Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!cs.utexas.edu!utastro!pjm
From: pjm@utastro.UUCP (Phillip MacQueen)
Newsgroups: sci.space.shuttle
Subject: SSME motion before lift-off.
Message-ID: <3200@utastro.UUCP>
Date: 30 Sep 88 15:41:50 GMT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 17


  During the six-or-so seconds that separate the ignitions of the SSMEs and
the SRBs, there is a brief period in which the orientation of the SSMEs rapidly
varies. What is the purpose of/reason for this motion?  Is it an intentional
test of the SSME mountings before the decision to ignite the SRBs is made, or
is it just a characteristic of the ignition process due to something like the
direction of their thrust vectors being unstable during that period?

  As a side note, my first impression of the apparent flame at the side of the
left SRB's nozzle was that it was a red flare from the camera lens due to the
intensity of the immediately adjacent SRB plume.  Unfortunately, the credibility
of this (desirable) explanation dwindled as I continued to watch.


Phillip MacQueen
McDonald Observatory
Austin, Texas.