Fobos-Grunt: decay estimate

From: Ted Molczan (
Date: Sat Dec 17 2011 - 16:18:45 UTC

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    The mean rate of decay of the semi-major axis of the twenty-three (23) USSTRATCOM TLEs from epoch 11346.58616089 to
    11351.54320883 (2011 Dec 12 14:04 - Dec 17 13:02 UTC) was 1.3197 km/d. 
    Using the STOAG propagator and actual space weather during that period, I found that the mean rate of decay could be
    accounted for using A/m = 0.0013191 mē/kg and Cd = 2.2.
    Using those values with predicted space weather, STOAG propagates the orbit to decay on 2012 Jan 12. Estimated
    uncertainty is +/- 5 days, based on the rule of thumb of 20 percent of the time remaining to decay.
    I extracted the actual and estimated space weather data required by STOAG from data provided by, which
    compiles data issued by official sources (mainly NOAA) and presents it in a convenient format:
    Ted Molczan
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