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From: asgard@cpro.UUCP (J.R. Stoner)
Newsgroups: sci.space.shuttle
Subject: Re: Throttling the Challenger
Message-ID: <362@cpro.UUCP>
Date: Fri, 16-Oct-87 00:07:41 EDT
Article-I.D.: cpro.362
Posted: Fri Oct 16 00:07:41 1987
Date-Received: Sat, 17-Oct-87 18:32:29 EDT
References: <340@ablnc.ATT.COM>
Organization: CompuPro/VIASYN Corporation, Hayward, CA
Lines: 35

in article <340@ablnc.ATT.COM>, rcpilz@ablnc.ATT.COM (Robert C. Pilz) says:
> One thing about the crash has been haunting me. When I saw
> the replays of the explosion, I heard the commands to the
> crew to be at 105% throttle. They acknowledged that. Then they
> were told to go to 80% (or so). They acknowledged that. Then
> they were told (very quickly) to go back to 105%. At this point,
> the explosion happened.

> This was never discussed in the national news. At least I never
> picked up on it. What were they (the flight people) trying to
> do? I have a strong feeling that they knew something was wrong
> at that point and were trying to do something?


> ....ihnp4!ablnc!rcpilz

[Henry et al - correct me if I am very wrong]

It does not have anything to do with the particular flight.  You will note
from programmed flight profiles that a mid-launch throttle-down followed by
a throttle-up is normal procedure.  The reason is that a layer of the upper
atmosphere (stratosphere?) is a region of particularly violent aerodynamic
pressures on the structures (where the jet stream resides?  Enquiring minds
want to know :-)  So the engines are throttled down to minimize vibrations
on the orbiter so that velocity is still high enough to allow continuing
upward motion but not enough to allow orbital insertion.  After this violent
atmosphere is passed the engines are throttled up to orbital insertion level.

All this occurs before SRB sep or MECO.

...ihnp4!hplabs!ptsfa!cpro!asgard.
-- 
"To prevent having to tell fools to RTFM don't let on you WTFM to begin with."
J.R. Stoner	asgard@cpro.UUCP    asgard@wotan.UUCP
P.S. I help CompuPro make computers.  They do not help me make my opinions.