Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: SSME's
Message-ID: <1990Nov23.051726.6388@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <5817@crash.cts.com>
Date: Fri, 23 Nov 90 05:17:26 GMT

In article <5817@crash.cts.com> gandalf@pro-canaveral.cts.com (Ken Hollis) writes:
>>People have explored more devious schemes, like variable-length nozzles,
>>but no real use has been made of them yet.
>
>The MX Missile uses a 2 piece extendible, variable length nozzle.

No, sorry, its nozzle telescopes for compact stowage -- this is also done
in sub-launched ballistic missiles, which are *very* cramped, and in the
shuttle's IUS upper stage -- but it extends to full length before ignition
and stays that way.  It is *not* variable length while the engine is firing,
which is the issue.

>Some other improvements (You be the judge on incremental or not...)
>
>Pratt & Whitney Turbopumps : Longer life expectancy between changeouts,
>beefier & heavier.

Very true... except that these are *not* incorporated in Endeavour's engines.
The P&W turbopumps, at the moment, are a prototyping exercise only.  There
is no commitment to *ever* use them as flight hardware.

If NASA *does* switch from the Rocketdyne pumps to the P&W ones, then yes,
I would agree that this is more than an incremental improvement.  "If".

>Large throat MCC (Main Combustion Chamber)

Recent progress on this is essentially zero.  And again, there is *no*
commitment to ever use it for flight hardware; it is being treated as
a technology experiment only, and a low-priority one at that.

NASA has been criticized for this attitude.  No change so far.

>>... Considering how badly Rocketdyne's SSME has
>>failed to meet its promises...
>
>At least give them credit for getting the performance requirements to 109% of
>design...

Sorry, I don't give credit for a capability that is not being used because
of fears that it is unsafe.  They don't run the SSMEs at 109% any more.
-- 
"I'm not sure it's possible            | Henry Spencer at U of Toronto Zoology
to explain how X works."               |  henry@zoo.toronto.edu   utzoo!henry