Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mcdchg!illusion!marcus
From: marcus@illusion.UUCP (Marcus Hall)
Newsgroups: sci.space.shuttle
Subject: Re: shuttle escape systems
Message-ID: <409@illusion.UUCP>
Date: 20 Oct 89 15:37:57 GMT
References: <538.252A3A3B@mamab.FIDONET.ORG> <34577@srcsip.UUCP> <126311@sun.Eng.Sun.COM> <1307@accuvax.nwu.edu> <15596@netnews.upenn.edu>
Reply-To: marcus@illusion.UUCP (Marcus Hall)
Organization: Magic Numbers Software, Bloomingdale, IL
Lines: 59


In article <1307@accuvax.nwu.edu> phil@delta.eecs.nwu.edu (William LeFebvre) writes
] The flight dynamics people probably saw something wrong as much as 10
] seconds before the explosion, because the trajectory was wrong and the
] engines were gimballing (sp?) a very large amount to try to 
] compensate.  Of course, they probably didn't associate that with
] impending disaster.  But even if they had known there was a problem,
] there wasn't a thing they could do about it until after SRB
] separation.

The trajectory deviation could easily have been due to unexpected wind
shear (possibly combined with slightly more than normal SRB thrust asymmetry)
which is NOT any reason to abort so long as the thrust vectoring is able
to keep up.  All aborts are considered higher risk (except perhaps abort to
orbit) since they subject the STS system to very large stresses.  The abort
procedures are *supposed* to work.  Nobody would actually want to try them
out unless its absolutely necessary.  So, if such indirect evidence is all
you have that something's wrong, it probably isn't a wise choice to try an
abort that *might* work (say even 50% chance of success) unless you know
that your current situation is worse that that chance.

BTW, does anybody know what the chances of the orbiter surviving the powered
pitch over maneuver in the RTLS abort sequence is?  Certainly if there was
some possible abort worked out before SRB termination it would have even less
chance than that.

]  It is acknowledged that the first two minutes of
] ascent---the time when the SRBs are burning---is the most critical and
] the most sensitive to disaster.  ...

In article <15596@netnews.upenn.edu> santerel@clarke.cis.upenn.edu.UUCP (Walter Santarelli) writes:
[ This is the reason I'm still amazed that we launch people on the
[ current system at all. I believe the original concept called for a
[ re-usable liquid fueled booster. Liquid fueled boosters offer the
[ advantage that they can be throttled. SRB's can't. They just go. When
[ I was an undergrad, I had a rocket propulsion professor who stated on
[ more than one occasion that using SRB's for manned space flight was
[ not smart safety-wise. In fact, before the Challenger accident, he
[ stated predicted that the SRB's would be the cause of the first major
[ accident. 

Actually, I believe that the landings (especially at Kennedy) are still
considered the most likely cause of an accident.  The SRBs were considered
a relatively simple system that wasn't likely to fail (and thus the lack
of an abort during SRB burn wasn't thought to be as big a risk as it is
thought today).  The SSME's are much more complicated and had some spectacular
failures during development.

Much more work went into reducing the risks that were precieved at the time.
Although it was recognized that the SRBs were a critical item, it was not
pushing any technologies significantly and was thought to be a problem well
understood and the resources were spent on reducing other "more likely"
failures.  In hind sight, the SRBs were ignored too much, but at the time
I'm sure it seemed like the proper way to spend the resources.

--

marcus hall			Time is an illusion
marcus@illusion.UUCP		Lunchtime doubly so - HHGTTG