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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.columbia
Subject: Re: main engine compressors
Message-ID: <6344@utzoo.UUCP>
Date: Mon, 3-Feb-86 15:19:55 EST
Article-I.D.: utzoo.6344
Posted: Mon Feb  3 15:19:55 1986
Date-Received: Mon, 3-Feb-86 15:19:55 EST
References: <785@leadsv.UUCP>
Organization: U of Toronto Zoology
Lines: 42

> I remember hearing that the main engine compressors have worn out much
> faster than had been predicted...

Actually, they're pumps rather than compressors.  They're pumping liquids
rather than compressing gases.  At the pressures they work at, mind you,
the distinction is sometimes a little fuzzy...

>	Are they axial or centrifugal ?

Axial, I believe.

>	What is their power source ?

The full fuel flow plus some of the oxidizer are "pre-burned" and the
moderately-hot gases from that run the pumps.  The gases then go into the
main combustion chamber where the rest of the oxidizer arrives to complete
the burn process.  This is unusual; earlier engines generally used only a
small fraction of the incoming propellants to run their pumps.  The SSMEs
run at such high pressure that they need a lot of pump power to get the
propellants in, hence the odd approach.

>	Why are they wearing out so fast ?

Because they work very hard in a very harsh environment.  There was little
experience with reusable large rocket engines, and practically none with
ultra-high-pressure engines like this, to guide the engineers.  So their
estimates of lifetime etc. were a little, uh, optimistic.

>	What is their design pressure ?

Don't have the exact numbers on hand; something like 2000-3000 psi.  (This
is roughly the same pressure as a big laboratory compressed-gas cylinder
at full pressure, and those pumps are pushing several tons of propellant
*per second* in against that pressure!)

> It has been speculated that a compressor failure could have caused a breach
> of the external tank, but I doubt that.

It probably would have caused other types of havoc first.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry