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Educator's Guide to Spotting Satellites
The Basics
Anyone who takes the time to go out after sunset or before dawn and observe the sky from a dark sky location away from city lights will be rewarded with some moving stars! These are actually Earth orbiting artificial satellites. There are over 7,000 objects in space for which orbital information is kept by military and civilian space organizations. Most of these objects are small but quite a few are large enough to be seen with the unaided eye. And some, like the Space Shuttle and the Russian Mir space station, are very large and appear very bright.
Since satellites do not give off light of their own, they can only be seen when there is sunlight reflecting off of their surface. But the daytime sky is too bright to see their reflected light. So only during a comparatively brief period after sunset and before dawn, when the sun is below the horizon for Earth based observers but is still illuminating space overhead, are they reflecting light in a dark sky. For that hour to hour-and-a-half it is easy, if you are patient, to see artificial satellites. The darker the sky, of course, the more (and fainter) you can see.
The best technique is to lie on the ground or in a reclining lounge chair and look at a group of stars overhead. Keep an eye out for a star-like object that is moving through the fixed stars. It may look like an airplane but will not change course, will not have flashing or colored lights and will, as you follow it, fade away before it reaches the horizon. You might be able to see more than one in the sky at the same time.
Satellites will orbit from west to east or from nearly pole to pole. If you learn the names of some of the constellations and stars in the sky you can direct others to your sighting. Saying that the satellite is, "over by that star," is not particularly helpful but saying, "it is moving through Cygnus the Swan," is much more instructive (if your fellow viewers know where to find Cygnus).
Space Shuttle, Mir and "Iridium" Observing
On some Space Shuttle missions, there are opportunities for many observers in the continental United States and Hawaii to see the orbiter fly overhead. Observers south of 28.5 degrees north latitude lie within the band overflown by all Shuttle flights. Shuttles are launched from the Kennedy Space Center in Florida which is at a latitude of 28.5 degrees north. That means that for most missions the orbiter's path is a circle around Earth that is inclined (tilted) 28.5 degrees relative to Earth's equator. Observers more than a little bit farther north than 28.5 degrees will not be able to see the orbiter. It will never rise above their local horizon.
But for some missions the "orbital inclination" will be as high as 57 degrees. That means that everyone in the band between 57 degrees north and south of the equator has a potential Shuttle over-flight. Because of the height of the Shuttle's orbit, just about every spot in this band, and for several degrees to the north and south, will be within the field of view of the orbiter and above the horizon for ground based observers. Hopefully, at some point during its mission, the Shuttle Orbiter will pass overhead during a dawn or dusk period when it can viewed from your location.
The Russian Mir space station orbits at an inclination of 51.6 degrees. It is very large, quite bright, in space all the time and impressive to view. The International Space Station will be in 51.6 degree orbit as well. Another set of excellent viewing targets are the satellites of the "Iridium" commercial satellite network. They produce "flares" of several seconds in length that occur, often, several times a day and some are very bright. There are now several WWW pages that ask for your geographic location and automatically generate predictions for you. Some of those sites can be found near the bottom of this Guide.
Correct a Misconception!
Most illustrations of the Space Shuttle and low Earth orbiting spacecraft flight paths greatly exaggerate the altitude of the orbiter. To give students a true sense of the orbiter's relationship to Earth use a pair of calipers or a paper ruler to measure approximately 200 miles on the surface of a globe. Distances between local landmarks will make the best impression on children. Then turn the calipers perpendicular to the globe so that they show altitude. You will see that Shuttle orbits just graze the globe. Also note that our atmosphere is less than 1/4 as high!
Orbit Tracking Programs
Generally it is going to be difficult to determine what satellite you are viewing. But you can usually figure it out if you have an orbit tracking program and current spacecraft orbital elements. Even more exciting, when there is a current space shuttle mission underway or if you want to see the Mir space station you can determine when they will actually be visible and plan to go out and observe at the right time. With bright objects like the shuttle and Mir you can view from even light polluted city skies.
There are orbit tracking programs for Macintosh and IBM compatible computers. They are either free or shareware (where the user can get the program for free but is obligated to send the (generally low) shareware fee to the developer if they decide to keep the program) and can be obtained from public access sites via a modem or Internet connection. They require updated orbital elements which can also be easily obtained.
Getting the Programs
The National Aeronautics and Space Administration (NASA) has public access site called NASA Spacelink with a tremendous amount of material for students, teachers and the public. Follow these directions to get the right program(s) and
data.
Connect to NASA Spacelink via the World Wide Web at http://spacelink.nasa.gov/.
Move through the directories Instructional.Materials, Multimedia, and Satellite.Tracking to "Satellite Tracking."
(Several of these programs, and others, are available on the Jet Propulsion Laboratory's World Wide Web page at http://www.jpl.nasa.gov/).
Getting the Orbital Elements
Orbit tracking programs require information about the shape and orientation of satellite orbits. These data are known as "Keplerian elements," named for Johannes Kepler. There are two forms of Keplerian elements; the long version which has each value described, and the short form or "two-line elements" (tle) which are a standard way of formatting the data so computer programs can read them automatically. Below are examples of both forms from the Space Shuttle mission flown in January 1998.
Long form:
Satellite: STS-89
Catalog number: 25143
Epoch time: 98028.54150584 = yrday.fracday
Element set: 911
Inclination: 51.6567 deg
RA of node: 32.2111 deg
Eccentricity: .0004328
Arg of perigee: 294.0456 deg
Mean anomaly: 66.0247 deg
Mean motion: 15.61858603 rev/day
Decay rate: 1.55300E-04 rev/day^2
Epoch rev: 86
Checksum: 293
Two-line elements:
STS-89
1 25143U 98003A 98028.54150584 .00015530 00000-0 20178-3 0 9113
2 25143 51.6567 32.2111 0004328 294.0456 66.0247 15.61858603 866
If you compare the numbers in the two-line element set with the long form you can see that the data in both is the same.
The following is an example of some orbital and visibility data as extracted from tles by the satellite tracking program:
To get the elements from NASA Spacelink, go through the folders Instructional.Materials, Software and Tracking.Elements. There you will find one or more text files that will include the word "element" somewhere in their title. Download the most recent set(s). The text will look like this (these are actual elements from January 1998; TOPEX is the TOPEX/Poseidon oceanography satellite, HST is the Hubble Space Telescope, Mir is the Russian space station):
TOPEX
1 22076U 92052A 98024.57067089 -.00000038 00000-0 10000-3 0 1099
2 22076 66.0458 74.7225 0008373 268.7787 91.2269 12.80929573255222
HST
1 20580U 90037B 98025.25348428 .00000584 00000-0 47997-4 0 228
2 20580 28.4673 60.4756 0014065 341.5793 18.4281 14.86593740226127
MIR
1 16609U 86017A 98026.43000941 -.00012716 00000-0 -13761-3 0 1868
2 16609 51.6566 42.8518 0004808 260.5240 99.5638 15.61880504681889
The computer programs will have a feature that allows it to read the text file directly into its database (from your computer, not the originating site). (In OrbiTrack use the "Read NASA2L" command from the "File" menu.) If the program has trouble seeing the file, try resaving the elements file as a text only/ASCII file.
NASA's Goddard Space Flight Center has an elements site that can be accessed by WWW or modem. Go toNASA/GSFC Orbital Data Bulletin Board at http://oigsysop.atsc.allied.com or call (301) 805-3251.
For another source of elements using the WWW or File Transfer Protocol (FTP) open: http://celestrak.com or FTP to archive.afit.af.mil
and cd to pub/space/. There you will find a lot of two-line elements (tle. or .tle) files. Download "tle.new" for the most up-to-date sets (tle.new will be the same as the tle. file with the largest number so you do not need to get any of the numbered files). There are sets of only one type of data, such as "mir.tle" for the Russian space station and all of its attached elements, and "visual.tle" for (potentially) visible satellites.
NASA's Space Shuttle WWW page also posts orbital elements for ongoing shuttle flights in the "http://shuttle.nasa.gov/sts-XX/orbit/orbiter/sighting/" page (where XX = the number of the current mission; for example, in January 1998, to get info on the STS-89 mission to Mir, you would insert "89" in place of the "XX"). Lots of current, past and future information (and pointers to up-to-date elements) can be found on the NASA Shuttle Web http://shuttle.nasa.gov.
Read all of the documentation for the computer programs. The programs are capable of showing you where spacecraft are currently, in the future or in the past. You can plot out their future orbits, their visibility from ground sites and, most exciting of all, the times when the large ones will be visible from your location at dawn and dusk.
They are a wonderful set of programs and, thanks to their developers and those that make the orbital elements easily available, allow us to get personally involved with "what's up."
WWW satellite tracking sites:
NOTE: These are not NASA sites and have not had their content reviewed. JPL/NASA provides no assurances that the content at these sites is not inappropriate.
VERY HOT:
GSOC Satellite Predictions - Start Page.
(Follow the directions and look out for "Iridium Flares.")
http://www2.gsoc.dlr.de/satvis/
Earth Satellite Ephemeris Service
http://www.chara.gsu.edu/sat.html
Satellite Tracking Prediction Form
http://www.acs.ncsu.edu/scripts/HamRadio/sattrack.perl
SatPasses Home Page
http://www.bester.com/satpasses.html
Visual Satellite Observer's Home Page
http://www2.plasma.mpe-garching.mpg.de/sat/vsohp/satintro.html
Sky Publishing Mir form
http://www.skypub.com/mir/mir.html
The Amateur Satellite Observers of Southeast Virginia
http://www1.seva.net/~jbyrd/
Satellite Observing Resources
http://www-leland.stanford.edu:80/~iburrell/sat/sattrack.html
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From Geoff Chester, Albert Einstein Planetarium:
Below is a list of 28 satellites which are brighter than 3rd magnitude on a good zenith pass. The list is based on personal observations by myself and others.
IntD :Name Radar Cross-sec (sq. meters)
03598:OAO 2 r 8.6
04786:Cosmos 382 7.6
05994:Pageos (DA) 12.0
06212:Radcat 12.2
08074:Pageos (H) 8.6
10967:Seasat 21.0
12054:Cosmos 1220 6.0
16182:Cosmos 1697 r 10.4
16609:Mir Complex 32.7
16910:EGP r 13.5
17974:Cosmos 1844 r 10.4
19120:Cosmos 1943 r 10.4
19625:KH 11-8 15.0
19650:Cosmos 1980 r 10.4
19671:Lacrosse 1 18.0
20322:COBE 4.9
20625:Cosmos 2082 r 10.4
21147:Lacrosse 2 18.0
21701:UARS 9.8
22251:USA 86 15.0
22285:Cosmos 2227 r 10.4
22566:Cosmos 2237 r 10.4
22803:Cosmos 2263 r 10.4
22808:Cosmos 2264 6.0
23336:Cosmos 2293 6.0
23343:Resurs 1-3 r 10.4
23405:Cosmos 2297 r 10.4
23596:Cosmos 2313 6.0
Note that several of the satellites are "Classified" US DoD payloads. PC and UNIX users can obtain orbital elements for these birds from the following URL: ftp://kilroy.jpl.nasa.gov/pub/space/elements/molczan/new_molc.Z
To uncompress this file, which contains orbital elements for over 800 satellites, updated weekly, use WinZip (see http://www.winzip.com). But it does bring up a box asking you to enter the original extension of the file; use "tle" (thanks Mark Hanning-Lee). Use a program called ELEMAN 1.9 to "cull" out the elements for the bright birds.
IMHO by far and away the *best* prediction software for tracking visual satellites is a small freeware package called QuickSat, by Mike McCants, which I use for the above mentioned predictions. It is not graphic, but instead generates a chronologically ordered tabular output of which satellites will pass over a given location, given a specified set of circumstances (minimum altitude, magnitude, time frame, etc.) I use it all the time and have seen hundreds of passes thanks to it. Embedded in the ZIP file is probably the best database on satellite magnitudes and radar cross sections. URL is: ftp://kestrel.umd.edu/pub/wxsat/programs/quiks210.zip
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