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Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!decvax!bellcore!petrus!karn
From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.space
Subject: Re: Re: Ariane destroyed
Message-ID: <539@petrus.UUCP>
Date: Sat, 14-Sep-85 23:06:18 EDT
Article-I.D.: petrus.539
Posted: Sat Sep 14 23:06:18 1985
Date-Received: Tue, 17-Sep-85 04:48:40 EDT
References: <536@petrus.UUCP> <528@riccb.UUCP>
Organization: Bell Communications Research, Inc
Lines: 39

> ...Strictly speaking, the Space Transportation
> System is one launcher which has NEVER failed to get a payload into orbit.
> Doesn't it seem likely that this will finally cause the insurance and
> satellite communications industries to realize that the shuttle is actually
> a more cost effective means of reaching orbit?

It's not quite that simple. True, the Shuttle has not yet had a launch
failure resulting in the complete loss of the payloads (and the launcher!)
before reaching orbit. However, Westar-6 and Palapa-B had PAM failures, and
PAMs are unnecessary with Ariane because the latter puts you directly in a
35800 x 200 km geostationary transfer orbit. Only one additional burn
is needed to reach a circular geostationary orbit.

What's important when it comes to insurance rates is the overall probability
of the spacecraft reaching its proper orbit and actually doing its job. It
doesn't matter whether the satellite goes down in the Atlantic, gets stuck
in a useless LEO, or arrives at GEO only to die (like the recently launched
Syncom).

When it works, Ariane is a much "friendlier" launcher for communications
satellites than the Shuttle. Its equatorial launch site gives you a lower
inclination transfer orbit. This means you can use a smaller apogee kick
motor, allowing increased payload weight. Ariane deploys you immediately
after reaching orbit; the Shuttle holds onto you for a day or two during
which time you have no solar power, attitude control or control over the
thermal environment.  Shuttle safety requirements require that you delay 45
minutes after separation before doing the PAM burn.  During this time many
satellites have to expend considerable amounts of hydrazine to maintain the
"excellent" attitude given them by the Shuttle.

It has been sheer luck that there have been three opportunities for in-space
salvage or repair of satellites launched on the shuttle whose upper stage
engines failed.  Once the satellite leaves the rather narrow set of orbits
that are accessible to the Shuttle, it's on its own.  If it had been the
apogee kick motors that failed on Westar, Palapa or Syncom, there would have
been no chance for in-orbit repair, just as there is no chance of an
in-orbit repair on the one that was just launched.

Phil


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