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From: fisher@star.DEC (Burns Fisher ZKO1-1/D42 DTN 381-1466)
Newsgroups: net.space
Subject: Slingshot effect
Message-ID: <1428@decwrl.UUCP>
Date: Thu, 14-Nov-85 09:45:27 EST
Article-I.D.: decwrl.1428
Posted: Thu Nov 14 09:45:27 1985
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//

I am not expert on this subject, but it was my impression that there are
two different kinds of effects going on here:

The first is a change of velocity, not necessarily speed.  If you whip around
the planet and zip off with a direction 180 degrees different (not really
possible, I guess, but I can talk about that without vector notation), you
have changed your velocity by -2V.  Similarly with different angles.  The
solar polar mission coming up uses Jupitor to sling the spacecraft into an
orbit which is ~90degrees to the ecliptic, nearly impossible using engines.

The second, I am a bit more fuzzy on, but I have heard that if you fire
your engines while you are down in the gravity well of a planet that it
has a multiplier effect of some sort.  That is, your final speed is higher
than if you waited until you got out of the well and then fired.  I guess
that makes some vague sense from a conservation of energy viewpoint...the
planet pulls down mass M, but only mass M-m goes back out (at a higher speed).

I'd be interested in hearing clarifications and/or corrections.

Burns