KFL@MIT-MC.ARPA ("Keith F. Lynch") (12/21/85)
From: Nicholas.Spies@h.cs.cmu.edu
Perhaps rail guns (like Tom Swift's Electric Gun) could be used to
shoot materials into space ... [Is air friction too much to allow orbital
velocities?]
You cannot shoot things into orbit from the Earth's surface. An
orbit is always an ellipse, a closed curve. The projectile would try
to return to its starting point -- from underneath!
You could, I think, cause the projectile to fly by the Moon in such
a way as to go into a very high Earth orbit. But this probably
wouldn't be stable since it would eventually get close to the Moon
again. Besides, that's really too high to be useful (for the near
term).
A more interesting possibilty is for the projectile to be 'caught'
and decelerated by a railgun in Earth orbit. This railgun in space
need not really be in orbit. It could be relatively stationary over
one point (a low altitude 'geosynchronous' 'sattelite') since it would
be getting frequent boosts from catching the projectiles. It would
use the energy gained by decelerating the projectiles to boost them
horizontally, into orbit (equal numbers in each direction, to prevent
the railgun from drifting horizontally).
...Keithmcgeer@JI (Rick McGeer) (12/24/85)
I thought of something related to the "catcher" idea, and I'm not sure it would work. This involves a transfer station in LEO, a two-way rail gun. Each shot is in pairs -- one side goes to GEO or moon-transfer orbit, the second is an earth entry orbit. It seems to me (no calculations, sadly) that one could, in principle, ship very large amounts of mass to HEO and beyond in this manner. In effect, each of the two payloads uses the other as reaction mass. The efficacy of the method is dependent upon how often you want to ship material both ways from LEO. -- Rick.
KFL@MIT-MC.ARPA ("Keith F. Lynch") (12/24/85)
Date: Mon, 23 Dec 85 15:51:43 PST
From: mcgeer@ji (Rick McGeer)
I thought of something related to the "catcher" idea, and I'm not sure
it would work. This involves a transfer station in LEO, a two-way rail
gun. Each shot is in pairs -- one side goes to GEO or moon-transfer
orbit, the second is an earth entry orbit. It seems to me (no
calculations, sadly) that one could, in principle, ship very large amounts
of mass to HEO and beyond in this manner. In effect, each of the two
payloads uses the other as reaction mass. ...
Ya, this should work. Please note that the orbit the projectile is shot
into would be an elliptical orbit whose perigee is at the same altitude as
the transfer station. Possibly a second transfer station could be set up in
GEO.
Also note that although the momentum could be made to balance (which is
important or the transfer station will fall out of the sky) but that you
still need lots of energy.
A way that does NOT need extra energy is the 'skyhook' idea propounded by
Hans Moravec among others. The skyhook does not need to be fastened to the
Earth, but could be freely rotating in Earth orbit. The latter is MUCH
easier. Spacecrafts can dock to one end of this rotating cable and undock
at the other end, having gotten 'free' delta-vee. This is possible because
of the remarkable property that all rotating objects have, namely that all
of the object (except the axis) is continually undergoing acceleration
without consuming any energy or reaction mass.
...Keith