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

From: Paul Salanitri (paul.salanitri@gmail.com)
Date: Wed Nov 30 2011 - 05:02:11 UTC

  • Next message: satrack@libero.it: "R: Re: Fobos-Grunt: no manoeuvring evident in TLEs after 2011 Nov 20 UTC"

    There has been a small anomalous change, not the orbit increase desired, but something has happened. We'll stay tuned....
    
    Paul S
    
    
    
    On 29/11/2011, at 23:07, "Ted Molczan" <ssl3molcz@rogers.com> wrote:
    
    > Manoeuvring was last clearly evident in the USSTRATCOM TLE of epoch 11324.94169617. It appeared to have ended by the
    > epoch 11325.19110916 TLE, and appeared not to have resumed as of the epoch 11333.12745729 TLE (2011 Nov 29 03:04 UTC). 
    > 
    > Orbit evolution for the latest 5-day period (11328.24537235 - 11333.12745729):
    > 
    > http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_orbit_evolution_v9.pdf
    > 
    > Assuming solar activity remains near the low end of normal, STOAG propagates the orbit to decay on 2012 Jan 16.
    > Uncertainty +/- 10 days, based on the rule of thumb of 20% of time remaining until predicted decay.
    > 
    > I have been watching some recent small variations between the TLEs and theory, that are too small for me to attribute to
    > manoeuvring, but perhaps worth noting. For example, the unusually high rate of precession of the argument of perigee was
    > one of the manifestations of the manoeuvres. The theoretical rate, per the SGP4 model was about 4.05 deg/d, but during
    > the manoeuvres it averaged ~5.21 deg/d, as shown on the following plot:
    > 
    > http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_precession_arg_of_perigee_v1.pdf
    > 
    > The red triangles are derived from the TLEs, calculated as the mean rate of precession between pairs of TLEs about 2
    > days apart. Shorter intervals yielded similar, but more scattered (noisy) results. This clear evidence of manoeuvres
    > ended late on Nov 20 or early Nov 21 UTC, and was fully reflected in the 2-day average by Nov 23 UTC. For the next few
    > days, the 2-day mean rate of precession was nearly identical to the theoretical rate, but then it began to rise on Nov
    > 26, reached a peak of 4.39 deg/d the following decay, then declined, and returned to nearly the theoretical rate as of
    > the latest TLE. The effect appears to have been real, but I suspect it was more likely due to a gradual correction of
    > the elements than a manoeuvre. During this period, the rate of orbital decay decreased slightly, and the rate of
    > decrease of the perigee distance was slightly less than predicted by STOAG for the same mean rate of decay, but these
    > effects appear to be normal variations.
    > 
    > Ted Molczan
    > 
    > 
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