Fobos-Grunt: decay estimate

From: Ted Molczan (
Date: Sun Jan 01 2012 - 22:07:36 UTC

  • Next message: George Roberts: "Re: red satellite"

    The mean rate of decay of the semi-major axis of the thirty-six (36) USSTRATCOM TLEs from epoch 11361.55720242 to
    12001.54966173 (2011 Dec 27 13:22 - Jan 01 13:12 UTC) was 1.9331 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 = 0.0011927 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 +/- 3 days, based on the rule of thumb of 20 percent of the time remaining to decay.
    Below is the plot of estimated A/m since the orbit manoeuvres ceased, through Dec 31. Most of the points are at ~2 day
    intervals, and typically span the preceding ~2 day period. For Cd = 2.2, the mean A/m was 0.0012786 mē/kg; those values,
    with predicted space weather, would advance the estimated date of decay by about one day, to Jan 15.
    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
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Sun Jan 01 2012 - 22:08:53 UTC