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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 18 Jan 2007 17:46:38 -0600
Message-ID: <005801c73b5a$e6313b30$3427e146_at_ATARIENGINE>

Hi, Rob,

    I see Ron just posted the explanation to you and
the List, but if you like colored line diagrams galore
and equations with delta's in them, take a look at:
http://en.wikipedia.org/wiki/Gravitational_slingshot

    Gotta love those little delta's. Sir Isaac would be
de-lighted.

    The article also explains the "powered slingshot"
when you do a engine burn at closest approach, which
adds the energy of the burn to the energy provided by
the planet, and to the energy the fuel picked up while
falling in. It all goes to the spacecraft, because after
you burn the fuel, it gets "left behind."

    The powered slingshot is why the Earth is a hopeless
candidate for spaceports of the future. You want to go
somewhere else in the solar system? Depart from the
Moon!

    It's got gentle escape velocity, no bothersome draggy
atmosphere, then you drop like a rock in a circumterrestial
orbit that skims the edge of that unhealthy Earth atmosphere.
and do your big burn there. Hello, Mars, Venus, wherever
you want to go!

    I'll be selling lunar condos in the lobby afterward, and
LunaPort construction bonds, too...


Sterling K. Webb
----------------------------------------------------------------
----- Original Message -----
From: "Rob McCafferty" <rob_mccafferty at yahoo.com>
To: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>;
<meteorite-list at meteoritecentral.com>
Sent: Thursday, January 18, 2007 4:33 PM
Subject: Re: [meteorite-list] NASA Spacecraft En Route to Pluto Prepares
forJupiter Encounter


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 06:46:38 PM PST