Fobos-Grunt: decay estimate

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Sat Dec 31 2011 - 21:05:33 UTC

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    The mean rate of decay of the semi-major axis of the thirty-four (34) USSTRATCOM TLEs from epoch 11360.56979805 to
    11365.50279151 (2011 Dec 26 13:41 - Dec 31 12:04 UTC) was 1.8542 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 = 0.0011742 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 29. 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 0.0012801 mē/kg; those values,
    with predicted space weather, would advance the estimated date of decay by about two days, to Jan 14.
    
    http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_area_to_mass_ratio_evolution_v6.pdf
    
    I extracted the actual and predicted space weather data required by STOAG from data provided by Celestrak.com, which
    compiles data issued by official sources (mainly NOAA) and presents it in a convenient format:
    
    http://celestrak.com/SpaceData
    
    http://celestrak.com/SpaceData/SpaceWx-format.asp
    
    Ted Molczan
    
    
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