The ISS did some thruster tests recently. That could account for the difference. ISS is a dynamic satellite. It has minor and major changes to its orbit and the "predicts" are sometime a bit behind the actual until things fall into a more stable state and get updated. I expect the numbers will be off again after the Soyuz undock today (tomorrow UTC).
Kenneth - N5VHO
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Patrick STODDARD (WD9EWK/VA7EWK) Sent: Wednesday, September 22, 2010 4:18 PM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: ISS keps
(after seeing weirdness in the message I sent, I will try it again so it looks better)
I checked against http://iss.astroviewer.net/. Today issue is better, however, still actual ISS posn about 100 miles ahead of SatPC32's displayed posn. My computer clock is off by no more than 1 second. For the clock to throw posn off by 100 miles, clock would need to be in error by about 15 seconds.
Just create an account at http://www.space-track.org/ and download the keps from there. I just logged into Space Track, and they have an ISS element set that was updated at approximately 2053 UTC today (not long before I sent this message).
Regardless of the freshness of the elements, it sometimes takes a little bit after the ISS has a boost raising its orbit to where the keps are back to being on the mark.
73!
Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/
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