[meteorite-list] NASA Spacecraft En Route to Pluto Prepares for Jupiter Encounter

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Thu, 18 Jan 2007 14:33:11 -0800 (PST)
Message-ID: <615572.49849.qm_at_web50908.mail.yahoo.com>

 Jupiter's
> gravity will
> accelerate New Horizons away from the sun by an
> additional 9,000
> miles per hour, pushing it past 52,000 mph and
> hurling it toward a
> pass through the Pluto system in July 2015.
>

Could someone clarify something which ahs been
bothering me for years about this gravity assist
technique?

Why does the spacecraft come out of the gravity well
going faster than it went in without thrust?

You remember the conservation of energy stuff from
school? GravPotential to Kinetic to GravPotential. A
ball rolling down a hill can only roll up the other
side to a height as high as it was released from.

Why does this not apply to spacecraft?
It's climbing out of the suns gravity well so it ought
to be slowing down all the way. When you drop into
Jupiters gravity well I can see that you're going to
speed up but on the way out surely it'll lose all that
speed and at the end of the encounter should be no
faster than it went in at. In fact, slower because
it's now further up the hill of the suns gravity well.

Please, will someone tell me what I'm missing. It
bothers me tremendously that I have a BSc in physics
and studied both astronomy and astrophysics subsids
and I don't get it.
It's the same with asteroids getting ejected into
orbits further out. How? How?

Sir Isaac would not be amused

Rob McC


 
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Received on Thu 18 Jan 2007 05:33:11 PM PST