Re: Slingshotting ships with gravity wells in SJ

>The so-called "slingshot maneuver" is a spectacular and dangerous trick to
>gain extra speed by dipping into a planet's gravity well, orbiting the
>planet for a short time, and then escaping it at just the right point that
>it adds momentum to your flight. It was popularized by 2001: A Space
>Oddyssey, and Star Trek at certain points. It's not the sort of thing you
>want to do on a regular basis.

NASA has utilised planetary slingshots on most missions that go past a
planetary body (or even the moon).  The savings are enormous.  I can't
exactly remember the first mission on which this was done (I think it may
have been Voyager, around Saturn), but I do remember something like the
mission time being cut from 7 years to about 3 years (to reach a particular
point further out in space).

One thing wrong with your basic ideas of 'a certain time in orbit give a
certain Interstellar Speed' is the amount of speed you can get out.  This
has *nothing to do* with the amount of time spent in orbit around a body.
It has everything to do with how close you approach the body.  The increase
in speed comes from the force the craft feels as it approaches the body,
and the closer you get, the faster you go.  Also, as you move away from the
body afterwards you lose speed as it is trying to pull you back.  *IF* you
do it right then you can come out of the whole encounter with more speed
than you went in (basically, you come out in roughly the same direction as
the planet is moving through space, and you get a bit of extra speed
because of relative motions).

Cheers

Andrew Tiffany