Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!apple!bionet!agate!ucbvax!hplabs!hplabsb!dsmith
From: dsmith@hplabsb.HP.COM (David Smith)
Newsgroups: sci.space.shuttle
Subject: Re: "Walking"
Message-ID: <4964@hplabsb.HP.COM>
Date: 27 Oct 88 17:59:42 GMT
References: <665@sas.UUCP>
Reply-To: dsmith@hplabsb.UUCP (David Smith)
Organization: Hewlett-Packard Labs, Palo Alto, CA
Lines: 20

In article <665@sas.UUCP> sasbrb@sas.UUCP (Brendan Bailey) writes:
>do something they called "walking" which took place when the
>main engines ignited...  the boosters actually move several feet
>from their original position to look as if it was "walking".  Maybe
>it wasn't when the main engines ignited, but the boosters ignited.

When the boosters ignited, the shuttle lifted off and became free to
"walk" under the side force of the liquid engines.  If you review a
tape of the STS-26 liftoff, you can see the lateral movement.
I seem to recall talk after STS-1 on the order of "Now that we know
how much it walks, we can compensate for it in the future."  But I don't
know why that aspect of the flight should have been an unknown to
the engineers, nor do I know how it is compensated.  It doesn't appear
to tip back any.  But STS-26 walked less than my fuzzy recall says
STS-1 did.
-- 

			David Smith
			HP Labs
			dsmith@hplabs.hp.com