Using the numerical integrator in GMAT 2014a, I found Cd=2.2 and A/m=0.0029 m^2/kg sufficient to account for the decay over the span of USSTRATCOM's TLEs of epoch 15127.69108536 and 15127.81228385. Allowing the propagation to continue until decay, results in impact (10 km altitude) on 2015 May 08 near 03:42 UTC. The uncertainty is 1.6 h, based on the rule of thumb of 20 percent of the estimated time remaining to decay, measured from the epoch of the latter of the two TLEs. The decay time derived from recent TLEs has been trending later. Using the epoch 15127.50860911 and 15127.63013248 TLEs as the starting point to calibrate the A/m, resulted in unrealistically low values, that would have put the decay at least 2 h later. USSTRATCOM issued three TLEs near the epoch of 15127.69. That of epoch 15127.69108536 was issued well after the other two, and somewhat increased the altitude. Using this as my starting point for calibration, yielded the above A/m value, which is in line with earlier values for this object, and within the range I consider reasonable, given its dimensions and approximate mass (my impression has been that it retains most of its fuel, but I am not certain of this). I converted the epoch 15127.69108536 for propagation by GMAT using TLE Analyzer 2.12. I configured GMAT to use its Dormand-Prince 78 numerical integrator, with the EGM-96 gravity model (degree 90, order 90), and the MSISE90 atmosphere model. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Thu May 07 2015 - 19:37:55 UTC
This archive was generated by hypermail 2.3.0 : Fri May 08 2015 - 00:37:55 UTC