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From: ccs025@ucdavis.UUCP (Johan)
Newsgroups: net.columbia
Subject: Re: Challenger SRBs
Message-ID: <121@ucdavis.UUCP>
Date: Fri, 31-Jan-86 19:13:14 EST
Article-I.D.: ucdavis.121
Posted: Fri Jan 31 19:13:14 1986
Date-Received: Mon, 3-Feb-86 06:21:27 EST
References: <4270@mhuxd.UUCP> <437@umich.UUCP>
Organization: University of California, Davis
Lines: 57

> In article <4270@mhuxd.UUCP> wolit@mhuxd.UUCP (Jan Wolitzky) writes:
> 
> >Am I correct in my understanding that,
> >under less catastrophic conditions, the SRBs are capable of
> >independent guidance, at least to keep them clear of the orbiter
> >after jettisoning following burnout or during an abort?
> 
> I would be surprised if the SRBs were capable of independent guidance.
> They have no control surfaces, and I doubt the SRB nozzles are on gimbals
> like those of the main engines.
          I agree. It would seem the three main engines would exert
enough control.

> At burnout explosive bolts separate the
> SRBs from the rest of the orbiter which continues to accelerate away
> on its main engines.  I'll admit I don't know the cause for the smooth
> peeling away of the SRBs following burnout.  Maybe the top bolts blow
> first, and the aerodynamics do the rest.
   And most importantly, the SRBs are usually not thrusting after
they are released.  Burnout occurs first, then they are released.
This leaves only drag to slow them down.  Durring the accident
the SRBs had thrust without a guidance system, hence the spiral.

> 
> During an abort I suspect the orbiter must be flown away from the
> tank/SRB assembly.  Does anyone know if there is a small fuel
> reserve within the orbiter for such an occasion?

  I do not know if there is a reserve tank for the main engines,
but there is always the OMS (orbital manuevering) engines
or the mant RCS (reaction control) engines.  BUT, at a point where
escape velocity will not be reached and orbit insertion is not possible,
NO engines would be used in an abort.  The vehicle is on it's back
and would disengage from the External Tank.  It would then fall
away as the tank continued by using the control surfaces (elevons,
rudder) if there was sufficient air density, or they would
fall until there was.  Even with the poor glide ratio the
shuttle has, when you are 10 miles up you have a decent chance
of making it back to Kennedy.  If not, then an ocean ditch would
be made.  Preperation for this possibility is the reason so
many ships and planes were ready to search for wreckage so fast.
The commander would be very busy trying to land safely, 
without having to worry what firing the engines would do.
The experts can correct me if I am in error, but I do not even
think the crew can manually control the gimbal of the main engines
without a series of lengthy computer entries.  The sticks in the
cockpit only control the smaller engines for fine-tuning once in
orbit. 
   But what do I know, I'm still a student of all this.
I have a few books with some specifics, and I will try to clarify
the above speculations, unless someone has completely slashed
my logic by then ;-).

-- 
                   Martin Van Ryswyk
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