Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site faron.UUCP
Path: utzoo!linus!faron!bs
From: bs@faron.UUCP (Robert D. Silverman)
Newsgroups: net.physics
Subject: Re: slingshot effect
Message-ID: <381@faron.UUCP>
Date: Thu, 14-Nov-85 11:54:36 EST
Article-I.D.: faron.381
Posted: Thu Nov 14 11:54:36 1985
Date-Received: Fri, 15-Nov-85 20:08:23 EST
References: <2358@watale.UUCP>
Distribution: net
Organization: The MITRE Coporation, Bedford, MA
Lines: 25

> Can anyone explain to me (in 250 words or less) the famed
> 'slingshot' effect that is used to accelerate space probes?
> 
> I understand this effect is used not only to change the
> trajectory of the craft, but also its *speed*.
> 
> I know it has to do with angular momentum, but *how* is the
> planet's momentum transfered to the space craft?
> 
> PS. keep it simple if possible..
> 
> thanx

It's fairly simple: An object entering the gravity well of a planet (or other
body) has potential energy of position. As it falls into the gravity well
it changes that potential energy into kinetic energy. If it burns NO fuel
then as it climbs out of the well it will change back the kinetic energy
it gained into potential energy. However, if it BURNS fuel at the bottom 
of the well its mass is reduced. The kinetic energy gained by the fuel
as it fell into the well goes directly into the ship itself as the fuel
is burned. Thus, it gains speed by falling, burns fuel (thus reducing its mass)
and as a result KEEPS the extra kinetic energy as it climbs out of the
gravity well. Angular momentum doesn't really play a part.

Bob Silverman   (they call me Mr. 9)