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From: KFL@MIT-MC.ARPA ("Keith F. Lynch")
Newsgroups: net.space
Subject: Re:  Shooting into orbit
Message-ID: <[MC.LCS.MIT.EDU].765230.851223.KFL>
Date: Mon, 23-Dec-85 22:14:01 EST
Article-I.D.: <[MC.LCS.MIT.EDU].765230.851223.KFL>
Posted: Mon Dec 23 22:14:01 1985
Date-Received: Wed, 25-Dec-85 01:50:01 EST
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    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