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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: Re: Fuels for rocket propulsion
Message-ID: <5953@utzoo.UUCP>
Date: Thu, 12-Sep-85 16:11:20 EDT
Article-I.D.: utzoo.5953
Posted: Thu Sep 12 16:11:20 1985
Date-Received: Thu, 12-Sep-85 16:11:20 EDT
References: <384@decwrl.UUCP>
Organization: U of Toronto Zoology
Lines: 43

I haven't read the Space World article yet, but its author evidently
doesn't know much about antimatter propulsion.  The following is mostly
from talks given by Robert Forward, who is (among other things) a
consultant on advanced space propulsion to the USAF.  Papers (some his)
on antimatter propulsion in the Journal of the British Interplanetary
Society are also worth reading.

Matter/antimatter reactions do *not* immediately yield gamma rays and
neutrinos.  A proton plus an antiproton yields a spray of particles,
all unstable, but mostly charged.  They will eventually decay into
neutrinos and other particles, whose reaction will eventually yield
gamma rays.  But the lifetime of the charged particles is amply long
enough to use a magnetic nozzle to collimate them into an exhaust jet.
Gamma-ray emission will still be substantial, but the nozzle problem
is manageable.

Production of antimatter appears to be a straightforward although very
expensive procedure.  There are plenty of apparently-viable approaches
to handling it, although a lot of development work would be needed on
the details.  Existing technology, suitably applied, appears adequate.

Costs are uncertain.  It seems quite likely that it can be brought down
to a few tens of millions of dollars per milligram, given a large
dedicated production facility.  If this sounds rather high to you, then
consider:

	Antimatter at $50M/mg is cost-competitive for in-space
	propulsion with H2/O2 lifted from the ground.

	At $20M/mg, antimatter is cost-competitive with fission rockets.

	At $10M/mg, antimatter is cost-competitive with fusion rockets.

Forward's work is being taken very seriously.  I'm told (this is not
directly from him) that there is a symposium in the works on the subject
of building a "National Facility for Low-Energy Antimatter".  That is,
a prototype antimatter factory and antimatter-handling-techniques lab.
This one's for real, folks.  I very much doubt that anyone is ever going
to bother building fission rockets now, and I wouldn't spend a lot of money
on shares in a fusion-rocket company.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry