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From: stu@splut.UUCP (Stu Cobb)
Newsgroups: sci.space.shuttle
Subject: Re: Throttling the Challenger
Message-ID: <201@splut.UUCP>
Date: Sat, 24-Oct-87 01:11:34 EST
Article-I.D.: splut.201
Posted: Sat Oct 24 01:11:34 1987
Date-Received: Mon, 26-Oct-87 05:48:59 EST
References: <340@ablnc.ATT.COM> <3143@ames.arpa>, <6563@ut-ngp.UUCP> <8796@utzoo.UUCP>
Organization: Confederate Microsystems, League City, TX
Lines: 18
Keywords: Challenger Throttle
Summary: thottle settings

In article <8796@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> Engines, like lightbulbs, generally do not have a single specific setting
> for which they are designed, in the sense that all other settings work
> poorly or not at all.  

Sorry, but I don't believe this is true.  The Shuttle engine is rather rare
in that it can be throttled over almost a 2:1 range.  Most rocket engines
are, in fact, designed to run at a particular setting.  This is primarily
because most rocket engines were designed before flexible control systems
were available.  They use pneumatic/hydraulic/fluidic controls (the
pinnacle of late-50's technology) which are fussy about their set-points.

This fact is what got the early OSCARs into space.  They couldn't throttle
down their boosters to match the weight of the primary payload; instead,
they had to carry ballast.  Don Stoner had the bright idea to carry
interesting ballast, which led to the OSCARs.

Stu