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From: djr@scdpyr.UUCP
Newsgroups: sci.space.shuttle
Subject: Throttling the Challenger
Message-ID: <187@scdpyr.UUCP>
Date: Wed, 21-Oct-87 03:33:27 EDT
Article-I.D.: scdpyr.187
Posted: Wed Oct 21 03:33:27 1987
Date-Received: Thu, 22-Oct-87 22:04:46 EDT
Organization: Natl Ctr Atmospheric Research, Boulder, CO
Lines: 35
Keywords: "Throttle up call"


	Since the throttle up call on the Challenger mission has become
a hot topic for discusion I thought I would throw in my 2 cents worth.

	Not too long ago I did some research on the shuttle program.
Two of my biggest sources were the Rogers commission report on the
Space Shuttle Challenger accident and Jane's all the Worlds Aircraft
1986-87.

	According to my sources the Space Shuttle Main Engines (SSME)
have a power range from 0-109%.  The performance for these engines
was based on the original design sepcifications.  The engines used on
STS-1 were different from the ones currently in use.  The engines on
Columbia could only go to 100%.  Improvments in the design for later
missions is the reason for the change in the performance ratings.

	Normal procedures are to ignite the SSME's 6 seconds prior to
launch.  At this point the SSMEs are at 100%.  As soon as the Shuttle
has cleared the tower the SSMEs are throttled up to 104%.  When the
Shuttle reaches MAX-Q the engines are reduced to 65%.  MAX-Q is the
period of maximum aerodynamic force on the Shuttle.  MAX-Q occurs
at Mach 1.(Gee, I wonder why? ;-)).  After MAX-Q, the engines are
throttled up to 104%.  The engines are not used at anything above 104%
even though they are capable of 109%.

	I can't recall the specific numbers right off of my head.
If someone hadn't swiped NCAR's copy of "Jane's" I would run and look
them up.  If anybody is curious about the specifics I suppose I could
find my notes.

	Hope this didn't add too much to the confusion.
-- 
	"Hey laser lips, your momma was a snow blower!"
					  -- Number 5
	Dave Rowland  at NCAR Boulder, Colorado  djr@scdpyr.UUCP