RE: GSSAP arrives in GEO

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 20 Aug 2016 11:35:43 -0400
Thanks to Scott Tilley, we have observations spanning a large fraction of the GTO and the first few minutes of the Delta
4 second stage's final orbit. With respect to the latter, the search elements (shown below), which were essentially Mike
McCants' elements from observations of the first GSSAP launch rotated to the time of yesterday's launch, proved to be
accurate. The object was about 48 s late, and within 0.05 deg cross-track. So it seems that this launch was close to a
"carbon-copy" of the first.

Pre-launch search elements
1 73704U 73704A   16232.49236112  .00000000  00000-0  00000-0 0    07
2 73704   0.4851  49.1111 0009503   3.2888 358.9484  0.98907630    07

Scott's observational arc was limited by bright twilight to just 5 minutes, which is insufficient for a complete orbit
analysis, which required making some assumptions about which elements to fix and which to allow to vary. I experimented
with various combinations of fixed and variable elements, before arriving at the following updated search elements:

GSSAP 3 r                                            36147 X 36202 km
1 73704U 73704A   16232.50440972  .00000000  00000-0  00000-0 0    00
2 73704   0.4851  44.8229 0006452 183.2891 187.3458  0.98907630    07
Arc 20160819.5-0819.5 WRMS resid 0.002 totl 0.002 xtrk

Along-track errors could be a significant fraction of a degree, per 24 h from epoch. I expect cross-track errors to be a
small fraction of a degree.

USSTRATCOM has catalogued three objects from the launch:

USA 270       2016-052A  41744
USA 271       2016-052B  41745
Delta 4 r/b   2016-052C  41746

The 73704 search TLE is for 2016-052C / 41746.

I intend to follow-up with revised LEO parking and GTO elements, which may inform our planning for future launches in
the series. I am interested in alternative solutions, so please post your results.

Ted Molczan


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Received on Sat Aug 20 2016 - 10:36:22 UTC

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