Newsgroups: sci.space.shuttle
Path: utzoo!kcarroll
From: kcarroll@utzoo.uucp (Kieran A. Carroll)
Subject: Re: Why 3 SSME's?
Message-ID: <1989Sep22.140437.526@utzoo.uucp>
Organization: U of Toronto Zoology
References: <24@loop.UUCP>
Date: Fri, 22 Sep 89 14:04:37 GMT

>keithl@loop.UUCP (Keith Lofstrom) writes:
>
>Why three 2 MegaNewton SSME's rather than one 6MN engine?
>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.  As long as Rocketdyne was developing a new engine
>from scratch, why did they choose three engines rather than one?
>

One good reason for multiple engines is in order to have a "one engine
out" capability --- that is, retaining the ability to attain orbit
even if an engine fails sometime during launch. This capability was
demonstrated on one of the early shuttle flights, when an apparent
fault in one engine forced it to be shut down early; the remaining two
engines were sufficient for an abort-to-orbit, as I recall.

-- 

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll kcarroll@zoo.toronto.edu