Thought some on this list might be interested in the following. I've been generating TLEs for a few "unusual" objects recently not tracked by Space-Track, including the Spektr-RG X-ray/gamma-ray observatory and its booster. The observatory itself will, we hope, go out to the Earth-Sun L2 point, about 1.5 million km away, and stay there (with the aid of occasional small maneuvers). The booster will go out there and just keep going into a heliocentric orbit. We won't see it again until June 2038, after it's completed 18 orbits around the sun and we've completed 19 : https://www.projectpluto.com/pluto/mpecs/19040b.htm Fitting TLEs to an object that's headed into heliocentric orbit has some odd consequences. The TLEs for this object are at https://github.com/Bill-Gray/tles/blob/master/19040b.tle with one TLE fitted for each day, up to October 1. At that point, the nominal eccentricity reaches one, and the mean motion (see the last TLE at the above page) reaches 0.00003600 revolutions/day, for an "orbital period" of about 76 years. Not that the object will actually do that, of course. But you do get a TLE that models the motion of the object to an accuracy of about 80 km, at a point where it's nearly three million kilometers away. I think this must be a record for a "TLE-able" object. Note that these TLEs may or may not work for you. With objects like these, you have to use SGP4 for an object that is undeniably not in a 225-minute or less orbit. If your software pays attention to the "ephemeris type" flag in a TLE, you'll be okay : https://www.projectpluto.com/tle_info.htm#eph_type If it assumes the "ephemeris type" is always zero or blank, these TLEs won't work for you. They'll definitely stress-test your programs, though. -- Bill _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Sun Aug 18 2019 - 15:10:04 UTC
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