Fobos-Grunt: decay estimate, area to mass ratio

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Tue Jan 10 2012 - 06:34:17 UTC

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    I estimate decay on 2012 Jan 16 near 07:00 UTC, based on USSTRATCOM's TLE of epoch 12010.14668728 (Jan 10 03:31 UTC),
    the long-term average area to mass ratio (A/m) of 0.0012502 mē/kg, Cd = 2.2, and the space weather forecast issued by
    the USAF on Jan 09 at 21:10 UTC. 
    
    The approximate time of day of the estimated decay is reported only to reveal trends. The uncertainty is about 1.3 days,
    based on the rule of thumb of 20 percent of the time remaining to decay. The exact hour of decay will only be known with
    certainty a few hours before the fact. 
    
    I used primarily STOAG, but since its output is at no less than one day intervals, and ceases when the semi-major axis
    falls below 140 km, I used Satana/Satevo to estimate the remaining time to decay, which was about one day.
    
    Using Satana and Satevo without STOAG, yields estimated decay on Jan 15 near 21:00 UTC. I used Satana to adjust the
    decay terms of the TLEs of epoch 12008.18627938, 12009.16691711 and 12010.14668728 for a better fit. Finally, I used
    Satevo to propagate the improved version of the last TLE of this series to decay. Without Satana, Satevo estimates decay
    on Jan 16 near 12:00 UTC. Solar flux was set to the mean value during the span of the TLEs, which was 139. Satana/Satevo
    do not employ forecast space weather, but nevertheless yield reasonably reliable estimates.
    
    I decided to base the STOAG decay estimate on the long-term A/m, instead of a recent short-term value, because my
    on-going analysis reveals zero correlation between A/m and time, as shown in this plot of values derived using STOAG,
    from historical orbital and space weather data since the spacecraft's orbit manoeuvres ceased in late November 2011,
    through Jan 08 UTC: 
    
    http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_area_to_mass_ratio_evolution_v11.pdf
    
    I extracted the actual and forecast 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.
    
    Ted Molczan
    
    
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