Updated MUOS 5 elements

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Tue, 16 Aug 2016 00:04:33 -0400
The following elements are based on observations by Scott Tilley and Brad Young:

MUOS 5                                               15776 X 35698 km
1 41622U 16041A   16228.48483796  .00000000  00000-0  00000-0 0    08
2 41622   9.7709 322.7292 3101661 182.2453 258.6457  1.50856454    04
Arc 20160812.65-0815.48 WRMS resid 0.002 totl 0.001 xtrk

As Scott noted, the manoeuvring seems to have been halted, at least for now.

The total delta-V due to the small manoeuvres that began in late July, several weeks after MUOS 5 was stranded in GTO,
is about 20 m/s. Since the LAE (Liquid Apogee Engine) appears to have malfunctioned, it is reasonable to guess that the
manoeuvres have been due to firings of the REA (Reaction Engine Assembly) thrusters, much like those performed by AEHF-1
in 2010, after it became stranded in GTO. If so, then they appear to have been of much shorter duration, and perhaps
lower thrust, than those of AEHF-1. 

The following table, first posted in September 2010, summarizes the estimated AEHF-1 REA burns, based on hobbyist
tracking and what was known and could be estimated of the performance of the REA:

http://satobs.org/seesat_ref/misc/AEHF_1_manoeuvres_v2.5.pdf

AEHF-1 completed 11 REA firings over a period of about 24 days, each of which resulted in delta-V between 11-65 m/s, for
total delta-V of 345 m/s. MUOS 5 has REA thrusters of the same make, model, number and thrust as those of AEHF-1, yet
has achieved a total delta-V of only about 20 m/s over a roughly similar period. 

I can think of no obvious reason for the REA of the two spacecraft to have been operated so differently, which leads me
to question whether MUOS 5 has in fact been firing its REA. Could it have been firing its LAE after all, perhaps testing
modes of operation that would enable salvaging as much as possible of the original mission? 

Another possibility perhaps worth investigating is whether MUOS 5 may have been venting unused oxidizer through its LAE,
in preparation for the REA firings? The LAE is a bi-propellant system, which burns hydrazine and an oxidizer. The REA is
a mono-propellant system, that burns hydrazine alone. If the LAE could no longer be fired, then any unburned oxidizer
would be dead weight. Venting it would reduce the s/c mass, which would reduce the fuel required by the REA to reach the
planned orbit. Perhaps the venting could also make a small contribution to the delta-V. Could the manoeuvres of the past
few weeks have been due to the venting of oxidizer?

Ted Molczan


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Received on Mon Aug 15 2016 - 23:05:11 UTC

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