Ted, Looking at the plot, if I read it correctly the actual perigee has remained constant and the apogee has decreased. If this is correct, isn't this normal? I thought that drag at perigee would slow it down decreasing the apogee. What am I missing? Perhaps the models have some generic problem? Bill Bard On Nov 22, 2011, at 1:53 AM, "Ted Molczan" <ssl3molcz@rogers.com> wrote: > The unusual evolution of the orbit of Fobos-Grunt (11065A / 37872) continued through 2011 Nov 21 UTC. Below is my > updated plot, using the methodology described earlier: > > http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_orbit_evolution_v3.pdf > > The plots now include the SPG4-propagated orbit, in addition to the STOAG, to make clear that both are in substantial > agreement on the expected evolution, and in disagreement with the actual, as revealed by USSTRATCOM's TLEs. Also, I have > added a plot of the mean eccentricity, which clearly shows that the orbit has circularized much more rapidly than > expected due to drag alone. The mean eccentricity is as defined in SGP4-based TLEs, i.e. for argument of perigee = zero. > > In case anyone is wondering whether USSTRATCOM's TLEs are somehow in error, I can state that the trajectory data reduced > from Paul Maley's recent time-stamped video is in close agreement with near-contemporaneous TLEs, in terms of time and > track, but relative earlier and later TLEs, the track residuals are very large, even after allowing for Earth's rotation > over the interval of the time residuals. This is mainly due to the ~35 percent faster than normal precession of the > argument of perigee, as well as the aforementioned circularization, which I believe to be manifestations of the same > phenomenon, probably due to a propulsive release of matter from the spacecraft, which may also explain the unusually low > rate of decay - barely half the expected value, based on the object's dimensions and mass. > > If anyone is aware of a natural phenomenon not modeled by SGP4 or STOAG, that could account for the evolution of the > orbit, I would be interested to see the results of supporting calculations. > > Finally, the list received word overnight of an observation of F-G from San Francisco, apparently the pass of Nov 22 at > 01:44 UTC, during which it was flashing with a period of variation of about 20 s. Have there been any other similar > reports? > > http://satobs.org/seesat/Nov-2011/0254.html > > Ted Molczan > > > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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