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From: bpendlet@esunix.UUCP (Bob Pendleton)
Newsgroups: sci.space,sci.space.shuttle
Subject: Re: Stopping Space and Light Pollution.
Message-ID: <1068@esunix.UUCP>
Date: 8 Nov 88 21:27:40 GMT
References: <809@cmx.npac.syr.edu>
Organization: Evans & Sutherland, Salt Lake City, Utah
Lines: 50

From article <809@cmx.npac.syr.edu>, by anand@amax.npac.syr.edu (Anand Rangachari):
> 
>   With all this talk about reducing the possibility of collision with debris,
> I am reminded of a scheme suggested in the book 'The songs of distant Earth'
> by Clarke. In this book, the ship Magellen pushes a shield made of ice
> ahead of it, sweeping a clean path. Maybe a similar shield could be
> made for the space shuttle from waste water and the water produced in the
> fuel cells. 

Not a bad idea, except that a starship traveling at some fraction of
the speed of light and a space shuttle in LEO are very different
physical systems. The shield would have to surround the shuttle, not
just sit in front of it. Debris in the same orbit as the as the
shuttle has very little (none if in the SAME orbit, going the SAME
direction) difference in velocity relative to the shuttle and is not a
threat. But debris in orbits that cross the shuttle orbit, and
therefore have high velocities relative to the shuttle are the danger.

A starship is moving quickly with respect to the interstellar dust and
gases and can (maybe) get away with not worrying about material in
trajectories that cross its path.

>   In fact it could be produced quite easily by creating a framework made
> from a shape memory alloy. Then, water could be sprayed on it to actually
> form the shield. 

In a vacuum ice sublimes. That is it converts directly from a solid to
a gas. This fact has been used to get rid of heat on manned spacecraft
for quite some time. I suppose that if the ice is cold enough this can
be reduced to a point where the loss is insignificant, but in LEO the
ice will be in sun light for about half of each orbit. The shield will
slowly melt away.

>                                                      R. Anand


Question: Liquid water released in orbit tends to convert into a cloud
of water vapor and ice cristals. The ice crystals later sublime to
water vapor. Could large clouds of ice crystals be used to "sweep"
orbits of small debris particles? 

Doesn't sound practicle, too large a volume, too few particles. But I
haven't heard it suggested before. Might it be useful for sheilding a
battle station from a kinetic engery attack using a bucket of b.b.s?

			Bob P.
-- 
              Bob Pendleton, speaking only for myself.
UUCP Address:  decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet

		Reality is what you make of it.