Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site mordor.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!mordor!@S1-A.ARPA,@MIT-MC.ARPA:FIRTH@TL-20B.ARPA
From: @S1-A.ARPA,@MIT-MC.ARPA:FIRTH@TL-20B.ARPA
Newsgroups: net.space
Subject: Space propulsion
Message-ID: <2272@mordor.UUCP>
Date: Thu, 13-Jun-85 10:01:23 EDT
Article-I.D.: mordor.2272
Posted: Thu Jun 13 10:01:23 1985
Date-Received: Mon, 17-Jun-85 00:09:46 EDT
Sender: daemon@mordor.UUCP
Lines: 46

From: FIRTH@TL-20B.ARPA

Here is a short list of ideas for space propulsion systems
that don't rely on taking stuff along and throwing it out
the back.  They range from the serious to the silly, and they
are all based on recollections of other people's work.

(1) Dean drive.  The assumption is that Newton's Third Law is
    wrong, and some combination of cams, levers, balls, cogwheels
    and electric drills will exhibit spontaneous motion.  The
    problem is that people seem to have studied Dean drives quite
    extensively and they really don't work.  This represents in
    my view the "silly" end of the spectrum

All other systems rely on using something already out there.  We
have four choices

(2) Bussard ramjet.  That is, we use the mass found in space as fuel
    or reaction mass.  The main problems are that the mass so dilute
    that we need fairly large scoops to collect it.  But that is an
    engineering problem, not one of principle.  This is I think the
    system most likely to work.

(3) Light sail.  The trouble is, there isn't enough light.  We need
    either an enormous sail or some space-based lasers.  I don't like
    the idea of space-based lasers - too dangerous and too much a
    "brute force" solution.

(4) Magnetic propulsion.  Useful only for the inner system, ie within
    the solar magnetosphere.  The energy is there, it's just a question
    of harnessing it somehow.

(5) Gravitic propulsion.  This one is really way out.  Currently, we have
    absolutely no idea how to interact with a gravity field in any
    controlled manner.  The interaction must be possible - inded, Hawking
    radiation is created by the breakdown of the vacuum under intense
    gravitic stress - but we lack an adequate theory.  Also, it's not
    clear what the energy flux would be.  If you believe Mach's principle,
    then a ship could use the entire mass of the universe to power a
    gravity drive.

Frankly, I'd like to see work on all four of the above.  Or do we wait
for an outsider ship to sell us one in exchange for Jupiter?

Robert Firth
-------