Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Orbiter/SRB separation
Message-ID: <1988May11.185145.592@utzoo.uucp>
Organization: U of Toronto Zoology
References: <48048@ti-csl.CSNET>, <1869@bigtex.uucp>
Date: Wed, 11 May 88 18:51:45 GMT

> Lastly, I'm not sure what if any provisions exist for steering SRB and
> external tank away from orbiter after separation...  I don't believe
> SRB nozzles can be gimbled.

The SRB nozzles are gimbaled -- they have to be, there isn't enough
control authority in the SSMEs when the SRBs are firing.  However, I
believe all the smarts are aboard the orbiter, so they effectively run
wild when you break that connection.

Separating the orbiter from the tank/SRB assembly while the SRBs are
firing is difficult.  There are high loads on the connecting links,
and the separation must be immediate and complete.  The current links
definitely are not designed for a safe separation under power; the rear
link wouldn't separate cleanly and the orbiter would pitch up belly-on
to the slipstream.  This would destroy it:  it's moderately heat-resistant
but not terribly strong, and not even jet fighters can survive that kind
of treatment at high speed.  Redesigning the links for clean separation
just might be possible, but it wouldn't be easy.

Assuming we have clean separation, we then have to worry about what
happens aerodynamically.  It is *not* trivial to make sure that two large
objects in close formation move away from each other in an orderly manner.
Fighters and the like are carefully tested for proper "stores separation",
and gravity often isn't enough:  missiles "dropped" from fighters usually
are blown or thrown clear, not just dropped.  For the shuttle, we don't
even have gravity pointing in the right direction to help, and it's
impractical to fly full-scale tests.

And *then* we have to worry about the shuttle being hit by the SRB exhausts,
which are hot, dense, and abrasive.  The shuttle re-enters in a carefully
controlled way in hot but very thin air; it's not built to survive a large
rocket exhaust at close range.

In short, it's not quite impossible, but it's a lot harder than it looks.
-- 
NASA is to spaceflight as            |  Henry Spencer @ U of Toronto Zoology
the Post Office is to mail.          | {ihnp4,decvax,uunet!mnetor}!utzoo!henry