Fobos-Grunt: decay estimate

From: Ted Molczan (
Date: Fri Dec 23 2011 - 10:52:48 UTC

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    The mean rate of decay of the semi-major axis of the twenty-two (22) USSTRATCOM TLEs from epoch 11352.16232839 to
    11357.23452446 (2011 Dec 18 03:54 - Dec 23 05:38 UTC) was 1.4620 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 = 0.0011888 mē/kg and Cd = 2.2.
    Using those values with predicted space weather, STOAG propagates the orbit to decay on 2012 Jan 16. Estimated
    uncertainty is +/- 5 days, based on the rule of thumb of 20 percent of the time remaining to decay.
    I have updated the plot of estimated A/m since the orbit manoeuvres ceased. Most of the points are at ~2 day intervals,
    and typically span the preceding ~2 day period.
    I extracted the actual and predicted 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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