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From: rt@cpsc53.UUCP (Ron Thompson)
Newsgroups: net.columbia
Subject: Re: Challenger SRBs
Message-ID: <100136@cpsc53.UUCP>
Date: Thu, 30-Jan-86 23:07:38 EST
Article-I.D.: cpsc53.100136
Posted: Thu Jan 30 23:07:38 1986
Date-Received: Sat, 1-Feb-86 07:41:45 EST
References: <4270@mhuxd.UUCP> <437@umich.UUCP>
Organization: ATT-IS CPSC, Atlanta, GA
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> >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.  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.

The SRB nozzles swivel (or gimbal) up to 6 degrees to direct the thrust
and steer the Shuttle. - THE SPACE SHUTTLE OPERATOR'S MANUAL,Joel/Kennedy

This, of course does not fully answer your question of independent
guidance - it would seem more likely though.

> 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?

There are three abort procedures, RTLS(return to launch site), AOA
(abort once around) and ATO(abort to orbit). "RTLS does not begin until
after the SRB's have burned out and have been jetisoned." At that point,
all remaining fuel is burned heading down-range by the main engines, both
OMS engines and the 4 aft-firing maneuvering rockets till a halfway mark
is reached. Direction is then reversed towards the launch site, remaining
fuel expended, external tank jettisoned and a normal landing. Should the
mains be out or turning out of the question, the Shuttle should land at
Naval Air Station, Spain.
      AOA is used when the mains fail or the SRC's burn out before orbit
can be acheived, and I suspect the mission is too far along for RTLS.
The OMS and RCS engines are used till emergency landing at White Plains.
      ATO is used after trouble in late ascent, the OMS are used to acheive
less than target orbit.

Probably important to note that there are no abort procedures until
the SRB's are finished. I've had the manual since last summer's visit
to the Cape and have enjoyed the good level of detail.


-- 
  Ron Thompson		AT&T Information Systems	Customer Programming  
  (404) 982-4217        Atlanta, Georgia		Services Center	      
  ..{ihnp4,akgua}!cpsc53!rt             (Opinions expressed are mine alone.)