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From: karn@allegra.UUCP (Phil Karn)
Newsgroups: net.space
Subject: Thoughts on Westar/Palapa
Message-ID: <2260@allegra.UUCP>
Date: Tue, 7-Feb-84 02:32:49 EST
Article-I.D.: allegra.2260
Posted: Tue Feb  7 02:32:49 1984
Date-Received: Thu, 9-Feb-84 03:46:22 EST
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 58

A few comments and bits of information regarding the Westar/Palapa
fiasco.

I talked with some of my friends in the satellite business today who
have heard some of the details which don't make it through the "noisy
channel" known as the media. The "working theory" regarding the PAM
failure has to do with an overpressure in the engine caused by a
temporarily blocked nozzle. The nozzle could have been blocked by a plug
of initiator material which could have become rigid if the temperature
was too low.  After the engine had burnt for a while, the pressure
eventually blew the nozzle apart. Once this happened, the chamber
pressure dropped too low to sustain combustion, and the engine "flamed
out".  It seems there was a minor design change made to both PAMs before
this mission, and...

Contrary to what you may have heard, it is indeed possible to stop a
solid fuel motor once it has started in a vacuum by doing just this -
blowing the nozzle off and reducing the chamber pressure.  For example,
the solid fuel kick motor flown on AMSAT Phase 3-A (the one that
was lost in 1980) was originally designed as a terminal vernier for a
Titan ICBM.  It had a deliberate "thrust termination feature" which
involves blowing off the nozzle - needless to say, we didn't need this
feature.

Western Union (and the Indonesian government, assuming their satellite
is in the same condition as Westar) has several options. Westar has
a full load of hydrazine and, presumably, a good apogee kick motor.
With these they could:

1. Circularize the orbit at its apogee altitude of 750 miles. It would
be stable here indefinitely, but not very useful for communications.
2. Fire the apogee kick motor to place the satellite in a highly
elliptical orbit resembling, interestingly enough, that of AMSAT
Oscar-10. Here someone could theoretically get a few hours per day use out
of the satellite while at apogee, where it would move slowly enough to
be tracked.
3. Upon request of NORAD to "keep the skies clean", they could fire the
kick motor to cause the satellite to re-enter the atmosphere and burn
up.

Obviously, all of these suggestions remove any possibility of shuttle
retrieval.  However, if I look at my STS user's manual, I note that the
shuttle is in fact capable of reaching fairly high apogees in ELLIPTICAL
orbits.  With integral tanking, it could carry a full load to a 28 deg
185 x 900 km orbit assuming that the deorbit burn is done from apogee. With
several OMS kits (extra fuel tanks) in place of payload, it could reach
1500 km (1 tank) 2250 km (2 tanks), etc.  On the other hand, it would be
much easier if the satellites could be dropped back to their circular
185 km orbits just before retrieval.  I don't know if there is enough
hydrazine on board to do that.

In any event there would be a LOT of practical problems (how do
you grab the satellite, reattach a new PAM, refuel the hydrazine tanks,
and re-deploy the satellite when it wasn't designed for this kind of
operation?)  Still makes an interesting problem for speculation, and
at a total stake of $200 M, who knows?  They might just try it.

Phil