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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: SRB Telemetry Clues
Message-ID: <8602011714.AA03500@s1-b.arpa>
Date: Sat, 1-Feb-86 11:17:21 EST
Article-I.D.: s1-b.8602011714.AA03500
Posted: Sat Feb  1 11:17:21 1986
Date-Received: Mon, 3-Feb-86 06:23:47 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 30

The NY Times today (2/1/86) reports that telemetry indicates the right
(far) SRB experienced a 4% drop in thrust and a 30 lb/in^2 drop in pressure
starting 10 seconds before the explosion.   The main engines and SRB
nozzles were swivled at that time to try to compensate.  Also, telemetry
indicates the main engines stopped several seconds before the explosion,
apparently because the oxygen line running down the side of the ET was cut.

My guess of the course of the accident is this: (1) the right SRB
was faulty, (2) when the burn-though on the side of the SRB occured
(either because of cracked propellant or casing) a jet of hot gas hit
the ET near the oxygen line, (3) it took several seconds for the
insulation and metal to burn through, (4) when the oxygen line went
gas began escaping and perhaps the tank structure itself (aluminum)
burned in the hot oxygen gas, (5) just before the explosion the
flames may have set off the range-safety charges on the ET, allowing
the fuels to mix and explode.  This could explain the small explosion
that occured several frames before the big blast.

It looks like proper software could have saved the shuttle.  The proper
course would have been to jettison the SRB's as soon as one acted up.
Unfortunately, SRB's have varying thrust, so perhaps NASA didn't want
to jettison one for just a 4% variation.  Even so, the shuttle could
have tried to get away when all the main engines failed, although it's
not clear enough time remained for it to get clear.

Does anyone know if the shuttle was in a position to return to Kennedy,
or did it already have too much lateral velocity to glide back on its
own?  Also, how close is the oxygen line to the right SRB?  If it runs
down the right side of the ET this could be considered a serious design
error (similarly for the range safety charges).