Fobos-Grunt: decay estimate

From: Ted Molczan (
Date: Sun Dec 25 2011 - 17:14:02 UTC

  • Next message: Joseph Remis: "38037 decay"

    The mean rate of decay of the semi-major axis of the twenty-two (22) USSTRATCOM TLEs from epoch 11354.57578212 to
    11359.5202604 (2011 Dec 20 13:49 - Dec 25 12:29 UTC) was 1.5846 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 = 0.0011925 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 +/- 4 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 23. 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
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Sun Dec 25 2011 - 17:15:54 UTC