Re: NROL-101 manoeuvre imaged from Joshua Tree?

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 15 Nov 2020 10:30:07 +0100
Hi all,

The image and video that Marco and Scott discovered provide some
interesting clues to the NROL-101 orbit. If we assume this is the fuel
dump of the Centaur upper stage, I think they seem to rule out the
Molniya hypothesis, as both images suggest the fuel dump was visible
around 02:30UTC, about 4 hours after launch.

For a Molniya orbit, the burn from the parking orbit to Molniya would
occur around 23:36UTC, and on geostationary transfer missions, S/C sep
is usually about 30 minutes after launch, with the Centaur CCAM
(collision and contamination avoidance maneuver) shortly afterwards
(within an hour?). For the Molniya orbit elements that Ted estimated,
the payload and Centaur would be nearing apogee at 02:30UTC.

My guess would be that the NROL-101 payload went to a MEO orbit, where
the Centaur performed a burn from the parking orbit to a transfer
orbit, as well as a circularization burn at the first apogee. The fuel
dump then occurred after circularization. This hypothesis would be
strengthened by the fact that the Centaur did not have a deorbit area
and has been catalogued by CSpOC. Jonathan McDowell kindly recorded
that at 01:49UTC (launch +3h17m), ULA called mission success.

It may be possible to determine the altitude of the MEO orbit from the
motion of the fuel dump cloud and the timing of mission success. I
will try to investigate.

Regards,
     Cees
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Received on Sun Nov 15 2020 - 03:31:21 UTC

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