Here we go again! NASA has updated the planned shuttle elements for the new liftoff time of 19:26:06 UT on 2-JUL-06. And once again I find a discrepancy for the coasting arc #1 TLEs which should be valid from 19:36:34 UT until 20:04:45 UT (2-JUL-06). My revised TLEs which are in line with the also given state vector are: STS-121 MECO 1 0 06183.81706019 0.00000000 00000-0 00000-0 0 1 2 0 51.6323 107.4833 0128427 347.8369 69.9206 16.48997116 1 As Dave has found out the epoch of the arc #1 TLEs is that of the first ascending node. But those TLEs show a 43 x 100 km orbit instead of the 56 x 225 km MECO orbit of the actually given state vector. Trying to change the epoch does not make them any better. Something is fishy here. Of course NASA flight dynamics will calculate shuttle orbits by numerically propagating state vectors. Whatever program they use to convert a state vector into TLEs has little relevance to them. The TLEs do come out correctly for *normal* orbits but they may not have properly tested their procedure for these low MECO orbits! If you are only interested in shuttle observations once it has crossed the Atlantic you could also use the arc #2 TLEs and propagate them backwards for the few minutes it takes to reach Europe let's say. Although not accurate it should normally be enough to roughly know when to look where for the shuttle (at least if the sky is dark and clear enough). Gerhard HOLTKAMP Darmstadt, Germany ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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