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From: @S1-A.ARPA:host.MIT-MC.ARPA
Newsgroups: net.space
Subject: Re: Galileo mission to Jupiter
Message-ID: <1744@mordor.UUCP>
Date: Fri, 10-May-85 14:06:19 EDT
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Posted: Fri May 10 14:06:19 1985
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From: Ross Finlayson <rsf@Pescadero>

The way I've always understood this is as follows:
If the gravity assisting planet (Mars say) were \stationary/ (wrt. some fixed
reference point), then after the gravity assist, the spacecraft's 
velocity (wrt. the reference point) would be unchanged, except for direction.
In practice, however, the planet is \itself/ in motion (around the Sun), so 
some of the planet's kinetic energy (and thus velocity) is transferred to the
spacecraft.  That is, gravity assist works because the planet effectively
"drags along" the spacecraft, not just because the planet is "sitting there".

Please correct me if this is wrong.

	Ross.