Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Why 3 SSME's?
Message-ID: <1989Sep29.165506.29240@utzoo.uucp>
Organization: U of Toronto Zoology
References: <24@loop.UUCP> <1979@hydra.gatech.EDU> <4337@wpi.wpi.edu> <2152@hydra.gatech.EDU>
Date: Fri, 29 Sep 89 16:55:06 GMT

In article <2152@hydra.gatech.EDU> ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) writes:
>I think that they cannot make [risk] as low as that of an airliner 
>because of the vertical take off phase which involves
>by definition enormous thrust levels...

The thrust:weight ratio of the shuttle at launch is not much higher than
modern jet fighters.  (Conventional ones, not Harriers [which *can* take
off vertically].)  And the shuttle's engines only have to run for a few
minutes between overhauls, while jet engines are expected to run for days.
There is no intrinsic reason why rockets should be less reliable than jets,
and NASP notwithstanding, they have enormous performance advantages.

(Max Hunter has commented, roughly:  "If the Wright Brothers had had engines
with the thrust:weight ratio of modern rockets, there probably wouldn't be
a runway on Earth.")
-- 
"Where is D.D. Harriman now,   |     Henry Spencer at U of Toronto Zoology
when we really *need* him?"    | uunet!attcan!utzoo!henry henry@zoo.toronto.edu