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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: rail guns
Message-ID: <8512201613.AA03236@s1-b.arpa>
Date: Fri, 20-Dec-85 09:01:25 EST
Article-I.D.: s1-b.8512201613.AA03236
Posted: Fri Dec 20 09:01:25 1985
Date-Received: Sun, 22-Dec-85 00:12:47 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 20

A problem with shooting matter into orbit with ground-based guns
is that the orbit will either escape from earth completely or will
intersect the ground.  There is no way to get into a stable elliptical
orbit without some additional acceleration in space.

I suggested some months ago that larger payloads (hundreds of kg) be
sent to the moon by electric gun; this could provide a cheap
way of sending rare volatiles into space.  Harvesting would be
simplified if the payloads were made to crash in a small area
on the moon's surface.  The large payloads are needed to make on-board
maneuvering rockets practical; these rockets are needed to correct
for velocity errors introduced by the passage throught the atmosphere.

To get matter into low earth orbit one would shoot it into a very elongated
elliptical orbit (with perigee beneath the earth's surface); at apogee
a rocket would fire to bring the perigee above the atmosphere.  The
farther out the apogee is the less of a burn is needed, since more
angular momentum will be supplied.  After the orbit is stable
aerobraking could be used to lower the apogee.  This again requires
projectiles of substantial mass to be practical.