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

From: satrack@libero.it
Date: Wed Nov 30 2011 - 06:53:37 UTC

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    SatEvo predicts now reentry on the last week of the year, about two weeks 
    earlier than predictions with the previous TLEs.
    Updated figures: 
    >----Messaggio originale----
    >Da: paul.salanitri@gmail.com
    >Data: 30-nov-2011 6.02
    >A: "Ted Molczan"<ssl3molcz@rogers.com>
    >Cc: "<seesat-l@satobs.org>"<seesat-l@satobs.org>
    >Ogg: 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 - 
    >> 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.
    >> 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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