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From: lvron@saturn.lerc.nasa.gov (Ronald E. Graham)
Newsgroups: sci.space,sci.space.shuttle
Subject: Re: space news from Nov 12 AW&ST
Message-ID: <1990Dec12.150211.14218@eagle.lerc.nasa.gov>
Date: 12 Dec 90 15:02:11 GMT
References: <1990Dec12.044442.2101@zoo.toronto.edu>
Reply-To: lvron@saturn.lerc.nasa.gov
Organization: NASA Lewis Research Center
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In article <1990Dec12.044442.2101@zoo.toronto.edu>, 
     henry@zoo.toronto.edu (Henry Spencer) writes...

Regarding Fred...

>Speaking of which...  Redesign work has been underway quietly for some time,
>but now it is out in the open.  The long truss is probably not long for this
>world, in particular:  a Goddard project to attach science payloads to it
>has been cancelled, and the request for bids for the assembly training
>facility in Houston has been withdrawn.  The leading idea right now is
>simply to retain the central cluster of modules, but kill the truss.
>Among other advantages, the resulting station should have gravity-gradient
>stability, eliminating attitude-control thruster firings that eat fuel and
>bother the microgravity people.

Gravity-gradient stability may not necessarily mean that all attitude control
firings are eliminated (although I'm not sure whether that's what the article
intended to say).  Although a body will tend to stay in a gravity-gradient
stable position once that position is reached, aero forces could perturb the
body.  If Fred retains solar arrays, those guys will have to be pointed, and
that would cause your aero to vary during the orbit.  That being the case,
you'd need your control-moment gyros to trim Fred, and you may need a firing
from time to time to "dump" the gyros.

The article didn't say anything about Fred's photovoltaic arrays, but we
have been hearing that *that* part of the design will most likely not be
changed much - only where they get positioned would get changed, and how 
many there would be, since "Assembly Complete" is now a wild dream.

Anyway, under those conditions, although you could reduce your firings, you
can't get rid of 'em altogether.  Looks like the reaction control system
would certainly be sized down, at least.

RG