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From: fisher@dvinci.DEC (Burns Fisher, MRO3-1/E13, 231-4108)
Newsgroups: net.columbia
Subject: What engines are what.
Message-ID: <7252@decwrl.UUCP>
Date: Fri, 20-Apr-84 09:57:48 EST
Article-I.D.: decwrl.7252
Posted: Fri Apr 20 09:57:48 1984
Date-Received: Sat, 21-Apr-84 02:23:19 EST
Organization: DEC Engineering Network
Lines: 49


NO!  There is absolutely no fuel left on board for the SSMEs (Space Shuttle
Main Engines) after the ET (External Tank) drops.  The SSMEs are not started
again until the next launch.  As a sanity check on this assertion, think of
what you would have to do to save any reasonable quantity of liquid H2 and
liquid O2.  (Insulation, high pressure tanks, etc etc).  Also think of how
little energy is actually required to start the reentry process as compared
to the amount required to get up into orbit to begin with.  Using the SSMEs
for deorbit does not make sense!

Here are the major engines on the shuttle and their acronyms (in order of 
power):

	SRBs  (Solid Rocket Boosters) - millions of pounds thrust.  Used only
		during first (1.5?) minutes after launch, then dropped off and
		recovered.

	SSME  (Space Shuttle Main Engines) - 10**5s of pounds thrust.  Used
		from launch until just before orbital insertion.  Draws fuel
		from ET (external tank) which is dropped just after the SSMEs
		stop.  Not used again until the next launch.

	OMS  (Orbital Maneuvering System) - 10**3s of pounds (?) thrust.  Used
		to insert the shuttle into a reasonable orbit after the SSMEs
		stop.  (OMS-1 and OMS-2 [OMS-1 was omitted during the last
		mission, because of the unusual trajectory/burn time planned
		for the SSMEs-required for the unusually high orbit])  Also
		used for orbital changes during the mission (e.g. rendezvous
		etc.), AND FOR DEORBIT BURN (retrofire for us old-timers).

	RCS  (Reaction Control System) (isn't every rocket?). - Small thrust.
		Used to change or maintain orbiter attitude while on orbit.
		Also can be used to make small orbital corrections for
		station-keeping or final phases of rendezvous.  Also used
		during the early phases of reentry for attitude control in
		various combinations with the control surfaces depending on
		the thickness of the atmosphere.

	RMS  (Remote manipulator system).  The "robot arm".  Not an engine.

Burns (picky picky) Fisher

<Is this coming close to being a flame?  Sorry...>

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