Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!uxh.cso.uiuc.edu!aae391aa
From: aae391aa@uxh.cso.uiuc.edu
Newsgroups: sci.space.shuttle
Subject: Re: Galileo Gravity Boost
Message-ID: <34700005@uxh.cso.uiuc.edu>
Date: 21 Oct 89 09:41:11 GMT
References: <12027@eerie.acsu.Buffalo.EDU>
Lines: 39
Nf-ID: #R:eerie.acsu.Buffalo.EDU:12027:uxh.cso.uiuc.edu:34700005:000:1631
Nf-From: uxh.cso.uiuc.edu!aae391aa    Oct 20 14:48:00 1989


I (aae391aa@uxh.cso.uiuc.edu) wrote

 > 4:00 pm  Oct 19, 1989, stein-c@acsu.Buffalo.EDU writes:
 > 
 >  > Can anyone explain how Galileo will be gaining energy by flying near
 >  > planets? I understand that the spacecraft will be gaining velocity due
 >  > to gravity forces as it approaches Venus, etc., but wouldn't all of that
 >  > energy be lost as Galileo goes away from the planet and has to go
 >  > against gravity forces? The only way I can see it is if Galileo picks up
 >  > some of the energy from the velocity of the planet. 
 > 
 > The spacecraft does not get a boost in its speed (it speeds up approaching a
 > 
 > [etc]

As has been pointed out, I was incorrect in that last statement.  Sorry.
Here is some of the e-mail I got pointing out the correct answer:

sw@groucho.att.com (Stuart Warmink) states:
 > I'm afraid you are mistaken; the probe *does*  gain speed. Just changing
 > the trajectory is pointless, they might as well have launched it in the 
 > right direction in the first place.
 > 
 > See Mariner 10, Pioneers 10 & 11, Voyagers 1 & 2, ...
 > 
 > The probes *gains* (or loses, depending on the approach) momentum at
 > the expense of the planet's. It does *not* loose all the speed gaines at
 > approach. See the many articles on the Net...

jwp@cupcake.sal.wisc.edu (Jeffrey W Percival) writes:
 > I'm sure you'll hear a lot about this, but the spacecraft
 > actually does pick up speed.  Remember, the planet is moving too,
 > and the idea that Galileo "gives back" all the speed it gained
 > falling in only works for a stationary planet.


					Erik A. Johnson
					johnsone@uxh.cso.uiuc.edu