The PC-SIG Library 10

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Text File | 1990-10-02 | 76KB | 1,771 lines

* ▒▒▒▒▒▒▒ ▒▒▒▒▒▒ ▒▒▒▒▒▒▒ ▒▒▒▒▒▒▒.▒▒▒▒▒▒▒ ▒▒▒▒▒▒▒ ▒ ▒▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒ ▒▒ ▒ ▒▒▒▒▒ ▒ ▒▒▒ ▒ ▒ ▒▒▒▒▒ ▒▒▒▒▒▒▒ ▒ ▒▒▒▒ ▒ ▒ ▒ ▒ ▒▒. ▒ ▒ ▒ ▒ ▒▒ ▒ ▒▒▒▒▒▒▒ ▒ ▒ ▒▒▒ ▒ ▒ ▒▒▒▒▒▒▒ ▒ ▒▒▒ . . . ░░░░░░░ ░░░ . . ░ ░ . . ░░░░░░░ ░ ░ ░ ░░░░░░░ ░░ ░░░░░ S I M P L I F I E D S A T E L L I T E T R A C K I N G CONGRATULATIONS You now have the easiest to use satellite tracking package available in shareware. The capabilities provided by PC-TRACK were previously limited to programs which were hard to use, expensive, and designed for mini- computers or more expensive 80286 and 80386 based personal computers. Now you can graphically track your favorite terrestrial satellites with ease, accuracy, and money left in your pocket. HISTORY PC-TRACK has its origin in a satellite tracking program I wrote to track the OSCAR (Orbiting Satellite Carrying Amateur Radio) series of amateur radio satellites back in 1980. That program was called OSCAR PATHFINDER and was the front cover feature article in the March 1982 edition of "73 Magazine For Radio Amateurs." That program was written for the Apple II plus computer in Applesoft BASIC. It was a revolutionary program at that time in that it was the only program that tracked satellites in real time (the Apple had no clock) and displayed the satellite path on a map on the Apple graphics screen. It was capable of only tracking circular orbiting satellites, but that was not a problem at that time because all of the amateur radio satellites were in circular orbits. OSCAR PATHFINDER was so enthusiastically received that I made the decision to make some improvements to the program and offer it commercially. This led to a venture called Computer Applications and I sold quite a number of copies of Pathfinder II. I then developed a version of the program for the TRS-80 Model III computer called Pathfinder III. After a year or so of selling these packages, myself and my partner decided (for various reasons) to pull the plug on this and go on to other things. Later, with the launch of several elliptical orbit amateur satellites, I tinkered with the program some more to include the math necessary to track such satellites. This resulted in Pathfinder X, which was never published, but I used it quite a bit at home for my own tracking needs. I had also started rewriting the program in UCSD Pascal because that offered a much more readable and manageable structure for the program. When I got my IBM PC/XT clone in 1985, I had a desire to port Pathfinder X over to my new "supercomputer" since it had an 8Mhz clock and would be able to do faster computations and have better graphics capabilities. Well, after many years of many distractions (other business ventures, kids being born, moving, etc.) I have finally put together my idea of a nifty package for tracking satellites, called PC-TRACK. PC-TRACK 1.1 was distributed late 1989. Version 2.0 contains new features such as ability to track up to 8 satellites simultaneously, multiple maps of different continents, and a text track capability for non-EGA machines. Version 2.1 added 3D track capabilities. COPYRIGHT AND DISCLAIMER STUFF PC-TRACK is marketed as SHAREWARE. IT IS NOT PUBLIC DOMAIN SOFTWARE! This means that anyone can make copies of PC-TRACK to distribute to others for the purpose of evaluating the package for usefulness. But if you decide that PC-TRACK will be useful to you and decide to use it regularly, you must register your copy. This means paying for the use of the software. See the file called REGISTER on the distribution disk for details on how to register. All rights to PC-TRACK are held by Thomas C. Johnson. Use of this program before or after registration is strictly at your own risk. I will not be held responsible for any damages that may occur as a result of using PC-TRACK. Although every effort has been made to make PC-TRACK as accurate as possible, it is intended for casual, non-critical predictions of satellite locations for hobby and educational purposes only. It is not intended for precise scientific analysis. ABOUT THIS MANUAL PC-TRACK was written to be simple enough to use without any documentation. It incorporates context sensitive on-line help to assist with any area of question. In an effort to make the program as useful as possible, this manual is also provided for your assistance. It will provide you with detailed explanations of the way PC-TRACK works and its features. It will also will provide you with helpful tips and information which will help you get the most from PC-TRACK. PC-TRACK is Copyright (C) 1990 by Thomas C. Johnson. GENERAL DESCRIPTION PC-TRACK is a general purpose satellite tracking package designed to take the complexity and confusion out of finding where earth orbiting satellites are in space and providing the antenna pointing data necessary to transmit signals to or receive signals from them. PC-TRACK provides a colorful, graphical means of visualizing satellite orbits. O P E R A T I O N GETTING STARTED Refer to the README file included on the distribution disk for instructions on how to get PC-TRACK installed and ready to run. RUNNING PC-TRACK To get PC-TRACK running all you have to enter at the DOS prompt is PCT21 <RETURN>. PC-TRACK begins by drawing the background screen. There will be a brief pause at this point while PC-TRACK loads in the help screens, data files, and maps. This takes a few seconds (depending on the computer used). You will see a message at the bottom of the hello screen showing what data it is reading. Once initialization is completed, you are presented with the main menu screen. This is a small shadowed window on the left side of the screen with the 4 main options listed. The four options are SETUP, TRACK, CONFIGURE, and QUIT. Selecting one of these options is done simply by moving the cursor (shown by the selected name being in a different color than the rest of the options listed) so that it highlights the module desired and pressing the RETURN key. NOTE: YOU MAY ALSO SELECT AN OPTION BY PRESSING THE FIRST LETTER OF THE DESIRED OPTION. FOR EXAMPLE, IF YOU WISHED TO SELECT THE TRACK OPTION, YOU WOULD PRESS THE 'T' KEY (EITHER UPPER OR LOWER CASE). USING THE ON-LINE HELP PC-TRACK ASSISTANT, the on-line help system for PC-TRACK, is available from anywhere in the program and can be accessed simply by pressing the F1 key. The information presented on the help screen will depend on where you are in the program. For example, if you are in the SETUP SATELLITES option with the cursor on the NAME field and you press the F1 key, the help screen will pop up and tell you how to enter information in the NAME field. Once you are in the help system, you may browse through the information provided by pressing the Page Up, Page Down, Up Arrow, or Down Arrow. Page Up does the same thing as the Up Arrow key and Page Down does the same thing as the Down Arrow key. You may get back to the original screen by pressing the HOME key. When going "down" in the system, you will be able to step through every screen in the help system. When going "up", you will skip up to the top screen of the previous major topic in the system. This allows you to move quickly through the screens to the one you wish to see. >>> S E T U P <<< The SETUP module is the built-in data manager for the satellites and observation points to be used in PC-TRACK. With it you can enter, edit, and delete all information necessary to do satellite tracking with PC- TRACK quite easily. To select the SETUP module, move the cursor using the arrow keys until it highlights SETUP and press the RETURN key. (Or just press S.) A second menu window will appear with the options OBSERVERS and SATELLITES. The OBSERVERS option handles data for the observation points and SATELLITES handles the data for the satellites. Select the desired option by again moving the cursor to highlight the one you want. There are various keys that will assist you in the entry and editing of observer or satellite data while in the SETUP module. They are as follows: F2 - ADD OBSERVER/SATELLITE This key allows you to create a new entry in the observer/satellite file where information about a new observer/satellite can be put. When this key is pressed, all the screen fields are cleared so you can begin entering new information. F3 - REMOVE OBSERVER/SATELLITE This key does just the opposite of the F2 key. It PERMANENTLY removes the currently visible observer/satellite from the file. Since this action is PERMANENT and IRREVOCABLE, a warning window pops up to alert you to the fact that this will occur if you continue. If you press RETURN in response to the warning window prompt, you will remove that observer/satellite from the file. If you press ESC or any other key, you will not remove the observer/satellite and you will go back to where you were when you pressed the F3 key. PAGE UP - PREVIOUS OBSERVER/SATELLITE This key will display the previous observer/satellite in the file. Observers/satellites are stored in the file in alphabetical order. Once the observer/satellite you desire is visible on the screen, you may edit any of its fields. If you step past the first observer/satellite in the file, the last will be displayed. PAGE DOWN - NEXT OBSERVER/SATELLITE This key will display the next observer/satellite in the file. If you go past the last observer/satellite in the file, the first will be displayed. SETUP OBSERVERS The OBSERVERS option opens up the data entry window on the right side of the screen. This window shows the six fields (pieces of information) held for each observation point you have in the file. The six pieces of information necessary to describe an observation point are as follows: DESCRIPTION: This field is your way of easily identifying each of the observation points you have in your file. This is a text field with room for up to 30 characters (anything you want). For example, you can put the names of the nearest associated city with the state, such as Dayton, Ohio. Or if you have a lot of observation points entered, you might devise some numbering system to systematic identify each location. This could be something like OH-39N-84W, which would be a location in the state of Ohio, near 39 north latitude and 84 west longitude. I'm sure you can devise some more sensible system because as you see below the latitude and longitude are already included. LATITUDE: This along with longitude defines the location of the observation point. Latitude is entered as degrees and decimal fractions of degrees. Latitude will be entered as a positive number if it is in the northern hemisphere and negative (-) for those in the southern hemisphere. For example a position with a northern hemisphere latitude of 34 degrees, 30 minutes, and 15 seconds would be entered as 34.5042. That same latitude in the southern hemisphere would be entered as -34.5042. This may be entered as a number between -90.0 to 90.0. LONGITUDE: This along with latitude defines the location on earth of the observation point. Longitude is entered like latitude as degrees and decimal fractions of degrees. Longitude is entered as positive values for the western hemisphere (North and South America, Greenland, etc.) and negative for the eastern hemisphere (Europe, Asia, Russia, etc). This may be entered as a number between -180.0 and 180.0. MINIMUM ELEVATION: This figure describes the lowest elevation at which the satellite may be visible from the observation point. An observation point with a perfectly clear horizon around it would have a minimum elevation of 0.0 degrees. If there are mountains or buildings around it the minimum elevation would be higher. This may be entered as a number between 0.0 and 90.0. This number is used as a filter for displaying and printing azimuth/elevation data. Only satellite look angles with elevations above the minimum will be displayed or printed. TIME ZONE: This describes the number of hours from UTC time (Coordinated Universal Time) (used to be called GMT or Greenwich Mean Time) your local time zone is. Time zones in the western hemisphere are entered as negative while eastern hemisphere zones are entered as positive. For example, Eastern Standard Time would be entered as -5 hours from UTC time. Pacific Standard Time would be -8 hours. Time Zone may be entered as whole numbers between -12 and 12. NOTE: IF YOU DESIRE TO TRACK USING UTC TIME, MAKE SURE YOUR DOS CLOCK IS SET TO UTC TIME AND USE THE CONFIG SYSTEM OPTION TO TELL PC-TRACK TO USE UTC TIME. HEIGHT: This describes the height your observation point is above Mean Sea Level (MSL). If you are not sure what the height is for the observation point, enter 0.0. Height may be entered as any value between -400.00 and 30,000 feet or between -122 and 9150 meters. SETUP SATELLITES The SATELLITES option also opens up the data entry window on the right side of the screen. This window shows the twelve fields used for each satellite you have in the file. This information is available from a number of sources. See appendix A for the cheapest and most reliable source for this information. The twelve pieces of information necessary to describe an satellite are as follows: NAME: This is a 10 character field which you can use to name the satellite for easy identification. CATALOG (SATELLITE) NUMBER: This is a 5 digit number assigned to each satellite. It is used as the reference number in the NASA source identified in Appendix A. EPOCH YEAR: This is the year of the specific time the rest of the data for the satellite is effective. When entering Epoch year, make sure you include all 4 digits of the year, ie. 1989. Some data sets such as those from NASA include only the last 2 digits of the year. PC-Track requires all 4. EPOCH DAY: This is the day and fraction of day for the specific time the data is effective. This number defines both the julian day (the whole number part of the value) and the time of day (fractional part of the value) of the data set. The julian day figure is simply the count of the number of days that particular date is from the beginning of the year. (January 1 would have a julian day of 1. Feb 28 would be 59.) This number may range from 1.0 to 366.999999999 (taking into account leap years). DECAY RATE: This is the rate of decay of the orbital period (time it takes to complete one revolution) due to atmospheric friction and other factors. It is a real number measured in terms of Revolutions per Day per Day (REV/DAY/DAY). INCLINATION: This number describes the angle of the plane of the orbit in relationship to the earths equator. Inclination is 0 degrees for a satellite orbiting directly over the earths equator and orbiting in the same direction as the earths rotation. It is 180 degrees for an satellite revolving directly over the equator counter to earths rotation. An satellite orbiting directly over the poles would have an inclination of 90 degrees. Inclination is given as a real number of degrees between 0.0 and 180.0 degrees. RIGHT ASCENSION OF ASCENDING NODE: This value describes the point the satellites crosses the equator from the southern hemisphere to the northern hemisphere (ascending node). This measured eastward along the equator from the vernal equinox (right ascension). It is given and entered as a real number of degrees from 0.0 to 360.0 degrees. ECCENTRICITY: This is a unitless number which describes the shape of the orbit in terms of how close to a perfect circle it is. This number is given in the range of 0.0 to less than 1.0. An perfectly circular orbit would have an eccentricity of 0.0. A number greater than 0.0 would represent an elliptical orbit with an increasingly flattened shape as the value approaches 1.0. ARGUMENT OF PERIGEE: This value is the number of degrees from the ascending node the perigee point occurs. The perigee point is the point where the satellite is the closest to the earth (assuming an orbit which is elliptical to some degree). This number may be entered as a real value between 0.0 and 360.0. MEAN ANOMALY This number represents the angular distance from the perigee point (closest point) to the satellites mean position. This is measured in degrees along the orbital plane in the direction of motion. This number is entered like the argument of perigee, as a value between 0.0 and 360.0. MEAN MOTION: This is the number of complete revolutions the satellite makes in one day. This number may be entered as a value greater than 0.0 and less than 20.0. When all of the pieces of information have been input for an satellite and you have no other satellites to enter, press ESC to get back to the main menu. REVOLUTION NUMBER This represents the number of revolutions the satellite has completed at the epoch time and date. This number is entered as an integer value between 1 and 99999. FREQUENCY This represents any downlink frequency that may be of importance to you. This frequency will be displayed on the screens and printed on the printout and will be adjusted according to the computed doppler shift associated with the relative range rate between the observer and the satellite. This number is entered between 0.0 and 9999.999999 and represents MHZ (megahertz). >>> TRACK <<< The TRACK module is the heart of PC-TRACK. It is where the satellite positions and look angles are computed. Moving the cursor to this option brings up a choice of either GRAPHICS or TEXT. Select the type of tracking you desire. If you do not have an EGA video adapter, you must select the TEXT option. GETTING READY TO TRACK GRAPHICS The GRAPHICS TRACK option is the heart of PC-TRACK. It tracks up to eight satellites at once on the EGA graphics screen. NOTE: If either observer, satellite, or map data has not been loaded due to an improper path designation or some other reason, then tracking will not begin when you select this option. An error window will appear indicating the reason why tracking cannot begin. Pressing RETURN will put you back at the TRACK window. If this occurs, you must either check the paths or enter new data (for observers or satellites). Selecting this option brings up a screen with four items to select; the observation point, the map to use, the globe view to use, and the satellite(s) to track. The default observation point selected in the CONFIG SYSTEM option will appear. To change that observation point, use the up and down arrow keys to select the new one desired. Press RETURN to proceed or ESC to go back to the MAIN MENU. The observation points displayed will be the ones in the OBSERVER database defined using the SETUP OBSERVERS option. Once you select an observation point, the default map identified in the CONFIG SYSTEM option is shown initially. To select some other map, simply use the up and down arrow keys to show the names of the available maps. When the one you want is visible, press the RETURN key to proceed or the ESC key to go back to the MAIN MENU. Once you select an map, the default globe view identified in the CONFIG SYSTEM option is shown initially. To select some other globe view, simply use the up and down arrow keys to show the names of the available views. When the one you want is visible, press the RETURN key to proceed or the ESC key to go back to the MAIN MENU. REMEMBER: You must have the MAPx.IMG and GLOBEx.IMG files in the map path specified in the SETUP SYSTEM option. Otherwise, no map or globe will be displayed during tracking. PC-TRACK is capable of tracking up to 8 satellites simultaneously. The selection of the ones to track is done as follows: There are 8 "slots" available to select satellites. Each slot may have any one of the satellites defined in the SETUP SATELLITES option. You are initially positioned in slot number 1. The default satellites identified in the CONFIG SYSTEM option are shown. At this point you may: Press the Page Up or Page Down key. This will move you to the next slot up or down. If you press the page down key, the cursor will move to the next slot down, and the next satellite down in the database will be showing. If you press the page up key, the cursor will move to the next slot up (will wrap to the bottom if you are at the top) and display the previous satellite in the database (will also wrap the bottom of the database if at the top). Press the Up or Down arrow key. This will change the satellite displayed to the next or previous satellite in the database. The up arrow will select previous satellite, the down arrow key will select the next. Press the Home Key to clear the current slot and move the cursor to the previous slot. This is handy to unselect a slot. You may fill any or all slots with satellites. You do not necessarily have to fill them all. You may have blanks slots. For example, you could set it up so there are only 2 satellites to track, one in slot 2 and one in slot 7. It's up to you. Press RETURN to complete the selection process and begin the tracking process. Remember, the Page Up and Page Down keys select the slot, the arrow keys select the satellite to go into the slot, the home key clears a slot, and the RETURN key finishes the selection process and starts tracking. TEXT The TEXT TRACK option is provided for computers which do not have an EGA graphics display capability. NOTE: If either observer or satellite, has not been loaded due to an improper path designation or some other reason, then tracking will not begin when you select this option. An error window will appear indicating the reason why tracking cannot begin. Pressing RETURN will put you back at the TRACK window. If this occurs, you must either check the paths or enter new data (for observers or satellites). Selecting this option brings up a screen with three items to select; The satellite, Observation point, and printing instructions. As described above, your selections are made by simply using either the Up or Down Key. Once the desired satellite or observation point is visible press RETURN. To go back to the MAIN MENU, press the ESC key. The initial satellite shown will be the number one default satellite (the top one) identified in the CONFIG SYSTEM option. The initial observation point will also be the default. After selecting which satellite to track and the observation point, you will be asked to define what data is to be printed (if printing is enabled) during track. You have a choice of either printing every point computed or only those which have satellite elevations from the observation point greater than the minimum elevation entered for that observation point. The desired answer is again provided by using the Up or Down keys and pressing RETURN. Tracking will then begin. THE TRACK PROCESS GRAPHICS BASED TRACK SCREEN During the tracking process information is provided within a number of separate boxes on the graphics screen. The general locations of these boxes on the track screen and the information presented are described below. The layout of the screen depends on which projection is selected and for the case of mercator projections, what size maps are selected. FOR SPHERICAL, OR MERCATOR WITH LARGE MAPS: ┌─────────────────────────────────────────────────────────────────────┐ │┌──────────────────────────────────────────────────────────────┐┌───┐│ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ T ││ ││ ││ ││ ││ ││ I ││ ││ ││ ││ ││ ││ T ││ ││ ││ ││ ││ ││ L ││ ││ ││ ││ ││ M A P O R G L O B E ││ E ││ ││ ││ ││ ││ B O X ││ ││ ││ ││ ││ ││ ││ B ││ ││ ││ ││ ││ ││ O ││ ││ ││ ││ ││ ││ X ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ │└──────────────────────────────────────────────────────────────┘└───┘│ │ ┌────────────────┐│ │┌──────────────────────────────────────────────────┤ ││ ││ DATE TIME INTERVAL │ O B J E C T ││ ││ BOX │ B O X ││ │└──────────────────────────────────────────────────┴────────────────┘│ └─────────────────────────────────────────────────────────────────────┘ NOTE: IN THIS SCREEN, THE STATUS DISPLAY IS SHOWN ALONG THE BOTTOM OF THE DATE TIME INTERVAL BOX. FOR MERCATOR WITH SMALL MAPS: ┌──────────────────────────────────────────────────────────────────────┐ │┌───────────────────────────────────────────────┐┌───────────────────┐│ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ ││ AZIMUTH/ ││ ││ ││ ││ ││ ││ ELEVATION ││ ││ M A P ││ ││ ││ ││ CHART ││ ││ ││ ││ ││ A R E A ││ ││ ││ ││ ││ ││ ││ ││ ││ │└───────────────────┘│ ││ │┌───────────────────┐│ ││ ││ ││ ││ ││ OBSERVATION ││ ││ ││ POINT ││ ││ ││ BOX ││ ││ ││ ││ ││ ││ ││ │└───────────────────────────────────────────────┘└───────────────────┘│ │┌─────────────────────────────────────────────────────┐┌─────────────┐│ ││ ││ ││ ││ ││ STATUS ││ ││ S A T E L L I T E ││ BOX ││ ││ ││ ││ ││ B O X │└─────────────┘│ ││ │┌─────────────┐│ ││ ││ ││ ││ ││ TITLE ││ ││ ││ ││ ││ ││ BOX ││ │└─────────────────────────────────────────────────────┘│ ││ │┌─────────────────────────────────────────────────────┐│ ││ ││ DATE TIME INTERVAL ││ ││ ││ BOX ││ ││ │└─────────────────────────────────────────────────────┘└─────────────┘│ └──────────────────────────────────────────────────────────────────────┘ MAP/GLOBE This is the area where the maps of various portions of the world are displayed for use in plotting the current satellite positions. AZIMUTH/ELEVATION CHART The AZEL chart shows graphically the look angles (azimuth and elevation) for each satellite. When a satellite is visible to the observation point (defined as when the elevation is greater than the minimum elevation defined in the SETUP OBSERVERS option) the reference number associated with the satellite is displayed on the chart. The number will be placed on the chart based on the current azimuth (bearing) and elevation needed to point an antenna (or to look) at the satellite from the observation point. The distance from the center of the chart represents the elevation. The farther the point is from the center, the lower the elevation. Elevation is indicated by the numbers shown along the horizontal line on the chart. The center represents 90 degrees elevation or directly overhead. The angular position from the vertical line represents the azimuth from the observation point to the satellite. Azimuths is numbered clockwise around the outside of the outermost circle drawn on the chart. Zero degrees azimuth (straight up) represents true north. OBSERVATION POINT BOX This box displays the name, latitude and longitude of the current observation point. STATUS BOX This box shows the status of the various modes available. The messages which will show up in this box are as follows... REAL TIME TRACK - Indicates PC-TRACK is tracking the satellite in real time. This is enabled by the F2 key. FAST TRACK - Indicates PC-TRACK is computing and displaying satellite positions as fast as possible ignoring the internal clock. This is enabled by the F2 key. PAUSING - Indicates PC-TRACK has temporarily halted the tracking process after the F3 key was pressed, and is waiting for the F3 key to be pressed again to resume tracking. PRINTING - Indicates printing is enables and depending on which ground track mode is selected, will print satellite position and look angles for the satellite selected. The satellite selected will have its name displayed in a different color than the rest of the satellites listed in the SATELLITES box. Printing is enabled by the F4 key. G.T. (IR) - Indicates that a + will be placed on the map and the AZEL chart for each sub-satellite point in which the satellite is in range of the observation point when using Mercator projections. Will mark satellite position and in-range points when using spherical projections. Enabled by the F6 key. G.T. (C) - Indicates that a + will be placed on the map and the AZEL chart for each sub-satellite point computed for Mercator projections and mark satellite position and ground track for spherical projections. This is the default condition, and can be changed by the F6 key. AUTOMAP - Indicates PC-TRACK will automatically select a map or globe which will display the position of the currently selected satellite (selected by PGUP/PGDN keys). This is enabled by the F9 key. NOTE: IN WHEN USING THE SPHERICAL PROJECTION SCREEN, OR THE MERCATOR PROJECTION SCREEN WITH LARGE MAPS, THE STATUS DISPLAY IS SHOWN ALONG THE BOTTOM OF THE DATE TIME INTERVAL BOX. SATELLITES BOX The satellite box shows all the information relating to the current position of the satellites begin tracked. The following information is displayed for each satellite: Reference Number : This is the number associated with the satellite, which shows up on the map and the azel chart to show its current position. Name: This is the name given to the satellite in the SETUP SATELLITES option. Latitude: Current latitude of the sub-satellite point. Longitude: Current longitude of the sub-satellite point. Altitude: Current altitude of the satellite. This will be in either kilometers or statute miles depending on what you have configured the program to display in the CONFIG SYSTEM option. Elevation: When the satellite is visible to the observation point, the current elevation will be displayed here. Azimuth: When the satellite is visible to the observation point, the current azimuth will be displayed here. Range: This is the current distance (again, either KM or Statute Miles) from the observation point to the satellite. This is displayed only when the satellite is visible to the observation point. Frequency: This is the base frequency defined for the satellite in the SETUP SATELLITES option adjusted for doppler shift. This is displayed only when the satellite is visible to the observation point. Currently Selected Satellite : This is shown by having the selected satellites name displayed in a different color. This may be changed by using PGUP and PGDN keys. DATE / TIME / INTERVAL BOX PC-TRACK is a time based tracking package, which means that it first obtains a time and date and then figures out where the satellite is at that time and date. This box displays the current date and time used to compute the current satellite position. The interval is added to the current track time (shown in the DATE TIME INTERVAL BOX) to generate the next date and time needed. This interval is initially set to 1 second. It may be modified as described below when in the Fast Track Mode. Interval is fixed at 1 second and not displayed in Real Time Mode. For example, if the current time shown is 09:03:32, and the interval is 00:00:05 (5 seconds) then the next time used to compute the satellite position will be 09:03:37. TITLE BOX This is where the advertisement goes. HELP SCREEN When the F1 help key is pressed a portion of the track screen is used by the PC-TRACK ASSISTANT to display the various help screens. This is the very same help system used in other parts of the program. When you are done with the help system, press ESC and the track screen will be restored as it was before help was requested. FUNCTION KEYS AVAILABLE There are several function keys set up to control various features of PC- TRACK which affect the tracking process. They are described as follows... F1 - HELP This is the key which brings up the PC-TRACK ASSISTANT as described earlier. It functions exactly as it does anywhere else in the program except the help screens show in the area of the world map. Once you exit the help system, the world map is restored to its original condition before help began. F2 - REAL TIME / FAST TRACK This key controls the tracking mode of PC-TRACK. When tracking first begins, it is in the REAL TIME TRACK mode. This means the position displayed represents the actual satellite position according to the time set in the computer (DOS time). The displays will be updated at the time interval shown in the TIME INTERVAL BOX (fixed to 1 second). Pressing the F2 key changes this to the FAST TRACK mode. This mode ignores the clock in the computer and simply computes and displays the satellite positions as fast as it can. The time between each point computed is determined by the time interval shown in the TIME INTERVAL box. This time interval is changeable according to the procedures shown below. The F2 key acts as a "toggle". This means that if you press it once, the mode changes to FAST TRACK. When you press it again, the mode changes back to REAL TIME TRACK. Pressing it again changes the mode again to FAST TRACK, etc. F3 - PAUSE TRACKING This key may be pressed at any time during tracking to "freeze" the display. This stops all computations and simply waits for the F3 key to be pressed again. Once it is pressed again, normal tracking resumes. When in the PAUSE mode, all of the other function keys perform normally. F4 - ENABLE/DISABLE PRINTER This key enables output to be sent to the printer during the tracking process. The amount of data sent to the printer is determined by the ground track mode selected. If ground track is disabled, or in the IR mode, then just points with elevations above the minimum elevation will be printed. If ground track is in the C mode, then all points will be printed. The currently selected satellite will have its data printed. F5 - REDRAW SCREEN The F5 key simply redraws the Map or Globe and the Azimuth/Elevation chart to remove clutter from extended use of ground tracks. F6 - GROUND TRACK - In the ground track mode, PC-TRACK plots the path each satellite has taken by marking each point plotted. There are 3 possible modes of ground track... - DISABLED - IR - CONT GROUND TRACK DISABLE - No path will be plotted on the maps, globes, or AZEL chart. Just the satellite reference numbers will be visible. Pressing the F6 key at this point will put ground track into the IR mode. GROUND TRACK (In Range) - With Mercator projections leaves a ground track only when the satellite is in range. With spherical projections the ground track shows as a series of black dots placed on the globe at the subsatellite points. In addition to this a white point is placed in space showing the current satellite position for each position computed, whether in-range or not. With mercator projections, A '+' is placed on the maps and the AZEL chart at the current sub-satellite point. Pressing the F6 key at this point will put ground track in the CONT mode. The STATUS BOX will display "G.T. (IR)". GROUND TRACK (Continuous) - This is the condition in effect when tracking begins. This leaves a ground track continuously. With spherical projections, a black + is placed on the globe at each subsatellite point that is in-range of the observation point and a light blue + for all other subsatellite points, and the white points representing the actual satellite position in space are plotted as above. With mercator projections, A '+' is placed on the map and the AZEL chart at each sub-satellite location computed. The STATUS BOX will display "G.T.(C)". Pressing the F6 key at this point will turn off ground track. F7 - SELECT NEW MAP/GLOBE VIEW - This allows you to change the map or globe view during tracking. This brings up the same selection of maps or globe views which were available when setting up to track. You may select a new map or globe view simply by pressing either the up or down arrow keys until the name of the desired map or view is shown. You may then press either ESC to keep then existing map or RETURN to begin using the new map or globe view selected. This key is functional only when AUTOMAP is disabled. NOTE: Depending on what map or globe view you select, the observation point may not be visible on the new map. CTRL F7 - SELECT PROJECTION - This feature enable you to select which type of projection to be used for displaying the satellite position. Spherical projections are shown on an image of the earth and plotted in such a way as to give a 3 dimensional effect. There are 4 different views of the earth for each of the two sizes available. The view of the globe is from the equator, at the longitude chosen when selecting the globe view (when setting up prior to tracking or with the F7 key). For example, selecting the 90 W Lon globe view will show you the earth from 0 deg latitude (equator) and 90 deg west longitude. The view on the screen will always be from that reference point, so the shapes of the satellite orbits will look somewhat twisted due to the effect of the rotation of the earth. Mercator projections will show the positions of the satellites on flat maps, with the inherent distortion that provides. It does however, give a somewhat more accurate picture of the current satellite position, particularly at higher latitudes. Due to extreme distortions at latitudes approaching the poles, the mercator projections only display positions to 80 degrees. When viewing on the world maps, if you cannot locate a satellite on the screen, check to see what the latitude is, it will most likely be above 80 deg (north or south). ALT F7 - CHANGE SIZE - This feature changes the size of the projection currently being viewed. When using spherical projection, this will just change the size of the globe. When using mercator projections, this will change the entire screen layout as shown above. With a small screen size selected, you will see the satellite, AZEL, observer, and status boxes. SPECIAL FEATURE: CHANGING GLOBE VIEWS MAY BE ACCOMPLISHED MORE RAPIDLY BY PRESSING CTRL OR CTRL (CONTROL RIGHT ARROW OR CONTROL LEFT ARROW). F8 - SELECT NEW OBSERVER - This allows you to change the observation point during tracking. This brings up the same selection of observation points which were available when setting up to track. You may select a new observation point simply by pressing either the up or down arrow keys until the name of the desired observation point is shown. You may then press either ESC to keep existing observer or RETURN to select the new observer. NOTE: If you are tracking with local times, the position(s) of the satellite(s) may change, since the time zone offset for the new observation point may be different than that of the old one. This will result in a different effective UTC time, which is used to predict the satellite(s) position(s). F9 - AUTOMAP - This enables PC-TRACKs automatic map/globe view selection feature which checks the current position of the selected satellite and makes sure it is visible on the currently displayed map or globe. If not, it will check the available maps or globes and select the next one which will show the position of the satellite. This key works like a toggle, ie. pressing once enables it, pressing again disables it. Whatever map or globe view was visible at the time AUTOMAP was disabled will remain on the screen until AUTOMAP is again enabled or a new map or globe view is selected using F7. F10 - SET DOS CLOCK - This key will take the currently displayed date and time and set the DOS clock with them. This allows you to easily change the real time clock to a desired date and time. The date and time are changed by using the arrow keys. NOTE: If you set the DOS clock with this option, the clock will retain that new time even after quitting PC-TRACK. ARROW KEYS - CHANGE DATE, TIME, AND INTERVAL - When in the FAST TRACK mode, you have the ability to change the date, time and interval to whatever you wish. To make changes, use the left and right arrow keys to move the highlighted cursor to whatever parameter you wish to change. For example after pressing F2 and getting into FAST TRACK mode, the highlighted cursor will not be visible, but pressing the left arrow key will highlight the SECONDS portion of the INTERVAL. This shows that you may now either increase or decrease that number. Once the parameter you wish to change is highlighted, you may do so by using the up and down arrow keys. The + or - sign associated with the interval shows the direction in time the interval is changing the computed time. If it is + (positive) then the computed time will be increase, if it is - (negative) then the computed time will decrease. If the interval is set to 00:00:00, then you may experiment with the date and time and compute the satellite position for a specific point in time and study it while PC-TRACK keeps computing all data. This is different than the pause (F3) feature which freezes computations. NOTE: When the increment is 00:00:00, the frequency computed and displayed for visible satellites will not show the doppler shift incorporated in the displayed value. PGUP/PGDN - CHANGE SELECTED SATELLITE - This changes the currently selected satellite shown highlighted in the SATELLITES box. The currently selected satellite is the one which will have its data sent to the printer and will be used in the AUTOMAP mode to determine the currently visible map. TEXT BASED TRACK SCREEN The text screen is laid out as shown in the example below: ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ CURRENT TRACKING DATA FOR OSCAR 10 │ │ CURRENT OBSERVATION POINT: Dayton, Ohio │ │ 39.45N Lat 84.15W Lon Time Zone: -5 │ │ MINIMUM ELEVATION: 2.00 HEIGHT ABOVE M.S.L.: 500 (Meters) │ │ ---------------------------------------------------------------- │ │ Date Time (UTC) Interval │ │ June 13, 1990 07:43:14 + 00:10:00 │ │ ********** S A T E L L I T E D A T A ********** │ │ Revolution Number │ │ 2469 │ │ Latitude Longitude Altitude (KM) │ │ 2.18 S 67.35 W 2950 │ │ │ │ ********** T R A C K I N G D A T A *********** │ │ Azimuth Elevation Slant Range (KM) │ │ 155.55 11.50 4923.4 │ │ Range Rate (KM/Sec) Frequency (MHZ) │ │ 2.0 145.808413 │ │ FAST TRACK PAUSING PRINTING │ │ PRESS F1 FOR HELP │ │ PRESS ESC TO QUIT TRACKING │ └─────────────────────────────────────────────────────────────────────┘ This screen displays essentially the same information displayed by the graphics screen (except for only one satellite). The top of the screen displays the name of the satellite and the observation point information. This information is simply the information entered using the SETUP OBSERVER option. Revolution number and Range Rate are provided on this screen, while they are not in the graphics tracking mode. The range rate is the change in distance between the observation point and the satellite. If it is positive, the distance is increasing. Range rate determines the doppler shift of the downlink frequency. FUNCTION KEYS AVAILABLE: F1 - HELP This is the key which brings up the PC-TRACK ASSISTANT as described earlier. F2 - REAL TIME / FAST TRACK This key controls the tracking mode of PC-TRACK. When tracking first begins, it is in the REAL TIME TRACK mode. This means the position displayed represents the actual satellite position according to the time set in the computer (DOS time). The displays will be updated at the time interval shown in the TIME INTERVAL (fixed to 1 second). Pressing the F2 key changes this to the FAST TRACK mode. This mode ignores the clock in the computer and simply computes and displays the satellite positions as fast as it can. The time between each point computed is determined by the time interval shown in the TIME INTERVAL. This time interval is changeable according to the procedures shown below. The F2 key acts as a "toggle". This means that if you press it once, the mode changes to FAST TRACK. When you press it again, the mode changes back to REAL TIME TRACK. Pressing it again changes the mode again to FAST TRACK, etc. F3 - PAUSE TRACKING This key may be pressed at any time during tracking to "freeze" the display. This stops all computations and simply waits for the F3 key to be pressed again. Once it is pressed again, normal tracking resumes. While in the pause mode, you may make changes to the time increment (described below), turn the printer on or off, and select Real Time or Fast Track mode. F4 - ENABLE PRINTER This key enables output to be sent to the printer during the tracking process. The amount of data sent to the printer is determined by your response to the prompt during the SELECT process just before tracking began, either all data or just points with elevations above the minimum elevation. NOTE: If PC-TRACK encounters a problem trying to print (out of paper, off-line, turned off, etc.) printing will automatically be disabled, and the PRINTING message at the lower portion of the screen will disappear. The F4 key operates as a toggle just as the F2 and F3 keys. If printing is enabled, just press F4 again to turn it off. ARROW KEYS - CHANGE DATE, TIME, AND INTERVAL - When in the FAST TRACK mode, you have the ability to change the date, time and interval to whatever you wish. To make changes, use the left and right arrow keys to move the highlighted cursor to whatever parameter you wish to change. For example after pressing F2 and getting into FAST TRACK mode, the highlighted cursor will not be visible, but pressing the left arrow key will highlight the SECONDS portion of the INTERVAL. This shows that you may now either increase or decrease that number. Once the parameter you wish to change is highlighted, you may do so by using the up and down arrow keys. The + or - sign associated with the interval shows the direction in time the interval is changing the computed time. If it is + (positive) then the computed time will be increase, if it is - (negative) then the computed time will decrease. If the interval is set to 00:00:00, then you may experiment with the date and time and compute the satellite position for a specific point in time and study it while PC-TRACK keeps computing all data. This is different than the pause (F3) feature which freezes computations. NOTE: When the increment is 00:00:00, the frequency computed and displayed for visible satellites will not show the doppler shift incorporated in the displayed value. >>> CONFIGURATION <<< This module allows you to modify certain things about the program which affect the way the program operates. The things you can change are text screen colors, printer control codes, distance and time units, and the file paths. CONFIGURE DISPLAY This option allows you to easily change the colors you see on the screen displays. This way you can get the screen displays to look the way you want. You are able to see the effects of changes on the screen while you make them. You can make changes to both the background and text colors with simple key strokes. These colors are effective throughout PC-TRACK, including the graphics screen. The only colors which are not affected are the World Map and the AZEL chart displays and the satellite position marks on them. The map and chart will always be blue with the position marks being yellow and the station location being in white. NOTE: While graphics mode tracking is not possible on a monochrome video system, all of the rest of PC-TRACK is, including the text base track screen. Using the color configuration option here will enable the colors to be manipulated until the correct gray shades are achieved in order to see the display adequately. Here's how to do it... Information is displayed on the screen using 7 different categories for the text and background colors... - NORMAL - HIGHLIGHTED - DATA ENTRY - TITLE - SCREEN COLOR - SHADOW COLOR (Background only) Only the combinations used in PC-TRACK are shown. The colors for both the background and text colors can be selected for each of these categories. Selecting Text Color Category Using the Left and Right arrow keys selects the category for text color changes. The currently selected category is shown by a down arrow pointing to it along the top of the matrix. Select Background Category Use the Up and Down arrow keys to select the category for background color changes. The currently selected category is shown by a right arrow pointing to it along the left side of the matrix. Change Text Color (F5) Pressing this key changes the color of the currently selected text category. There are 16 colors to choose from. Change Background Color (F6) Pressing this key changes the color of the currently selected background category. There are 2 sets of 8 identical colors. One set causes the text to be non-blinking while the other causes blinking text. CONFIGURE SYSTEM This option allows you to define the default observation point, map, and satellites to use in the TRACK option. This will enable to you set up PC- TRACK to track the satellites you want and then not have to go through the process again unless you wish to change it. This reduces the effort needed to begin tracking to just a few keystrokes. It also allows you to define whether or not to use metric measurements, Coordinated Universal Time, and where PC-TRACK looks on your disk to find the files it needs to operate with. Default Observation Point The default observation point is selected first. The initial observation point to appear is either the first one in the observer database (if none is already selected), or the one previously selected. To change that observation point, use the up and down arrow keys to select the new one desired. Press RETURN to proceed or ESC to finish making changes in the CONFIG SYSTEM option. The observation points displayed will be the ones in the OBSERVER database defined using the SETUP OBSERVERS option. NOTE: If there are no observers in the database (either none entered yet or the DATA PATH is incorrect), this part will be skipped. You will not be able to select a default observer. Default Map Once you select an observation point, the default map is identified. To select a map, simply use the up and down arrow keys to show the names of the available maps. When the one you want is visible, press the RETURN key to proceed or the ESC key to finish up with CONFIG SYSTEM. NOTE: If there are no maps in the MAP PATH identified below, this part will be skipped. You will not be able to select a default map. Default Globe view Once you select a map, the default globe view is identified. To select another globe view, simply use the up and down arrow keys to show the names of the available views. When the one you want is visible, press the RETURN key to proceed or the ESC key to finish up with CONFIG SYSTEM. NOTE: If there are no globes in the MAP PATH identified below, this part will be skipped. You will not be able to select a default globe view. Default Satellites PC-TRACK is capable of storing up to 100 satellites in its database (using SETUP SATELLITES) and tracking up to 8 satellites simultaneously. This option selects up to 8 of the possible 100 to be initially selected for GRAPHICS TRACK. There are 8 "slots" available to select satellites. Each slot may have any one of the satellites defined in the SETUP SATELLITES option. You are initially positioned in slot number 1. NOTE: If there are no satellites in the database (either none entered yet or the DATA PATH is incorrect), this part will be skipped. You will not be able to select any default satellites. At this point you may: Press the Page Up or Page Down key. This will move you to the next slot up or down. If you press the page down key, the cursor will move to the next slot down, and the next satellite down in the database will be showing. If you press the page up key, the cursor will move to the next slot up (will wrap to the bottom if you are at the top) and display the previous satellite in the database (will also wrap the bottom of the database if at the top). Press the Up or Down arrow key. This will change the satellite displayed to the next or previous satellite in the database. The up arrow will select previous satellite, the down arrow key will select the next. Press the Home Key to clear the current slot and move the cursor to the previous slot. This is handy to unselect a slot. You may fill any or all slots with satellites. You do not necessarily have to fill them all. You may have blanks slots. For example, you could set it up so there are only 2 satellites to track, one in slot 2 and one in slot 7. It's up to you. Press RETURN to complete the selection of default satellites and move on to the PATH. Press ESC to finish CONFIG SYSTEM. Remember, the Page Up and Page Down keys select the slot, the arrow keys select the satellite to go into the slot, the home key clears a slot, and the RETURN key finishes the default satellite selection process. Data Path This line tells PC-TRACK what disk drive and what directories and subdirectory on that disk to use as the storage area for the data files it uses. This line of text will be in the form of an MS-DOS path name. If you have PC-TRACK on your C drive and you have a special subdirectory called "\TRACK\DATA", then you would enter "C:\TRACK\DATA\" on this line. The path defined here is where PC-TRACK will look for the OBJECTS.DAT and OBSERVER.DAT files. NOTE: If you enter a non-existent path, an error window will appear and will indicate that fact. You must press RETURN at this point and try again. If you cannot remember what the path is, you can just clear the line out by using the BACKSPACE, DELETE, OR CTRL X keys. This will specify the default path. Map Path This line tells PC-TRACK what disk drive and what directories and subdirectory on that disk to use as the storage area for the map and globe files it uses. This line of text will also be in the form of an MS- DOS path name. This is entered exactly the same as described above. See the note above on non-existent paths. Metric System This tells PC-TRACK to use either metric (meters and kilometers) or English (feet and statute miles) measurements for distance. Press the INSert key to change the answer or RETURN to move to another parameter, and ESC to finish the CONFIG SYSTEM option. UTC Time This tells PC-TRACK whether to interpret the date and time displayed as Coordinate Universal Time (UTC) or Local Time. If the answer to the question is 'UTC' then PC-TRACK will interpret it as UTC time, otherwise it will be Local time. When using local time, PC-TRACK uses the time zone specified for the observation point selected to compute UTC time for use internally. This time zone is defined in the SETUP OBSERVERS option. If you select Local time display (answer 'LOCAL') PC-TRACK will subtract the time zone from the displayed time to get UTC time, since PC-TRACK must use UTC time internally to compute satellite data. All displays and printouts, however, will reflect the local time. Finishing Up As described above, you may press ESC any time to end the CONFIG SYSTEM option. You will be asked if everything is correct. At this point you may enter: 'Y' or RETURN to save the changes you have made and go back to the CONFIG menu. 'N' to go back and continue to make more changes. ESC to quit without saving the changes and go back to the CONFIG menu. CONFIGURE PRINTER This option allows you to change the control codes sent to your printer to make it print the PC-TRACK reports correctly. Printer Codes Printer codes are sequences of special control characters sent to your printer. PC-TRACK displays and accepts them from you as the decimal equivalents of each control character separated by a slash (/). For example, the ESC character has a decimal value of 27 so it is shown on the screen as the number "27". Notice each print command has a code sequence to turn it on and one to turn it off. Some codes do not need to be turned off, so those portions are left blank. Some printers may not be capable of printing some of these features. In that case, leave the CODE TO TURN ON for that feature blank. You have up to 20 characters (including slashes) to define each of the codes. You may move the cursor around on the screen to the desired code sequence by using the arrow keys or just pressing RETURN. APPENDIX A OBTAINING SATELLITE INFORMATION The information required by PC-TRACK can be obtained by requesting the "NASA PREDICTION BULLETIN" or the "TWO LINE ORBITAL ELEMENTS" for each of the satellites desired, referenced by CATALOG NUMBER from: PROJECT OPERATIONS BRANCH (CODE 513) NASA/GODDARD SPACE FLIGHT CENTER GREENBELT, MD. 20771 You may also request a package of prediction bulletins for certain categories of satellites such as weather or amateur radio satellites rather than by individual CATALOG NUMBERS. If you do not know the CATALOG NUMBER of the satellites you wish to order data for, you can request the current "SATELLITE SITUATION REPORT". To the best of my knowledge, there is no charge for this document and it can be obtained from the above address. The Satellite Situation Report lists almost every satellite currently in orbit. Each satellite is cataloged by the International Designation and by Catalog number. It also lists the name, launch date, orbital period in minutes, inclination, apogee, perigee, and transmitting frequency. By using this document you can determine the catalog numbers of the satellites you wish to track with PC-TRACK. APPENDIX B HOW TO USE THE ORBITAL DATA FROM NASA The data required by PC-TRACK is contained in the Two Line Orbital Elements. As described above, these elements are a part of the NASA Prediction Bulletin described in Appendix A. The following is an example of the format of the elements received from NASA. The Two Line Orbital Elements look like this when you get them from NASA... 1 13923U 83153.41230725 0.00000215 11423-3 0 376 2 13923 98.7483 183.1938 0017844 74.4610 285.8536 14.22303248 9340 Here are the pieces that PC-TRACK requires, broken out for you... LINE 1 EPOCH YEAR PERIOD DECAY ■■ RATE │ ■■ ■─────┴──■ 1 13923U 90153.41230725 0.00000215 11423-3 0 376 ■ ■ ■ ■ ■ │ └─────┬────┘ └──────┬──────┘ │ ■ │ │ EPOCH DAY.FRACTION ■ │ NOT USED └───■ CATALOG NUMBER (ignore letter) LINE 2 CATALOG NUMBER ■ │ INCLINATION ECCENTRICITY MEAN ANOMALY │ ■ ■ ■ │ │ RIGHT ASC. │ ARGUMENT │ MEAN MOTION ┌───┤ ┌────┴┐ OF NODE │ OF PERIGEE │ ■ ■ ■ ■ ■ ■────┴─■ ■─────┘ ■────┴■ ■─────┴■ ■────┴────■ 2 13923 98.7483 183.1938 0017844 74.4610 285.8536 14.22603248 9340 ■┬■ │ REVOLUTION NUMBER■──┘ AT EPOCH NOTICE THAT THERE IS NO DECIMAL POINT PRINTED FOR ECCENTRICITY. THE DECIMAL POINT GOES IN FRONT OF THE NUMBER. FOR EXAMPLE, THE NUMBER SHOWN ABOVE FOR ECCENTRICITY WOULD BE ENTERED AS .0017844. APPENDIX C G L O S S A R Y The following are some terms used in the satellite tracking business and are described in layman's terms. APOGEE The point in a satellite's orbit farthest from the Earth's center. ARGUMENT OF PERIGEE The angular distance measured in the orbit plane, in the direction of motion of the satellite, from the point of intersection of the orbit and equatorial planes, to the perigee point. The perigee point is the point in the orbit where the satellite is closest to the earth's surface. ASCENDING NODE Point at which the satellite crosses the equatorial plane from the southern hemisphere to the northern hemisphere. (See also RIGHT ASCENSION OF THE ASCENDING NODE.) AZIMUTH The angle measured in the plane of the horizon from true North clockwise to the vertical plane through the satellite. CATALOG NUMBER A 5 digit number assigned to a cataloged orbiting satellite. This number may be found in the NASA Satellite Situation Report and on the NASA Prediction Bulletins. COORDINATED UNIVERSAL TIME (UTC) Also known as Greenwich Mean Time (GMT). Local time at zero degrees longitude at the Greenwich Observatory, England. Uses 24 hour clock, ie. 2:00 pm is 1400 hrs. CULMINATION The point at which a satellite reaches its highest position or elevation in the sky relative to an observer. (Also known as the Closest Point of Approach) DECLINATION The angular distance from the equator to the satellite measured positive north and negative south. DRAG The force exerted on a satellite by its passage through the atmosphere of the Earth, acting to slow the satellite down. ECCENTRICITY The degree of flattening of the orbit or its departure from a circle. The greater the eccentricity, the more elliptical the orbit is. ELEMENT SET See ORBITAL ELEMENTS. EPHEMERIS A tabulation of a series of points which define the position and motion of a satellite. EPOCH A specific time and date which is used as a point of reference; the time at which an element set for a satellite was last updated. EQUATORIAL PLANE An imaginary plane running through the center of the earth and the Earth's equator. INCLINATION The angle between the orbit plane and the Earth's equatorial plane, measured counter-clockwise. 0 (zero) degrees inclination would describe a satellite orbiting in the same direction as the Earth's rotation directly above the equator (orbit plane = equatorial plane). 90 degrees inclination would have the satellite orbiting directly over both poles of the earth (orbit plane displaced 90 degrees from the equatorial plane). An inclination of 180 degrees would have the satellite orbiting again directly over the equator, but in the opposite direction of the Earth's rotation. INTERNATIONAL DESIGNATOR An internationally agreed upon naming convention for satellites. Contains the last two digits of the launch year, the launch number of the year and the piece of the launch, ie. A-indicates payload, B-the rocket booster, or second payload, etc. LATITUDE Also called the geodetic latitude. the angle between the perpendicular to the Earth's surface (plane of the horizon) at a location and the equatorial plane of the earth. LONGITUDE The angular distance from the Greenwich (zero degree) meridian, along the equator. This can is measured either east or west to the 180th meridian (180 degrees) or 0 to 360 degrees west. For example, Ohio includes 85 degrees west longitude, while India includes 85 degrees east longitude. But 85 degrees east longitude could also be measured as 275 degrees west longitude. MEAN ANOMALY Angular distance measured in the orbit plane, in the direction of motion, from the perigee point to the satellite's mean position. MEAN MOTION The number of complete revolutions a satellite makes in a given unit of time, usually measured in revolutions per day. (see also DECAY) NASA PREDICTION BULLETINS Report published by NASA Goddard Space Flight Center providing latest orbital information on a particular satellite. This report gives information in 3 parts: 1) two line orbital elements, 2) Longitude of the South to North equatorial crossings, and 3) longitude and heights of the satellite crossings for other latitudes (besides the 0 degree latitude shown in part two). OBJECT A satellite. Something in space to be tracked. ORBITAL ELEMENTS Also called Classical Elements, Satellite Elements, Element Set, etc. Includes the catalog Number; epoch year, day, and fraction of day; period decay rate; argument of perigee, inclination, eccentricity; right ascension of ascending node; mean anomaly; mean motion; revolution number at epoch; and element set number. This data is contained in the TWO LINE ORBITAL ELEMENTS provided by NASA in the NASA Prediction Bulletin. PERIOD DECAY RATE Also known as Decay. This is the tendency of a satellite to lose orbital velocity due to the influence of atmospheric drag and gravitational forces. A decaying satellite eventually impacts with the surface of the Earth or burns up in the atmosphere. This parameter directly affects the satellite's MEAN MOTION. It is measured in various ways but PC-TRACK, the NASA Prediction Bulletins and the Two Line Orbital Elements use revolutions per day per day. PERIGEE - The point in the satellite's orbit where it is closest to the surface of the earth. POSIGRADE ORBIT Satellite motion which is in the same direction as the rotation of the Earth. RETROGRADE ORBIT Satellite motion which is opposite in direction to the rotation of the Earth. REVOLUTION NUMBER AT EPOCH The number of revolutions or ascending node passages that a satellite has completed at the time (epoch) of the element set since it was launched. The orbit number from launch to the first ascending node is designated zero, thereafter the number increases by one at each ascending node. RIGHT ASCENSION OF THE ASCENDING NODE The angular distance from the vernal equinox measured eastward in the equatorial plane to the point of intersection of the orbit plane where the satellite crosses the equatorial plane from south to north. SATELLITE SITUATION REPORT A report published by NASA Goddard Space Flight Center listing all known man-made Earth orbiting satellites. This report lists the Catalog Number, International Designator, Name, Country of origin, launch date, orbital period, inclination, beacon frequency, and status (orbiting or decayed). SUB-SATELLITE Location of the point of intersection of the earth's surface by a line between the center of the earth and the satellite (the point on the earth directly beneath the satellite). TWO LINE ORBITAL ELEMENTS See ORBITAL ELEMENTS. VERNAL EQUINOX Also known as the first point of Aries, being the point where the Sun crosses the Earth's equator going from south to north in the spring. This point in space is essentially fixed and represents the reference axis of a coordinate system used extensively in Astronomy and Astrodynamics.