From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: gravity assists to escape solar system
Date: Fri, 15 Aug 1997 00:10:18 GMT

In article <19970814051700.BAA02564@ladder02.news.aol.com>,
Guff12345 <guff12345@aol.com> wrote:
>"Assuming one used as many gravity assist flyby trajectories as possible
>(regardless of how long such a convoluted path would take -- even if it
>takes centuries) by how much would the required velocity needed to escape
>the solar system be decreased?"

If you can reach an elliptical orbit whose apogee is most of the way to
the Moon, that is sufficient.  (That requires very nearly Earth escape
velocity.)  With careful planning, you can use lunar perturbations to pump
the orbit up enough for a lunar flyby.  You can then use multiple lunar
flybys, with very complex mission planning, to exit the Earth-Moon system
at 2km/s or so, according to Ed Belbruno.  You can then use multiple Earth
flybys, and eventually possibly some Venus and Mars flybys, to pump up
your solar orbit enough to reach Jupiter.  And one Jupiter flyby and
you're gone.

It's hard to do much better than that, alas.  Beyond Jupiter, the planets
move rather slowly and it's hard to get a lot of boost from them.  If
you had a *lot* of patience, many decades' worth, you might be able to
make multiple Jupiter flybys, by carefully planning the early ones so
that they *didn't* expel you from the solar system, and that might get
you some extra boost from the final one.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu