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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: Re: Most Dangerous: Launch or Landing?
Message-ID: <8602241623.AA01553@s1-b.arpa>
Date: Mon, 24-Feb-86 10:25:46 EST
Article-I.D.: s1-b.8602241623.AA01553
Posted: Mon Feb 24 10:25:46 1986
Date-Received: Wed, 26-Feb-86 20:10:49 EST
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Organization: The ARPA Internet
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Did the RAND study say the dangerous part of landing was the reentry or
the touchdown?  I wonder what the chances of disaster are if a tile
comes off the bottom of the orbiter.

The shuttle's problem may be that recognized flaws are difficult to fix,
not just that there are many low probability unknown flaws.  For example,
it's known that there's no abort mode for the first two minutes of
flight, but this is a fundamental feature of the shuttle design and cannot
be easily changed.

One flaw I worry about during liftoffs is catastrophic failure of the
SSME turbopumps.  These pumps have suffered from cavitation on previous
flights; if one of the pumps were to fly apart high velocity metal
fragments could go flying through the engine compartment.  This was one
early speculation about the Challenger accident (since discarded).

Continuing upgrades of the shuttle make extrapolations of reliability
suspect.  For example, if and when the SSME's are upgraded to 109%
of rated thrust we won't be able to use previous flights as indicators
of their reliability.