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From: bl@hplabsb.UUCP (Bruce T. Lowerre)
Newsgroups: net.columbia
Subject: Re: orbiter assent attitude
Message-ID: <3266@hplabsb.UUCP>
Date: Thu, 6-Feb-86 16:14:40 EST
Article-I.D.: hplabsb.3266
Posted: Thu Feb  6 16:14:40 1986
Date-Received: Sun, 9-Feb-86 05:47:09 EST
References: <999@burl.UUCP>
Distribution: net
Organization: Hewlett Packard Labs, Palo Alto CA
Lines: 15

> Can anyone explain why during assent the orbiter flies upside-down?
> I remember reading somewhere that it was necessary for the crew to
> see the earth's horizon during assent and that it is difficult to do
> that with a normal attitude because the tank and boosters would be 
> in the way.  With todays guidance control systems, it has been hard
> for me to buy that argument completely.  Does anyone know the true
> poop on this subject?

A rocket's thrust line must go through its center of mass, otherwise
it will tumble.  The center of mass for the shuttle structure at
launch is located within the ET.  The three main engines on the
shuttle are offset and are pointing upwards toward the rear when
viewed setting on its wheels.  Thus, during ascent, the shuttle must
be on its back so as to allow the engines to lift the center of
mass of the entire launch vehicle.