Fobos-Grunt: no manoeuvring evident in TLEs after 2011 Nov 20 UTC

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Thu Nov 24 2011 - 00:44:03 UTC

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    In my last report, I stated that the unusual evolution of the orbit of Fobos-Grunt (11065A / 37872) (now generally
    accepted to have been the result of manoeuvring) had continued through 2011 Nov 21 UTC. My analysis of subsequent
    USSTRATCOM TLEs reveals that by Nov 21 the manoeuvring had in fact ceased, and the object remained on a ballistic
    trajectory as of the latest available TLE. 
    
    Sometime between the TLEs of epoch 11324.94169617 and 11325.19110916, the object began to decay at about the rate
    expected of an object of its dimensions and mass, given the existing orbit and space weather. 
    
    The following plot is of the same format, and results from the same methodology as before, but covers Nov 21 UTC to the
    present (epoch 11325.19110916 to 11327.87148743):
    
    http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_orbit_evolution_v4b.pdf
    
    The A/m input to STOAG that explains the observed rate of decay was 0.001176 m^2/kg, which is within about 10 percent
    (on the low side) of the value expected based on the object's dimensions and mass. This is double the value during the
    period when the object manoeuvred.
    
    The rate of circularization of the orbit was close to the rate predicted by SGP4 and STOAG. As a result, the perigee and
    apogee distance both decreased, and at about the rate predicted by SGP4 and STOAG. During the period of manoeuvring, the
    perigee increased, and the apogee decreased more rapidly than expected.
    
    The observed precession of the argument of perigee was at nearly the rate predicted by SGP4 and STOAG. During the period
    of manoeuvring it was 30 percent greater than predicted.
    
    The orbital evolution since Nov 21 UTC appears to be unique since at least early in the mission, perhaps since the
    launch. I noticed that during most of Nov 13-15 UTC the rate of decay was almost as great as it has been since Nov 21,
    so I looked for evidence of normal ballistic flight during that period, but my analysis clearly reveals that that the
    manoeuvring was occurring:
    
    http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_orbit_evolution_v4a.pdf
    
    I intend to continue to follow the evolution of the orbit and provide occasional updates.
    
    Ted Molczan
    
    
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