There's a Satellite in your Backyard! ===================================== Tips & Techniques for the Novice Naked-Eye Satellite Spotter by Alan Bose When the Space Age was young (and so was I), I can remember my father taking us out in the backyard to watch the Echo satellite fly over. It was a great event. It was even covered "live" on the radio. An entire city looking for a point of light racing across the sky. Today we take the marvels of space exploration for granted. We forget that space is not something distant and remote. It's as close as our own backyards. A satellite is visible from the ground because the sun has recently set and our sky is dark, but the satellite overhead is still in full sunlight. On any clear night numerous satellites can be seen during the hours after sunset if you just sit back and watch. Points of light racing across the sky that suddenly disappear as they fly into the earth's shadow. Not to be confused with high-flying aircraft, satellites do not have visible navigation lights or strobes, nor do they change direction, make noise, or leave contrails. The "Satellite Spotters Guide" has become a recurring segment on the Spike O'Dell radio program, afternoons on WGN-AM 720 in Chicago. The satellite predictions announced on the air are usually the biggest, brightest, easy-to-spot targets. For your viewing enjoyment, here are some tips to successful satellite spotting. Satellite Spotters Tip #1 -- Time --------------------------------- Set your watch to the WGN time signal at the top of the hour, or use some other accurate time standard. (Warning: some radio/TV time signals are not all that accurate.) Since satellites in low-earth orbit move across the sky quickly, a minute or two can make a big difference. Satellite Spotters Tip #2 -- Eyes --------------------------------- Get outside a few minutes early and let your eyes become acclimated to the dark, especially if you're coming out of a brightly lit house. Choose the darkest location possible, shielded from bright light sources such as street lights or nearby windows. Just turning off a few lights in the house can darken your own backyard considerably. In and near the city, "light pollution" overhead makes viewing especially difficult by washing out all but the brightest objects. Satellite Spotters Tip #3 -- Bearings ------------------------------------- Get your bearings. Know which way is north. Know from which direction the satellite will rise and in which direction it will set. Satellite Spotters Tip #4 -- Zenith ----------------------------------- Very important. Know where the satellite's zenith will be (its highest point in the sky). It is not enough to know that it will rise in the west and set in the east, without knowing if it will pass to the north of you, to the south of you, or directly overhead. Yes, I have stood in the backyard scanning the sky in vain to the south while the bird I was looking for passed quickly and quietly behind my head to the north! Unfortunately, the zenith calculated for Chicago may or may not apply for Rockford, Champaign or Milwaukee, depending on the satellite's track. The satellite will certainly be visible, but it may be in a totally different part of the sky from your vantage point! Knowing the satellite's track may help you figure out the general area to look. Satellite Spotters Tip #5 -- Scan --------------------------------- When waiting for the satellite to rise, don't stare at the horizon. Even the brightest satellite won't be visible until it gets at least 20 degrees or so above the horizon -- above the atmospheric haze. Instead, scan the entire path across the sky. The satellite could be a few minutes early, and already at its zenith while you're staring at the horizon. (I've done that too.) Satellite Spotters Tip #6 -- Backlighting ----------------------------------------- When a satellite rises in the west in the evening, the sun is below our horizon, but it is still behind the satellite from our point of view. In other words, as we look west we are looking at the unlit side of the satellite. For this reason a satellite low on the west- ern horizon in the evening (or low on the eastern horizon in the morning) can be quite dim or impossible to see -- at least until it climbs higher in the sky, where we can see some of its sunlit side. Satellite Spotters Tip #7 -- Uncontrollables -------------------------------------------- As timely & accurate as we try to be with these satellite visibility forecasts, there are several variables that remain beyond our control. One is the orientation of the satellite itself. The Mir space station, for example, is more than 100 feet long with a vast array of solar panels. It is currently the brightest artificial object in the sky. (Our Skylab was the brightest, I'm told.) What we see on the ground is sunlight reflecting off this large surface area -- assuming it is oriented properly. As an experiment, have a friend hold up a pencil across a dimly-lit room. In most any orientation you will have little trouble seeing the pencil. But if he holds it with only the end facing you, it will be quite difficult to tell if he is holding anything between his fingers or not. In the same manner, if the station is end-on to either us or the sun, its apparent brightness can vary considerably, and on occasion it can be almost impossible to see. Another uncontrollable is when a satellite's orbit changes. The Mir is an active space station, and permanently manned, but each day it looses a few meters of altitude. If not corrected it would eventually re-enter the earth's atmosphere. To prevent this, it is given a slight boost every couple months to kick it back up to the desired orbit, but in the process it throws our orbital forecasts out the window. Since the Russians don't announce the changes, we only find out second hand, after the fact. If the changes aren't too great it may only mean that the it shows up a couple minutes earlier or later than planned. We strive to use only the most current tracking data publicly available. Sometimes it is just not soon enough. The best remedies are to go outside a few minutes early (Tip #2) and to immediately scan the expected track (Tip #5). Satellite Spotters Tip #8 -- Serendipity ---------------------------------------- How do you spot a hardy satellite spotter? He's the one who leaves his reclining lawn chair out in the back yard all winter! (He also sits there on summer evenings and "feeds the mosquitoes".) You'll be amazed how many satellites you can spot just by sitting back and looking up. Most are quite dim and only visible for a brief moment directly overhead on clear nights. Some spent rocket boosters and decommissioned satellites tumble slowly and appear to wink on and off as they cross the sky (not to be confused with high-altitude aircraft which can be identified by their navigation lights). Satellites in polar orbit (north/south directions) tend to be spy satellites with an occasional earth-resource satellite like the Landsats or Seasat. Spy satellites are generally in low orbits so they can get better detail in their pictures. But their low orbits also make them good targets for satellite spotters. A favorite challenge for satellite spotters is the Lacrosse, a top- secret U.S. spy satellite deployed on a shuttle mission a few years back. Its not hard to see - it's unusually big and bright for a satellite in a near-polar orbit. It's just that you can't tell when or where it will show up since current tracking data isn't made public. On the other hand, a global network of amateur satellite spotters often deduces the orbits of these 'secret' satellites from as little as two or three accurate naked-eye observations. Satellite Spotters Tip #9 -- 'Standard' Orbits ---------------------------------------------- Is the Space Shuttle visible? Yes, the Hubble Space Telescope and the Space Shuttles are exceptionally bright objects -- if you live in the southern tier of states from Los Angeles to Atlanta. Unfortunately, most Shuttle missions do not venture as far north as Chicago. The Kennedy Space Center is located at 28.4 degrees north latitude. As such, the most energy efficient orbit (the greatest payload in the highest orbit on the least fuel) is confined to 28.4 degrees north and south of the equator -- far from Chicago at 42 degrees north latitude. Most Shuttle missions pass just below our horizon to the south. The Hubble Space Telescope follows the same orbit, but at a higher altitude. The HST peeks above our southern horizon briefly, though scarcely enough to be seen through the atmospheric haze under the best conditions. The HST is in the highest orbit attainable by the present Shuttle system. Only large objects in low orbit stand a chance at being seen from the ground with the naked eye. Higher orbits, such as the geosynchronous orbits, are simply too high up for naked-eye observation. Numerous satellites are in our sky constantly, but it is rare that we are aware of them. Every once in a while we just need to sit still, look up and watch! Satellite Spotters Tip #10 -- How it's done. You can do it too! ---------------------------------------------------------------- The question that has been asked over and over is, "How does he do that?" How is it possible for an average citizen like myself to calculate and predict the passage of all these various satellites? The personal computer, that's how. The average personal computer sitting on your desk today has a couple hundred times the power of the computers sent aboard the Voyager spacecraft in 1977 to explore Jupiter, Saturn, Uranus, Neptune and beyond. It is this power that can be applied to the serious number crunching required to predict satellite movement and visibility. The second requirement is accurate tracking data with periodic updates to feed to your computer. First, you need a personal computer. Either a Macintosh or an IBM- compatible. Satellite computations are extremely math-intensive. A computer with math co-processor is highly recommended. A lower powered machine can do the computations just fine, as long as you're willing to walk away and let it work. Overnight, if need be. Tracking data is publicly available in a computer-readable file called the "NASA Prediction Bulletin". Of course data on certain spy satellites is withheld. The data is simply two lines of numbers for each satellite (see Figure 1). The data is available for downloading from a variety of public and private computer bulletin board services, if you have a modem and suitable communications software and are willing to make a 3-4 minute long-distance call. Bulletin boards that cater to amateur astronomy and/or amateur radio generally carry the files on a regular basis. The BBS systems listed here all run 8 data bits, no parity, 1 stop bit. Each operates 24-hours a day. Celestial BBS, Fairborn, Ohio Canadian Space Soc. BBS, Toronto 513/427-0674 - 1200/2400 baud 416/458-5907 - 1200/2400 baud Good, but very, very busy Specialty: spy satellites CocoLoco BBS, Houston, Texas RPV BBS, Rancho Palos Verdes, CA 713/923-6809 - 1200 baud only 213/541-7299 - 1200/2400 baud Type "KEP" at the first prompt Next you need a satellite tracking program that will take that data from the Prediction Bulletin file and calculate where each satellite is (or will be) at any particular time. There are two excellent programs that I use regularly: MacSat written by Bill Bard for the Macintosh, and TRAKSAT written by Paul Taufler for DOS compatibles. MacSat $10 (disc & manual) TRAKSAT $10 (disc w/ docs) Bill Bard $20 (disc & manual) BEK Developers Paul E. Traufler 1732 74th Circle NE 111 Emerald Drive St. Petersburg, FL 33702 Harvest, AL 35749 Both programs are well documented. You will need to know your location, in terms of latitude and longitude. For anyone in the Chicago area 42 degrees north latitude and 88 degrees west longitude will work fine. TRAKSAT comes with a long list of cites already entered. For other areas, just stop by your nearest airport. Any private pilot will be happy to tell you your latitude and longitude. Since satellites are visible over a wide, wide area you don't need to calculate the latitude and longitude for your own backyard! Close (within 10-20 miles) will do fine. However, accurate satellite forecasts do depend on supplying your program with the most current tracking data available. If a satellite doesn't show up as predicted, it might be that your tracking data is old. If your data is more than a month old, you might want to call in again for fresh data. If you're a regular satellite spotter, updating your data every other week should generate forecasts that are quite reliable. Both programs will calculate when a satellite will be above your horizon (Figure 3). They will also calculate when it might be visible. They can both draw you a real-time map of the planet and show you where a satellite is located, just like the big map you see on the wall at Mission Control in Houston. Other than minor differences, both programs work very well and do everything needed for successful satellite spotting. Careful, both programs use time in 24-hour format. 0700 is 7:00am. Twelve hours later, 7:00pm is 1900 (7+12=19). TRAKSAT is a bit trickier still in that it uses UTC (what used to be called Greenwich Mean Time) which is 6 hours ahead of Central Standard, or 5 hours ahead of Central Daylight. 1900 Sunday Central Standard Time in Chicago is 0100 Monday UTC (1:00am of the following day in London). It can be a little confusing if you're not careful. So, now that you can calculate where these satellites will be, can you really see them? Well, there are only a few excellent targets. The Russian Mir, the American Hubble Space Telescope, or any of the Space Shuttle flights are all easy naked-eye targets. Unfortunately, the HST and most Shuttle missions don't come far enough north (see Tip #9). But don't give up. There are plenty of sights to see. You just have to look a little more carefully. For viewing around the Chicago area, you should select satellites that have and inclination of at least 40 degrees, and have a mean motion of 14.5 or more (which is the same as a period of 99 minutes or less, depending on how your program displays its data). This simply means that the orbit is tilted at least 40 degrees with respect to earth's equator, and as such will pass over points as far north as 40 degrees north latitude and points as far south as 40 degrees south latitude. The mean motion is simply the number of orbits per day a satellite makes. Period is how long one orbit takes. The lower the orbit, the more orbits per day, and the shorter the period. Even then, the satellite you've selected might only be the size of a beach ball. Trying to see a beach ball 300 kilometers overhead with the unaided eye just won't work. Binoculars and dark skies will help spot dimmer targets, but the smallest birds will still fly over unseen. A few you might want to try are: COBE - variable, spins once every 10 seconds. Occasionally bright. Cosmos 604 & Cosmos 1689 - dim, but quite visible directly overhead. Cosmos 1689 r - rocket booster for Cosmos 1689, slow 90-second tumble. Bright for 5 seconds of the 90, but otherwise dark & invisible. ERBS - Earth Radiation Budget Satellite. Dim. Landsat 4 - tumbling every 15 seconds. Visible, but mainly dark. Pegsat - pretty good target. Be patient and trust your prediction program. Someone told me that for satellite spotting, patience isn't a virtue, it's a requirement! The times may be off slightly, but the path across the sky is usually right on. For $30 a pair of binoculars will help you find many dimmer satellites. A small 7x35 pair will do fine, though for $80-$100 a pair of 7x50s will collect even more light. (For dim objects it is light gathering power (the second number), not magnification, that is the desired feature.) A telescope is far too cumbersome. A scope's high power and narrow field of view make it almost impossible to zero in on a fast moving satellite. And you're not going to see antennas hanging out. It's just too small and too far away for that. Binoculars are ideal. Get everything you need from CompuServe. ---------------------------------------- Everything you need to get started with satellite spotting is available in one place. It was on the CompuServe Information Service that I found, and downloaded these programs that got me started. I also found other satellite spotters all around the globe. If you already subscribe to similar services like Delphi, GEnie, America Online, or others, check around for an astronomy or ham radio area with files available for downloading. Prodigy is not suitable since they do not allow you to download programs and datafiles for use offline. I've worked out a method using CompuServe that will let you: 1) get all the programs and data files at little or no cost, and 2) ask questions via electronic mail (my CompuServe ID is 76703,3044. MacSat author Bill Bard is at 75366,2557). You'll also have the opportunity to meet a wide variety of amateur and professional astronomers and space enthusiasts. The only thing you'll need in addition to your computer and modem is a CompuServe User ID to get access to the system. Call CompuServe Customer Service toll-free at 1-800-848-8199. Ask for Operator 176. They will send you a free Starter Kit that includes a User ID and password, and comes with $15 of free connect time. If you also need communications software for your computer, they will offer the CompuServe Information Manager for $25 (this also includes $25 of connect time, so your cost is a wash). When you get your kit, it will include your User ID, password, and a directory of telephone access numbers across the country. When you log on, you will want to make your way to the Astronomy Forum. Depending on your software you'll probably type GO ASTROFORUM. If you're using the CompuServe Information Manager, use the GO option under the Services menu and type ASTROFORUM. Each forum maintains up to 18 libraries loaded with files available for downloading. In this case we are interested in: Library 7 "Astrocomputing" and the files MACSAT.DOC and MACSAT.SIT (for Macintosh users) or the files TRKSAT.DOC and TRKSAT.EXE (for DOS users) Library 17 "New Uploads" for datafiles KEPELE.NAS or SATLOW.DAT for all users. (Updated frequently.) The file TRKSAT.EXE is the largest file at 329,000 bytes, and will take about 48 minutes to download with a 1200 baud modem, or 24 minutes with a 2400 baud modem. MACSAT.SIT is only 105,000 bytes long (approx 14 minutes at 1200 baud, 7 minutes at 2400). So, now you know how the Satellite Spotters Guide is created. You can do it yourself anytime at all. While I can't answer all questions about every program on every machine, I do run both Macintoshes and DOS clones. Feel free to drop me a note via E-Mail on CompuServe at 76703,3044. +--------------------------------------------------------------------+ Mir 1 16609U 86 17 A 90183.89213145 .00020188 00000-0 22865-3 0 7711 2 16609 51.6127 251.5145 0010974 101.2360 258.9979 15.62331916250556 +--------------------------------------------------------------------+ Figure 1. The Keplerian elements (named after Johannes Kepler who first worked out the orbit of Mars and proved Copernican theory of the solar system correct) are a set of numbers that describe the path and motion of an object in orbit. The data files you download are in "NASA 2-line format" shown here. These numbers describe the exact position and motion of a satellite at a given time. With this information we can calculate its current (or future) position and motion. +-------------------------------------------------------------------------+ | | | Satellite Mir NORAD Number 16609 | | Int'l Designation 1986 017A Epoch 90 183.89213145 | | Inclination 51.6127 Deg RAAN 251.5145 Deg | | Eccentricity 0.00109740 Argument of Perigee 101.2360 Deg | | Mean Anomaly 258.9979 Deg Mean Motion 15.62331916 Rev/Day | | Epoch Revolution 25055 | | | | Semimajor Axis 6759.0 Km Period 92.17 Min | | Apogee 388.27 Km Perigee 373.44 Km | | | +-------------------------------------------------------------------------+ Figure 2. The NASA 2-line format is decoded showing Mir's orbit inclined to the earth's equator at an angle of 51.6 degrees. This means it will pass directly over points as far as 51.6 degrees latitude north and south of the equator. (Chicago is 42 degrees north.) It's mean motion of 15.6 means it is low enough to be a candidate for visual observation. MacSat allows you choose satellites by inclination or mean motion and display the data as shown here. On DOS machines a separate program called EDSAT is needed. EDSAT is available in the CompuServe libraries, but is not required to generate satellite forecasts. +------------------------------------------------------------------------+ | Time CDT Az El Range Height North West RA Decl | | MM DD YY HHMM:SS Deg Deg Km Km Lat Long Hr Min Deg Min | | | | 07 10 90 2238:30 238 22 893 379.7 37.84 95.62 13 33.4 -6 38.1 | | 07 10 90 2239:00 239 31 706 379.4 39.04 93.77 13 52.7 0 32.7 | | 07 10 90 2239:30 241 44 540 379.2 40.19 91.85 14 23.5 11 55.8 | | 07 10 90 2240:00 248 66 421 378.9 41.31 89.86 15 21.3 30 9.8 | | 07 10 90 2240:30 23 80 394 378.7 42.39 87.79 17 27.6 51 3.3 | | 07 10 90 2241:00 48 54 475 378.4 43.43 85.66 20 35.1 56 29.2 | | 07 10 90 2241:30 51 36 623 378.2 44.42 83.44 22 26.2 50 23.3 | | 07 10 90 2242:00 53 26 801 378.0 45.36 81.15 23 17.5 44 8.6 | +------------------------------------------------------------------------+ Figure 3. Using the Keplerian elements, MacSat and TRAKSAT can then calculate when a satellite will be above your horizon, if it is illuminated by the sun at the time, and if the sun is below your horizon, making a visual sighting theoretically possible. Here we show a passage that begins with the satellite to our southwest (azimuth 238 degrees) at 10:38pm (2238) low in the sky (elevation 20 degrees). It reaches its highest point in the sky at 10:40pm (2240) to the northeast (azimuth 23 degrees) almost directly overhead (elevation 80 degrees). Azimuth refers to the direction to look, measured in degrees from north. 0/360 = north. 90 = east. 180 = south. 270 = west. Elevation is the angle above the horizon. 0 degrees is the horizon, 90 degrees is directly overhead. The North Star is 42 degrees above our northern horizon, which corresponds to Chicago's latitude of 42 degrees. Today's students are tomorrow's explorers. The "Satellite Spotters Guide" is dedicated to the proposition that the United States has the will, the determination and the resources to remain a leader in future space exploration. Please pardon the fact that this is a simple ASCII version of a typeset flyer complete with illustrations. Recently we sent hundreds of flyers to interested Chicagoans who regularly catch the "Satellite Spotters Guide" on WGN-AM 720. If you must have the finished, typeset, illustrated, printed version (for your astronomy club or school?) please by send $1 plus a stamped, self-addressed, #10 (business size) envelope to: Satellite Spotters Guide, P.O. Box 366, Itasca IL 60143. Please mention which BBS or service you found this file on. Yes, it does look a whole lot nicer. My special thanks to John Williams [73615,1407] of the Dallas Remote Imaging Group for all of his help and suggestions in preparing this paper. My thanks also to T.S. Kelso of the Celestial BBS; Ted Molczan of the Canadian Space Society; Conrad Kirksey [71575,1677] of the CocoLoco BBS; and David Ransom of the RPV Astronomy BBS. These guys are the *real* satellite trackers and observers. And finally my thanks to Bill Bard [75366,2557] and Paul Traufler for their well written programs that make it all seem so easy. Alan Bose is Manager of Information Services at a large commercial printer in the northwest suburbs of Chicago. He is also a speaker and author on the use of computers and barcodes in the printing and paper industries. He is a graduate of the Institute of Design at the Illinois Institute of Technology. His interest in computers, astronomy, aviation and space exploration dates back to the heady days during our race to the moon. As a private pilot he has written computer software for aircraft navigation and flown the North Atlantic in a light plane. Over the past ten years he has been one of the system operators on AVSIG - the Aviation Forum on CompuServe. As an amateur astronomer, he is a member of the Northwest Suburban Astronomers, and has been doing naked-eye satellite spotting since 1989, and stirring up interest in Chicago by forecasting brighter objects on WGN Radio since July 1990. Skiing, Cub Scouts and classical music consume any remaining time. (c) Copyright 1991 Alan Bose All rights reserved. For quantity/educational reprints, please write: Satellite Spotters Guide, P.O. Box 366, Itasca IL 60143