The mean rate of decay of the semi-major axis of the twenty-four (24) USSTRATCOM TLEs from epoch 11357.54351775 to 11362.60588000 (2011 Dec 23 13:023 - Dec 28 14:32 UTC) was 1.7179 km/d. Using the STOAG propagator and actual space weather during that period, I found that the mean rate of decay could be accounted for using A/m = 0.0011873 mē/kg and Cd = 2.2. Using those values with predicted space weather, STOAG propagates the orbit to decay on 2012 Jan 15. Estimated uncertainty is +/- 4 days, based on the rule of thumb of 20 percent of the time remaining to decay. Below is the plot of estimated A/m since the orbit manoeuvres ceased, through Dec 25. Most of the points are at ~2 day intervals, and typically span the preceding ~2 day period. For Cd = 2.2, the mean A/m was 0.0012534 mē/kg; those values, with predicted space weather, would advance the estimated date of decay by about one day, to Jan 14. http://satobs.org/seesat_ref/phsrm/Fobos-Grunt_area_to_mass_ratio_evolution_v4.pdf I extracted the actual and predicted 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 http://celestrak.com/SpaceData/SpaceWx-format.asp Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
This archive was generated by hypermail 2b29 : Wed Dec 28 2011 - 16:17:15 UTC