Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Blowing up the Shuttle
Message-ID: <1990Apr7.221851.14080@utzoo.uucp>
Organization: U of Toronto Zoology
References: <10556.1574.forumexp@mts.rpi.edu> <1990Apr5.035158.23244@utzoo.uucp> <10884@portia.Stanford.EDU>
Date: Sat, 7 Apr 90 22:18:51 GMT

In article <10884@portia.Stanford.EDU> mdbomber@portia.Stanford.EDU (Matt Bartley) writes:
>What first touched off the breakup?  I thought the burnthrough of the SRB
>caused the external tank to explode, from either burning through tank and
>lighting off the H2, or heating and pressurizing the stuff until the tank
>burst...

At about the same moment, (a) the external tank, having had a substantial
flame playing on it for some seconds, suffered a major structural failure,
and (b) the aft support struts for the SRB, exposed to the same flame,
failed, and the SRB pivoted on its forward struts, mashing in the side
of the tank near the top end.  The hydrogen did not "light off", as
far as is known, until the tank failed (in any case, it can't light off 
inside a tank with no oxidizer present), and tank pressures were not
grossly outside normal bounds.  There was no explosion, just a large fire
as hydrogen from the disintegrating tank burned.

>In the video, it seemed like the orbiter was blow to bits.  It didn't look
>like the tank blew and then the orbiter flew into pieces like you said.
>It looked too fast for that.  I thought the thing was vaporized.

In a word, no.  Read the Rogers Commission report, which based its
conclusions on detailed studies of the technical evidence.  Things do
happen very quickly with major structural failure at hypersonic speeds.
It is possible, although not certain, that the pivoting SRB struck the
orbiter's wing as an additional contributing factor.

The orbiter most certainly was not vaporized; in particular, the cabin
held together well enough that the astronauts were alive (although
probably unconscious) until water impact, and the TDRS payload was
found more or less in one piece.  Both the cabin and the main engines
were identifiable in the photos immediately after the breakup; the Rogers
report points them out.  A good bit of the orbiter was reconstructed from
salvaged debris, and probably most of it could have been if recovery
efforts had been more persistent.
-- 
Apollo @ 8yrs: one small step.|     Henry Spencer at U of Toronto Zoology
Space station @ 8yrs:        .| uunet!attcan!utzoo!henry henry@zoo.toronto.edu