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+--------------------------------------+ ! InstantTrack V1.00 ! ! Copyright (c) Franklin Antonio, 1989 ! +--------------------------------------+ Introduction... --------------- InstantTrack was designed to assist amateur radio operators who need to track a large number of earth-orbiting satellites, point antennas at them in real time, estimate when communications links will be possible with operators in other parts of the world, etc. InstantTrack is copyrighted software. See the copyright and distribution information later in this document. InstantTrack has several features that make it unique among satellite tracking programs, and a few features which, while not unique, are relatively uncommon among low cost satellite tracking programs. I've taken the liberty of listing a few of these here, Speed -- InstantTrack is faster than any other tracking program. Humans should never wait for computers. Ease of use -- Most commands are a single keystroke. Usually tedious functions are fully automated. Automated orbital element entry -- InstantTrack reads the popular NASA and AMSAT format satellite element files and updates its database automatically. You need never again manually enter dozens of 10 digit numbers. Automated time setting -- InstantTrack automatically sets time on your computer by accessing the NBS time service via your modem. Instant Visibility -- InstantTrack shows you the positions of your "favorite" satellites, even before you issue the first keystroke. The menu of 200 satellites shows you which are visible from your location even before you select a satellite. The menu of 1754 cities shows you which cities are visible from the selected satellite even before... etc. Graphics -- InstantTrack displays full color high resolution (EGA/VGA) maps of the Earth, showing satellite and observers position, two kinds of satellite footprint, grayline, etc. (Map projec- tion is selectable.) Users can also select either a diagram of the satellite's orbit showing orientation of the satellite, or a map of the sky, showing the satellite's position against the field of stars. You can move from map to map or satellite to satellite with a single keystroke, instantly. Large # of Sats & Stations -- InstantTrack supports a database of 200 satellites and 50 observer locations. A unique grouping feature allows you to categorize satellites, and perform most operations on either a selected group, or the entire database. City Database -- InstantTrack includes a database of 1754 cities worldwide. Locations of the satellite (sub-satellite points) and observers are displayed relative to the nearest city! Observing stations can be specified by entering as little as their city name! Grid Squares -- InstantTrack understands the gridsquare system. Observing stations can be specifyed by typing only their gridsquare. Satellite Covisibility -- InstantTrack shows you when satellites can see other satellites (i.e when crosslinks are possible), when satellites are in eclipse (in the shadow of the earth), etc. This display, of course, updates in real-time, so you can see crosslinks appear and disappear. Satellite Offpointing -- (sometimes called Squint Angle) InstantTrack computes the angle by which the satellite's antennas are pointed away from you. Helps you understand why quality of communications via satellites such as Oscar-10 and Oscar-13 (spin-stabilized satellites with directional antennas) varies. InstantTrack's graphics show you where a satellite's antennas are pointing. Maps display a contour line of squint angle. Stations within this line have low squint, and can establish the best links via such satellites. Path Loss -- InstantTrack shows the path loss between your station and the satellite in realtime. Schedules -- InstantTrack can show you the next three weeks schedule for a satellite , or one day's schedule for 20 satellites on one easy-to-read screen. Realtime Rotor Control -- InstantTrack supports realtime antenna rotor control via the Kansas-City-Tracker interface. Background Mode --A unique background mode allows you to track satellites & point antennas in real-time while you run other programs. Sun & Moon -- InstantTrack tracks the Sun & Moon as well as the satellites in its database. Fast Rise-Time Finder -- InstantTrack computes the time at which a satellite will rise over the horizon without the usual delay caused by stepping through small time increments between now and then. Tracking Multiple Stations -- You can see the computed parameters (azimuth, elevation, squint, etc) both from your perspective and from the perspective of the station at the other end of the satellite link. Documentation -- Extensive and Tutorial. Online Help -- InstantTrack contains an online help facility which can be entered from almost any screen. IT's Been Tested -- InstantTrack has been extensively beta tested by a group of 12 volunteers on three continents for six months prior to release. Required Hardware... -------------------- Any IBMPC, or AT, PS2, clone, etc with at least 512k memory. Any display type is ok for the text mode screens. Maps presently require EGA or VGA display. I'm not particularly fond of the ancient CGA boards; If you have one of those, beware that i have taken no steps to avoid 'CGA snow'. A numeric coprocessor (8087 or 80287) is NOT required, but it is recommended. InstantTrack isn't really Instant without a coprocessor, but it will still probably be faster at most things than any other tracking program. A mouse is NOT required, but can be used on the map screens. Due to the large file sizes involved, a hard disk is strongly advised. Getting Started... ------------------ There are only two things you must do to get started... set your time zone, and enter your station elements. These are described in the sections titled "Setting Your Time zone", and "Station Elements (Where Are You?)" which follow. You then run one of the following two programs... IT -- if your computer has an 8087 or 80287 ITNCP -- if your computer does NOT have an 8087 or 80287 (the letters NCP stand for No Co-Processor) Organization of This Document... -------------------------------- The remainder of this file is organized as follows... The Main Menu Screen Help Screens Time, Timezones, etc Setting Time Accurately Setting Your Time zone How Time Is Displayed and Entered Station Elements (Where Are You?) Satellite Elements & Parameters (What Are The Orbits?) Entering Satellite Elements Automatic Satellite Element Entry Manual Satellite Element Entry Satellite Elements Maintenance Functions Understanding Satellite Elements Understanding Satellite Parameters Realtime Tracking A Satellite (Text or Map) Choosing A Satellite Understanding The Real time (Text) Display Commands Controlling the Observer List Setting a Specific Time Understanding The Realtime (Map) Display Commands Driving an Automatic Antenna Rotor Satellite Position Table (Ephemeris) Parameter Entry Understanding The Display Commands Satellite Schedule Display Understanding The Display Commands Satellite Covisibility Display Understanding The Display Commands Setting Time via NBS What is NBS ACTS? Procedure What Can Go Wrong? Technical Notes re Dialing Modems, etc. Nonnumerical Geography: Maps, Cities, Gridsquares, etc. Maps Cities Gridsquares Files Used by InstantTrack Copyright Notice, Distribution Policy, etc. Warranty Acknowledgements Appendix 1 -- Example Satellite Element File Formats NASA Format AMSAT Format Bibliography The Main Menu Screen... ----------------------- The main menu is the first screen to appear when you fire up InstantTrack. This screen is a simple menu which allows you to pick among the basic functions that InstantTrack performs. Each of these functions is described in a later section of this DOC file. At the bottom of the main menu screen, there is a horizontal red line, below which appear your present pointing angles (azim/elev) to five selected satellites, and also the Sun and Moon. Each pair of angles is displayed in yellow if the object is now above your horizon, and green if it is below. (These colors are consistent in displays throughout InstantTrack) On slower computers, it may take a couple of seconds for these numbers to appear. (although on faster machines, they appear instantly) It is important for you to realize that you do not have to wait for these numbers to appear before making your menu selection. As soon as you type a key, this program will jump instantly to the desired function. That's how i've tried to make InstantTrack work -- you (almost) never wait for anything. Help Screens... --------------- InstantTrack contains a modest online help facility. Select "HELP" at the main menu to get online help, or type '?' while in any of the major function screens. You may then navigate among the help pages using the PgUp and PgDn keys. Return from a help screen by typing 'Q'. Time, Timezones, etc... ----------------------- InstantTrack must know time correctly, before it can locate satellites. The program reads your computer's DOS clock (which we assume is set to your local time zone). Local time is then converted to UTC (also known as Greenwich Mean Time) which is used in the orbit calculations. So, there are two requirements. First, you must set your computer's DOS clock reasonably accurately. Second, you must tell InstantTrack what time zone it is in. Setting Time Accurately... -------------------------- How accurately must you set your computer's DOS clock? The answer depends on orbital mechanics, and geometry. Assuming the goal is to point an antenna at a satellite, we can determine how much time error will produce a certain amount of antenna pointing error. There are several sources of antenna pointing "error" of course. Time error is just one contribution. Low-Earth-Orbiting satellites move the fastest, and therefore require the most accurate time. Consider a satellite orbiting at 250 km altitude. This is about as low as useful satellites go. The angles change fastest when the satellite is directly overhead, so we'll compute that case. Pointing error for 250km satellite directly overhead.. Time Error --> Pointing Error 1 second 1.8 degrees 10 seconds 17. degrees 1 minute 61. degrees This is a worst case! In most amateur radio satellite situations, time accurate to 30 seconds is probably fine. There are several ways to set your computer's clock. You can do it by hand, of course, getting time information from the phone company, or WWV. This works very well. InstantTrack can also set your computer's clock for you by accessing a new National Bureau of Standards (NBS) telephone time service called ACTS. With NBS-ACTS, your computer uses your modem to make a very quick long-distance call to a modem at NBS. This feature is described in more detail in a later section. Setting Your Time zone... ------------------------ You tell InstantTrack the name of the local time zone by setting a DOS environment variable called "TZ". (short for Time zone) You should put the command to set it in your autoexec.bat file, so that you never forget. You must set TZ to your time zone by executing a DOS command like this... SET TZ=PST8PDT The first three letters (PST in this case) are the name of a time zone, followed by an optionally signed number indicating the number of hours difference between UTC and your time zone, followed by an optional three letter name of a daylight-savings-time time zone. If you live in an area where daylight-savings-time is not used, you should leave off the last three letters. Other examples.. SET TZ=EST5EDT or SET TZ=MST7MDT, etc. If you don't set TZ at all, it defaults to PST. How Time is Displayed and Entered --------------------------------- Many InstantTrack screens display date and time. These dates & times may be displayed as either UTC or LOCAL time. You get to choose. Some users prefer to "think" in UTC, others become totally confused trying to mentally convert back and forth between UTC and LOCAL time. Most of us are somewhere in between. When InstantTrack starts up, time display is in UTC. At any time during most screens, you can type the Z command, which toggles the time display mode between UTC and LOCAL. (Z stands for timeZone) You can always tell which mode you're in. A realtime time display appears at the top left corner of most screens, and it contains the timezone name. For example, the time displayed might be "03/01/92 06:22:37 UTC". If i then type Z, the display will instantly become "02/29/92 23:22:37 PDT". What about time entry? A few InstantTrack screens will prompt you to enter a time. In most cases, you can just respond by typing the Enter key. InstantTrack will accept this to mean "right now". If you need to enter some other time, InstantTrack will accept any of the following formats... mm/dd/yy hh:mm:ss -- fully specified date & time mm/dd/yy hh:mm -- seconds default to 00 mm/dd/yy -- time defaults to 00:00:00 hh:mm:ss -- day defaults to today hh:mm -- and seconds default to 00 The examples above show a 2-digit year. That's all that you normally need to type. For example 90 means 1990. IT will assume that a 2-digit year is in the range [1950..2049], which is, of course, what you normally want. You may type the full 4 digit year if you wish. You may also omit leading zeros. For example 3/2/89 22:0 is a legal entry. Time entry always assumes the same timezone as time display. In other words, if you have InstantTrack displaying times in UTC, it will assume you will enter times in UTC. Station Elements (Where Are You?)... ------------------------------------ To tell InstantTrack where you are located, or where your friends are located, select "Update Station Elements" at the main menu. You will then be presented with a "Station Selection Menu". InstantTrack contains a database which remembers the locations of up to 50 stations. The first station (station #1) in this database is special. InstantTrack expects first station to be where YOU are located. The other 49 entries can be used to specify the location of stations you often communicate with. The parameters of the stations you enter in the station database will be saved on disk (in the file IT.QTH), and will be available next time you run InstantTrack. The program also understands the concept of a "visiting station", that is one you may want to define for the moment, but which does not get entered into the permanent database. More about visitors later. Pick a station to edit. The first time you run InstantTrack, you should edit station #1 so that it represents your station's location! A station edit screen will appear, and the present station latitude, longi- tude, and elevation above sea level will be displayed, along with some "computed information" which is displayed to help you verify that you've entered your station location correctly. Editing station data is simple. Use up-arrow and down-arrow keys to move the cursor to the line you want to change. To change a value, type the = key followed by the new value. Type the enter key to enter the value. To exit this screen, type the Q key. (All screens in InstantTrack exit when you type the Q key. Q stands for Quit.) Latitude and longitude are entered in degrees. (Not degrees:minutes:seconds) Latitude must be a number in the range [-90,+90]. Longitude must be a number in the range [-180,+180]. Altitude is measured in meters above sea-level. By convention, longitude is negative to the West of the Greenwich Meridian, and positive to the East. Some satellite tracking programs have used the opposite convention, so be alert. *All stations in the United States have negative longitude.* If I forget the minus sign when entering my station longitude, I move from "17 mi NW of San Diego, CA" to "161 mi South of Suchow, China". This could happen to you too. Beware. You should try to find your latitude and longitude to at least two places after the decimal point. Altitude is not nearly so important; you can guess. Satellite Elements & Parameters (What Are The Orbits?)... --------------------------------------------------------- Satellite Orbital Elements are numbers that tell us the orbit of each satellite. Elements for common satellites are distributed through amateur radio bulletin boards, and other means. InstantTrack comes with elements for many satellites already defined. You can update these elements by telling InstantTrack to read in files containing new elements, or by entering elements manually. InstantTrack can read satellite element files in two common formats. Entering satellite elements is easy. Understanding them is a bit more difficult. I have tried to make the section titled "Understanding Satellite Elements" as easy to read as possible. In addition to the "classical" Orbital Elements, InstantTrack's satellite database contains several other pieces of information about each satellite (schedule, beacon frequency, etc). These are stored in the same database, and edited the same way that the orbital elements are edited. They're described in a separate section below, titled "Understanding Satellite Parameters". Entering Satellite Elements --------------------------- Satellite elements are widely distributed via Amateur Radio bulletin boards of both the telephone and the packet radio variety. They are also distrib- uted in the HAMNET forum on CompuServe (a commercial service), and via the rec.ham-radio newsgroup on Internet and Usenet. Many amateurs involved in satellite operation have tuned in to one of these sources. These sources have a tremendous advantage over printed sources (AMSAT newsletters, NASA Predic- tion Bulletins, etc), because the elements are available in computer-readable form. There are two common formats in which orbital elements are distributed. These are called the "NASA" and "AMSAT" formats. Both are ascii text files that are both human and computer-readable, although the "NASA" format is difficult for humans to read. InstantTrack can read either format. Ideally, you will find a source for elements in computer-readable form, and never be forced to type in elements by hand! To enter satellite elements, select "Update Satellite Elements" on the main menu. This will take you to the Update Elements menu. Here you can choose from a variety of satellite database update functions... 1. ALL: Read in elements for ALL satellites in file. 2. ONE: Read in elements for ONE specific satellite. 3. UPDATE: Read in elements for ALL satellites EXCEPT those for which the program already has newer elements. 4. OLD: Delete satellites with old orbital elements. 5. CRASH: Delete satellites that have crashed. 6. DELETE: Delete a satellite manually. 7. SQUISH: Compact the satellite elements database. 8. EDIT: View / Edit satellite elements by hand. These functions are described below. Automatic Sat. Element Entry ---------------------------- In most cases, you will probably specify option 3. Under option 3, as InstantTrack reads in elements for each satellite, it compares the Epoch of the element set in the database to the Epoch of the element set in the file. The element set from the file is only read in if its Epoch is later than the Epoch of the element set you already have. There are some interesting cases where you may wish to update only the ele- ments for one particular satellite (option 2). For example, shortly after Oscar 13 was launched, an incorrect NASA element set was widely distributed. If you load new elements, then find that the orbit for one satellite is fouled up, you can use this feature to recover an older set of elements for that satellite (assuming you have kept the AMSAT or NASA text files around). You will be asked whether the file is in "NASA" or "AMSAT" format and the name of the "NASA" or "AMSAT" file you want to read. Examples of these formats can be found in an appendix at the end of this document As InstantTrack reads the file, it lists the name of each satellite it finds, followed by a brief description of what action was taken. This may be... "updated" meaning the element set was correctly formatted, and has been read into the database, or "mandatory fields missing or misformatted" meaning that part of the file you are reading in was garbled, or "no match; no action" meaning that particular satellite did not match the name you specified (under option 2), or "file contains old elements; no action" meaning that elements read from the file contained elements with an earlier Epoch than the corresponding element set already in the database (under option 3), or "no space in database" which is self-explanatory, "mod 10 line checksum failed" which means that a line of text in a NASA format file was garbled There are several other similar messages possible while reading NASA format files. Because NASA format files are a little human-unfriendly, the program prints the offending line in the file with the error message, and asks you whether you want to continue with the next satellite in the file, or quit. If you have trouble reading a file of satellite elements, look at the file format information in the appendix. Note that AMSAT format files contain guide words that InstantTrack uses to locate each orbital element. This allows the program to ignore extraneous information which might appear in the file (explanatory headings, etc). NASA format files, on the other hand, have a rigid structure, with no guide words. Therefore, you must ensure that NASA format files do not contain extraneous text. The file must contain 3 lines of text for each satellite (as described in the appendix) and nothing else. You may need to strip extraneous headers or other text from a NASA file using your favorite text editor before feeding it to InstantTrack. After updating satellite elements, the database file IT.ORB is automatically updated. Manual Satellite Element Entry ------------------------------ To examine orbital elements of satellites in the InstantTrack database, or manually enter or edit them, specify option 8 (View / Edit Satellite Elements) on the Update Sat. Elements screen. InstantTrack will then present you with a satellite selection menu, so that you can specify which satellite elements you want to view or edit. After you pick a satellite, the "Manual Edit Satellite Elements" screen will appear, showing the present elements for the satellite you picked. For example... Satellite: ao-13 Object Number: 19216 NASA Designation: 1988-51b Epoch Time, T0: 88 361.0000000 12/26/1988 00:00:0.00 Epoch Rev, K0: 377 Mean Anomaly, M0: 126.35640° Mean Motion, N0: 2.096985043 Inclination, I0: 57.40580° Eccentricity, E0: 0.66206910 Arg Perigee, W0: 195.23090° R.A.A.N., O0: 228.38820° Beacon Frq, F1: 145.8120 Decay, N1: 7.00000e-008 Schedule: 003B100J150B240O Attitude: 2,212 Diameter: 3 Groups: a The meaning of each of these values is explained in the following section labelled "Understanding Satellite Elements". At this point the following commands can be used... Up Arrow -- move cursor to previous element Down Arrow -- move cursor to next element Left Arrow -- move to previous satellite in database Right Arrow -- move to next satellite in database = -- edit this element D -- view derived values Q -- quit editing. go back to main menu To change the value of an element, move the cursor to the appropriate line, type the = key, then type a new value for the element, followed by the enter key. The program will not allow inappropriate values to be entered. Note that Epoch Time is displayed on two lines. The first line displays epoch as a year and day number. The second line displays the same epoch in common units. Epoch may manually entered on either of these two lines. Enter on the first line if you are typing a time in the year and day number format, and on the second line if you are using the more familiar m/d/y h:m:s form. As you make changes to the elements, these changes are recorded in the copy of the satellite elements database that InstantTrack is holding in memory. If you have changed any elements, InstantTrack will ask you whether the changes should be written to the satellite elements file on disk. The D command causes derived values to appear on the right hand side of the screen. These values are explained below, in the section labelled "Under- standing Derived Values". Satellite Elements Maintenance Functions ---------------------------------------- The Update Satellite Elements Menu allows you to do some additional things besides the basic functions described above. Specifically... 4. OLD: Delete satellites with old orbital elements. 5. CRASH: Delete satellites that have crashed. 6. DELETE: Delete a satellite manually. 7. SQUISH: Compact the satellite elements database. Because InstantTrack can handle such a large number of satellites, you will probably never need to delete anything from the database. My philosophy is that if you don't NEED to delete objects, then you should probably leave them in the database, and i urge you to adopt this philosophy. However, if you often load elements for short-lived objects or missions (discarded boosters, shuttle missions, etc) the database may become cluttered with entries which are no longer valid, or the database may simply fill up. Selections 4,5,6 allow you to get rid of unwanted objects. Option 4 "OLD" deletes all satellites with an epoch older than some number of days. You can specify the age cutoff. It defaults to 100 days. Option 5 "CRASH" deletes all satellites where IT computes a perigee which is below the surface of the earth. The object may have actually crashed, or the element set you have may no longer be valid. The files of NASA elements distributed by T.S.Kelso often contain some very short-lived objects. It is not uncommon to find a couple of objects that crash within days after you get a new file of elements. It is not necessary to delete these objects, but IT will find them and delete them for you if you wish. Option 6 lets you delete a specific satellite. This is straightforward. Option 7: As you delete satellites from the database, you leave holes. In other words, if you delete satellite #33, then #33 will show as blank on the satellite menu. Option 7 slides all the satellites down in the database to fill in the holes. This is also entirely optional. Understanding Satellite Elements -------------------------------- Seven numbers are required to define a satellite orbit. This set of seven numbers is called the satellite orbital elements, or sometimes "Keplerian" elements (after Johann Kepler [1571-1630]), or just elements. These numbers define an ellipse, orient it about the earth, and place the satellite on the ellipse at a particular time. In the Keplerian model, satellites orbit in an ellipse of constant shape and orientation. The real world is slightly more complex than the Keplerian model, and the program compensates for this by introducing minor corrections to the Keplerian model. These corrections are known as perturbations. The perturbations that this program knows about are due to the lumpiness of the earth's gravitational field (which luckily you don't have to specify), and the "drag" on the satellite due to atmosphere. Drag becomes an optional eighth orbital element. Orbital elements remain a mystery to most people. This is due i think first to the aversion many people (including me) have to thinking in three dimensions, and second to the horrible names the ancient astronomers gave these seven simple numbers and a few related concepts. To make matters worse, sometimes several different names are used to specify the same number. Vocabulary is the hardest part of celestial mechanics! The basic orbital elements are... 1. Epoch 2. Orbital Inclination 3. Right Ascension of Ascending Node 4. Argument of Perigee 5. Eccentricity 6. Mean Motion 7. Mean Anomaly And the optional... 8. Drag The following definitions are intended to be easy to understand. More rigor- ous definitions can be found in almost any book on the subject. I've used aka as an abbreviation for "also known as" in the following text. 1. "Epoch" [aka "Epoch Time" or "T0"] A set of orbital elements is a snapshot, at a particular time, of the orbit of a satellite. Epoch is simply a number which specifies the time at which the snapshot was taken. 2. "Orbital Inclination" [aka "Inclination" or "I0"] The orbit ellipse lies in a plane known as the orbital plane. The orbital plane always goes thru the center of the earth, but may be tilted any angle relative to the equator. Inclination is the angle between the orbital plane and the equatorial plane. By convention, inclination is a number between 0 and 180 degrees. Some vocabulary: Orbits with inclination near 0 degrees are called "equatorial" orbits (because the satellite stays nearly over the equator). Orbits with inclination near 90 degrees are called "polar" (because the satellite crosses over the north and south poles). The intersection of the equatorial plane and the orbital plane is a line which is called the "line of nodes". More about that later. 3. "Right Ascension of Ascending Node" [aka "RAAN" or "RA of Node" or "O0" and occasionally called "Longitude of Ascending Node"] RAAN wins the prize for most horribly named orbital element. Two numbers orient the orbital plane in space. The first number was Inclination. This is the second. After we've specified inclination, there are still an infinite number of orbital planes possible. The "line of nodes" can poke out the anywhere along the equator. If we specify where along the equator the line of nodes pokes out, we will have the orbital plane fully specified. The line of nodes pokes out two places, of course. We only need to specify one of them. One is called the ascending node (where the satellite crosses the equator going from south to north. The other is called the descending node (where the satellite crosses the equa- tor going from north to south)). By convention, we specify the location of the ascending node. Now, the earth is spinning. This means that we can't use the common latitude/longitude coordinate system to specify where the line-of-nodes points. Instead, we use an astronomical coordinate system, known as the right_ascension/declination coordinate system, which does not spin with the earth. Right ascension is another fancy word for an angle, in this case, an angle measured in the equatorial plane from a reference point in the sky where right ascension is defined to be zero. This point is called, by astronomers, the vernal equinox. Finally, "right ascension of ascending node" is an angle, measured at the center of the earth, from the vernal equinox to the ascending node. I know this is getting complicated. Here's an example. Draw a line from the center of the earth to the point where our satellite crosses the equa- tor (going from south to north). If this line points directly at the vernal equinox, then RAAN = 0 degrees. By convention, RAAN is a number in the range 0 to 360 degrees. I used the term "vernal equinox" above without really defining it. If you can tolerate a minor digression, i'll do that now. Teachers have told children for years that the vernal equinox is "the place in the sky where the sun rises on the first day of Spring". This is a horrible definition. Most teachers, and students, have no idea what the first day of spring is (except a date on a calendar), and no idea why the sun should be in the same place in the sky on that date every year. You now have enough astronomy vocabulary to get a better definition. Consider the orbit of the sun around the earth. I know in school they told you the earth orbits around the sun, but the math is equally valid either way, and it suits our needs at this instant to think of the sun orbiting the earth. The orbit of the sun has an inclination of about 23.5 degrees. (Astronomers don't usually call this 23.5 degree angle an 'inclination', by the way. They use an infinitely more obscure name: 'The Obliquity of The Ecliptic'.) The orbit of the sun is divided (by humans) into four equally sized portions called seasons. The one called Spring begins when the sun pops up past the equator. In other words, the first day of Spring is the day that the sun crosses through the equatorial plane going from South to North. We have a name for that! It's the ascending node of the Sun's orbit. So finally, the vernal equinox is nothing more than the ascending node of the Sun's orbit. The Sun's orbit has RAAN = 0 simply because we've defined the Sun's ascending node as the place from which all ascending nodes are measured. The RAAN of your satellite's orbit is just the angle (measured at the center of the earth) between the place the Sun's orbit pops up past the equator, and the place your satellite's orbit pops up past the equator. 4. "Argument of Perigee" [aka "ARGP" or "W0"] Argument is yet another fancy word for angle. Now that we've oriented the orbital plane in space, we need to orient the orbit ellipse in the orbital plane. We do this by specifying a single angle known as argument of perigee. A few words about elliptical orbits.. The point where the satellite is closest to the earth is called perigee, although it's sometimes called periapsis or perifocus. We'll call it perigee. The point where the satellite is farthest from earth is called apogee (aka apoapsis, or apifocus). If we draw a line from perigee to apogee, this line is called the line-of-apsides. (Apsides is, of course, the plural if apsis.) I know, this is getting complicated again. Sometimes the line-of-apsides is called the major-axis of the ellipse. It's just a line drawn through the ellipse the "long way". The line-of-apsides passes through the center of the earth. We've previously identified another line passing through the center of the earth. That was the line-of-nodes. The angle between these two lines is called the argument of perigee. Where any two lines intersect, they form two complimentary angles, so to be specific, we say that argument of perigee is the angle (measured at the center of the earth) from the ascending node to perigee. Example: When ARGP = 0, the perigee occurs at the same place as the ascending node. That means that the satellite would be closest to earth just as it rises up over the equator. When ARGP = 180 degrees, apogee would occur at the same place as the ascending node. That means that the satellite would be farthest from earth just as it rises up over the equator. By convention, ARGP is an angle between 0 and 360 degrees. 5. "Eccentricity" [aka "ecce" or "E0" or "e"] This one is simple. In the Keplerian orbit model, the satellite orbit is an ellipse. Eccentricity tells us the "shape" of the ellipse. When e=0, the ellipse is a circle. When e is very near 1., the ellipse is very long and skinny. (To be precise, the Keplerian orbit is a conic section, which can be either an ellipse, which includes circles, a parabola, a hyperbola, or a straight line! But here, we are only interested in elliptical orbits. The other kinds of orbits are not used for satellites, at least not on purpose, and InstantTrack isn't programmed to handle them.) For our purposes, eccentricity must be in the range 0 <= e < 1. 6. "Mean Motion" [aka "N0"] (related to "orbit period" and "semimajor-axis") So far we've nailed down the orientation of the orbital plane, the orientation of the orbit ellipse in the orbital plane, and the shape of the orbit ellipse. Now we need to know the "size" of the orbit ellipse. In other words, how far away is the satellite? Kepler's third law of orbital motion gives us a precise relationship between the speed of the satellite and its distance from the earth. Satellites that are close to the earth orbit very quickly. Satellites far away orbit slowly. This means that we could accomplish the same thing by specifying either the speed at which the satellite is moving, or its distance from the earth! Satellites in circular orbits travel at a constant speed. Simple. We just specify that speed, and we're done. Satellites in non-circular (i.e eccentricity > 0) orbits move faster when they are closer to the earth, and slower when they are farther away. The common practice is to average the speed. You could call this number "average speed", but astronomers call it the "Mean Motion". Common units are revolutions per day. We have to be careful, even with simple words like revolution. In this context, a revolution or period is defined as the time from one perigee to the next. Sometimes "orbit period" is specified as an orbital element instead of Mean Motion. Period is simply the reciprocal of Mean Motion. A satellite with a Mean Motion of 2 revs per day, for example, has a period of 12 hours. Sometimes semi-major-axis (SMA) is specified instead of Mean Motion. SMA is one-half the length (measured the long way) of the orbit ellipse, and is directly related to mean motion by a simple equation. Typically, satellites have Mean Motions in the range of 1 rev/day to about 16 rev/day. 7. "Mean Anomaly" [aka "M0" or "MA" or "Phase"] Now that we have the size, shape, and orientation of the orbit firmly established, the only thing left to do is specify where exactly the satellite is on this orbit ellipse at some particular time. Our very first orbital element (Epoch) specified a particular time, so all we need to do now is specify where, on the ellipse, our satellite was exactly at the Epoch time. "Anomaly" is yet another astronomer-word for angle. Mean anomaly is simply an angle that marches uniformly in time from 0 to 360 degrees during one revolution. It is defined to be 0 degrees at perigee, hence is 180 degrees at apogee. If you had a satellite in a circular orbit (therefore moving at constant speed) and you stood in the center of the earth and measured this angle from perigee, you would point directly at the satellite. Satellites in non-circular orbits move at a non-constant speed, so this simple relation doesn't hold. This relation does hold for two important points on the orbit, however, no matter what the eccentricity. Perigee always occurs at MA = 0, and apogee always occurs at MA = 180 degrees. It has become common practice with radio amateur satellites to use Mean Anomaly to schedule satellite operations. Satellites commonly change modes or turn on or off at specific places in their orbits, specified by Mean Anomaly. Unfortunately, when used this way, it is common to specify MA in units of 256ths of a circle instead of degrees! To minimize confusion, when I display MA in units of 256ths of a circle, I call it "Phase" instead of "Mean Anomaly". When entering Mean Anomaly as an orbital element, it must, however, be specified in degrees, between 0 and 360! Example: Suppose Oscar-99 has a period of 12 hours, and is turned off from Phase 240 to 16. That means it's off for 32 ticks of phase. There are 256 of these ticks in the entire 12 hour orbit, so it's off for (32/256)x12hrs = 1.5 hours. Note that the off time is centered on perigee. Satellites in highly eccentric orbits are often turned off near perigee when they're moving the fastest, and therefore difficult to use. 8. "Drag" [aka "N1"] Drag caused by the earth's atmosphere causes satellites to spiral downward. As they spiral downward, they speed up. The Drag orbital element simply tells us the rate at which Mean Motion is changing due to drag or other related effects. Precisely, Drag is one half the first time derivative of Mean Motion. Its units are revolutions per day per day. It is typically a *very* small number. Common values for low-earth-orbiting satellites are on the order of 10^-4. Common values for high-orbiting satellites are on the order of 10^-7 or smaller. Occasionally, published orbital elements for a high-orbiting satellite will show a negative Drag! At first, this may seem absurd. Drag due to friction with the earth's atmosphere can only make a satellite spiral downward, never upward. There are several potential reasons for negative drag. First, the measurement which produced the orbital elements may have been in error. It is common to estimate orbital elements from a small number of observations made over a short period of time. With such measurements, it is extremely difficult to estimate Drag. Very ordinary small errors in measurement can produce a small negative drag. The second potential cause for a negative drag in published elements is a little more complex. A satellite is subject to many forces besides the two we have discussed so far (earth's gravity, and atmospheric drag). Some of these forces (for example gravity of the sun and moon) may act together to cause a satellite to be pulled upward by a very slight amount. This can happen if the Sun and Moon are aligned with the satellite's orbit in a particular way. If the orbit is measured when this is happening, a small negative Drag term may actually provide the best possible 'fit' to the motion the satellite is actually performing over a *short* period of time. You typically want a set of orbital elements to estimate the position of a satellite reasonably well for as long as possible. (often several months) Negative Drag never accurately reflects what's happening over a long period of time. This program will accept negative values for Drag, but I don't approve of them. Feel free to substitute zero in place of any published negative Drag value. Understanding Satellite Parameters ---------------------------------- All the satellite parameters described below are optional. They allow InstantTrack to perform some of its more sophisticated (and fun) calculations, so you are urged to read this section, even though you are not required to enter these parameters. Beacon Frequency You can specify a frequency of interest for each satellite. This is typically the frequency of a beacon transmitter on the satellite. This number is used in the calculation of doppler, path loss and Tsky. (Doppler and path loss are described in the section on realtime tracking.) Schedule Many satellites have several operating modes, and switch from one mode to another at predefined places in their orbits. InstantTrack understands satellite schedules which are based on "phase" (mean anomaly expressed in units of 256ths of a circle.) This is the common scheduling technique for amateur radio satellites. If given a schedule, InstantTrack will calculate and display the satellite mode. The schedule is a string of numbers and letters. A three digit number specifies the phase at which a mode begins, then a single letter specifies the mode. This is repeated up to 6 times. (In other words, a schedule may contain up to six mode changes, but no more.) The numbers in the string should be in an ascending sequence. No spaces are allowed. For example, a recent OSCAR-13 schedule read... Phase Mode 000-002 Off 003-099 mode-B 100-149 mode-JL 150-239 mode-B 240-255 Off The schedule string you would enter into InstantTrack in this case is 002B100J150B240O . Read this as, "At phase 002 change to mode B. At phase 100 change to mode J.", etc. Attitude The spacecraft attitude is a measure of how the satellite is oriented in space. Hopefully, it is oriented so that its antennas point toward earth! There are several orientation schemes used in satellites. This program assumes that the satellite maintains a constant inertial orientation, i.e that it's antennas point a fixed direction in space. (true of some, but not all satellites). Such a satellite is sometimes called spin-stabilized. If spacecraft attitude has not been set, then it will display as "None Set" in the satellite element editor. In this case, InstantTrack will not know the spacecraft attitude, and therefore will not calculate offpoint (squint) angles, or the good squint angle regions on the map. This will not affect operation of the more basic calculations (Azimuth, Elevation, Doppler, etc). Attitude is optional. Attitude is described by two angles, often called Bahn Latitude, and Bahn Longitude. These are published from time to time for the elliptical-orbit amateur radio satellites in the AMSAT ASR, and they don't often change. All you have to do is enter these two numbers, LATITUDE FIRST, then a comma, THEN LONGITUDE. For highly elliptical orbits (Oscar-10, Oscar-13, etc) these numbers are usually in the vicinity of: 0,180. This means that the antennas point directly toward earth when the satellite is at apogee. These two numbers describe a direction in a spherical coordinate system, just as geographic latitude and longitude describe a direction from the center of the earth. In this case, however, the primary axis is along the vector from the satellite to the center of the earth when the satellite is at perigee. It's yet another coordinate system! An excellent description of Bahn coordinates can be found in Phil Karn's "Bahn Coordinates Guide". See the bibliography. Diameter This parameter gives InstantTrack a rough idea of the size of the satellite. Diameter is specified in units of Meters. In version 0.93, this param. is not yet used. Groups Because InstantTrack contains such a large database of satellites, it is convenient to categorize satellites in the database, so that some functions can operate on a subset of the database. There are 27 "groups" of satel- lites that you are allowed to define. They are named A thru Z, and ! . There are also two predefined groups named * and %. Each satellite may be a member of up to eight groups. The following groupnames have special meaning... * -- This group contains all satellites. ! -- Your "favorite satellites" group. Displayed on main menu. % -- All satellites that do not belong to an A-Z group. Here are some groups that I have defined. You may use these same meanings for these letters, or any other meanings you choose. A = Amateur Radio Satellites (Oscars) G = GPS (Navstar) Navigation Satellites L = Low Earth Orbiting Satellites P = Pacsats (Amateur Packet-Radio Satellites) R = Russian Satellites W = Weather Satellites You specify which groups a satellite is in by entering a "groups" string in the satellite element editor. Example: The satellite RS10 shows Groups: rla This means it is Russian and Low-Earth-Orbiting and an Amateur Radio Satellite. Understanding Derived Values ---------------------------- The D command causes several "derived values" to be displayed on the right hand side of the satellite elements edit screen. These numbers are derived from the orbital elements of each satellite (but are not easily computed in your head). They are intended to provide a more convenient description of the orbit (at least for humans), than the original elements. Epoch Age This is simply the time since the "epoch". This tells you how old the orbital element set has become. Satellite Age This is a quick and dirty estimate of how long ago the satellite was launched. It is computed from Epoch Rev and Mean Motion. Of course, mean motion changes during a satellite's life, and the elements don't give us any historical information, so we just assume for this calculation that mean motion has been constant. For most satellites, the error in the computed age seems to be less than 1%. For low-earth-orbiting satellites near end-of-life, the error will be larger, because mean-motion HAS been changing. For Oscar-10, the computed age may be completely wrong, depending on the source of your elements, because NASA publishes an incorrect epoch rev! Orbital Period This is the duration of one orbit, measured from perigee to perigee. Computed from mean-motion and decay. Perigee Height Apogee Height This is the distance from the earth's surface to the satellite (ie height) when the satellite is closest (ie at perigee), and farthest (ie at apogee). Latitude of Apogee Satellites in highly elliptic orbits are usually used when they are near apogee. It is therefore useful to picture above what part of the earth apogee will occur. Latitude of apogee is computed from argument of perigee and R.A.A.N. Because both of these quantities change with time, latitude of apogee also changes with time. Both the present value and rate of change are shown. Argument of Perigee & R.A.A.N. These values change with time. (The values contained in the orbital elements are the values as they were at Epoch.) Both the present value and rate of change are shown on the right hand side of the screen. Realtime Tracking a Satellite...(Text or Map Version) ----------------------------------------------------- When you choose either of the "Realtime Track 1 Satellite" items on the main menu, you are immediately presented with a satellite selection menu. After you choose a satellite, all the information about that satellite appears. Choosing a Satellite -------------------- The satellite selection menu appears whenever you enter any mode which will display information about one particular satellite. Initially, you see the first page of the menu, which contains the first 50 satellites. You can use the PgUp and PgDn keys to move between pages of the menu. The satellite names are displayed in one of three colors: white, green, or yellow, with the following meanings.. White -- InstantTrack has not recently calculated this sat's position. Green -- This satellite is below the horizon right now. Yellow -- This satellite is above the horizon right now. All are initially white, of course. While waiting for you to make your choice, InstantTrack whips thru all the satellites in the database, calculat- ing their position, turning each name green or yellow. This only takes a few seconds, and lets you know, even before selecting a satellite, whether or not it is above the horizon! Initially, the selection menu displays all satellites in the database. There is also a "group" command which restricts the selection menu to display only a certain group of satellites. The group command is the character "g" followed by a one-letter group name. The group concept is explained in the section on satellite parameters. After you select your satellite, and type Enter, the realtime tracking screen appears. You do NOT need to wait for the names to change color before typing your choice. Understanding The Realtime (Text) Display ----------------------------------------- This screen contains almost everything you would ever want to know about the present location of one satellite, and the view of that satellite from one or several observers on Earth. The display normally operates in realtime, which means that it displays information about the satellite which is valid right now. It is also possible to enter a specific time, which is not "right now" using the T command. Included on this screen are... Azimuth and Elevation.. These are the angles you use to point an antenna from your station to the satellite. When Elevation is negative, the satellite is below the horizon, and not visible from your station. Range and dR/dt Range is the distance (in km) from your station to the satellite. dR/dt is the rate at which Range is changing, in (km/second). dR/dt determines Doppler. Offpointing Angle (OFP) Many satellites use directional antennas. Unfortunately, the satellite antenna is seldom pointed directly at you! This angle is a measure of how far away from you the satellite antenna is pointed. It is 0 degrees when the satellite antenna is pointed directly at you. If you know the beamwidth of the satellite antenna (this information has been published) you can estimate how much degradation the link will suffer due to the offpointing. For example, if the satellite has an antenna with a 3db beamwidth of 24 degrees, (i.e 12 degree half-beamwidth) then you will suffer 3db of loss when the offpoint angle is 12 degrees. When the offpointing is more than twice the half-beamwidth, it becomes difficult to predict the satellite antenna's performance, because you're in the region where antenna sidelobes begin to appear. Oscar-10 and Oscar-13 both have considerable asymmetries in some of their antennas. Because the satellites are spinning, these antenna asymmetries cause the signal to vary in amplitude. This is often called spin modulation. The spin modulation should be least when the offpoint- ing angle is small. This angle is sometimes called "squint". Path Loss Path Loss is the amount by which a signal is attenuated as it travels from your station to the satellite, or vice versa. This is a function of frequency (as set in the satellite element database), and range from your station to the satellite. Path loss is only displayed if the current satellite is above the horizon, and a frequency has been entered for this satellite in the database. Satellites commonly operate on two or more frequencies simultaneously. At this time, I only display the path loss at one frequency. You can scale this number to produce path loss at a different frequency if you wish. Path loss increases 1dB for every 12.2% increase in freq. For example, amateur radio satellites often use uplink/downlink bands separated in frequency by a factor of 3. (i.e 145MHz / 435MHz) A factor of 3 in frequency corresponds to approx 9.5dB change in path loss. I suggest you use path loss as a relative indication (for a given frequency, mode, earth station configuration, etc.) of expected link quality. Satellite communications is almost always downlink limited. The downlink signal power available at your receiver is (all numbers in dB)... Transmitter power + Xmit antenna gain + Path Loss + Rcv antenna gain If all other things were constant, receive signal power would vary directly with path loss. If you keep track of the path loss shown on the screen when communications is possible, ***ADD MORE HERE*** Subsatellite Point ... If you draw a line from the satellite to the center of the earth, the point where this line intersects the earth's surface is called the subsatellite point. The coordinates of the subsat point are displayed three different ways. Latitude/Longitude... This is the coordinate system in which the subsat point is traditionally displayed. It is useful when comparing results against other programs. Unfortunately, most humans don't think in terms of latitude and longitude. These are not user-friendly coordinates. Nearest City... This is the user-friendly way to describe a location on the earth. It displays the distance and direction to the nearest city. The nearest city is chosen from InstantTrack's database of over 1700 cities worldwide. For example, the subsat point lat=40.0, lon= -110.0 would be displayed as "142.7 Km East of Provo, Utah". ARRL Gridsquare... Radio Amateur operators sometimes use a gridsquare coordinate system to identify places on the earth. InstantTrack also displays the subsat point as a gridsquare. Our example [40.0,-110.0] is in gridsquare DM59ax. An article listed in the bibliography describes the gridsquare system. Phase This is a number that increments from 0 thru 255 during each orbit of the satellite. See the discussion of mean anomaly in the "Understanding Satellite Elements" section. Mode This is the operating mode of the satellite. Determined by the satell- ite schedule. See "Understanding Satellite Parameters" for a discussion of schedules. Note that mode will only be displayed if a valid schedule has been entered for this satellite. XYZ-Coordinates These are the coordinates of the satellite and the observer in the cart- esian geocentric inertial coordinate system. These are called IJK coordinates in some books. The X axis points from the center of the earth toward the vernal equinox. The Y axis points 90 degrees to the east of the X axis. The Z axis points straight up thru the North Pole. Units are Kilometers. All the other numbers on this screen are calcu- lated from the cartesian coordinates of the satellite and observer. Next Rise/Set This is the time at which the satellite is next expected to rise or set over the horizon. This is only calculated if you have enabled this feature, via the "w" command. R.A. / Dec These are the Right Acension and Declination of the satellite as viewed from your location. Right Acension and Declination are coordinates used by astronomers to locate objects in the sky. They are similar to longi- tude and lattitude, except that they represent locations on the celest- ial sphere instead of the Earth. R.A. and Dec are the coordinates shown on star charts. Tsky This is the sky noise temperature in the direction of the satellite (ie the direction in which your antennas are pointed). The stars generate radio noise. (That's what Radio Astronomy is about.) This noise is largest when your antennas are pointed toward the plane of the galaxy (also known as the milky way), and very large when pointed toward the center of the galaxy. Tsky also depends on frequency. (Tsky is larger at lower frequencies.) If you have entered a frequency in the satellite database for a particular satellite then InstantTrack will compute and display the expected sky temperature. Noise temperatures can be added directly. You can therefore add Tsky to the temperatures of other noise sources in your receiving system (preamp, cable attenuation, sidelobes) when calculating receiving system performance. See the ARRL Handbook. Commands -------- While in the realtime tracking (text) screen, the following one-character commands apply... space -- freeze/unfreeze the display. B -- enable/disable the bottom-row display C -- enable/disable nearest-city display E -- look at orbital elements for this satellite I -- enable/disable display of XYZ coordinates. O -- add/delete a station (observer). W -- enable/disable computation & display of next rise/set time. R -- enable/disable antenna rotor control S -- enable/disable RA/Dec/Tsky display T -- set a specific time, or return to realtime. Q -- quit tracking. go back to main menu. Left Arrow -- advance to next satellite. Right Arrow -- go back to previous satellite. If you don't remember all these commands, remember that you can type ? while the realtime text screen is running, and this menu of possibilities will appear instantly on your screen. To exit that help screen, as usual, type Q. All these commands should operate in a fairly obvious fashion except for the "O" and "T" commands, which are described here... Setting a Specific Time ----------------------- InstantTrack normally displays satellite positions in realtime. In other words, the calculations assume the position of the earth and satellite "right now". If you want to see the calculations for some specific time, type the character T. You will then be prompted to enter a specific time. Here, and all other places that InstantTrack prompts for a time, any of several formats will be accepted. See the section "How Time is Displayed and Entered" for more detail. You can return to realtime calculations by typing T followed by a return. Controlling the Observer-List ----------------------------- The realtime text screen will display station-related parameters (azimuth, elevation, squint, path-loss, etc) for a list of up to four stations. When you first fire up the screen, only one station is shown. This is always the first station (station #0) from the station database. This section describes how you can add stations to or delete stations from the station list using the "O" command. After you type "O", you will be prompted to specify the station you want to add to the list... Observer name, city, gridsquare, lat/lon, s, c, or d# : What this prompt tells you is that you can type almost anything you know about the observer you'd like to add, and InstantTrack will try to use that information. Because there are several options here, the explanation begins to sound complicated. Stay tuned. It's very simple! We'll take these one at a time. If you know the name (callsign) of the station you'd like to add, and that station is in the station database, you can just type the callsign. InstantTrack will search the database, and find the station information. For example, if you've just started a conversation with KB5MU via your favorite satellite, then you can just type KB5MU. If you know the station you want to add is in the database, but you can't remember the callsign, then you can type "s", which gets you to the station selection menu, which displays all the stations which you have defined, and where you can pick the station you want. If the station you want to add is not in the station database, and you don't want to take the time to edit the database, you can describe a "visiting" station. This can be done several ways!. By city name, gridsquare, or latitude/longitude... If you know the gridsquare of the station you want to add, you can just type the gridsquare. For example, if you've started a conversation with someone who says he's at grid "DM12", then you can just type DM12 . Either the four character or six character gridsquare will be accepted. Most Amateur Radio operators know their gridsquare. Asking "What's your gridsquare?" then typing it into InstantTrack is usually a very convenient way to get the station at the "other end" of the satellite link into your computer. If you know the name of a reasonably large city (large enough to be in InstantTrack's database of 1754 cities) near the fellow you want to add, you can just type the name of the city or any part of the name! InstantTrack will search the city database, and display a menu of cities that matched the string you typed, allowing you to select which one you want. For example, if you type "Berlin", the menu will have two entries: "New Berlin, WI" and "West Berlin, West Germany". If you have trouble spelling the name of the city.. Is it "Gdansk" or "Gadansc" or "Gedansik"? You can just type "Poland". All the cities InstantTrack knows about in Poland will be displayed, and you can pick the one you want. You can also enter a menu of all cities known to InstantTrack by typing "c". Finally, if you know the latitude and longitude of the station you want to add, you can just type them in. Type latitude first, followed by a slash, then longitude. If he's at the north pole, for example, you would type 90/0 . The "O" command can also be used to delete a station from the list. After the "O", type "d" followed by the position in the list of the station you want to delete. "d1" would delete the second station on the screen, "d2" would delete the third, etc. You are not allowed to delete the first station on the list. That's you! If you are using InstantTrack to drive an antenna rotor in realtime, you should know that the program assumes that the antenna is located at the coordinates of the first station on the list. Understanding The Realtime (Map) Display ----------------------------------------- The Realtime Map Display is similar to the Realtime Text Display described above, except that there is a map on the screen, and less room for text. Four different kinds of map can be displayed. Two of these (Cylindrical Equidistant and Orthographic) are maps of Earth. The third (Orbit-View) is a geometric view of the orbit ellipse and earth. The fourth (Sky-View) is a map of the sky, as viewed from your location. The Map displays are ONLY available if you have an EGA or VGA display. Maps of Earth ------------- The map of the world can be displayed in either a Cylindrical Equidistant or Orthographic projection. Cylindrical Equidistant is a "rectangular looking" map projection. It is similar to the Mercator projection, which was probably what you first used in the 2nd grade or so for your first introduction to geography. This projec- tion has the advantage that we can display it VERY quickly. (because it always looks the same). The Orthographic projection is a perspective view of the earth from a long distance away, like the photographs of earth taken from the moon, or an earth globe held at arm's length. It has the advantage of a very realistic look and very low distortion, except near the edges of the globe. It has the disadvan- tage that it is much slower to draw, because of the amount of math required to calculate screen coordinates. You can use either projection, or flip between them (by typing "p") at any time. Cylindrical maps are (roughly) centered on 0.0 longitude, unless you enable scroll mode (by typing "s"), after which cylindrical maps will be centered (roughly) on the satellite. By putting the satellite near the center of the screen, the scrolling mode avoids the possibility that the satellite footprint will wrap around the sides of the screen. I am personally more comfortable with the non-scrolling mode. Take your pick. These maps show the whole earth, including boundaries between countries. Displayed on the map are... 1. The observer. (you!) A yellow "x" marks the location of the observer. 2. The sun. A purple dot appears at the "sub-sun point" on the earth. If you stood at this point on the earth, the sun would be straight up. 3. The grayline (sometimes called the terminator). This shows what parts of the Earth are in sunlight. The grayline is drawn in two shades of purple. The lighter purple is the sunlit side of the grayline. 4. The satellite. A white dot appears at the "sub-satellite point" on the earth. 5. The satellite's geometric footprint. This shows what parts of the Earth are in view of the chosen satellite. I call it the geometric footprint because it is determined by geometry alone (with no consideration of which direction the satellite's antenna may be pointing). Other software calls this simply "the footprint". The geometric footprint is drawn in white. 6. The satellite's antenna footprint. This shows what parts of the Earth are in the "good" part of the satellite's antenna pattern. Specifically, this is a line of constant offpoint angle = 20 degrees. (See discussion of offpoint angle in Understanding the (Text) Display above.) The antenna footprint is drawn in light blue. There are several situations in which the antenna footprint is not drawn.. a. No antenna footprint is drawn if the satellite's "attitude" has not been set. Some satellites do not have directional antennas, and others do not have published attitudes. This avoids displaying an antenna foot- print when it would not be appropriate. b. No antenna footprint is drawn in the case where all area in the geo- metric footprint has a "good" offpoint angle. Think of the antenna pattern as a cone shining down from the satellite. The antenna foot- print is the intersection of this cone with the Earth. If this cone encloses the entire Earth, there is no intersection, and the antenna pattern is good everywhere. c. No antenna footprint is drawn in the case where all area in the geo- metric footprint has a "bad" offpoint angle. If the satellite's antenna points away from the Earth (Oscar 13 near perigee, for example), then the antenna pattern "cone" misses the Earth entirely, then there is no intersection, hence no antenna footprint, and the antenna pattern is bad everywhere. Because the antenna pattern footprint may be a new concept for you, it may be a little confusing. Don't let this bother you. If you can't visualize what the antenna footprint means on the cylindrical map, switch to the Orthographic map (see below), where things seem to be much more obvious. These sun, satellite, and various footprints are redrawn from time to time as the satellite and sun move. The Orbit-View -------------- The Orbit-View projection is a simple stick-figure diagram showing the orbit ellipse, and the Earth, drawn to scale. Similar diagrams can be found in any book on orbital mechanics. The satellite is shown in its current position on the orbit ellipse, but of course the satellite is drawn larger than scale! This view is designed to help you visualize the relative geometry of the orbit, and the satellite attitude. The orbit ellipse is drawn as if it were in the same plane as your computer's display screen, with perigee on the left, and apogee on the right. The orbit ellipse is white, the earth is brown, and the satellite is shown as a red dot. The satellite travels counterclockwise on this ellipse. If you have set the satellite's attitude, then then the direction of the sat- ellite's antennas is shown with a small light-blue arrow. Ideally, this blue arrow would point directly at the yellow x (your location)! Because this ar- row may not lie in the orbital plane (ie Bahn Latitude may not = 0), two addi- tional views of the orbit appear. These are edge views. The one on the left of the screen is a view of the orbit from the direction of perigee. In other words it is as if you bent your head around and looked at the orbit ellipse from the left side of your screen. The view on top is similar, as if you viewed the orbit ellipse from the top of your screen looking down. At the time I am writing this, Oscar-10 has an unusual attitude (62,-26), and is therefore a good example. Select the map screen by typing 2 at the main menu, then select Oscar-10 from the satellite menu, then switch to the orbit- view by typing 3P . A note for students of Celestial Mechanics.. In the center view, the W vector points toward you, out of the screen. In the edge view on the left, the P vector, and in the edge view at the top the Q vector points out of the screen. The Sky-View ------------ The sky-view projection is a map of the sky from the perspective of an obser- ver at your location, looking directly toward the satellite. The satellite is shown on this map along with the 790 brightest stars, and possibly the sun and the horizon, if they happen to be in view. The map is a Gnomic projection (which is a fancy way of saying that it is a perspective projection of the celestial sphere from the viewpoint of a person at the center of the sphere), with a field-of-view that extends 100 degrees horizontally, and 60 degrees vertically. The sky-view is always centered on the satellite. The satellite is drawn as a red dot. Stars are small white dots, of various sizes, depending on the magnitude of the star. The sun (if present) is shown as a yellow dot. The horizon, if present, is a horizontal gray line. The map is always drawn right-side-up, so stars shown below the horizon line are, in fact, below the horizon. Such stars are not blanked, even though you cannot see them through the earth, because they will help you recognize constellations near the horizon. As an aid in locating the correct portion of the sky on star charts, etc, the Right Ascension and Declination of the satellite are shown at the bottom of the screen. (RA and Dec are coordinates used by astronomers to locate objects in the sky. They are similar to longitude and lattitude, except that they represent locations on the celestial sphere instead of the Earth.) Like the other maps, the sky-view is automatically updated, as the earth turns and the satellite moves. Commands -------- While in the realtime tracking (map) screen, the following one-character commands apply... space -- freeze/unfreeze the display E -- look at orbital elements for this satellite F -- start/stop fast-forward mode O -- add/delete an observer P -- change the map projection 1P -- change to cylindrical equidistant 2P -- change to orthographic 3P -- change to orbit-view 4P -- change to sky-view R -- enable/disable antenna rotor control (via Kansas City Tracker) S -- toggle scroll mode (for cylindrical map) T -- set a specific time, or return to realtime. U -- force an update of the map now. W -- enable/disable next Rise/Set time calculation & display. Q -- quit tracking. go back to main menu. Left Arrow -- advance to next satellite Right Arrow -- go back to previous satellite When you initially start up the map screen, it will be running in "realtime", computing the position of the satellite, earth, etc "right now". There are three commands that can be used to change this: "space", "F", and "T". The spacebar simply stops the screen, like the freeze-frame button on a VCR. Typing the spacebar again pops you back to realtime. The "T" command also produces a screen that stands still, but "T" allows you to enter a specific time for which you want the calculations performed. For example, if you are scheduled to use Oscar-13 at 4pm this afternoon, and you'd like to see where the Sat. will be at that time, you can type T, then respond to the prompt by typing 16:00 follwed by Enter. InstantTrack will immediately calculate and display everything for that specific time. At this time prompt, you may enter a date&time in mm/dd/yy hh:mm:ss format, or a date only in mm/dd/yy format (time defaults to midnight), or a time only in hh:mm:ss or hh:mm format (date defaults to today) or you can just type Enter, in which case you will pop back to realtime operation. Finally, the "F" command puts the program in a simple fast-forward mode. This is useful when you want to see where a satellite is going in the next few minutes or hours. (Actually, you probably want to see where it's foot- print, Offpointing Angle, Doppler, etc are going.) When you type "F", this screen will start to move ahead in time steps which are approximately 1/100th of an orbital period for the chosen satellite. Typing a second "F" will pop you back to realtime. At the risk of belaboring the explanation, I will point out that these commands can be used together. You can use "T" to jump to next tuesday, then "F" to fast-forward from there, and then "space" to momentarily freeze the fast-forward. Driving an Automatic Antenna Rotor ---------------------------------- InstantTrack will optionally drive an automatic antenna rotor controller, to make your antennas track a satellite in realtime. At this time, the only such device that InstantTrack is programmed to handle is the "Kansas City Tracker" sold by L.L.Grace Communications Products. The KCT is a single board interface that plugs into an IBM-PC style backplane. The address for L.L.Grace can be found in the bibliography. The author has no affiliation with this company. When InstantTrack is in one of its realtime screens, the "R" command enables or disables realtime rotor control. InstantTrack communicates with the rotor controller driver TSR, which must be previously loaded. The "R" command tests for the presence of such a driver. If present, an "R" appears on the top line of the screen. Otherwise, Instant- Track beeps, then continues. InstantTrack can also work in concert with a TSR program called OrbitDRV which allows your computer to track satellites and control your antennas "in the background" while you use your computer for other things. OrbitDRV is described in detail in the file ORBITDRV.DOC. An alternate command interface for OrbitDRV is described in the file ITRACK.DOC. Satellite Position Table (Ephemeris) ------------------------------------ This is the "old standard" display you expect from a satellite tracking program. Its a table of the computed position of a satellite at various times in the future. The info in the table is a subset of the data on the realtime tracking screen. Each item has therefore already been explained. Note that the display has two formats, and you can toggle between them with the C com- mand. Entering Parameters ------------------- You will be asked to select a satellite, using the standard satellite selec- tion menu. After that, you will be asked for a starting time, and a time increment. In each case, the program provides a reasonable default value which you can select by simply typing the Enter key in response to each question. Start time defaults to right now, and the time increment defaults to .01 / Mean Motion (which means the time increments will be smaller for faster moving satellites). Understanding The Display ------------------------- The numeric information presented on this display is a subset of the infor- mation on the realtime text display. See explanations in the text display section. Commands -------- While displaying a table of satellite positions, the following commands apply. Enter Key -- display the next page of the table. Q -- quit tracking. go back to main menu. Left Arrow -- advance to next satellite Right Arrow -- go back to previous satellite C -- toggle the display format. (Lat/Lon vs Cities) S -- toggle the scroll mode. (Page-at-a-time vs Scrolling) W -- toggle the fast rise-time finder on/off. Most of these commands are self-explanatory. The "W" command is here only to help me verify InstantTrack's fast satellite rise-time finding algorithm. When this is disabled, the word "SLO" will appear in the upper left corner of the screen, and the program will use the simpler but slower method of stepping time and recalcing satellite position until the satellite appears above the horizon. Results should always be the same either way. The times displayed will be slightly different, because the slow method has a time granularity of one time step. The Satellite Schedule Display... --------------------------------- This display is an attempt to provide you with a quick indication of when satellite operations may be possible. The schedule shows you when a satellite will be above the horizon as viewed from your station. If you have entered a satellite schedule for this satellite (in the satellite database), then the satellite operating mode will also be shown whenever the satellite is up. There are two forms of the display. You can display a single satellite for 20 days, or 20 satellites on a single day. You will be prompted for the starting date&time. As with all time prompts in InstantTrack, you may enter the either or both date & time. You may also type neither, in which case starting time will default to right now. If you have asked for a single-satellite schedule, you will then select a satellite on the satellite selection menu. If you have asked for a multiple- satellite schedule, you will be prompted for the name of a satellite group. If you do not enter a group name, the group will default to *, (ie all sat- ellites). Groups are explained in the section on Satellite Parameters. Understanding The Display ------------------------- In the first form, each day is shown as a row on the display. Each column indicates a 20 minute period during the day. A portion of the display looks like this... Satellite: Oscar-13 Station: N6NKF Hours UTC 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 23 05/21/89------------oooBBBBBBJJJBBBBB-------------- ... -- 05/22/89------------------BJJJ----------B---------- ... -- 05/23/89----------------BJ----------BBBB----------- ... -- In the second form, each satellite is shown as a row on the display. A portion of the display looks like this... Day: 05/21/89 Station: N6NKF Hours UTC 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 23 Sun ------------******************************* ... -- Moon -*************************----------------- ... -- Oscar 13------------oooBBBBBBJJJBBBBB-------------- ... -- "-" indicates that the satellite is below the horizon. Any other character indicates that the satellite is above the horizon. If you have entered a schedule for this satellite, then these characters will correspond to the operating mode. If you have not entered a schedule, then "*" is used to indicate above horizon. Even though the display only has room for three columns per hour (one point every 20 minutes), this display will reliably indicate the presence of satellite passes as small as 1 minute! As with other displays, yellow and green are used to indicate above and below the horizon. I have carefully avoided use of special characters which might not appear properly on a printer. After the schedule is complete, use Shift-PrtSc to capture a copy to your printer. To try something familiar, display a schedule for the moon. The idea for this display format came from a program written by John Mezak, K2RDX. Commands -------- During the schedule display, the following commands apply... Q -- quit the schedule. go back to main menu. The Satellite Covisibility Display... ------------------------------------- Some satellites have the capability of establishing a communications link directly with another satellite. This is called a crosslink. Crosslinks are only possible when one satellite can "see" the other, i.e when the earth doesn't get in the way of the direct line-of-sight path from one satellite to the other satellite. This display shows you, in realtime, which satellites "see" which satellites, i.e where crosslinks are theoretically possible. Crosslinks are possible an amazingly large fraction of the time. There is growing interest in recent years in very small communications satellites in low earth orbit (LEO). These are cheaper to build and launch than large satellites, and many can be launched at one time. The AMSAT micro- sat project has designed a very small (9" cube) amateur radio digital communi- cations satellite, and is at the time of this writing building several for an upcoming launch. A disadvantage of low earth orbit is that any one low satellite can see a very small fraction of the earth's surface at any time, making long distance communication impossible. The AMSAT micro-sat overcomes this difficulty by operating in a store-and-forward mode. An alternative solution would be to design microsats with crosslink capabilities. Looking forward to the day when amateur satellites will support crosslinks, this display tells you when such crosslinks are possible. Understanding The Display ------------------------- The display is a matrix. Each row and column represents a satellite. There is a small green dot at the intersection of any row & column if the two satellites cannot see each other, and a big yellow dot if they can. Unfortunately, I can only fit 20 x 58 of this matrix on the screen at any one time. The four arrow keys scroll the display in various directions so you can see any part of the entire 150 x 150 matrix. Two additional columns on the left are labelled "O" and "S". These stand for "Observer" (that's you), and "Sun". Dots in the O column indicate whether the satellite named to the left is visible to you at the present time. Dots in the S column indicate whether the satellite named to the left can see the sun. (LEO satellites are in the earth's shadow a much larger fraction of the time than higher orbiting satellites.) A small dot next to the date & time in the upper left of the screen blinks once every time that the computer has recomputed the positions of all the satellites and updated the display. Commands -------- arrow keys -- cause scrolling, so you can view selected portion of the covisibility display. Q -- quit this screen. Setting Time via NBS... ----------------------- What is NBS ACTS? ----------------- NBS ACTS is the Advanced Computer Time Service provided by the US Government National Bureau of Standards. The NBS Time Service presently uses an ordinary phone number in the 303 area code. The only cost of using the service is the cost of a very quick long-distance call. The NBS plans to switch to a 900- number in the future. Procedure --------- To set your computer's DOS clock via NBS ACTS, select "Update Time (NBS)" at the main menu. InstantTrack will tell your modem to dial, and all characters exchanged between the modem and computer will be displayed on the screen. The NBS sends one time-stamp every second. As soon as NBSCOM has correctly received two time stamps in a row, it will hang up the phone, and tell you the results. An example session follows. At any time during the modem dialog, you can type any key, and the program will hang up the phone and exit immediately. A sample session... --- Modem dialog follows --- Type any key to abort. --- ? = HELP National Bureau of Standards Telephone Time Service D L D MJD YR MO DA H M S ST S UT1 msADV OTM 47511 88-12-16 06:03:44 00 0 -.1 045.0 UTC(NBS) * 47511 88-12-16 06:03:45 00 0 -.1 045.0 UTC(NBS) * --- Setting DOS Date & Time to local: 12/15/1988 22:03:44 --- --- Your DOS time was ahead of NBS by 5.22 seconds --- --- Info only: Your hardware real time clock reads: 12/15/1988 22:04:44 --- --- Done --- Phone call duration was 20.4 seconds. --- Note that your DOS clock is set to your "local" time zone, controlled by your setting of the "TZ" environment variable. This is described earlier in this document. The "Info only" line about your hardware realtime clock is only printed if you have an IBM AT, or a machine with an AT-compatible BIOS. NBSCOM reads the AT RTC, but does not, at this time, attempt to set it. It makes no attempt to read or write the large variety of different third-party aftermarket RTCs that are present in many IBM PC's and XT's. The average phone call duration is about 20 seconds. If there is phone line noise that garbles some of the characters, it will take a little longer. InstantTrack contains a timeout to prevent phone calls longer than 90 seconds. The NBS has provided a timeout which hangs up the phone at their end at 55 seconds. What Can Go Wrong? ------------------ The most common thing that can go wrong is that your modem may require different commands than the one i've provided, or you may have your modem on a different com port. You may edit the file NBSCOM.INI to correct these problems. Technical Notes re Dialing modems, etc. --------------------------------------- One of the challenges when writing any program that attempts to dial and interact with a modem is the very large variety of different brands and models of modems in use. They all support a slightly different set of commands, and handle the various RS232 modem control signals in a slightly different way. Furthermore, there are an amazing variety of different ways that RS232 cables can be wired. Most commercial communications programs (Crosstalk, MIRROR, ProComm,...) solve this problem by providing a large number (as many as 20) different config- uration files which tell the program how to interact with each different kind of modem. These differences include the command set, handling of modem con- trol signals (which are required, and which are provided by the modem), hand- shake timing, call progress indications, etc. I've taken a different approach. I've written serial i/o routines which are completely oblivious to the state of the RS232 modem-control signals. If your modem happens to not provide one of the modem-control signals, or use one of them in an unusual way, NBSCOM doesn't care. (The standard IBM BIOS, on the other hand, requires that the modem raise DSR and CTS.) For outgoing modem-control signals, NBSCOM raises DTR and RTS, which, hopefully will satisfy all modems that care. (The stan- dard IBM BIOS raises DTR, but then toggles RTS, depending on whether you are reading or writing to the serial port.) I've also provided an NBSCOM.INI file where you can specify the exact character strings that should be sent to your modem to dial and hang up. The Hayes-type commands that i've included by default will probably work with 90% of all modems, but if you require something different, you can just change it. The program also raises DTR and RTS before dialing, and drops them after dialing. Some modems hang up the phone in response to a falling DTR instead of a command. Finally, while most commercial programs attempt to interact with the call progress indications (i.e detection of dial-tone, busy signal, etc) provided by most modern modems, i have ignored them completely. I simply dial, then wait for characters from the modem that look like the NBS format. This has the disadvantage that if anything goes wrong during the call (say, for exam- ple, a busy signal) this program will simply wait 'til its timeout occurs. A program that listens for the call-progress info from a modem would know that that had happened immediately, and tell you. This simple-minded approach has the advantage that it is compatible with a wide variety of modems, and it has not yet been an inconvenience. I have yet to get a busy signal from NBS! You can, of course, immediately abort a call at any time manually, by typing any key on the keyboard. Nonnumerical Geography: Maps, Cities, Gridsquares, etc... --------------------------------------------------------- Traditionally, satellite tracking programs have indicated the position of a satellite by displaying two numbers: latitude and longitude. I don't know about you, but I don't immediately recognize a location, its distance from me or other known locations, etc when presented with lat/lon coordinates. InstantTrack uses three hopefully more human-friendly methods.. Maps ---- Of course, pointing at a map is the most user-friendly way to specify a location. InstantTrack contains a map of the world, and a map of the sky, both of which are described above under the heading "Understanding the Real- time (Map) Display". Cities ------ InstantTrack contains a database of the names and locations of 1754 cities worldwide. About half of these cities are in the United States, and the other half scattered around the rest of the world. Data for U.S. cities were obtained from magnetic tapes available from the U.S. Geological Survey. The selection criteria for U.S. cities was population. West of -99 deg longitude, all cities >20,000 pop are included. East of -99 deg longitude, all cities >29,000 pop are included. I typed in the data for non-U.S. cities from atlases and other reference books. Gridsquares ----------- The Grid Locator System, or gridsquares, (in Europe it's called the Maidenhead Locator System) is used by amateur radio operators. It is simply an encoding of latitude and longitude into a four or six character string. Its quicker to say "DM12it" over the radio than "I'm at 32.817 degrees North latitude, 117.267 degrees East longitude". See Tyson's article in QST. It's listed in the bibliography. Files used by InstantTrack... ----------------------------- Computer readable files used by InstantTrack... IT.EXE This is the executable program. ITNCP.EXE Alternate executable program if you have No math CoProcessor. IT.ORB Library of satellite orbital elements. IT.QTH Library of station elements. IT.CTY Library of 1754 city locations worldwide. IT.MP? Maps of earth. IT.STR Map of 790 bright stars. IT.HLB Text for the online help screens. Human readable files that come with InstantTrack... IT.DOC The documentation file you are now reading. IT.UPD Info about recent changes, bugs, etc. in InstantTrack. NBSCOM.INI Configuration info for dialing NBS ACTS. Documentation for related programs... ORBITDRV.DOC The documentation file for OrbitDRV ITRACK.DOC The documentation file for ITRACK Generally, all the computer-readable files should be placed in the same directory, and IT should be run while connected to that directory. If you wish to run InstantTrack while connected to directories other than the one in which you have placed these files, you should define a DOS environment variable named INSTANTTRACK, and make it point at the directory containing the InstantTrack files. Example: SET INSTANTTRACK=D:\it You may also wish to put the directory containing the InstantTrack .EXE files in your PATH definition, so that DOS will know where to find them when you type IT or ITNCP. Example: SET PATH=C:\;C:\bin;D:\it Copyright Notice, Distribution Policy, etc... --------------------------------------------- This program is Copyright (c) Franklin Antonio, 1989, All Rights Reserved. Copies of InstantTrack may be purchased in the United States from AMSAT-NA, a non-profit organization which constructs and launches amateur radio satellites. When you purchase a copy of InstantTrack from AMSAT-NA, the entire purchase price goes toward the amateur radio space program. InstantTrack is distributed in the United Kingdom by AMSAT-UK, and in Australia by AMSAT-Australia. Address information for the AMSAT organizations can be found in the appendix. Any distribution of InstantTrack requires a license. Warranty... ----------- No warranty is expressed or implied. This software has been written as an amateur hobby effort, and I will only support it at that level. You are encouraged to report bugs however. Acknowledgements... ------------------- I've borrowed most of the good ideas from other tracking programs i've used. Namely, the W0SL tracking program written by Roy Welch (W0SL), which is a derivative of the W3IWI Orbit program by Tom Clark (W3IWI), and of course, QuikTrak(tm) by Bob McGwier (N4HY). The idea for the compact schedule display came from John Mezak (K2RDX). All the code in InstantTrack, however, is my own. Paul Williamson (KB5MU), provided extensive assistance testing this program. Paul also wrote the "TSR" part of OrbitDRV, and all of ITRACK and DUMMYKCT. Other beta-testers included Mike Brock (WB6HHV), Dave Guimont, (WB6LLO), Steve Wilmet (WB6BDY), Harry Bluestein (N6TE), Ross Forbes (WB6GFJ), John Fail (KL7GRF), Glenn Moody (N4OUL), Vern Hajek (K6UGS), Chuck Dowling (KI6TG), Graham Ratcliff (VK5AGR), Steve Roberts (N4RVE), Courtney Duncan (N5BF), Ron Broadbent (G3AAJ), Tom Lafleur (KA6IQA). Steve wrote a review of InstantTrack in the Nov '89 issue of '73 magazine. Appendix 1 -- Example Satellite Element File Formats... ------------------------------------------------------- NASA Format ----------- This is the format used by NASA to distribute satellite elements in their "NASA Prediction Bulletin". The origin of the format is unknown. Some old NORAD reports refer to this as T-card format. NASA documents often call it the "2-line" format. InstantTrack expects a file which contains groups of 3 lines: One line containing the satellite's name, followed by the NASA 2 lines of numbers. Files of this format are distributed by T.S.Kelso to two nationwide computer networks, and end up on BBS's and electronic mail systems around the country. On usenet these can be found in the rec.ham-radio newsgroup. On internet, in the INFO-HAMS digest. If you don't have access to usenet or internet, they are also available on his telephone BBS "The Celestial RCP/M" (513) 427-0674. NASA format files look like this... OSCAR 10 1 14129U 88230.56274695 0.00000042 10000-3 0 3478 2 14129 27.2218 308.9614 6028281 329.3891 6.4794 2.05877164 10960 GPS-0008 1 14189U 88230.24001475 0.00000013 0 5423 2 14189 63.0801 108.8864 0128028 212.9347 146.3600 2.00555575 37348 Each number is in a specified fixed column. Spaces are significant. The last digit on each line is a mod-10 check digit, which is checked by the program. The program also checks the sequence numbers (first column), and checks each orbital element for reasonable range. This is a very good set of checks, so this format is very safe, and robust. I have noticed recently files of "almost NASA format" elements on some BBSs. Specifically, some people have been leaving off the check digits, and adding commentary to the first line. There is no excuse for this. We can only exchange data if we adhere to standards. An almost NASA format file is no better than a diskette that's "almost" the right size to fit in that little slot in the front of your computer. The following description, which i obtained from T.S.Kelso, describes the NASA format in detail... From: tskelso@ut-emx.UUCP (TS Kelso) Subject: NASA Prediction Bulletin Format Date: 21 Aug 88 16:49:21 GMT Organization: The University of Texas at Austin, Austin, Texas Data for each satellite consists of three lines in the following format: AAAAAAAAAAA 1 NNNNNU NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN 2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN Line 1 is a eleven-character name. Lines 2 and 3 are the standard Two-Line Orbital Element Set Format identical to that used by NASA and NORAD. The format description is: Line 2 Column Description 01-01 Line Number of Element Data 03-07 Satellite Number 10-11 International Designator (Last two digits of launch year) 12-14 International Designator (Launch number of the year) 15-17 International Designator (Piece of launch) 19-20 Epoch Year (Last two digits of year) 21-32 Epoch (Julian Day and fractional portion of the day) 34-43 First Time Derivative of the Mean Motion divided by 2. or Ballistic Coefficient (Depending of ephemeris type) 45-52 Second Time Derivative of Mean Motion divided by 6. (Blank if N/A) 54-61 BSTAR drag term if GP4 general perturbation theory was used. Otherwise, radiation pressure coefficient. 63-63 Ephemeris type 65-68 Element number 69-69 Check Sum (Modulo 10) (Letters, blanks, periods = 0; minus sign = 1; plus sign = 2) Line 3 Column Description 01-01 Line Number of Element Data 03-07 Satellite Number 09-16 Inclination [Degrees] 18-25 Right Ascension of the Ascending Node [Degrees] 27-33 Eccentricity (decimal point assumed) 35-42 Argument of Perigee [Degrees] 44-51 Mean Anomaly [Degrees] 53-63 Mean Motion [Revs per day] 64-68 Revolution number at epoch [Revs] 69-69 Check Sum (Modulo 10) All other columns are blank or fixed. Note that the International Designator fields are usually blank, as issued in the NASA Prediction Bulletins. AMSAT Format ------------ There are several very similar formats generated by several different people that seem to be called "AMSAT" format. I have tried to make InstantTrack compatible with all of them. This format is very user-friendly, and can be easily read and/or edited by humans. Spaces are not significant. Each orbital element must appear on a separate line. The order in which orbital elements appear is not significant, except that each element set should begin with a line containing the word "satellite". This file format does not contain any check digits or other error detection techniques. InstantTrack searches each line of the file for several possible keywords, and a correctly formatted number. One nice implication of this is that additional information, as long as it is carried on additional lines (commentary, information about satellite schedule, etc) can be added to these files, and it will not bother InstantTrack. Each orbital element is checked for correct range, and element sets containing out-of-range elements are discarded.. First example AMSAT format, as distributed by Conrad Kirksey W5BWF.. Satellite: AO-10 Int'l Object Number: 14129 NASA Designation: 1983-058B Epoch Time, T0: 88239.30510271 Fri Aug 26, 1988. Epoch Rev, K0: 1114 Mean Anomaly, M0: 6.0030 deg Mean Motion, N0: 2.05882335 rev/day Inclination, I0: 27.1492 deg Eccentricity, E0: 0.6027104 Arg Perigee, W0: 331.5568 deg RAAN, O0: 307.6972 deg Period: 699.428632 min/rev Increment: 174.857158 deg/rev Beacon, F1: 145.8100 MHz Decay, N1: -1.38E-06 rev/day^2 Element Set: 352 Second example AMSATish format, as distributed in an ARRL bulletin... KEPLERIAN BULLETIN 77 ARLK077 FROM ARRL HEADQUARTERS NEWINGTON CT SEPTEMBER 24, 1988 TO ALL RADIO AMATEURS Satellite: oscar-10 Catalog number: 14129 Epoch time: 88248.53312992 Element set: 353 Inclination: 27.1605 deg RA of node: 306.2255 deg Eccentricity: 0.6029797 Arg of perigee: 333.9978 deg Mean anomaly: 5.4273 deg Mean motion: 2.05877131 rev/day Decay rate: 4.4e-07 rev/day sq Epoch rev: 3933 Both of these formats, and many other similar ones, will be read correctly. Since the AMSAT format is not precisely defined, however, i cannot guarantee that everything anyone might call "AMSAT" format in the future will work. Appendix 2 -- Known Bugs, Problems, Futures, etc. ------------------------------------------------- See IT.UPD for information about recent changes, etc. As with any project this large, the product is never complete. There are more good ideas than time to implement them. I had to stop somewhere, and the result is release 1.00 . I make no commitment about future versions, however I do have a long wish list of ideas which I hope can be implemented in future versions of InstantTrack. These include some of the obvious things (support for schedules & ephemeris to printer, visual observability predictions, multiple-observer schedules, etc) and some new ideas which I'm going to keep to myself for now. The beta test group has provided me with a long list of things I could have done better. Fixing isn't as much fun as implementing new features, but some of this work might happen too. Stay tuned. Bibliography... --------------- The Satellite Experimenter's Handbook, by Martin R. Davidoff, K2UBC 1985, published by ARRL, 225 Main St., Newington, CT 06111 This is an excellent introduction to amateur radio satellites, basic orbital mechanics, operating procedure, etc, and is highly recommended. Methods of Orbit Determination, by Pedro Escobal, 1965, corrected reprint 1973, published by Krieger Publishing, and John Wiley & Sons. ISBN 0-88275-319-3. This is the best orbit mechanics book i have found. Fairly technical and expensive, but logically organized, understandable, and complete. This book peaked my interest in Celestial Mechanics again, after many years of neglect. Celestial Mechanics: A Compuational Guide for the Practitioner by Laurence J. Taff, 1985, published by John Wiley & Sons. ISBN 0-471-89316-1 This book provides a refreshingly candid assessment of compuational techniques. Taff makes his opinions clearly known, in a style atypical of most textbooks. Lots of good material here. Not suggested as a first text on the subject however. "Bahn Coordinates Guide -- Satellite Orbits", by Phil Karn (KA9Q), AMSAT Satellite Journal, Jan-Feb 1986, pp 8-11. Describes the coordinate system that AMSAT uses to describe satellite attitude. "Conversion Between Geodetic and Grid Locator Systems", by Edmund T. Tyson, QST Magazine, January 1989. This article gives a clear explanation of the grid locator system. "The Satellite Sky", published by Air & Space, Smithsonian Institution, Washington DC, 20560, ISSN-0886-2257. This is a 21" x 34" poster, listing over 250 satellites, and their name, purpose, owning nation, launch site, launch date, altitude, etc. Commmuni- cations, Weather, Photo Recon, Electronic Surveillance, Navigation, Earth Sensor, and Research satellites are listed. Amateur radio satellites are not. The RAE Table of Earth Satellites 1957-1986, compiled at The Royal Aircraft Establishment, Farnborough, Hants, England, by D.G. King-Hele, et al. Published in U.S. by Stockton Press, New York. ISBN 0-333-39275-2. <I've also seen it listed as ISBN 0-935859-05-5.> This book lists 17000 objects from 2869 launches (many of the objects are fragments), and their name, designation, launch date, estimated lifetime, mass, shape, dimensions, and basic orbital parameters. Costs $160 ! Probably can be found in the reference section of your local college library. The following sources for satellite data are listed in Taff's book. I have not tried them... a. "Satellite Situation Report", available from NASA, Office of Public Affairs, Goddard Space Flight Center, Greenbelt, Maryland b. "Satellite Situation Summary", available from U.S. Navy, Commanding Officer, Naval Space Surveillance System, Dahlgren, Virginia c. "Table of Space Vehicles", available from Royal Aircraft Establishment, Procurement Executive, Ministry of Defence, Farnborough, Hants, Great England, (or from U.S. Defense Documentation Center, Cameron Station, Alexandria, Virginia 22314, as document AD-A109363). d. "Satellite Catalog Compilations", NORAD, Peterson AFB, Colorado, 80914 "Your Window for Visually Observing Satellites" by Vern Riportella, WA2LQQ, in QEX magazine, #77, July 1988, published by American Radio Relay League, 225 Main St., Newington, CT 06111 Nice introductory article on criteria for visual observability of satel- lites. Artificial Space Debris, by Nicholas L. Johnson & Darren S. McKnight, 1987, Orbit Book Co., Inc, Krieger Publishing Co., Melbourne FL, 111 pages, ISBN 0-89464-012-7, $34.50 "Only 5 % of the 7,000 trackable objects in orbit are functioning satel- lites." Nifty book on the debris pollution of near-earth space. "A Non-Cosmetic Improvement to the W3IWI Tracking Algorithm" by Bob McGwier, N4HY, in AMSAT-NA Technical Journal, V1 #1, Summer 1987. (Available from AMSAT-NA) Describes the computational technique for quickly finding a satellite's rise time. Strong mathematical content. AMSAT-NA --> The Radio Amateur Satellite Corporation (AMSAT) Post Office Box 27 Washington, DC 20044 Phone: (301) 589-6062 This is a North American non-profit group that builds and launches amateur satellites. They have a variety of materials useful to anyone learning about amateur radio satellite operation. They publish biweekly newsletter "Amateur Satellite Report", and a quarterly "The AMSAT Journal". Please consider becoming a member of AMSAT-NA. AMSAT-UK --> AMSAT-UK 94 Herongate Road Wanstead Park London E12 5EQ, England Phone: 01-989 6741 This is a U.K. non-profit group similar in purpose to AMSAT-NA. They publish a very good newsletter "Oscar News" once every two months, and publish other material useful to beginners. AMSAT-Australia --> AMSAT-Australia G.P.O. Box 2141 Adelaide 5001 Phone: (08) 297 5104 This is an Australian non-profit group similar in purpose to AMSAT-NA. Recent issues of their newsletter have contained Oscar-13 schedules produced by InstantTrack! Project OSCAR --> Project OSCAR P.O. Box 1136 Los Altos, CA 94023-1136 This group publishes "The OSCAR Letter", containing information about amateur radio satellites, and also distributes amateur satellite related software written by hams in other countries. Subscribe by sending $10. and six #10 SASE to Project OSCAR. NASA --> NASA Prediction Bulletins Goddard Spaceflight Center Project Operations Branch Code 513 Greenbelt, MD 20771 These folks publish orbital elements for a large number of satellites. If you need elements for a particular sat. not available through the many networks and bbs's, you can get them from NASA. Unfortunately, NASA only distributes elements in human-readable form (Xerox'd) at this time. NBS --> NBS-ACTS Time and Frequency Division Mail Stop 52 325 Broadway Boulder, CO 80303 These people run the National Bureau of Standards ACTS telephone time service. Send any questions or comments about that service to them. KCT --> L. L. Grace Communcations Products 41 Acadia Drive Voorhees, NJ 08043 (609) 751-1018 This company manufactures the "Kansas City Tracker". I have no affiliation with L.L.Grace. Send any questions regarding the KCT to them. Author--> Franklin Antonio, N6NKF 2765 Cordoba Cove Del Mar, CA 92014 CompuServe ID: 76337,1365 InstantTrack was written by Franklin Antonio, who welcomes your constructive comments about this software. If you write to me and would like a response, please enclose a self-addressed stamped envelope. ----END of IT.DOC----