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From: KFL@MC.LCS.MIT.EDU ("Keith F. Lynch")
Newsgroups: net.space
Subject: Re: Fusion
Message-ID: <[MC.LCS.MIT.EDU].848806.860312.KFL>
Date: Wed, 12-Mar-86 21:17:13 EST
Article-I.D.: <[MC.LCS.MIT.EDU].848806.860312.KFL>
Posted: Wed Mar 12 21:17:13 1986
Date-Received: Sat, 15-Mar-86 18:54:18 EST
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    From: ulysses!ihnp4!ihuxl!dcn@ucbvax.berkeley.edu

    I think it's likely that fusion engines will soon be surpassed by
    antimatter engines.

  One problem with antimatter is where does one get it?  Hydrogen (the
fuel for fusion) is very common, but antimatter is not known to occur
naturally anywhere.
  Antimatter can be manufactured, but only by the use of the same
amount of energy as you can get out of it later.  Much more energy,
actually, because of the low efficiencies of manufacture.
  The only known way to store antimatter is as ions circling around in
a large circular vacuum chamber.  The ions keep giving off synchrotron
radiation and slowing down as they change direction, so a constant
input of energy is needed to maintain the storage.  Less energy is
needed for this in a larger ring, but rings are already many miles
around.  And not much antimatter can be stored in one, since the ions
all tend to repel eachother.
  Cold storage, as solid pellets, also has severe problems.  The
pellet must never touch the walls of its container.  Not even one
stray gas atom must touch the pellet.  If one did, it would make a
tiny explosion that would free millions of anti-atoms from the pellet,
most of which would collide with the walls of the container causing
millions of tiny explosions that would free trillions of atoms from
the walls of the container, many of which would collide with the
pellet ... rapidly escalating into a full scale annihilation explosion
with the force of trillions of H-bombs.  Such antimatter pellets
should be allowed to exist only millions of miles from Earth, lest all
life on one side of Earth be incinerated by an explosion within a few
thousand miles of Earth.
  Even if you had a way to store antimatter, you still have to find a
way to remove it from storage in a smooth flow, react it with matter
in a controlled manner, cause it to make thrust rather than heat, and
keep the deadly gamma rays away from the crew and the electronics and
the antimatter storage (gamma rays can cause atoms and anti-atoms to
suddenly go flying off in random directions, like into eachother).
  This sounds like a technology that is much further in the future
than controlled fusion.  If possible at all.

  One theory says that antimatter is identical to matter only switched
left to right.  This theory says that if Alice had stepped into the
looking glass, she would have annihilated most of England.  If this
theory is true, then all we have to do is somehow put a half twist on
a small section of space, sort of like making an H shaped cut in a
piece of paper and then taping the ends back together after giving
each one a quarter twist in opposite directions, only in three
dimensions.  Then, any matter put through the twist would come through
the other side as antimatter.  This would allow total conversion of
any sort of matter into energy, and would avoid the storage problems I
mentioned since no antimatter is ever stored, it is generated when it
is needed.
  According to relativity, space is curved.  The curvature can be
changed by rearranging masses.  So, while I see no way to put a half
twist into space, it is by no means theoretically impossible or
unthinkable.  The consequences of such a technology falling into the
wrong hands may be unthinkable, however.  At least I don't want to
think about it.
								...Keith