Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Shuttle engine failure on the pad
Message-ID: <1990Mar17.234512.10044@utzoo.uucp>
Organization: U of Toronto Zoology
References: <140@caslon.cs.arizona.edu>
Date: Sat, 17 Mar 90 23:45:12 GMT

In article <140@caslon.cs.arizona.edu> kevin@cs.arizona.edu (Kevin Strietzel) writes:
>What happens if one SRB ignites, but the second won't go?
>Or one (or more) of the SSME's won't go?

An SSME problem before SRB ignition just results in a shutdown; this has
happened once or twice.  A single SSME failure after launch results in an
emergency landing somewhere if it happens early, or continuation of the
mission at least as far as one orbit if it happens late.  (There has been
one case of an SSME shutdown late in the climb.)  Multiple SSME failures
after launch can lead to continuation, emergency landing, ditching in
the ocean, or death, depending on timing.

But if only one SRB lights, this is known as an "unsurvivable accident".

>Presumably the pad would melt and/or burn if it just sat there -- if that's
>even possible.  I can't remember if the shuttle is held down by anything
>besides gravity at engine ignition time...

They blow the hold-down bolts simultaneously with SRB ignition, so there
is no option at that point.  I've always thought this was a little dumb,
but there may be good reasons for it.

>If you could physically hold the
>shuttle down, would the torque of a single SRB flip the whole pad on its side?

No.  The pad is *lots* heavier than the shuttle.

>Seems like an SRB could separate on the pad, and it'd leave pretty quick
>without a shuttle holding it down, and they're slightly steerable.  But don't
>they help support the orbiter on the pad?  And isn't its exhaust going to make
>a mess of the shuttle, despite quick departure?  And I'd guess their steering
>system is totally dependent on the orbiter's computers, and even if it weren't,
>would it be stable solo?

The orbiter and tank are entirely supported by the SRBs from stacking to
launch.  Departure of one SRB would almost certainly mean massive structural
failure of the tank, which would mean loss of the orbiter and probably the
crew.  The exhaust of the departing SRB would add to the problem.  And you
are correct, the SRBs are controlled by the orbiter.  I suspect they could
fly reasonably well independently, if they had the brains to.
-- 
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry henry@zoo.toronto.edu