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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!zehntel!dual!mordor!space@mit-mc
From: space@mit-mc
Newsgroups: net.space
Subject: Re: Momentum transfer in light sails
Message-ID: <788@mordor.UUCP>
Date: Fri, 1-Mar-85 17:33:32 EST
Article-I.D.: mordor.788
Posted: Fri Mar  1 17:33:32 1985
Date-Received: Sun, 3-Mar-85 03:09:36 EST
Sender: daemon@mordor.UUCP
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From: Rick McGeer (on an aaa-60-s) 

	Sure there is.  Use various sails, of differing sizes, at varying
angles and distances from your craft.  The momentum vector of your craft
is the sum of the momentum vectors of the various light sails, which are all
radial to the sun (but the sum vector need not be).

	The restriction is that net momentum is always *away* from the sun:
you can't accelerate in a sunward direction using a light sail.

	Actually, now that I think of it, there's no reason that the
momentum vector of a sail need be radial to the sun: if the sail were
forced to deform, so that pole of the sail was not in its centre, then the
resultant vector *wouldn't* be radial to the sun.

	Further thought on tacking into the sun: yes, it can be done, if you
use gravitational interactions.  That is, tack in an outbound direction
against your current elliptical solar orbit: you'll kill your radial
velocity and fall inward.

							Rick.