TLEs for distant artificial satellites

TLEs for distant artificial satellites

Updated 10 June 2005

I will provide TLE (two-line element) data for some high-orbiting artificial satellites from time to time. The elements are computed using the astrometry given on this page. These are objects that could be (in most cases, already have been) confused with "real, interesting" natural objects.

You can click here to download the TLEs (about 84KBytes ZIPped, 399 KBytes unZIPped). Some warnings about what you'll get:

Included are elements for 1983-020A and 1983-020B (the ASTRON rocket and its booster), GEOTAIL = 1992-044A, IMP-8 = 1973-078A, 1969-046F, and XMM-Newton = 1999-066A. I'll add more as I get data for them. I'll have to come up with something other than TLEs to represent WMAP; I've a perfectly good orbit for it (assuming it hasn't maneuvered, which it probably has), but the TLE model breaks down for that object.

I generated these elements by solving for their orbits, usually with solar radiation terms and planetary and (of course) lunar perturbations and the earth's J2, J3, and J4. The fits were usually good to within a few arcseconds. Then I generated ephemerides and fitted said ephemerides at one-day intervals. The worst error (TLE compared to integrated ephemeris), in kilometers, is given for each TLE. Note that usually, said error is a few kilometers, which corresponds to a few arcseconds at the usual distances of these objects, and is good enough to let you ID objects. I wasn't trying to get absolute pinpoint accuracy; to get that, I'd either have to junk the SDP4 model or use a step size a lot smaller than one day.

The epoch given is for the start of the day covered. So if you wanted to compute where objects are on (say) 21.99 June 2005, you should use the TLEs for 21 June 2005, not those for the (closer) date of 22 June 2005. You'll see some lines at the top of the file that mention this fact; I intend to revise some of my software to be bright enough to say, "Huh! This file says its elements are good from the time of epoch to one day later!"

Quite a bit of astronomy software uses TLEs. If you're writing your own, you may want to look here for source code for implementing SDP4 (and other satellite methods... but the objects in this file are all high-flying objects and therefore use SDP4.)

Updated 10 June 2005: Some more recent observations have been included. Also, Peter Birtwhistle was able to recover 1969-046F, which enabled me to compute a decent orbit for it and to provide TLEs.