SBIRS GEO 1 elements

From: Ted Molczan (
Date: Sun May 08 2011 - 11:47:47 UTC

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    Kevin Fetter has reported four observations of what appears to be SBIRS GEO 1. 
    The observations were about 45 s early, and very close to the track predicted by the 11019B elset I posted overnight.
    Here are approximate elements based on Kevin's observations:
    SBIRS GEO 1                                            185 X 35817 km
    1 37481U 11019A   11128.00311397  .00000000  00000-0  00000-0 0    05
    2 37481  21.6360 319.7624 7307920 178.3079 187.4348  2.28138000    07
    Arc 20110507.79-0508.36 WRMS resid 0.016 totl 0.014 xtrk
    I added a synthetic observation based on the 11019B elset, taken at its epoch. I allowed only the argument of perigee
    and mean anomaly to vary.
    Assuming that the observation times correspond to flashes, then linear regression reveals a period of variation is 601.8
    s, with r^2 near unity. As Kevin pointed out, A2100 satellites rotate at this stage of their mission. The typical rate
    is 0.1 RPM, which corresponds to the observed period of variation, assuming one flash per revolution. It is more common
    to find two flashes per revolution, but that would have resulted in a ~300 s period of variation.
    Once the spacecraft begins its planned manoeuvres to geosynchronous orbit, we are likely to lose it for a time; until
    then, I suggest allowing several minutes prediction time uncertainty using the above elements.
    Ted Molczan
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