Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!lll-winken!uunet!bfmny0!tneff
From: tneff@bfmny0.UUCP (Tom Neff)
Newsgroups: sci.space
Subject: Re: Magellan Status for 07/17/89 (Forwarded)
Message-ID: <14480@bfmny0.UUCP>
Date: 21 Jul 89 14:27:37 GMT
References: <28782@ames.arc.nasa.gov> <805@eutrc3.urc.tue.nl> <12864@bloom-beacon.MIT.EDU>
Reply-To: tneff@bfmny0.UUCP (Tom Neff)
Organization: ^
Lines: 23

In article <12864@bloom-beacon.MIT.EDU> pgf@space.mit.edu (Peter G. Ford) writes:
>But what, you ask, is a "momentum wheel desaturation?" Well, the wheels
>are much less massive than the rest of the spacecraft (technically,
>their moments of inertia are much smaller), so they must spin up to
>very high rates to turn Magellan in a reasonable time. To avoid their
>spinning so fast that they fly apart, there are auxiliary rockets on
>Magellan that are fired from time to time to give the spacecraft a
>strong twist in the opposite direction, thereby allowing the wheels to
                     ^^^^^^^^
>be spun down and "desaturated".

Jeez I hate to disagree with someone on the Project, but wouldn't the
thruster burns be twisting the spacecraft in the SAME direction as the
momentum wheels' accumulated spin, rather than in the OPPOSITE
direction?  If you add more opposite torque you'd have to spin the
wheels even faster to compensate.  By tweaking in the same direction,
you allow[require] spindown of the wheels to compensate.

That's what I said in my mailed explanation anyway.  If it's wrong I'd
like to know it.
-- 
"My God, Thiokol, when do you     \\	Tom Neff
want me to launch -- next April?"  \\	uunet!bfmny0!tneff