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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 18 Jan 2007 14:55:24 -0800 (PST)
Message-ID: <200701182255.OAA22516_at_zagami.jpl.nasa.gov>

>
> 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?
>
> Why does this not apply to spacecraft?

It does apply. Gravity assists always involve 3 bodies,
and the relative velocities to each other.
In this case, the three bodies are the spacecraft,
Jupiter and Sun. After New Horizons flies by Jupiter,
there is no velocity change RELATIVE TO JUPITER.
But the spacecraft does pick up extra velocity RELATIVE
TO THE SUN. In return, Jupiter will slow down RELATIVE
TO THE SUN. The velocity changes RELATIVE TO THE SUN
are related to their respective masses. Since the
spacecraft is so much smaller in mass than Jupiter,
the velocity increase for the spacecraft is rather
substantial. Jupiter's slowdown will be very
miniscule because of its larger mass.

Make sense now?

Ron Baalke
Received on Thu 18 Jan 2007 05:55:24 PM PST