Path: utzoo!attcan!utgpu!watmath!iuvax!cica!gatech!prism!ccsupos
From: ccsupos@prism.gatech.EDU (SCHREIBER, O. A.)
Newsgroups: sci.space.shuttle
Subject: Re: Why 3 SSME's?
Message-ID: <1979@hydra.gatech.EDU>
Date: 22 Sep 89 01:10:31 GMT
References: <24@loop.UUCP>
Reply-To: ccsupos@prism.gatech.EDU (SCHREIBER, O. A.)
Organization: Georgia Institute of Technology
Lines: 49

In article <24@loop.UUCP> keithl@loop.UUCP (Keith Lofstrom) writes:
>
>Why three 2 MegaNewton SSME's rather than one 6MN engine?
>
Would an F-1 have been possible? Less specific impulse but denser
fuel.
>Back when NASA was choosing contractors for the SSME, Pratt & Whitney
>had a 2MN LH/LOX engine on the shelf;  NASA went with Rocketdyne for
>political reasons.
I read about that too. For what market did P&W intend its product
or why was it ready so much earlier than Rocketdyne's?
Also, about the shuttle, I have an issue of "Discover" (end of   
'85) that deals with the design history of the shuttle.
In addition to the early horizontal takeoff and landing
configurations which make sense to me (less thrust necessary
on the vehicle) my attention was caught by the mention that
in '74 two features were dropped from the design:
Air breathing engines for rentry flight
and Abort rockets.
If the orbiter weighs 80 tons and one has two 50 tons abort rockets
to lift away the orbiter from the rest of the stack in case of
SRB ("major") malfunction during ascent I think it would have
been worthwhile to keep that feature in the design of what was 
supposed to become a routine access to space vehicle. I must
add that on the drawing of 'Discover', the two rockets were
positioned at the trailing edge of the wing of the Orbiter.
After all, all the early manned space vehicle had abort rockets
albeit in the form of escape towers. It seems to me that you don't
just design a manned space vehicle by being satisfied with a
percentage of catastrophic failure low enough, you ought to
supply a backup escape system at least in the most traumatic 
sequence of flight (vertical ascent).
About the Challenger accident,
the public was struck by the fact that once the problem 
occured, the astronauts could not do anything and the press,
long after Challenger exploded kept on speculating on how
long some of the crew members stayed conscious.
Sure, there was nothing that could be done about the shuttle
to prevent the loss of the crew or may be there was...back in 
1974 when they drop the escape rockets from the design.
By the way, the Europeans quickly put an escape system in the
planning of their Hermes project soon after the accident whereas
they had not planned for any prior to that.

-- 
Olivier Schreiber (404)894 6147, Office of Computing Services
Georgia Institute of Technology, Atlanta Georgia, 30332
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