Re: SPACE: Mass transit idea

Hal Finney (
Tue, 31 Dec 1996 14:29:51 -0800

From: Michael Lorrey <>
> Essentially, you have one station at geosynch, that is say a hundred
> miles long, containing a main EM rail system, and an
> accelerator/decellerator rail in parallel. On the opposite side of the
> planet, you've got a ground station, with a similar EM setup.
> [...]
> The cars would, when reaching the geosynch station, be traveling at the
> same velocity as the station, from which they can either dump their
> load, accept a load, or be switched to the parallel system for
> changeover to an accelerator for transition to higher orbit or
> interplanetary trajectory.

My orbital mechanics is pretty rusty, but I think the cars would
actually have a significant velocity relative to the geosynch station
(having climbed all the way up from Earth), and similarly would need a
big kick on leaving the station so that they would drop out of geosync
orbit all the way down to a perigee of 1 earth radius. This is quite
a big drop. My very rough calculations came out with a value of about
10,000 m/s for the velocity differential between the circular orbit and
the elliptical one at apogee. Maybe that is tolerable with your EM rail,
if it is long enough. A similar velocity differential exists at the
Earth side as well. (Obviously you need greater than LEO speed there,
which is about 7000 m/s.)