Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!tektronix!zeus!athena!jhb
From: jhb@athena.TEK.COM (John Burgess)
Newsgroups: sci.space.shuttle
Subject: Re: Throttling the Challenger
Message-ID: <1804@athena.TEK.COM>
Date: Fri, 16-Oct-87 09:08:24 EDT
Article-I.D.: athena.1804
Posted: Fri Oct 16 09:08:24 1987
Date-Received: Sun, 18-Oct-87 03:11:19 EDT
References: <340@ablnc.ATT.COM>
Reply-To: jhb@athena.UUCP (John Burgess)
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 37
Keywords: Challenger Throttle
Fcc: outbox


In article <340@ablnc.ATT.COM> rcpilz@ablnc.ATT.COM (Robert C. Pilz) writes:
>
>One thing about the crash has been haunting me. When I saw
>the replays of the explosion, I heard the commands to the
>crew to be at 105% throttle. They acknowledged that. Then they
>were told to go to 80% (or so). They acknowledged that. Then
>they were told (very quickly) to go back to 105%. At this point,
>the explosion happened.

Depending on what you mean by "very quickly", it sounds quite routine.

The way I've heard it is this:

    1) It is possible, using full throttle, to exceed the aerodynamics of
        the system early on in the flight.  They start at full throttle,
        then they reduce power when the speed gets "real high", finally,
        as the air thins out more, they can go back to full power.
    
    1a) So how do they reduce throttle of the solid boosters?  The boosters
        are built with concentric circular layers of propellant so, when
        they are launched, there is a hole down the middle of the propellant.
        This burns from the inside out at a known rate.  During manufacturing
        some of the layers have inhibitors built in so that, at the right
        time, the burn rate decreases and power goes down.

    2) The earlier shuttle engines were'nt as powerful as the newer ones
        used recently.  But in order to use a constant frame of reference,
        they still use the max power of the older engines as the starting
        point.  So, it is not uncommon to hear "105%" throttle.
    
And if you believe that ...  As stated, this is what I've heard, and it
does sound plausible enough to me that I'll beleive it and repeat it.

--------
John Burgess;  tektronix!athena!jhb
CAE Systems Division, Tektronix, Inc   
Phone: 629-1150;   Del Sta 92-822