Re: [OT] BFG Questions ? -Reply

ShldWulf@aol.com wrote:
> 
> In a message dated 4/3/99 5:12:41 PM Mountain Daylight Time,
> laserlight@cwix.com writes:
> 
> << If I recall correctly, you slingshot by entering an orbit with high
>  gravitational potential energy (GPE), go down the well until you're
at low
>  GPE (and high velocity), and then burn your fuel before you start
climbing
>  up the well again.  It's the fact that you had your fuel coming in
and don't
>  have it going out that makes it work.  I don't recall the math but
I'm sure
>  someone like Nyrath or Keith W would if you asked prettily. >>
> 
> Can't be I don't think. Our space probes that have used it don't have
any
> on-board acceleration fuel. Just low power thusters. So they use the
sling
> shot to change course and keep thier velocity. Same thing I guess if
you DO
> have power.

	I believe that a couple of things are being confused here.

	A "gravitational slingshot" does not take any fuel.
	I am unsure if one can gain velocity this way, 
	I have a feeling that one can.

	What Lasterlight is talking about is the way to get the
	most value for the fuel you burn or the propellant you
	expell.  You do a close parabolic trajectory past a planet
	and do the burn while closest to the planet.
	It is one of the few times when the laws of physics
	lets you have your cake and eat it too.

	In all cases, any gain in momentum is balanced by
	an equal loss in the momentum of the planet.
	Because the planet is several trillion times as
	massive, the velocity loss is microscopic.

	I'm sorry about the vagueness of the above, most of
	my books are packed due to an impending move.