILE Program STSORBIT PLUS Satellite Orbit Simulation Page 91 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 [7]: 1 = Azimuth, Elevation, Range 2 = Latitude, Longitude, Orbit Altitude 3 = Right Ascension, Declination 4 = Ascending Node X-Y-Z State Vector 5 = Precision X-Y-Z State Vector (2-Line Data) 6 = Precision X-Y-Z State Vector (Comma Delimited) 7 = Precision X-Y-X State Vector (Labeled Data) 8 = Doppler Shift Frequency Predictions 9 = Tabular Line-of-Sight Predictions Press the "8" or "9" number key to select one of the pass predictions or press ENTER to select the choice shown in square brackets. See the Data Mode Formats in the following sections for specific details on the data included in each data mode. For tabular line-of-sight predictions, STSPLUS must know the time zone for which data is to be displayed. The choices are UTC/GMT or the LOCAL time zone: Use UTC or PDT time [PDT]: (Use LEFT LETTER of abbreviation to select); Depending upon the user's choice when the UTCOffset was set, either "UTC" or "GMT" will be displayed along with the abbreviation for the local time zone. Use the left-most letter of the desired time zone, or press ENTER to accept the time zone shown in the square brackets ("[PDT]" in the example). STSPLUS now returns to the initial parameter display and again asks if the parameters are correct. As before, press "Y" to proceed with pass predictions AND sending the data to the specified destination device, "N" to change parameters, or "X" return to the Main Menu and display the pass predictions on the screen WITHOUT sending the data to a destination device. For both pass prediction modes, the data are displayed on the screen Program STSORBIT PLUS Satellite Orbit Simulation Page 92 as calculated and optionally (for Line-of-Sight Predictions ONLY) 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 final prompt for Doppler Shift Frequency Predictions is similar: Repeat for NEXT 48 HOURS or CALCULATE DOPPLER [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. For Line-of-Sight Pass Predictions, the user may select either UTC/GMT or LOCAL date and times for pass predictions. If other than UTC is selected, substitute the appropriate time zone abbreviation as required. The date is given only for AOS; since passes may span 00:00:00 hours for the selected time zone, the actual date for MAX VISIBILITY and/or LOS may have to be incremented. Times are calculated to the nearest second, altitudes are rounded to the nearest degree, and azimuths are rounded to the nearest tenth of a degree. Azimuth is always calculated in the sense NESW where North = 0 degrees, West = 90 degrees, etc. Note that the degree symbol will appear on the display for all "Azm" and "Alt" data but has been deleted in the sample above in order to maintain compatibility with various printers; the actual display is thus four columns wider than the example above. Press ENTER while the passes are being calculated to stop the calculations. When all calculations for the current 48 hour block have been completed, the time elapsed for the calculations is displayed and the user is asked if another set of calculations is desired of if a particular pass should be displayed. Press "N" or ENTER to return to the Main Menu, or Program STSORBIT PLUS Satellite Orbit Simulation Page 93 press "Y" to perform the next 48 hour block of calculations. The calculations will be stopped when 99 passes have been listed. Typically, from four to sixteen passes are listed for each 48 hour block, the number being related to the characteristics of the current satellite's orbit. If additional passes beyond that time are desired, set simulated time (F8+F3 from the Main Menu) to the desired start time and repeat the predictions. To display a particular pass, enter the listed pass number. Passes are assigned arbitrary numbers from 1 to 99 beginning with the first pass which occurs during or subsequent to the current real or simulated time. Any pass number may be selected, from pass #1 to the last listed pass shown on the screen. (Attempting to enter a pass number larger than the last one shown will cause the computer to "beep" and the prompt will be repeated.) STSPLUS will set simulated time to approximately 30 seconds prior to the mid-point of the selected pass and prepare the display. The pass may then be examined for details of lighting, ground track, and so forth. STSPLUS displays "VIS" next to the orbit inclination if a visual sighting may be possible. While examining the pass, use F6 to PAUSE the display, then use the "+" or "-" keys to adjust the simulated time forward or backward. The default time step is one second; press F4 to select a different time step: 1, 10, or 60 seconds. Press ENTER to return to normal operation from the PAUSE mode. For Doppler Shift Frequency Predictions only, the displayed pass begins just before AOS (Acquisition of Signal) instead of near the maximum elevation. Doppler shift frequency data will be sent to the output device only after AOS is reached and until LOS (Loss of Signal) is reached. The user may use "fast time" to speed up the operation but there may be some loss of accuracy. Press ENTER once the pass has been completed to return to 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. Note that STSPLUS automatically sets simulated time to display a predicted pass, and that new simulated time remains in effect until the user returns to the Main Menu, at which point the time is restored to the real or simulated time in effect BEFORE the pass prediction was displayed. Repeated use of pass predictions will therefore generally produce the same list of passes; however, if sufficient time elapses between predictions that a pass "comes and goes", new pass numbers will be displayed. Program STSORBIT PLUS Satellite Orbit Simulation Page 94 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 95 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 96 Data Mode 3: Topocentric RA/DEC Data Format ------------------------------------------- 1 2 3 4 01234567890123456789012345678901234567890123456 ----------------------------------------------- 02/11/1993 13:47:20 20580 7.111 -25.941 [CR/LF] -----+---- ----+--- --+-- ----+--- ----+--- | | | | | | | | | +----------- DEC | | | | | | | +--------------------- RA | | | | | +------------------------------ NORAD # | | | +-------------------------------------- UTC Time | +------------------------------------------------- UTC Date UTC Date: Current date in Universal Coordinated Time, mm/dd/yyyy UTC Time: Current time in Universal Coordinated Time, hh:mm:ss NORAD #: Satellite NORAD Number RA: Topocentric Right Ascension in hours DEC: Topocentric Declination in degrees [CR/LF]: Each data line is terminated with a CR and LF in addition to the 46 printing characters shown, for a total of 48 characters per data line. NOTES: 1. Topocentric coordinates give the right ascension and declination as seen from the current user's location on the surface of the Earth. 2. Coordinates are equator and equinox of date. Program STSORBIT PLUS Satellite Orbit Simulation Page 97 Data Mode 4: Ascending Node X-Y-X State Vector ---------------------------------------------- STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 4 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93206.71622934028 07/25/1993 17:11:22.215 UTC ECI X: 6083.74442210995 km Y: 2969.71930867257 km Z: 0.01043524694 km Xdot: -2.09290827983 km/sec Ydot: 4.27922666083 km/sec Zdot: 6.01892329735 km/sec Ndot/2 (Drag): 0.00056174000 Nndot/6: 0.00000000000 B-Star: 0.00071196000 ElSet #: 196.00000000000 Rev @ Epoch: 42514.00433526011 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 14 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93206.71622934028 07/25/1993 17:11:22.215 UTC ECI X: 19959752.12027331000 ft Y: 9743154.40544174400 ft Z: 34.23630116129 ft Xdot: -6866.48346437341 ft/sec Ydot: 14039.42991197058 ft/sec Zdot: 19747.08480675116 ft/sec Ndot/2 (Drag): 0.00056174000 Nndot/6: 0.00000000000 B-Star: 0.00071196000 ElSet #: 196.00000000000 Rev @ Epoch: 42514.00523843931 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 24 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93206.71622934028 07/25/1993 17:11:22.215 UTC ECI X: 3284.95919120368 nm Y: 1603.52014507239 nm Z: 0.00563458372 nm Xdot: -1.13008006471 nm/sec Ydot: 2.31059754904 nm/sec Zdot: 3.24995858388 nm/sec Ndot/2 (Drag): 0.00056174000 Nndot/6: 0.00000000000 B-Star: 0.00071196000 ElSet #: 196.00000000000 Rev @ Epoch: 42514.00325144509 Program STSORBIT PLUS Satellite Orbit Simulation Page 98 NOTES: 1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis is pointing toward the vernal equinox, the Z-Axis is pointing toward the North Pole, and the Y-Axis is mutually orthogonal to the other axes in a right-handed axis system. All coordinates are for true equator and equinox of date. 2. The units of measure for the state vector may be determined by the tens digit of the Data Mode in the initial header line as well as being indicated with the data: 4 Kilometers and kilometers per second 14 Feet and feet per second 24 Nautical miles and nautical miles per second 3. One data item is given per line, labeled as shown in the examples. The data in the first four lines (Satellite Name, Catalog Number, and two lines of Date/Time) begin in column 25. The remaining numeric data items begin in column 21 and use a FORTRAN-like format statement F21.11. 4. The Catalog Number is given first as the NORAD Number ("16609" in the example) and then as the International Designation ("86017A"). The International Designation is from 1 to 3 letters. Some 2-line elements omit the International Designation, in which case that portion will be blank. 5. Note that the Date/Time is presented on two lines in two different formats. The first format is the NASA Day-of-Year ("DOY") format, YYDDD.DDDDDD, since that is the format used by NASA/JSC for X-Y-Z state vectors for the Space Shuttle, in 2-line elements, and in program VEC2TLE. In the DOY format, time is counted from midnight (00:00 UTC) each day. Some calculations may require instead the Julian Date format which counts time from noon (12:00 UTC) each day. The Date/Time is also "decoded" and given in the more conventional "MM/DD/YYYY HH/MM/SS.SSS" format for clarity using Coordinated Universal Time (UTC/GMT). 6. The ElSet Number is specified in the 2-line elements used to generate the ground track and is always given as an integer. Note that ElSet Numbers may not necessarily follow in sequence and that different sources will use different sequences of ElSet numbers. 7. The Rev Number at Epoch (the orbit number at the time the data is sampled) is based upon the Rev Number specified in the 2-line elements used to generate the ground track. The fractional part is calculated by STSPLUS geometrically from the ascending node. Note that US Space Command uses a different orbit numbering convention than does NASA for space shuttle missions; US Space Command usually specifies the first (partial) orbit number as Rev 0, while NASA specifies that orbit number as Rev 1. For satellites which have been in orbit for long periods of time, the Rev Number may be arbitrary. Program STSORBIT PLUS Satellite Orbit Simulation Page 99 Data Mode 5: Precision X-Y-Z Cartesian State Vector, 2 Data Lines ----------------------------------------------------------------- STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 5 20580 93110.043125 4920.98348 4440.02814 -2158.84295 -4.02147461570 5.78870948196 2.74131815428 20580 93110.043171 4904.85124 4463.14112 -2147.85724 -4.04461763461 5.76773962933 2.75148946765 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 15 20580 93110.045081 13656864.66720 17514322.54968 -5452252.42794 -16168.27686974290 15789.75251859515 10248.33566657315 20580 93110.045139 13575822.39276 17593013.13238 -5400930.14914 -16248.48336702945 15686.35334359047 10280.38786725583 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 25 20580 93110.046829 1817.50246 3234.50460 -631.72242 -3.02340746009 2.05326951871 1.82336359537 20580 93110.046991 1774.96638 3262.87575 -606.12299 -3.05304428709 1.99966800523 1.83360328215 NOTES: 1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis is pointing toward the vernal equinox, the Z-Axis is pointing toward the North Pole, and the Y-Axis is mutually orthogonal to the other axes in a right-handed axis system. All coordinates are for true equator and equinox of date. 2. The units of measure for the state vector may be determined by the tens digit of the Data Mode in the initial header line: 5 Kilometers and kilometers per second 15 Feet and feet per second 25 Nautical miles and nautical miles per second 3. The NASA Day-of-Year format is used here for date and time since that is the format used by JSC for X-Y-Z state vectors and also in 2-line elements. In the DOY format, time is counted from midnight (00:00 UTC) each day. Some calculations may require instead the Julian Date format which counts time from noon (12:00 UTC) each day. 4. Two successive data samples are shown for each data mode. 5. The following FORTRAN-like format statements may be used to read the two lines of data in this mode for all units of measure: First Line: ----------- Catalog #: I5 2X Date/Time: F15.9 X: F15.5 4X Program STSORBIT PLUS Satellite Orbit Simulation Page 100 Y: F15.5 4X Z: F15.5 CR/LF Second Line: ------------ 23X Xdot: F18.11 1X Ydot: F18.11 1X Zdot: F18.11 CR/LF Program STSORBIT PLUS Satellite Orbit Simulation Page 101 Data Mode 6: Precision X-Y-Z Cartesian State Vector, Comma Delimited -------------------------------------------------------------------- STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 6 0,0,20580,93110.0476041667,2982.28779295502,6229.01725815628,-940.796339818487, -5.85010701911522,3.3199940892324,3.46047048985284 0,0,20580,93110.0476851852,2941.25120957693,6252.07713790904,-916.54588610151, -5.87454395677527,3.2685046500327,3.46815363454982 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 16 0,1,20580,93110.0482060185,8771281.06140276,20969911.6226162,-2491608.1429704, -19762.0576284838,9623.02409449012,11524.6952898439 0,1,20580,93110.0482638889,8672341.7437806,21017717.5456987,-2433947.77946384, -19813.4647395816,9499.28476766938,11539.2506632381 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 26 0,2,20580,93110.0493865741,1103.65585656622,3591.279279101,-214.476932551084, -3.4057330597861,1.1598790254898,1.9344163566285 0,2,20580,93110.049537037,1059.27271053518,3605.99939807939,-189.308779132495, -3.42231018081901,1.10471766926502,1.93751948609809 NOTES: 1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis is pointing toward the vernal equinox, the Z-Axis is pointing toward the North Pole, and the Y-Axis is mutually orthogonal to the other axes in a right-handed axis system. All coordinates are for true equator and equinox of date. 2. The units of measure for the state vector may be determined by the tens digit of the Data Mode in the initial header line as well as the second parameter in the comma delimited data string: Data Param Mode #2 Units ----------------------------------------------------------- 6 0 Kilometers and kilometers per second 16 1 Feet and feet per second 26 2 Nautical miles and nautical miles per second 3. The comma delimited data are generated as a single line terminated by CR/LF. The examples above have been split into two lines for printing purposes. 4. The data are written in a single data line in the following order, separated by a comma between items: Epoch Flag, always zero signifying equator and equinox of date. Units Flag (see Note 1 above) Catalog/NORAD number Date (YYDDD.DDDDDDDD... format) ECI X ECI Y ECI Z Program STSORBIT PLUS Satellite Orbit Simulation Page 102 ECI Xdot ECI Ydot ECI Zdot 5. Line length will vary as a function of the data. 6. Two successive data samples are shown for each data mode. Program STSORBIT PLUS Satellite Orbit Simulation Page 103 Data Mode 7: Precision X-Y-Z Cartesian State Vector, Labeled Data ----------------------------------------------------------------- STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 7 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93192.11956018518 07/11/1993 02:52:10.000 UTC ECI X: -3441.20195444797 km Y: -3110.29870646026 km Z: 4920.32069520120 km Xdot: 2.90216455238 km/sec Ydot: -6.74909064951 km/sec Zdot: -2.23710677970 km/sec Ndot/2 (Drag): 0.00008567000 Nndot/6: 0.00000000000 B-Star: 0.00011546000 ElSet #: 167.00000000000 Rev @ Epoch: 42286.31052536559 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 17 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93192.12233796297 07/11/1993 02:56:10.000 UTC ECI X: -8617248.92526347200 ft Y: -15077459.08108566000 ft Z: 13806887.09734187000 ft Xdot: 12614.26230523560 ft/sec Ydot: -18214.71804776612 ft/sec Zdot: -12006.04438377176 ft/sec Ndot/2 (Drag): 0.00008567000 Nndot/6: 0.00000000000 B-Star: 0.00011546000 ElSet #: 167.00000000000 Rev @ Epoch: 42286.35385448637 STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 27 Satellite Name: MIR Space Station Catalog Number: 16609 86 17 A Epoch Date/Time: 93192.12280092592 07/11/1993 02:56:50.000 UTC ECI X: -1333.74601094830 nm Y: -2598.74977950943 nm Z: 2190.96899536823 nm Xdot: 2.14691236531 nm/sec Ydot: -2.86693936350 nm/sec Zdot: -2.09121400862 nm/sec Ndot/2 (Drag): 0.00008567000 Nndot/6: 0.00000000000 B-Star: 0.00011546000 ElSet #: 167.00000000000 Rev @ Epoch: 42286.36107600650 Program STSORBIT PLUS Satellite Orbit Simulation Page 104 NOTES: 1. The X-Y-Z Cartesian State Vector is given as a standard Earth-centered inertial ("ECI") cartesian 6-dimensional state vector where the X-Axis is pointing toward the vernal equinox, the Z-Axis is pointing toward the North Pole, and the Y-Axis is mutually orthogonal to the other axes in a right-handed axis system. All coordinates are for true equator and equinox of date. 2. The units of measure for the state vector may be determined by the tens digit of the Data Mode in the initial header line as well as being indicated with the data: 4 Kilometers and kilometers per second 14 Feet and feet per second 24 Nautical miles and nautical miles per second 3. One data item is given per line, labeled as shown in the examples. The data in the first four lines (Satellite Name, Catalog Number, and two lines of Date/Time) begin in column 25. The remaining numeric data items begin in column 21 and use a FORTRAN-like format statement F21.11. 4. The Catalog Number is given first as the NORAD Number ("16609" in the example) and then as the International Designation ("86017A"). The International Designation is from 1 to 3 letters. Some 2-line elements omit the International Designation, in which case that portion will be blank. 5. Note that the Date/Time is presented on two lines in two different formats. The first format is the NASA Day-of-Year ("DOY") format, YYDDD.DDDDDD, since that is the format used by NASA/JSC for X-Y-Z state vectors for the Space Shuttle, in 2-line elements, and in program VEC2TLE. In the DOY format, time is counted from midnight (00:00 UTC) each day. Some calculations may require instead the Julian Date format which counts time from noon (12:00 UTC) each day. The Date/Time is also "decoded" and given in the more conventional "MM/DD/YYYY HH/MM/SS.SSS" format for clarity using Coordinated Universal Time (UTC/GMT). 6. The ElSet Number is specified in the 2-line elements used to generate the ground track and is always given as an integer. Note that ElSet Numbers may not necessarily follow in sequence and that different sources will use different sequences of ElSet numbers. 7. The Rev Number at Epoch (the orbit number at the time the data is sampled) is based upon the Rev Number specified in the 2-line elements used to generate the ground track. The fractional part is calculated by STSPLUS geometrically from the ascending node. Note that US Space Command uses a different orbit numbering convention than does NASA for space shuttle missions; US Space Command usually specifies the first (partial) orbit number as Rev 0, while NASA specifies that orbit number as Rev 1. For satellites which have been in orbit for long periods of time, the Rev Number may be arbitrary. Program STSORBIT PLUS Satellite Orbit Simulation Page 105 Data Mode 8: Doppler Shift Predictions -------------------------------------- STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 8 Satellite Name: AO-27 Catalog Number: 22825 93061C Uplink Center Frequency: 145.85000 MHz Dnlink Center Frequency: 436.80000 MHz Freq Diff in Hz MM/DD TIME Sat Lat Sat Lon Sat Elv Sat Azm Uplink DnLink ------------------------------------------------------------------------ 07/31 18:21:00 UTC 56.992 -102.805 1.748 19.947 -3171 9497 07/31 18:22:00 UTC 53.549 -104.703 5.777 22.118 -3135 9388 07/31 18:23:00 UTC 50.085 -106.353 10.523 24.984 -3062 9170 07/31 18:24:00 UTC 46.604 -107.814 16.339 29.016 -2926 8764 07/31 18:25:00 UTC 43.109 -109.129 23.770 35.186 -2673 8005 07/31 18:26:00 UTC 39.603 -110.330 33.417 45.735 -2189 6555 07/31 18:27:00 UTC 36.088 -111.439 44.547 65.985 -1291 3865 07/31 18:28:00 UTC 32.565 -112.475 50.407 101.881 63 -188 07/31 18:29:00 UTC 29.035 -113.452 43.796 136.739 1389 -4161 07/31 18:30:00 UTC 25.501 -114.381 32.707 155.928 2247 -6730 07/31 18:31:00 UTC 21.962 -115.271 23.276 165.962 2707 -8108 07/31 18:32:00 UTC 18.419 -116.131 16.011 171.851 2949 -8832 07/31 18:33:00 UTC 14.873 -116.966 10.302 175.688 3080 -9223 07/31 18:34:00 UTC 11.326 -117.782 5.625 178.391 3150 -9435 07/31 18:35:00 UTC 7.777 -118.584 1.638 180.406 3186 -9543 NOTES: 1. The header information gives the satellite name and catalog number, the Epoch Date/Time of the TLEs, and the center frequencies for the Uplink and the Downlink (usually in units of MHz) as read from file STSPLUS.FRQ (if present) or the default value of 100 MHz. 2. One data line is generated for each time step. For the date, only the month and day ("MM/DD") are given in order to accommodate line length restrictions. The time is given in Coordinated Universal Time (UTC). 3. The satellite geodetic coordinates, latitude and longitude, are given in degrees. Negative latitude is South, negative longitude is West. 4. The satellite horizon coordinates, elevation and azimuth, are given in degrees and the sense is NESW, North = 0, East = 90, etc. 5. The doppler shift calculations are shown as the frequency difference (in Hz) from the corresponding center frequency (in MHz, shown in the header) at 60 second intervals throughout the pass. Program STSORBIT PLUS Satellite Orbit Simulation Page 106 Data Mode 9: Pass Predictions ----------------------------- --------#20580 AOS-------- --MAX VISIBILITY-- ------LOS------ # UTC Date UTC Time Azm UTC Time Alt Azm UTC Time Azm Duration 1 02/27/1993 03:58:09 205.1 04:03:00 9 157.9 04:07:52 110.8 0:09:43 -+ ---------+--------- --+-- ----+--- -+ --+-- ----+--- --+-- ----+--- | | | | | | | | | Pass # | | | | | | | | | | | | | | | | +----------+ | | | | | | | | | | | | | | | | +---------------------+ | | | | | | | | | | | | | | | +----- AOS Azimuth (degrees) | | | | | | | | | | | | | +-------- AOS Date/Time | | | | | | (mm/dd/yyyy hh:mm:ss) | | | | | | | | | | | | +---------------------------------+ | | | | | | | | | | | | +-------------------------------------+ | | | | | | | | | | | | +--------------------------------------+ | | | | | | | | | | | +-- MAX Azimuth (degrees) | | | | | | | | | +----- MAX Altitude (degrees) | | | | | | | +-------- MAX Time (hh:mm:ss) | | | | | | +-----------------------------------------------------+ | | | | | | +----------------------------------------------------------+ | | | | | +----- LOS Azimuth (degrees) | | | +-------- LOS Time (hh:mm:ss) | | Total Pass Duration (hh:mm:ss) --+ NOTES: 1. When the Data Output mode is set up for pass predictions, dates and times for pass predictions may be selected for UTC/GMT or local time and the selected time zone abbreviation and time scale will be used. Substitute the appropriate abbreviation for "UTC" as required if other than UTC has been selected. When UTC or GMT is selected, the Data Mode will be given as "9"; when local time is selected, the Data Mode will be given as "19". 2. The Pass # is an arbitrary number assigned by STSPLUS during the pass calculations and is a function of the real or simulated time at which the calculations are performed. If the real or simulated time is changed, the pass numbers may change and different passes may be Program STSORBIT PLUS Satellite Orbit Simulation Page 107 shown. 3. The satellite NORAD number is included in the heading, "20580" in the sample above. 4. The Date (UTC/GMT or local) is given only for AOS. Since a pass may span 00:00:00 hours, the date for MAX VISIBILITY and/or LOS may have to be incremented from that shown for AOS. 5. All azimuths ("Azm") have been rounded to the nearest 0.1 degree; the MAX VISIBILITY altitude ("Alt") has been rounded to the nearest degree. Program STSORBIT PLUS Satellite Orbit Simulation Page 108 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 109 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 110 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 Set/Read/Save TDRS and Real Time Satellites -------------------------------------------------- STSPLUS is able to display up to 32 additional TDRS (or other geosynchronous/geostationary) or Real Time satellites. The first menu selection allows the user to select the desired satellite for each of the sixteen available "slots" as well as abbreviation, mode, and icon/label color. Note that these features are enabled and disabled using F10+F3+F2 from the Main Menu. The following menu is displayed: TDRS and Real Time Satellite Maintenance Menu F1 Display/Modify satellite assignments F2 Save SCF Satellite Configuration File F3 Read SCF Satellite Configuration File F4 Select new PRIMARY SATELLITE F5 Select new TARGET SATELLITE F6 Clear Static and Real Time Satellites Press function key for desired choice or ENTER for Main Menu: Press ENTER to return to the Main Menu, or press the desired function key to select the indicated function. Before the current position of each satellite can be calculated, 2- line elements must be read or updated using F2 from the Main Menu. After this has been performed once, the position will be calculated based upon those 2-line elements. The user is reminded that the 2-line elements should be updated periodically so that the calculated position accurately reflects the actual position. NOTE: Users of prior versions of STSPLUS will note that Function Key F6 has been reassigned for its present function. Switching between MET and T+Epoch may now be accomplished ONLY by pressing F5 while the ground track is displayed. F1 Display/Modify Satellite Assignments ---------------------------------------- This menu selection displays the current TDRS and Real Time Satellite assignments and option selections as a table: Program STSORBIT PLUS Satellite Orbit Simulation Page 111 -------------------------------------------------------------------------- TDRS and Real Time Satellite Setup Sat# NORAD# Abbr Mode Color Size Label Vis Color Chart 1 19883 TDRE Static 10 o 3 ON 2 21639 TDRW Static 10 o 3 ON 1 = XXXXX 3 22314 TDR5 Static 2 o 3 ON OFF 2 = XXXXX 4 19548 TDR2 Static 2 o 3 ON OFF 3 = XXXXX 5 13969 TDR1 Static 2 o 3 ON OFF 4 = XXXXX 6 16609 MIR Primary 12 o ON ON 5 = XXXXX 7 21701 UARS Real Time 13 o ON OFF 6 = XXXXX 8 20580 HST Real Time 14 o ON OFF 7 = XXXXX 9 20638 ROSAT Real Time 13 o ON OFF 8 = XXXXX 10 22076 TOPEX OFF 13 o ON OFF 9 = XXXXX 11 0 (not used) 10 = XXXXX 12 0 (not used) 11 = XXXXX 13 0 (not used) 12 = XXXXX 14 0 (not used) 13 = XXXXX 15 0 (not used) 14 = XXXXX 16 0 (not used) 15 = XXXXX Enter Satellite # to edit or press ENTER when done: (The maximum Satellite # available is 32) -------------------------------------------------------------------------- NOTE: The first two satellite slots, #1 and #2, are reserved for the standard TDRS East and TDRS West satellites, currently NORAD Numbers 19833 and 21639. Instead of conventional circles of visibility, these two satellites generate commumications coverage circles. Assigning different satellites, especially satellites which are not geostationary, may produce unpredictable results. The Satellite Setup table headings indicate: Sat# Satellite Assignment Number, 1 to 32. If an asterisk ("*") appears to the right of the number, the epoch (date) of the associated orbital elements is more than 10 days (Real Time) or 60 days (Static) old as in this example: 8* 22920 ARRAY Real Time 14 o ON OFF and the following caution note will appear at the bottom of the display: * 2-Line Elements more than 10 (Real Time) or 60 (Static) days old! The caution note has no effect on orbital caculations and is simply a reminder that the orbital elements may be out of date and may or may not be valid. Use F2 from the Main Menu with "&" as the satellite name to update TLEs from a current data file. NORAD# The NORAD Number of the assigned satellite, or "0" if no satellite is assigned to this slot. Program STSORBIT PLUS Satellite Orbit Simulation Page 112 Abbr The five character abbreviation assigned to this satellite. Use only letters and numbers; the common satellite name or NORAD Number are the recommended choices. This abbreviation will be used as a label on the map if the Label is ON. May be left blank. Mode Five mode classifications are available: Primary Primary satellite selected for full tracking, selected using F2 or F6+F4 (below). The primary satellite may not be present in the satellite list. Static Geosynchronous or geostationary satellites (including TDRS). Plotted when map is drawn and NOT updated. Real Time Satellites tracked dynamically; updated every second (386/387 or higher), every ten seconds (286 or no coprocessor). OFF The satellite is included in the data but is not plotted. Used to temporarily disable satellite slots. (not used) Unassigned satellite slot(s). Color A number selected from the Color Chart at the right which indicates the color to be used to display the satellite icon and label (if enabled). Each "XXXXX" in the Color Chart appears on color monitors as a bar of the corresponding color. The "o" character to the right of the number is displayed as a small diamond in the selected color. Size For Static satellites only, selects the relative size of the icon used to represent the satellite. Values may range from 3 to 6. This column is blank for Real Time satellites since the icon size is fixed for these satellites. Label May be set to "ON" or "OFF" to indicate if the satellite abbreviation is to be displayed. The label color will be the same as that selected for the satellite. Vis May be set to "ON" or "OFF" to indicate if the satellite circle of visibility is to be drawn. The circle of visibility is drawn only for Static satellite on normal maps but is drawn for all satellites on Motion maps. Color The color chart displays the 15 available icon and label Chart colors (BLACK is omitted). When a monochrone display is used and the "/M" command line option is specified, two levels of gray will normally be displayed instead of colors. Each color is assigned a standard color number which is used for all data entries. Program STSORBIT PLUS Satellite Orbit Simulation Page 113 As indicated by the prompt, simply press ENTER if all data in the Satellite Setup is correct. You will return to the F6 menu above. If you wish to add a satellite or change the selections for an existing satellite, enter the satellite slot number (Sat# in the left column of the table). The following prompts will be displayed in turn: Enter NORAD Number: (Enter 0 to clear the satellite entry) STSPLUS expects the NORAD number for the desired satellite. This number will be used to "capture" the 2-line elements when this satellite is subsequently displayed. Enter Satellite Abbreviation: Enter any desired abbreviation, 5 characters or less, or the NORAD number. Use only letters, numbers, and the period ("."), dash ("-"), and comma (",") with no leading spaces. The Satellite Abbreviation is used as the satellite label on the map display (see below) and may be left blank if no label is desired. Enter Mode (0=STATIC, 1=REAL TIME, 2=OFF): Enter "0", "1", or "2". STATIC satellites are drawn each time the map is redrawn on the screen. REAL TIME satellites are updated every 1 or 10 seconds (depending upon the processor/coprocessor present) or as often as the processor can complete the required calculations. Satellites set to OFF and not processed but their data is retained so that they may be returned to STATIC or REAL TIME subsequently. Enter satellite color (1 to 15): Enter the number for the desired color, as shown on the Color Chart at the right of the screen. An illegal color number will default to YELLOW. Display satellite Label (0=NO, 1=YES): Enter "0" or "1". The label will be displayed directly below the satellite icon in the same color as that selected for the icon in the preceeding step. For Real Time satellites, the label is only drawn when the map is redrawn and remains stationary EXCEPT when using the Motion Map (in which case it follows with the icon). Display Cir of Visibility (0=NO, 1=YES): Enter "0" or "1". The circle of visibility is drawn (when enabled) for all Static satellites, and also for all Real Time satellites when using the Motion Map. When a new satellite is entered, a double asterisk ("**") will appear at the right for that satellite slot. This is to remind the user to display the ground track for that satellite so that 2-line elements may be stored in the TLE memory associated with that slot. The following message will also appear below the chart: Program STSORBIT PLUS Satellite Orbit Simulation Page 114 ** Update TLEs (F2+'&') or display ground track for this satellite! When STSPLUS adds a new Secondary Satellite, a skeletal 2-line element set (TLE) is saved which includes only the NORAD number. Before the satellite can be tracked, real TLEs must be present. This may be accomplished by updating the TLEs using F2 from the Main Menu and selecting AUTO UPDATE (satellite name entered is "&"). Alternatively, the satellite ground track may be displayed; to display the ground track, press F2 from the Main Menu, select the file of 2-line elements which includes the satellite in question, and enter the NORAD Number ("#nnnnn", where "nnnnn" is the NORAD Number). In either case, the 2-line elements will be saved for future use. Although 2-line elements are saved for all TDRS and Real Time satellites, the user is reminded that these elements have a limited lifetime. That lifetime varies considerably from satellite to satellite. For geosynchronous satellites, 4 to 8 weeks is probably reasonable; for other active satellites, 1 to 2 weeks should be an upper limit before new elements are used. Use F2 from the Main Menu and enter the satellite name as "&" to scan through the 2-line elements file and update all elements which are more recent than those now saved. F2 Save SCF Satellite Configuration File ----------------------------------------- Users may wish to switch among several sets of TDRS and Real Time satellites from time to time. Since it can be tedious to re-enter all the information repeatedly, STSPLUS can save and read Satellite Configuration Files, identified by the filetype .SCF. All parameters are saved and restored, exactly as if entered at the time. The current satellite configuration is automatically saved in file STSPLUS.INI each time the program is exited and is restored when the program is restarted. The following prompt is displayed: Save SCF Satellite Configuration File Enter SCF FILENAME, ENTER to quit: Current .SCF files are: STANDARD.SCF STSPLUS.SCF STSPLUS displays a list of available SCF files, up to a maximum of 90 files. Press ENTER to cancel the operation. Type the desired filename with or without the .SCF filetype; STSPLUS automatically appends the may be no longer than 8 characters. If the file already exists, STSPLUS will display a warning message: File STANDARD.SCF already exists! Overwrite [y/N]: where "STANDARD.SCF" will be the requested file including the .SCF filetype. Press "Y" or "y" to allow the existing file to be overwritten; press any other key to cancel the write operation, and then press ENTER to resume program operation. If the file does not exist, it will be created. Do not use filename STSPLUS since a sample file by that name is included with the distribution package (unless you wish to overwrite the supplied Program STSORBIT PLUS Satellite Orbit Simulation Page 115 file). F3 Read SCF Satellite Configuration File ----------------------------------------- See the comments above for saving SCF files. The following prompt is displayed: Read SCF Satellite Configuration File Enter SCF FILENAME, ENTER to quit: Current .SCF files are: STANDARD.SCF STSPLUS.SCF STSPLUS displays a list of available SCF files, up to a maximum of 90 files. Press ENTER to cancel the operation. Type the desired filename with or without the .SCF filetype; STSPLUS automatically appends the may be no longer than 8 characters. If the file does not exist, an error message will be displayed. F4 Select New PRIMARY Satellite -------------------------------- This function allows the user to select a new Primary Satellite, the satellite for which the data block is calculated, from the list of Secondary Satellites. The current list of Secondary Satellites is first displayed: ------------------------------------------------------- TDRS and Real Time Satellite Setup Sat# NORAD# Abbr Mode Color Size Label Vis 1 19883 TDRE Static 10 o 3 ON 2 21639 TDRW Static 10 o 3 ON 3 22314 TDR5 Static 2 o 3 ON OFF 4 19548 TDR2 Static 2 o 3 ON OFF 5 13969 TDR1 Static 2 o 3 ON OFF 6 16609 MIR Real Time 12 o ON ON 7 21701 UARS Primary 13 o ON ON 8 22920 ARRAY Real Time 14 o ON OFF 9 20638 ROSAT Real Time 13 o ON ON 10 22076 TOPEX Real Time 13 o ON ON 11 21225 GRO Real Time 13 o ON ON 12 21987 EUVE Real Time 13 o ON ON 13 20580 HST Real Time 14 o ON OFF 14 0 (not used) 15 0 (not used) 16 0 (not used) Enter New PRIMARY Satellite # or press ENTER to accept: Program STSORBIT PLUS Satellite Orbit Simulation Page 116 ------------------------------------------------------- Select the satellite which is to be the new Primary Satellite by entering its Sat# at the prompt, or press ENTER to cancel. Do NOT select a satellite which displays "**" at the right; valid 2-Line Elements are not available for that satellite! If "6" is entered for the example shown, the current 2- Line Elements for MIR will be displayed for approval: 2-Line Elements for new PRIMARY satellite: MIR 1 16609U 86017A 93351.25309831 .00007289 00000-0 97866-4 0 331 2 16609 51.6188 19.7769 0005725 99.5487 260.6154 15.59089672447666 Accept this Primary Satellite [Y/n]: Review the 2-Line Elements to be sure that valid elements are present and that they are for the desired satellite. Press "Y" (or ENTER) to accept the data shown as the new Primary Satellite, or press any other key to cancel. F5 Select New TARGET Satellite ------------------------------- This function allows the user to select a new Target Satellite, the satellite for which the Relative Range and Velocity may be calculated, from the list of Secondary Satellites. The current list of Secondary Satellites is first displayed: ---------------------------------------------------------------------- TDRS and Real Time Satellite Setup Sat# NORAD# Abbr Mode Color Size Label Vis 1 19883 TDRE Static 10 o 3 ON 2 21639 TDRW Static 10 o 3 ON 3 22314 TDR5 Static 2 o 3 ON OFF 4 19548 TDR2 Static 2 o 3 ON OFF 5 13969 TDR1 Static 2 o 3 ON OFF 6 16609 MIR Real Time 12 o ON ON 7 21701 UARS Real Time 13 o ON ON 8 22920 ARRAY Real Time 14 o ON OFF 9 20638 ROSAT Real Time 13 o ON ON 10 22076 TOPEX Real Time 13 o ON ON 11 21225 GRO Real Time 13 o ON ON 12 21987 EUVE Real Time 13 o ON ON 13 20580 HST Target 14 o ON OFF 14 22917 STS61 Primary 14 o ON OFF 15 0 (not used) 16 0 (not used) Enter New TARGET Satellite #, '0' to cancel, or press ENTER to accept: ---------------------------------------------------------------------- Select the satellite which is to be the new Target Satellite by entering its Sat# at the prompt, enter the digit zero ("0") to cancel the current Program STSORBIT PLUS Satellite Orbit Simulation Page 117 Target Satellite, or press ENTER to cancel and leave the current selection unchanged. Do NOT select a satellite which displays "**" at the right; valid 2-Line Elements are not available for that satellite! If "6" is entered for the example shown, the Target Satellite will be changed from #20580 (HST) to #16609 (MIR) and the current 2-Line Elements for MIR will be displayed for approval: 2-Line Elements for new TARGET satellite: MIR 1 16609U 86017A 93351.25309831 .00007289 00000-0 97866-4 0 331 2 16609 51.6188 19.7769 0005725 99.5487 260.6154 15.59089672447666 Accept this TARGET Satellite [Y/n]: Review the 2-Line Elements to be sure that valid elements are present and that they are for the desired satellite. Press "Y" (or ENTER) to accept the new Target Satellite, or press any other key to cancel. If MIR is accepted, it will then be used as the Target Satellite and Relative Range and Relative Velocity with respect to the Primary Satellite (STS-61 in the example) may be displayed using F10+F4 from the Main Menu OR by pressing F10 while the map is displayed. F6 Clear Static and Real Time Satellites ----------------------------------------- Use this function to clear selected static and/or real time satellites with slot numbers 3 through 32. STSPLUS asks the user to enter the first and last slot to clear, and to confirm the operation to avoid accidental clearing. NOTE: Slots 1 and 2 are reserved for TDRS satellites and should ALWAYS contain TDRS or similar geosynchronous satellites. The program may perform unpredictably if these slots are cleared or have other types of satellites. 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: [I:\TLE\] F2 Set TRACKING STATION filename: [STSPLUS.TRK] F3 Set MAP DATABASE FILES path: [D:\MAPDATA\] F4 Set FEATURES LABEL filename: [STSPLUS.LOC] F5 Set TRAKSTAR path: [D:\STSPLUS\] F6 Set CITYFILE filename: [STSPLUS.CTY] Enter selection or ENTER: Press the indicated function key for the item you wish to change. The Program STSORBIT PLUS Satellite Orbit Simulation Page 118 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. A drive and directory may also be included if desired. 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 (e.g. "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 Space Shuttle and Satellite Orbit Simulation Version 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 119 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 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 may be entered as "MM/DD/YYYY" or "MM/DD/YY" (US style) or as Program STSORBIT PLUS Satellite Orbit Simulation Page 120 "DD.MM.YYYY" or "DD.MM.YY" (European style) 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 delimiter used ("/" or ".") determines the method of interpretation: Entry Interpreted as --------- -------------- 12/8/94 12 AUG 1994 12/8/1994 12 AUG 1994 8.12.94 12 AUG 1994 8.12.1994 12 AUG 1994 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 Space Shuttle and Satellite Orbit Simulation Version 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 Program STSORBIT PLUS Satellite Orbit Simulation Page 121 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 PDT Enter DATE: 20 AUG 1994 Use US Style 'MM/DD/YYYY' or European Style 'DD.MM.YYYY' 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 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 Press ENTER to leave an item unchanged Enter SIMULATED TIME [12:05:06]: 13:00:00 PDT 20:00:00 UTC Enter SIMULATED DATE [07/26/1994]: 08 AUG 1994 08 AUG 1994 Use US Style 'MM/DD/YYYY' or European Style 'DD.MM.YYYY' 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. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 122 entered. Program STSORBIT PLUS Space Shuttle and Satellite Orbit Simulation Version 9435 Simulated time: 00:17:18 PST 08:17:18 UTC Simulated date: 10/09/1994 10/09/1994 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 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 123 F10 Set UTC 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 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: Program STSORBIT PLUS Satellite Orbit Simulation Page 124 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. F9 DOS Shell (CAUTION: DOS 3.2 or higher 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. All files used by STSPLUS are closed. 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 3.2 or higher! Systems with less than 640K memory may fail to execute the shell and applications requiring large amounts of memory may also fail. CAUTION: The BASIC SHELL function does NOT perform reliably when STSPLUS is executed under Windows and a BASIC ERROR or other unpredictable results may follow! Instead, close STSPLUS and use the MS-DOS PROMPT function from the FILE MANAGER. 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 125 ENTER Resume Mission --------------------- Pressing ENTER resumes the current mission shown in parentheses to the right of the command on the Main Menu. The 2-line elements file from which the data was read is shown in square brackets. ENTER Resume Mission (STS-41 [STS41F]) Any manually entered data is retained. "ENTER" means the key marked ENTER, RETURN, or with a left pointing arrow -- but not the backspace or cursor position keys which may also be marked with arrows! (I am afflicted with too long a memory; once upon a time this function was known as Carriage Return and was often shortened to RETURN or even CR. With the advent of electronic typewriters, video terminals, dot matrix printers and all the rest, "carriages" have long since disappeared but old habits die hard! Most PC keyboards are now marked with "ENTER".) Use ENTER to resume plotting a mission in progress after returning to the Main Menu to perform some change (such as enabling the node display, enabling the NASA tracking stations, or adjusting the time or date). ESC Quit STSORBIT PLUS and Save Current Mission -------------------------------------------------- Press ESC (the key marked "ESC" or "Esc", not the letters E+S+C) to quit program STSORBIT PLUS. If you press ESC to quit the program and have manually entered orbital data, STSPLUS will save all required mission data in file STSPLUS.INI prior to terminating. This will be the data available with the ENTER key the next time you execute the program. The demonstration data will not be saved, preserving any previously saved mission data. When you have finished with STSPLUS, press ESC at the Main Menu to return to DOS. The data (and any adjustments you have made) for the current mission are saved in file STSPLUS.INI, but the map data is lost and will be re-read when you next use program STSPLUS. Program STSORBIT PLUS Satellite Orbit Simulation Page 126 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 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 F1 Program STSORBIT PLUS Information F2 Set New Local Coordinates (Palos Verdes, CA) F3 Select Display Features F4 TGT Set Satellite Coordinates: Ra/Dec, Elv/Azm, XYZ, TARGET F5 OFF Show Ascending & Descending Node Data F6 ORTHO Set Map Projection and Size F7 ON Enable/Disable EVENT TIMERS F8 OFF Enable/Disable Audible ALARMS F9 -8.00 Set UTC Time Offset and Daylight Flag F10 OFF Enable/Disable Printer Logging ENTER Return to MAIN MENU Select desired function: F1 Program STSORBIT PLUS Information ---------------------------------------- Function Key F1 displays information about program STSORBIT PLUS including the copyright notice, version number, my name and address, and the telephone number of my RPV ASTRONOMY BBS (Bulletin Board System). The current version of STSORBIT PLUS is always posted on the BBS. The BBS has a power controller; if it hasn't answered after the THIRD RING, hang up and call back in two minutes. The BBS is available 24 hours per day at 9600, 2400 and 1200 baud. F2 Set New Local Coordinates -------------------------------- In order to perform the calculations related to satellite visibility and altitude/azimuth, STSPLUS must know the geographic (geodetic) coordinates for the user's location. The names of the current PRIMARY and SECONDARY (if present) locations are shown. When STSPLUS is first started, Program STSORBIT PLUS Satellite Orbit Simulation Page 127 the default coordinates for the PRIMARY location are set to Palos Verdes, California, near Los Angeles, and the SECONDARY location is disabled. The current PRIMARY location is indicated by the name in parentheses on the Options Menu. The program provides two methods for setting your own coordinates: reading a file of city or place names and coordinates (STSPLUS.CTY is the default filename); or manually entering the information. Pressing F2 at the Main Menu will display the Local Coordinates Menu: Current PRIMARY Location: Palos Verdes, CA Current active CITYFILE: STSPLUS.CTY F1 Search CITYFILE for PRIMARY location F2 Search CITYFILE for SECONDARY location F3 Enter coordinates for PRIMARY location F4 Enter coordinates for SECONDARY location ENTER Return to Program Options & Features Menu Enter desired selection: Or, if a SECONDARY location is currently enabled, the following Local Coordinates Menu will be displayed: Current PRIMARY Location: Palos Verdes, CA Current SECONDARY Location: Washington (USNO), DC Current active CITYFILE: STSPLUS.CTY F1 Search CITYFILE for PRIMARY location F2 Search CITYFILE for SECONDARY location F3 Enter coordinates for PRIMARY location F4 Enter coordinates for SECONDARY location F5 Clear (disable) SECONDARY location ENTER Return to Program Options & Features Menu Enter desired selection: Press the indicated function key to perform the desired function, or press ENTER to return to the Program Options & Features Menu. The F5 selection will only appear if a SECONDARY Location is currently enabled. NOTE: To change the current active CITYFILE, use F7 from the Main Menu. NOTE: If the current active CITYFILE is not the one you wish to use, press ENTER twice to return to the Main Menu and then use F7 to set a new CITYFILE path and/or name. F1/F2 Search CITYFILE for Location ---------------------------------- Pressing F1 or F2 will search the current CITYFILE for the full or partial name (the "CITYNAME") you enter. The following prompt appears: Enter partial NAME to match: Program STSORBIT PLUS Satellite Orbit Simulation Page 128 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 current city file. For example, 'SAN' matches 'SAN diego' as well as 'SANta ana" 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, F2 was pressed and the name 'santa' was entered for the search: Processing record 1616 Location: Santa Ana, CA Latitude: 33.7633 Longitude: -117.8650 Elevation: 20 meters Press ENTER to ACCEPT this city as your SECONDARY location, OR Press ESC to cancel, SPACE to search for next location: If the city displayed is the one you wish to use as your PRIMARY or SECONDARY location (depending upon which function key you selected, F1 or F2), press ENTER. The information will be used by STSPLUS and subsequently saved in file STSPLUS.INI. If you wish to search further in the file, press the SPACE BAR. If you wish to cancel the search, press ESC to return to the Local Coordinates Menu. NOTE: Some of the elevations contained in file STSPLUS.CTY are zero because the elevation (in meters) above mean sea level was unknown when the file entry was prepared. 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 2000 cities. If users send me their correct elevations (or additional cities they wish added), I will incorporate that data into subsequent releases of file STSPLUS.CTY. F3/F4 Enter New Coordinates for Location ---------------------------------------- To enter location data manually, press F3 (for the PRIMARY location) or F2 (for the SECONDARY location). You will be prompted for the city name, latitude, longitude, and elevation. Latitude and longitude may be entered using three different formats for convenience (note the use of comma and decimal point): DDD.DDDDD Degrees and decimal fraction DD,MM.MMM Degrees, minutes and decimal fraction DD,MM,SS.SS Degrees, minutes, seconds and fraction The decimal point and decimal fraction are not required in any of the formats. For example, to enter 33 degrees and 17 minutes, type "33,17". Program STSORBIT PLUS Satellite Orbit Simulation Page 129 Note that SOUTH latitude must be entered as a NEGATIVE number as measured south of the Equator. Longitudes may be entered as EAST Longitude, the number of detrees East of the Prime Meridian at Greenwich (0 to 360 degrees) OR as WEST longitude( 0 to -180 degrees), the NEGATIVE number of degrees West of the Prime Meridian at Greenwich; regardless of the manner entered, the longitude will be automatically converted to the range of -180 degrees through 180 degrees. 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 and decimal fraction or integer meters as appropriate, regardless of the format or 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 as your PRIMARY location, OR Press ESC or SPACE to cancel this data: If you are entering data for the secondary location, the word "SECONDARY" will appear instead of "PRIMARY" in the prompt. Press ENTER to accept the data as shown or press ESC or the SPACE BAR to cancel the data and return to the Local Coordinates 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 current city file shown in the prompt, OR press "N" to use the data but not modify the current city file. F5 Clear (disable) Secondary Location ------------------------------------- If a SECONDARY Location is displayed on the Local Coordinates Menu and you wish to cancel (disable) that feature, press F5. If the secondary location is already disabled, the F5 menu item will not be displayed. 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 130 F4 Set 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). Elv/Azm Elevation and Azimuth. Elevation (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). 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. TARGET Relative Range and Velocity for a Target Satellite selected from among the current Secondary Satellites. Use F6+F5 from the Main Menu to select the Target Satellite BEFORE selecting this mode. When enabled, the data are displayed im metric or English units: TARGET: 20580 Target NORAD Number Rng: 1661.69 km Relative Range, kilometers Vel: -1.85 m/s Relative Velocity, meters/second or: TARGET: 20580 Target NORAD Number Rng: 902.55 nm Relative Range, nautical miles Vel: -6.4 ft/s Relative Velocity, feet/second NOTE: This mode cannot be enabled if a Target Satellite has not been selected. Relative Velocity is displayed ONLY if the Relative Range is less than 5000 kilometers. For all modes, select the desired units of measure using F9 while the map is displayed. The desired satellite coordinates may also be selected using F10 while the map is displayed. 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. Program STSORBIT PLUS Satellite Orbit Simulation Page 131 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 30 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. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 132 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 User-Definable Map Colors ------------------------------------ STSPLUS allows the user to set the colors for certain map features. These features are the Local Station circle of visibility, the concentric isocontours used in the Location and Tracking Modes, and the Tracking Station circle of visibility color. Pressing Function Key F9 displays the current color assignments (and a color chart on the right of the screen): Current User-Definable Map Colors ----- 13 Local Station Color ----- 14 Isocontour Color ----- 12 Tracking Station Color Press ENTER to ACCEPT, SPACE to CHANGE: The "-----" in the example is a solid line illustrating the map color. The number to its right is the number used to represent that color. The colors shown in the example are the default colors. If the colors shown are acceptable, press ENTER. To change the color assignments, press the SPACE BAR and the color assignments will be prompted in turn: Enter color for Local Station: 5 Enter color for Isocontours: 6 Enter color for Tracking Stns: 4 Use the color chart at the right of the screen to select new colors and enter the corresponding number. Press ENTER to leave a color unchanged. As each color is assigned, the display sample will change accordingly. When the last color has been assigned, the initial display will be repeated: Current User-Definable Map Colors ----- 5 Local Station Color ----- 6 Isocontour Color ----- 4 Tracking Station Color Press ENTER to ACCEPT, SPACE to CHANGE: Press ENTER if the new colors are acceptable, or press SPACE BAR again to change again. Program STSORBIT PLUS Satellite Orbit Simulation Page 133 F10 Enable/Disable Printer Logging ------------------------------------- I have found it interesting to log the orbital data and the ascending and descending node information on my printer when analyzing the mission data over long periods of time. The F10 command toggles the printer logging function on and off. The first page of the log includes the current orbital data and subsequent pages contain only node information. In addition to the information presented on the display, the printer log also calculates the current orbital time, the time from one ascending (descending) node to the next, for the third and subsequent nodes. A typical log is shown below. IMPORTANT: BE SURE THE PRINTER IS TURNED ON PRIOR TO ENTERING THE F10 COMMAND. STSORBIT: Space Shuttle Tracking Program, Version 9435 Page 1 ORBITAL DATA for STS-31 Discovery/HST NORAD Number: 20580 Launch Date: 04/24/1990 Launch Time: 05:33:52 Orbit Inclination: 28.4695 Orbit Altitude: 329.50 nm UT DATE UT TIME ORBIT LONG MET TIME Ascend Node: 04/28/1990 20:32:52 70 -69.95 4/14:58:07 Dscend Node: 04/28/1990 21:20:52 70 97.64 4/15:46:35 Ascend Node: 04/28/1990 22:09:52 71 -94.77 4/16:35:02 1:36:55 When printer logging is enabled and the ground track is displayed, the word "LOG" will appear in red at the right of the text area. Enabling printer logging also automatically enagles the display of ascending and descending node information. The Launch Date and Launch Time entries are given if that information has been entered indepentently. The Epoch Date and Epoch Time are always shown. Note also that the orbit altitude shown is the altitude at the time the log was started and will not be correct for subsequent entries, especially if the satellite has an elliptical orbit (high eccentricity). A printer log may be prepared in advance of a mission by enabling printer logging from the Set Options Menu (with the F10+F10 command), setting the desired simulation time (F8+F3 command), then starting the ground track display with ENTER; once the ground track has appeared on the screen, pressing the F key twice to set STSPLUS in the X60 fast time mode will generate the date relatively quickly (although the UT TIME printed may be off by as much as one minute in the X60 mode). Allow the simulation to run for the desired length of time, then press ENTER to return to the Main Menu. While the ground track is active Function Key F3 performs the same function as the F10+F10 command to enable or disable printer logging. Program STSORBIT PLUS Satellite Orbit Simulation Page 134 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 9435 Current time: 19:01:57 PDT 02:01:57 UTC Current date: 26 JUL 1994 27 JUL 1994 F1 ON Display LOCAL Circles of Visibility F2 ON Display TDRS and Real Time Satellites 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 and Real Time Satellites -------------------------------------------- This command allows the user to display TDRS and/or selected real time and static satellites. The command cycles through "OFF", "TDRS", "SATS", and "BOTH". When "TDRS" or "BOTH" is selected,the communications coverage for the Tracking and Data Relay Satellites (TDRS) or other geosynchronous Program STSORBIT PLUS Satellite Orbit Simulation Page 135 satellites is also shown. The TDRS coverage boundaries overlap between the East and West TDRS satellites and Mission Control may select either satellite during the overlap period. STSPLUS displays the areas covered by each satellite and the times for acquisition and loss of signal (AOS and LOS). See the section "TDRS and Real Time 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 180 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 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 all rectangular map modes and for orthographic map modes with MAG > 500 except for polar and near polar views, each latitude grid line is labeled at the left and each longitude grid line at the top 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 136 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. 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 Program STSORBIT PLUS Satellite Orbit Simulation Page 137 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: * 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 138 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 139 sets along with other numerical and statistical data. The U.S Space Command, (formerly NORAD, the North American Air Defense Command) headquartered in Cheyenne Mountain, Colorado, developed the SGP4 and SDP4 orbital models and the 2-line element format many years ago as part of their satellite tracking efforts and NASA subsequently adopted the same format -- more or less. NASA and NORAD do not always use the same definition for revolution (orbit) numbers; NASA frequently gives a number one (or two) greater than NORAD, calling the first partial orbit number one while NORAD calls that same partial orbit number zero. Except for short duration missions, such as the Space Shuttle, revolution numbers are of no practical importance. Having timely and accurate orbital data is of little help without a computer model or program which can use those data. NORAD has rather arbitrarily divided satellite orbits into two categories: near Earth orbits and deep space orbits. Near Earth orbits are defined as those with orbital periods of 225 minutes or less and deep space orbits are all others. Computer models are described in the literature for each category. STSORBIT PLUS employs the SGP4 Near Earth Model only, using a composite of code of my own combined with translated Fortran and Basic source supplied by Paul Traufler and C source by Paul Hirose. I plan to add the SDP4 deep space model in due course. Not only are the near Earth orbits generally of more interest to observers, but the errors associated with deep space orbits processed with the SGP4 model (rather than the correct SDP4 model) are not particularly significant for the purposes of a program such as STSORBIT PLUS. Further, watching a geostationary satellite orbit on the screen is not unlike watching grass grow and is about as exciting. Program STSORBIT PLUS Satellite Orbit Simulation Page 140 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 Canada 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 141 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 142 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 PRECISION TIME (below) 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 143 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 144 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 shareware 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 or higher, 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 145 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 146 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 147 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 148 Program PRECISION TIME ---------------------- Program PRECISION TIME, a commercial product by Crystalogic, Inc., provides in a single program the time setting and time maintenance functions to keep a PC clock running accurately. An AT-class (80286 or higher) computer is required and, as with all such programs, the computer's hardware clock must be "reasonably" stable and predictable with respect to cold and warm drift rates in order to maintain long term accuracy. PRECISION TIME is suitable for applications which require an absolute accuracy of approximately +/-1 second referenced to NIST or USNO; applications requiring higher accuracy should consider alternative solutions. The one second granularity of the program's time adjustments may also cause difficulties for certain applications. PRECISION TIME ("PTIME") is an "all-in-one" program which calls a telephone time service (NIST or USNO), sets the computer's hardware and software clocks, then executes as a TSR (Terminate and Stay Resident) program to maintain the accuracy of the hardware clock to within one second. Calling the telephone time service may be performed manually on demand or at predetermined intervals (1 to 999 days). PTIME "guards" against inadvertent setting of the time or date EXCEPT by PTIME using a telephone time service. PTIME may be configured to handle the changes between Standard Time and Daylight Savings Time automatically. All program activity may be logged for future reference in a log file, PTIME.LOG. PTIME is well documented with a printed manual and installs easily and quickly. Although PTIME does not adjust the hardware clock as frequently nor to comparable precision as do programs such as RIGHTIME (above), this may make its internal interface somewhat more robust and reliable in complex hardware or software environments. During the entire time that PTIME has been operating on the RPV ASTRONOMY BBS there have been no failures or system crashes. As the following (edited) excerpt from PTIME.LOG illustrates, the system clock is updated periodically and is kept within approximately one second of the correct time as received from NIST: 06/21/1994 07:24:11.00 PTIME - Time adjusted one second backwards. 06/21/1994 10:32:16.01 PTIME - Time adjusted one second backwards. 06/21/1994 13:40:18.01 PTIME - Time adjusted one second backwards. 06/21/1994 16:48:24.03 PTIME - Time adjusted one second backwards. 06/21/1994 19:56:28.03 PTIME - Time adjusted one second backwards. 06/21/1994 23:04:34.00 PTIME - Time adjusted one second backwards. 06/22/1994 02:00:41.04 Time was changed by: Calling an Atomic Clock Drift amount was: 00:00:00.98 06/22/1994 05:08:42.01 PTIME - Time adjusted one second backwards. 06/22/1994 08:18:49.00 PTIME - Time adjusted one second backwards. In fact, the error of 0.98 seconds was the largest seen in two months of operation and, after an initial calibration period, NIST is called only every five days. (The RPV ASTRONOMY BBS primary computer is always turned on except for very brief maintenance periods.) The user may view the current status of PTIME and its adjustments at any time. The following is an example screen: Program STSORBIT PLUS Satellite Orbit Simulation Page 149 ----------------- Time Adjustments ------------------ Calibration Driver Version: 1.56 Last Sleep Time: 06/22/1994 06:55:28.05 Last Wake Time: 06/22/1994 06:57:37.39 Last Wakeup Adjustment: +0 seconds Current Time: 17:40:58.10 Seconds Between Adjustments: 11282 Hundredths/Sec to Adjust: -100 Seconds Until Next Adjustment: 7771 Adjustments Handled: 262 Error Count: 0 Last Adjustment 06/24/1994 16:42:29.03 Sleep Time Since Last Call: 129 (0%) Awake Time Since Last Call: 229151 (100%) PRECISION TIME is available from: Crystalogic, Inc. 2525 Perimeter Place Drive, Suite 121 Nashville, TN 37214 Voice: (615) 391-9100 FAX: (615) 391-9997 BBS: (615) 391-8065 As of 1 May 1994, the list price for PRECISION TIME was $79.95 plus shipping and handling. Contact Crystalogic for current information. Program STSORBIT PLUS Satellite Orbit Simulation Page 150 Computer Bulletin Board Systems ------------------------------- RPV Astronomy BBS (310) 541-7299 CELESTIAL BBS (513) 253-9767 <-- Note new number 1/06/94 NASA GSFC OIG RBBS (301) 262-6784 <-- Note new number 7/24/93 NASA Spacelink BBS (205) 895-0028 CSS BBS (905) 458-5907 <-- Note new number 3/15/94 JPL PAO BBS (818) 354-1333 JSC PAO BBS (713) 244-5625 Timely 2-line orbital elements are essential for accurate satellite tracking. In addition to my own bulletin board systems, five other bulletin board systems provide authoritatve data for the general public. Some or all files on these systems are compressed to reduce download time and must be decompressed before use; compressed files may be recognized by file types such as ".ZIP", ".ARJ", ".ARC", ".PAK", etc. I have maintained my RPV Astronomy BBS (computer bulletin board system) as a public service since 1987, (310) 541-7299, 2400-14400 baud with 2 lines. The system has some 2000+ files, 150MB, available for download. During Space Shuttle missions, I post current 2-line elements at least daily (provided I'm in town!). The system usually also has current 2- line elements for a large number of satellites in addition to other files of interest to space and astronomy enthusiasts. The system is very popular and, therefore, is frequently busy! The RPV Astronomy BBS is open to all callers but first time callers are granted more limited access and time than registered users. Since the mid-1980s, Lt. Col. 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) 253-9767, 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 a number such as "420", 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; this text may have to be edited out before use. 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) 262-6784, 4 lines @ 1200 and 2400 baud. The OIG database contains elements for some 7000+ satellites and is Program STSORBIT PLUS Satellite Orbit Simulation Page 151 updated every weekday morning except holidays. Elements for popular satellites are posted in a file called GROUPTLE.ZIP which contains seven ".TLE" files for some 750+ popular satellites. The data for the entire database of satellites are available on a query basis. Access time is limited to 20 minutes per caller per day. I regularly post a combined and sorted set of the .TLE data as file GSFCnnn.ZIP on my own RPV ASTRONOMY BBS where "nnn" is a number like "408". 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 @ 300-9600 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. 2-line elements for selected satellites are also available. 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 152 STSORBIT PLUS Revision History ------------------------------ Each released version of STSPLUS uses a four digit revision code such as 9435. 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 9435A -- August 1994 ---------------------------- -Version 9435A corrects a problem with certain country codes (such as those which use the "YY-MM-DD" date format) which still caused "BASIC Error = 5" in the orthographic mode for Version 9435. The program should now be independent of the country code. -Corrected a minor bug with amateur radio satellite frequencies. If the primary satellite was changed with F6, the frequency file (STSPLUS.FRQ) was not rescanned and the frequencies from the prior satellite remained. STSPLUS will now always rescan file STSPLUS.FRQ if the primary satellite is changed. Version 9435 -- August 1994 --------------------------- -This release repairs an unfortunate bug which surfaced when I added the NORAD-style date on the orthographic display. Only users who set DOS to non-US-style date formats were affected. The problem occurred immediately when drawing the orthographic map as "BASIC Error = 5" and returned the user to DOS. -Added satellite name cross-reference in file STSPLUS.XRF. When TLEs are read and accepted, STSPLUS now checks for the cross-reference file and, if the file is present in the current directory, checks for the NORAD Number of the satellite and a cross-reference name. If found, the new name is substituted for that found in the TLE file. The file is standard ASCII and each entry consists of a SPACE, the five-digit NORAD Number, a SPACE, and then the satellite name. A sample file: 22920 HST Solar Array 22076 Topex/Poseidon 21225 Gamma Ray Observ 20638 Rosat Observatory 20580 Hubble Telescope Program STSORBIT PLUS Satellite Orbit Simulation Page 153 16609 MIR Space Station NOTE: The leading space is required for file compatibility with my program ORBITEL (but is optional for STSPLUS). The NORAD Number MUST be 5 digits; pad with leading zeroes if necessary. Only one entry is read per satellite. If the satellite name is longer than 19 characters, only the left 19 characters will be used. This feature may be used to substitute any name for that given in a TLE file (which is not always consistent from source to source) or to specify a payload piggy-backed on another satellite (as is frequently the case with amateur radio transponders). A number of XRF files are posted on my RPV Astronomy BBS; such files must be renamed for use with STSPLUS. -Repaired a minor bug which caused the pass predictions (F3 from Main Menu to repeat a pass indefinitely when that pass was a grazing pass with a maximum elevation of less than one degree (0.14 degrees in the test case reported by Ken Ernandes). -Corrected a bug in read/save .SCF files (F6 from the Main Menu). If a fileltype is entered (".SCF" or whatever), it is now ignored and ".SCF" is automatically appended to the filename. Thanks to Paul Becker for reporting the problem. -In response to many requests, the date input routine has been modified to permit entry in the European style "dd.mm.yyyy" in addition to the US style "mm/dd/yyyy". The choice of delimiter ("." or "/") determines the method of interpretation. In both cases, the year may be entered as the last two digits only, "yy", if desired; "50" through "99" will be interpreted as "1950" through "1999" and all others as 2000+yy. Dates are displayed as "dd MMM yyyy" where "MMM" is the English abbreviation for the month. -All current .SCF files are now displayed for both SAVE and READ functions (F6+F2 and F6+F3 from the Main Menu). -Improved backspace processing and error checking when entering TLE filenames (F2 from the Main Menu). -Corrected "West Latitude" to "West Longitude" in the data entry section for local coordinates (F10+F2). -Various minor cosmetic changes. -Version 9434 was released as a Beta Version to selected users and included all changes in Version 9435 EXCEPT the repair to the NORAD-style date bug. Version 9432A -- August 1994 ---------------------------- -As too often happens, a bug was discovered in Version 9432 just after it was released. The elevation ("Elv") and azimuth ("Azm") in the rectangular projections either remained at zeroes or at the last value calculated during orthographic projection. There was no workaround. The problem has been repaired. My apologies to those who received the defective version. Version 9432 -- July 1994 ------------------------- -Version 9432 adds several new features and corrects a number of program errors and/or "bugs". Several minor cosmetic changes were also made. -Added Data Output Mode 8 to generate tabular output for Doppler Shift calculations for a selected pass while the tracking map is displayed. Use F3 from the Main Menu and select Mode 8; setup features are identical to other modes (output device, interval, etc.). See text for details. Program STSORBIT PLUS Satellite Orbit Simulation Page 154 -Look angle calculations [elevation ("Elv") and azimuth ("Azm")] during the tracking map display are more accurate thanks to an improved algorithm supplied by Ken Ernandes. Users should note that near culmination (maximum elevation) for passes near the user's zenith (approaching 90 degrees elevation) there is some uncertainty and ambituity as to azimuth although the angular error remains very small. -Changed "Alt" to "Elv" as the label for satellite elevation (altitude) above mean sea level to conform to standard satellite tracking convention. -Because STSPLUS is used worldwide, I have reformatted all displayed dates throughout the program to avoid confusion of the day versus the month. For orthographic displays, the display now shows the current UTC date and time ("dd MMM hh:mm:ss UTC") and then the local time ("dd mmm hh:mm:ss PDT" where "PDT" is replaced by the local time abbreviation). For both dates, the year is implied. The MET/T+E is moved up one line. A typical time display will show: 15 JUL 19:57:36 UTC 15 JUL 12:57:36 PDT 7/03:14:36 MET For the Main Menu and rectangular projections, the dates are all given as "dd MMM yyyy". Data locations are unchanged. A typical date and time will now be displayed as: 15 JUL 1994 19:57:36 UTC For all cases, "MMM" is the three letter English abbreviation for the month, "JAN" for January, "FEB" for February, etc. IMPORTANT NOTE: Keyboard entry of dates is still in the American numeric format, "mm/dd/yyyy" or "mm/dd/yy". -For orthographic projections, the current time using NORAD convention ("yyddd.dddddd") is displayed immediately beneath the current TLE filename: 94196.831667 This provides an immediate method to identify the current year and day-of- the-year, "94" and "196" respectively in the example above. -Added an additional data line in orthographic display to show the current orbital period ("Per'd" using the format "hh:mm:ss") for normal display OR, for satellites with Eccentricity >= 0.005, satellite Phase, defined as Mean Anomaly normalized to the range 0-256 ("Phase" using the format "nnn.n") for use with the Doppler Shift mode [press F8 while the map is displayed] and satellites which change transponder mode based upon phase. Although Phase is technically defined as an integer value from 0 through 255, STSPLUS displays it to one decimal place to alert users to upcoming phase/transponder changes. Other users may also be interested in two important Phase or Mean Anomaly angles: Phase=0.0 (Mean Anomaly is 0 degrees) corresponds to perigee and Phase=128.0 (Mean Anomaly is 180 degrees) corresponds to apogee. NOTE: Mean Anomaly (and therefore Phase) becomes undefined for a perfectly circular orbit. In practice, satellites with eccentricity less than 0.005 will display some ambiguity as to Mean Anomaly and Phase. Note also that the "Elv" is the geodetic elevation (altitude) of the satellite above Mean Sea Level and NOT the geocentric radius of the satellite's orbit, the paramter used to determine apogee and perigee; the difference due to the shape of the Earth is as much as 21 km. See the section "Satellite Communications and Amateur Radio" for additional discussion! Program STSORBIT PLUS Satellite Orbit Simulation Page 155 -Repaired the Tracking Station color feature (F10+F9) so that it operates correctly. Versions 9415/9414 caused the entire screen to turn light red when the Tracking Station color was changed due to a careless coding error. -Rewrote the local coordinates code and text (F10+F2) to improve clarity and add several features. Now uses a function key menu to select action to perform. Press ENTER to return to prior menu. When entering new coordinates, an illegal latitude or longitude will cause that coordinate to be set to zero. Longitude may be entered as East Longitude (0 to +360) or West Longitude (0 to -180); the longitude is converted if necessary and stored in the range from -180 to 0 to +180. -The threshold for generating the "Satellite may have decayed!" message has been increased to a Mean Motion of 16.4 revs/day to reduce the probability of the message appearing during low shuttle flights. -Added code to check for synchronization and data errors in the .INI file between the "short form" satellite position data and the 2-line elements. If the NORAD numbers do not agree, the "short form" data will be set to the TLE NORAD number and the remaining data reset; if TLEs are not present, dummy TLEs are inserted. Use F6 to verify and/or correct the secondary satellites, then use F2+& to update data from TLE file(s). -Adjusted the "trigger" for automatic redraw in orthographic modes with higher zoom factors to compensate for high speed processors such as the 90MHz Pentium. (Under some circumstances, redraw was being triggered continuously.) -Repaired a minor bug that caused the TDRS and Sun AOS/LOS data to be missing on the rectangular display when Doppler Shift mode had been selected on the orthographic display. -Corrected the conversion factor used to convert meters to feet. Thanks to Steve Lenz for reporting the bug! -Removed all references to the RPV HOTLINE BBS since that telephone line is now in rotary with the main number, (310) 541-7299. -Versions 9424, 9429, and 9431 were beta test versions not released publicly and included some of the features and changes in this release. For Version 9424, the precision of Doppler shift frequencies was increased to 5 digits (10 Hz) to the right of the decimal point but this proved confusing and has been restored to 4 digits (100 Hz). Version 9415 -- April 1994 -------------------------- -This release repairs a problem in rectangular projections which caused the Alt/Az calculations to be incorrect. (The data in orthographic projections were alright.) The problem was traced to a duplicated variable name which was added to shared common. Only file STSPLUS.EXE is changed. Version 9414 -- March 1994 -------------------------- -This is a MAJOR UPGRADE, adding new features for satellite communications and amateur radio, user-definable map colors for certain map features, improving RA/DEC coordinates, and incorporating several bug fixes. -See also the notes below for Version 9406 (not released publicly). ENHANCEMENTS FOR SATELLITE COMMUNICATIONS AND AMATEUR RADIO: ------------------------------------------------------------ Program STSORBIT PLUS Satellite Orbit Simulation Page 156 -By popular request and with the assistance of Ken Ernandes, N2WWD, I have added Doppler shift calculations for uplink and downlink frequencies. The calculated uplink (XMIT) and downlink (RECV) frequencies have been tested in full duplex with RS-10 and yield excellent results. The Doppler shift calculations are available in orthographic projections ONLY for this release. See the text for complete discussion. -The satellite NORAD Number, UPLINK and DOWNLINK frequencies (referenced to the satellite), and the transponder mode are specified in file STSPLUS.FRQ in that order, separated by commas and without any leading or trailing spaces. A sample file might include: 00000,100,100,1 (Default values if sat # not found) 18129,145.8900,29.3900,1 (Parameters for NORAD #18129) --+-- ----+--- ---+--- + | | | | | | | +-- Transponder Mode: 1 = NORMAL | | | -1 = INVERTED | | | | | +------- DownLink Center Frequency (MHz) | | | +--------------- UpLink Center Frequency (MHz) | +----------------------- Satellite NORAD Number The first sample line shows the "00000" entry which determines the default parameters if the satellite is NOT included in file STSPLUS.FRQ. This should be the FIRST LINE in file STSPLUS.FRQ. The second line gives real parameters for a specific satellite; the frequencies shown select the Mode A voice passband for Radio Sputnik 10 (RS-10, piggybacked on COSMOS 1861, NORAD #18129). The uplink and downlink frequencies should not exceed 99000.0000 MHz to avoid an overflow condition on the display. -File STSPLUS.FRQ may be created or edited with any ASCII editor; word processor users, use the "non-document" mode. Note that only minimum error checking is performed and the user must observe the required format exactly for each line in the file. -The Doppler shift calculations replace the TDRS and Sun AOS/LOS data in the data block to the right of the orthographic map. To enable display of these frequencies, press F8 while the map is displayed; to return to the AOS/LOS calculations, press F8 again while the map is displayed. F8 is NOT active when in PAUSE mode. The following example illustrates the display as a satellite approaches the ground station (using 1000 MHZ for both frequencies to show the relative transmit and receive ratios): UpLink: 1000.0000 Uplink frequency received by satellite XMIT: 999.9761 TRANSMIT frequency at ground station DnLink: 1000.0000 Downlink frequency xmitted by satellite RECV: 1000.0239 RECEIVE frequency at ground station The XMIT and RECV frequencies will be shown in color on EGA/VGA color monitors: RED Satellite is below receiver's horizon YELLOW Satellite is 5 degrees or less above receiver's horizon GREEN Satellite is 5 degrees or more above receiver's horizon Program STSORBIT PLUS Satellite Orbit Simulation Page 157 Transmissions will not normally be possible when RED is shown. Transmissions MAY be possible when YELLOW is shown. Transmissions should be practical when GREEN is shown provided the ground station has a clear horizon in the direction of the satellite. -STSPLUS includes a "fine tuning" feature for the uplink and downlink frequencies. While in the Doppler shift calculation mode, the following keys have a different function from the normal map modes: UP Arrow Increase RECV frequency by 100 Hz DOWN Arrow Decrease RECV frequency by 100 Hz PgUp Increase RECV frequency by 1 KHz PgDn Decrease RECV frequency by 1 KHz Home Restore Uplink and DnLink frequencies to those read in from file STSPLUS.FRQ End (not used) If the satellite transponder is NORMAL, the XMIT frequency will be increased or decreased by the same amount as the RECV frequency. If the satellite transponder is INVERTED, the amount of change in the XMIT frequency will be the same magnitude but in the opposite direction as the change to the RECV frequency. OTHER SOFTWARE ENHANCEMENTS AND CHANGES IN THIS RELEASE: -------------------------------------------------------- -In response to numerous user requests, the colors for certain map features are now user-definable. The assignable features are: Local Station circle of visibility Isocontour circles in Location and Tracking Station modes Tracking Station circles of visibility From the Main Menu, use F10+F9 to set these colors. The new colors will be saved in file STSPLUS.INI for future use. To those users who want to change EVERYTHING, my response is: a) that's a non-trivial programming exercise, and b) I've spent considerable time designing the program to have a certain "look and feel" which I wish to retain. - The Program Features and Options menu has been changed. Function Key F9 is now used for User-Definable Colors (above) and not for setting the UTC Offset and Daylight Flag. Use F8+F10 from the Main Menu to set the UTC Offset and Daylight Flag. -Users are reminded that STSPLUS expects ground station coordinates (latitude and longitude) in the geodetic coordinate system, as commonly used on maps (WGS-72 System). Ground station altitude (elevation above Mean Sea Level) is expected in METERS; if a ground station is significantly above Mean Sea Level, accuracy will be substantially improved if an accurate altitude is used. Many cities in file STSPLUS.CTY have ZERO given as the altitude if no altitude was available in the source(s) used for preparation of the file. The same comments apply to Tracking Stations in file STSPLUS.TRK. -The coordinates for Right Ascension and Declination were incorrect in prior versions. The ground station's GEODETIC latitude instead of the GEOCENTRIC latitude was used in the calculations. The error was greatest (especially the Declination) for ground stations in mid-latitudes as a satellite approached local zenith. Thanks to Alan Nutley of Australia for putting me on the track of this one! -Local horizon coordinates were also affected by the latitude error. The Program STSORBIT PLUS Satellite Orbit Simulation Page 158 typical error near maximum was one or two degrees in altitude (elevation). -The keyboard response time has been improved; except when the map is actually being drawn, response is immediate instead of waiting for the next second. In the Doppler Shift Mode, the arrow keys and PgUp and PgDn may be held down to repeat. During rapid key repeats, map and data updates may be deferred; waiting for a second will allow the map and data to be updated. -The primary satellite's circle of visibility did not display on the World Map when the Motion Map (Dual-Page EGA Mode) was enabled. This has been corrected. Thanks to Todd Sherman for reporting the bug. -Corrected a problem which caused BASIC ERROR 6 on restart when the SHELL TO DOS (F9 from the Main Menu) was used and the program was in orthographic projection. -Various minor bug fixes and cosmetic changes. -Versions 9412 and 9413 were BETA VERSIONS released on a limited basis. -Special thanks to Ken Ernandes, N2WWD, for his assistance and testing of the satellite communications and amateur radio features! Version 9406 -- February 1994 ----------------------------- -This version was for Beta Test only and was not released publicly. -Several users have reported that file STSPLUS.INI sometimes became corrupt and I have (finally) found and corrected the problem. An array index was overrunning the bounds of the array and overwriting other data in SHARED COMMON. This usually only affected the data in secondary satellites but was potentially more dangerous. The problem also caused some dot colors on the ground track to be incorrect. -When no STSPLUS.INI file is present (or when the UTCOffset is set to -99), the user is automatically asked to set filenames and paths. -In response to quite a number of user requests, I have added the "/SS" command line option to force STSPLUS into a "screen saver" mode. In this mode the program displays the full orthographic globe, ground track and all selected map features but NO DATA at the right. Use ENTER or ESC to return to DOS. -New command line options have been added to control certain display features (especially from batch files). The new feature status is saved in file STSPLUS.INI. +L Include Location and Feature Labels -L Exculde Location and Feature Labels +R Include Rivers and Lakes -R Exclude Rivers and Lakes +T Include Tracking Stations -T Exculde Tracking Stations +V Include Local Circle of Visibility -V Exclude Local Circle of Visibility -Because of problems reported with word processors which add the 8th bit to some characters (and have been used to edit TLE files), I have added code to strip off the 8th bit in Line 0 of TLEs. However, this is not foolproof, and users are cautioned to use ONLY editors which do NOT add the 8th bit and which maintain the "standard" CR/LF at the end of each text line. Program STSORBIT PLUS Satellite Orbit Simulation Page 159 Version 9405 -- January 1994 ---------------------------- -Version 9405 is a MAINTENANCE UPDATE, correcting a number of relatively minor bugs and updating the documentation to reflect changes in Versions 9403 and 9405. -Rewrote MET calculations to (hopefully) avoid truncation and rounding errors which sometimes caused MET to be one second off. The problem was dependent upon both launch and epoch times. -Added default filenames and paths if UTCFlag is set to -99. (Setting UTCFlag to -99 may be used to distribute STSPLUS.INI files when the ultimate user's time zone is unknown. This procedure forces the user to set the UTC and DAYLIGHT values, and is NOT recommended for the novice!) Filenames and paths should ALWAYS be checked and set if necessary using F7 from the Main Menu whenever upgrading to a new version. -Improved calculation algorithm for "Calculating Orbital Data" phase of program initialization for satellites with mean motion less than 15 and greater than 2. The improvement may only be apparent on slower processors or systems without a math coprocessor. -Corrected a cosmetic bug which caused the time portion of negative MET to appear at the left on the next line in rectangular projection modes. (Missing semicolon!) Version 9403 -- January 1994 ---------------------------- -In response to numerous complaints about BASIC ERROR 6 ("Overflow") when using Relative Target Tracking with rectangular map projection, I have corrected a condition while calculating relative velocity which could generate the overflow error. The error may be related to processor speed and/or specific 2-line elements and has been difficult to reproduce. -Corrected several differences between rectangular and orthographic maps so that rectangular maps are processed as close as practical to the way that orthographic maps are processed. This eliminated some spurious data that was displayed momentarily as the rectangular map was first drawn and may also help avoid the BASIC ERROR 6 problem (above). -Corrected a cosmetic bug which caused the "s" in "ft/s" and "m/s" to remain on the screen when switching coordinates from target data to other coordinates using F10 while the map is displayed. -Several minor cosmetic changes. Version 9402 -- January 1994 ---------------------------- -Corrected (I hope) a bug which caused BASIC ERROR = 6 when switching from MET to T+E while using a Target Satellite. The problem was traced to a variable which was not re-initialized when F5 was pressed while the map was displayed. Version 9353 -- December 1993 ----------------------------- -Added Relative Target Tracking (not included in Beta Test Versions 9351 and 9352) to report relative range [km or nm] and velocity [m/s or ft/s] between the Primary Satellite and a Target Satellite selected from among the Secondary Satellites. Relative Velocity data is presented ONLY if the Program STSORBIT PLUS Satellite Orbit Simulation Page 160 Relative Range is less than 5000 km. The Target Satellite is selected with F6+F5 and the relative tracking data is enabled by F3+F6 from the Main Menu or F9 while the map is displayed. See text for details. -The Secondary Satellite code has been modified to save a skeletal TLE when a new satellite is added. This permits the user to use F2+'&' to update TLEs INCLUDING the new satellite(s). The warning message for satellites without TLEs in F6 has been modified to remind users that they may either update the TLEs or display the satellite ground track. -I seem to have tracked down an internal timing anomaly that caused errors in the tracking data of about +/-0.5 seconds. Worst case, this caused an error in calculated position on the order of tens of meters (about the length of the space shuttle!) and would not be easily detectable under most circumstances. Thanks to Ken Ernandes for first reporting the problem several months ago. -Corrected a problem which caused the STSPLUS.INI file to become corrupt if Event Timers were set to OFF. Thanks to Chuck Dean for reporting the bug! -Corrected a problem with secondary satellites and .SCF files when one or more secondary satellites was deleted, leaving blank satellite slots. Secondary satellites may now occupy any slot with or without intervening blank slots. -The Primary Satellite is now labeled "Primary" and shown in YELLOW if it is included in the satellite configuration data (F6+F1). -When displaying the satellite configuration data (F6+F1), the 2-line elements are checked for epoch. If the epoch is more than 10 days (Real Time) or 60 days (Static) prior to the current/simulated time, a flashing RED asterisk ("*") is shown next to the satellite number and a warning is shown at the botton of the screen. NOTE: This is a caution warning only; the elements may or may not still be valid. -Added an "OFF" mode for Secondary Satellites (F6+F1). The OFF mode permits one or more satellites to be disabled (not displayed) without removing the data from the secondary satellite data. All data are retained and the satellite may be re-enabled at any time. Thanks to Paul Grupp for the suggestion! -Added grid labels in the orthographic displays (when Additional Grid Lines are enabled with F10+F3+F3) for latitude and longitude when the MAG factor is 500 or greater. Latitude labels are always at the left side of the map; longitude labels are at the top or the bottom depending upon the map center. The labels are disabled for polar and near polar maps because of the projection. -Changed the plot update interval for secondary satellites to EVERY SECOND if a 386 or higher processor AND a math coprocessor are present. This avoids a "leapfrogging" effect between the primary and secondary satellites during close proximity operations. For other processor/coprocessor combinations, the plot update interval remains TEN SECONDS as in prior versions. In all cases, the ground track for secondary satellites is only plotted every ten seconds in order to avoid cluttering the display. -Changed the orbit number calculation after considerable debate. The code used in all prior versions caused the TLE orbit number to be incremented if the epoch of the TLE was in the latter half of the orbit (at or past the descending node). The new method increments the TLE orbit number only if the epoch is within 0.1 orbit of the ascending node. CAUTION: This change may cause orbit numbers to be different if prior missions are replayed using TLEs which were adjusted to compensate for STSPLUS' prior orbit numbering conventions. -Removed code which translated satellite names. Names beginning with "HST" Program STSORBIT PLUS Satellite Orbit Simulation Page 161 were changed to "Hubble Space Telescope"; with the jettisoning of the "HST Solar Array", that debris was being renamed also. A similar problem occured with MIR debris. If you wish to rename one or more satellites, use my program ORBITEL (available free on my BBS or for a donation of US$10.00 by mail). -Corrected a cosmetic bug which caused stray pixels to appear when a secondary satellite intersected the circle of visibility for the primary satellite. Thanks to Joel Runes for spotting the problem. -Added the International Date Line in orthographic displays as a dotted bright blue line where it is different from the 180th meridian. -Corrected a cosmetic bug for map drawing time in orthographic mode. If the operation spanned midnight, the drawing time overflowed the field with a number like "%-86300.12", wrapping around to the left side of the screen. -Removed the function to disable solar features (Sun and Terminator) from the map using F8 while the map is displayed. The function is now available ONLY from the Main Menu using F10+F3+F8. -Changed the "Additional Grid Lines" function, F10+F3+F3, to ON or OFF. -USSPACECOM has changed the format of the 3-character "Launch Piece" portion of the International Designator in their 2-line elements (TLE) from right justified to left justified. This caused STSPLUS to show "(n/a)" for the launch piece. The data displayed when the elements are presented for user approval have been changed from numeric to the alpha designation given in the TLE. In other words, launch piece "B" will be so shown instead of "2" as in prior versions. -All references to "IAU Designation" have been changed to "International Designation" or "Int'l Designation". -Changed the limits on UTC Offset to allow +13 hours and -13 hours to conform to civil practice for certain areas in the South Pacific. -Removed the "FOV" (field of view) data from the orthographic data block. The calculation was incorrect and misleading. -Various cosmetic changes and improvements. Versions 9351 and 9352 were BETA TEST VERSIONS with limited distribution. A number of minor bugs were reported and have been corrected for this release: -Selecting a new Primary Satellite before a map was displayed sometimes failed. -Selecting a new Primary Satellite did not set MET correctly. The MET was calculated for the prior Primary Satellite. Thanks to David Cottle! -Secondary satellites set to OFF were drawn (but not updated) on the rectangular projection. -Corrected a cosmetic bug which caused the thousands digit of MET DAYS not to be erased when switching large clock times (Mag=100, VGA only) with F2. Similarly, the colon (":") was omitted when switching from MET to/from T+E using F2. Version 9338 -- September 1993 ------------------------------ -Repaired a bug in multi-satellite modes which caused a "trail of dots" to be left behind if the primary satellite icon fell on top of a secondary satellite icon (such as during close proximity operations). -Repaired a bug when reading SCF files. In prior versions, the primary satellite was changed if the SCF file had a different primary satellite. The primary satellite in the SCF file is now ignored. The format of the SCF Program STSORBIT PLUS Satellite Orbit Simulation Page 162 file is unchanged to maintain compatibility with prior versions. -Modified the World and Zoom Maps in rectangular projection so that the PgDn key switches to Zoom Map (180 degrees) from World Map, and the PgUp key switches to World Map from Zoom Map (180 degrees). -Added list of available .SCF files when reading, F6+F3 from the Main Menu. -Added a warning when writing .SCF files if the requested file already exists. F6+F2 from the Main Menu. User must now press "Y" to overwrite an existing file, ENTER or any other key to cancel. -By user request, modified the small character set (used for labels) to include the DASH ("-"). -After numerous user complaints, I've finally repaired the BLINK mode so that for most systems the primary satellite icon will blink on and off once per second. Press "B" while the map is displayed to toggle the BLINK mode. -Repaired a minor bug which caused the message "Pause ... press ENTER" not to be displayed if the map was redrawn during Pause Mode. -Thanks to the many users who took the time to carefully document these bugs, enabling me to find and fix them! Version 9334 -- August 1993 --------------------------- -The maximum number of Static and Real Time satellites is increased to 32. This permits the entire GPS constellation, currently 25 active Block I and Block II satellites, to be tracked. The satellite setup display, F6+F1 from the Main Menu, has been modified to two display pages of 16 satellites each; the second page of 16 is not displayed if no active satellites are present. -Added "Clear Static and Real Time Satellites", F6+F4 from the Main Menu, to speed reconfiguration of these satellites. It may be used to clear any block of satellites NOT INCLUDING #1 AND #2 (which are assigned to TDRS East and TDRS West and must be cleared manually). Users are cautioned that once cleared, the satellite data for the cleared satellites is lost. If in doubt, save the current satellite configuration to a SCF file using F2 BEFORE clearing! -Somehow the "bullseye" was lost in the Tracking Mode for rectangular projection several releases back. It has now returned. Thanks to Alan Pound for reporting the problem! -As an experiment, I changed the color of land boundaries from Light Cyan to Cyan to make multi-satellites and other display features a little easier to spot. Feedback welcome! -When Extra Grid Lines are OFF (F10+F3+F3), changed the color of the grid lines from Light Blue to Blue and added lines of latitude at +80 and -80 degrees. -Various repairs to eliminate spurious pixels and other minor problems associated with multi-satellites. Version 9333 -- August 1993 --------------------------- -This is a MAJOR UPGRADE, adding multi-satellite capability. This is the first in a series of upgrades for tracking multiple satellites and rendezvous missions. Comments, suggestions, and bug reports are welcome! -Special thanks to Joel Runes for his assistance during beta testing! -OPERATIONAL HINT: With the addition of multi-satellite tracking, the Motion Map feature now really comes into its own; press "M" when the normal Program STSORBIT PLUS Satellite Orbit Simulation Page 163 map is displayed to switch to the EGA Motion Map, press "M" or ENTER to return to normal map or to the Main Menu. All satellites are updated as fast as the computer can draw the map. See the notes on a "vanilla" boot without memory managers for dedicated STSPLUS uses. -The format of file STSPLUS.INI has been substantially modified and files from prior versions of STSPLUS will be ignored. The configuration information must therefore be re-entered. -Increased to sixteen the number of additional TDRS and real time satellite positions in file STSPLUS.INI so that all active satellites may be updated and displayed. Sample data are shown below. See the section "TDRS and Real Time Satellite Features" for additional information. 19883,"TDRE ", -0.04218, -41.14169,10014 21639,"TDRW ", -0.03643,-174.14074,10014 22314,"TDR5 ", -0.31155,-138.36021,10004 19548,"TDR2 ", 0.05352, -61.66467,10004 13969,"TDR1 ", -6.59117,-170.55876,10004 16609,"MIR ",-17.45706,-178.73251,14115 -TLEs for each active satellite are now saved in the .INI file so that accurate positions may be calculated dynamically. These TLEs should be updated periodically. -TLEs are may now also be saved in and read from special .SCF (Satellite Configuration File) files so that multiple TDRS and Real Time satellite configurations may be saved and/or selected. A sample file, STSPLUS.SCF is included in the standard distribution. Function Key F6 from the Main Menu is used to display, modify, save, or read these data. -The 5-character abbreviation of each TDRS satellite may now be used to label the satellite. The size and color of the icon used to display each TDRS or real time satellite may now be independently controlled. -STSPLUS now uses the calculated LATITUDE for the display of all TDRS satellites. This will cause TDRS1, for example, to appear up to 7 degrees North or South of the Equator (as of 8/9/93). -The drive, path, and name of the .CTY file may now be set with F7 from the Main Menu. -The Motion Map is now available for the World Map in rectangular projection. This is helpful with multiple real time satellites. -Repaired an infrequent bug discovered by Joel Runes which causes the orthographic map to be redrawn continuously when a) the satellite has a high eccentricity (.73 in the test case), and b) when the map is being drawn at approximately the time of perigee. The code has been modified to take the Eccentricity into account in calculating the map offset time. -Corrected a minor bug which caused MET in excess of 9999 days to overflow the assigned format statement for the data block and appear as "%12038/00:00:00 MET" with the "MET" wrapping around to the left side of the screen. Obviously, there aren't many satellites with this problem, but NORAD #00051 is one such. The STSPLUS.LTD entry for this satellite is: 00051,2437158.90208333,0 and the problem was noted because of the pre-launch "temporary" NORAD number assignment for STS-51. -A similar problem occured with the large clock displays. In both projection modes, only the last four days of MET are now displayed (12038 days will display as "2038"). Program STSORBIT PLUS Satellite Orbit Simulation Page 164 -Added a reminder in the text that when entering filenames using F7 from the Main Menu, a drive and path may also be included if desired. That capability has been present for some time but was not stated explicitly. -Changed the precision that the "plain English" display of the elements Epoch Time is displayed for approval (F2 from the Main Menu) from [rounded] integer seconds to 0.001 seconds, coordinated with VEC2TLE V9331. -Several V9332 Beta Versions were released privately for testing. Version 9331 -- July 1993 ------------------------- -In coordination with Ken Ernandes' VEC2TLE, the data output for Format 7, ECI State Vector (Labeled Data), has been modified. The data have been supplemented by the addition of two lines: Element Set Number; and, Rev Number at Epoch. The International Designation has been added to the Catalog Number line and the Epoch Time is now given to .001 seconds. The data output for Format 4 has been changed so that it is identical to Format 7. See text for details. -Per Ken Ernandes, the Format 4 & 7 label "Ndot/3" is changed to "Nndot/6". -I have received NO REPORTS from anyone using Data Formats 5 and 6. Those formats may not continue to be supported indefinitely UNLESS I am informed of applications which use them. CAUTION: STSPLUS Version 9331 Data Formats 4 and 7 are NOT compatible with VEC2TLE Version 9322 when multiple state vectors are generated! Use a release of VEC2TLE with a version number equal to or greater than 9331. (However, manually editing the data to remove the Elset and Rev Number lines can restore compatibility with the older version.) NOTE: Users are urged to update to VEC2TLE Version 9331 or the current version, which ever is later! Not only does the current version of VEC2TLE maintain compatibility with STSPLUS but several important new features have been added and a bug in Version 9322 which affected data accuracy under certain circumstances has been repaired. -The Tracking Station Mode is now active in both Orthographic and Rectangular projections. The projection used will same as the one which is active when the "T" key is pressed. -Repaired a bug which caused the NORAD number displayed in the Pass Prediction Mode to be incorrect under certain circumstances. Thanks to Grant Pinto! -Repaired a bug in the pass prediction logic which caused the MAX VISIBILITY data to be missstated by a significant amount for certain satellites, especially ones with higher eccentricities. Thanks to Grant Pinto for spotting and reporting the bug! -Changed the default time zone abbreviation for unrecognized (foreign) time zones from all spaces (which confused the Pass Prediction setup!) to "LCL". -Corrected a bug using F2 from the Main Menu which showed no 2-line elements files if no .TXT files were found in the current directory but one or more .TLE files were present. Thanks to Bob Krohn for reporting the bug. If no files of either filetype are found, an error is displayed and the user is returned to the Main Menu. -Corrected a bug in default paths if the root directory was used. (Path defaulted to "B:\\" instead of "B:\" for drive B:, etc.) -Corrected a bug in the NORAD number for F2 from the Main Menu. If the Program STSORBIT PLUS Satellite Orbit Simulation Page 165 NORAD number was greater than 32767, a negative nunber was shown. -Disabled RIGHTIME detection for 8086/8088 processors. The detection process affected the time in certain XT-class machines. -Corrected a minor bug which caused the "blink" feature for the satellite icon not to function under certain circumstances. -Corrected a minor bug which initialized the Location Flag incorrectly for CGA systems when file STSPLUS.INI was not present. Locations and Features were displayed even though the menu display indicated they were OFF. -Various cosmetic changes. -Most of the changes in this release were included in Beta Version 9329. Version 9320 -- May 1993 ------------------------ -This is a MAJOR UPGRADE, adding new improvements and features along with high precision state vector data output for use with Ken Ernandes' program VEC2TLE. -By popular request, STSPLUS now estimates if a satellite may be visible to the naked eye or binoculars, and displays "VIS" in bright white next to the orbit inclination if a visual sighting may be possible. See the section "Satellite Visibility" for additional discussion. -Also by popular request, the pass predections (F3, Data Mode 9) have been enhanced to permit dates and times to be displayed for either UTC/GMT or LOCAL time. An additional prompt has been added for that selection. -When displaying predicted passes (F3, Data Mode 9), the satellite is now approximately centered in the display (instead of being well to one side). -After considerable confusion and several user comments, I have reworked the pass prediction logic so that when the user returns to the Main Menu after the ground track for a predicted pass is displayed, the time is automatically restored to the real or simulated time in effect BEFORE the pass prediction was displayed. This means that repeated use of the pass prediction feature will generally display the same list of numbered passes and the user no longer needs to restore real time (or reset simulated time) after displaying predicted passes. -Corrected a cosmetic bug on pass predictions when an illegal pass number (greater than the last pass number displayed) was entered at the prompt. -Added an asterisk ("*") at the left of each event timer when the satellite is AOS (signal/Sun is being received). This will particularly benefit users with monochrome or shades of gray. -Enhanced the Precision X-Y-Z State Vector Data Modes (F3, Data Modes 4 through 7) to include four output formats: multi-line Ascending Node with state vector, 2 numeric data lines, comma delimited, and multi-line labeled data. State vectors may now be logged continuously, for a specific time, or for a specified time span. See text for details. -Corrected a problem with state vectors being generated at the wrong time (Data Modes 5 through 7) when the time was entered in UTC and local time was a different date. -Removed the low precision state vector data output (F3, Data Mode 4). -Changed the angle used to calculate the Earth's partial penumbra from 1.2 degrees to 0.3 degrees to better correspond with observed lighting. The Sun AOS and LOS penumbral calculations were also slightly adjusted; timings during STS-56 indicated about a 15 to 20 second error before these changes. -Updated the TDRS information in the section "TDRS Satellite Features" and all five TDRS satellites are now displayed on the maps at their approximate locations as of 05/05/93. Thanks to Jim Walls for reminding me! Program STSORBIT PLUS Satellite Orbit Simulation Page 166 -Corrected a bug which caused "BASIC Error = 5" when the selected satellite had probably decayed. #22209 MIR Debris was an example in file TLE180.TXT. STSPLUS now displays a warning message if the satellite has a current altitude less than 75 nautical miles and then returns to the Main Menu. -Corrected the conversion from kilometers to feet per Ken Ernandes. (My original conversion factor was taken from a 40+ year old Handbook of Chemistry and Physics and was very slightly in error!) -Repaired (I think...) a truncation problem which sometimes caused MET/T+E to run one second slow. -For all those who refuse to read documentation, I added a reminder to the Main Menu: "WHILE MAP IS DISPLAYED: F1 = HELP, ENTER = Main Menu". -Special thanks to Ken Ernandes, Joes Runes, and Willie Musty for state vectors, testing, and validation of the new features in recent versions! -Version 9319 was released privately for beta testing. (Intermediate update notes deleted to save space, available on request.) Beta Version 9137 -- September, 1991 ------------------------------------ -Initial public beta version.