From: shoham@ll.mit.edu (Daniel Shoham)
Subject: Re: Unrealistic space scenes
Keywords: n
Organization: MIT Lincoln Laboratory
Date: Tue, 15 Dec 92 03:03:00 GMT

In article <1gijgjEINN8jo@uni-erlangen.de> uhschreg@cip.informatik.uni-erlangen.de (Ulrich Schreglmann) writes:
>news@sunfse.ese.lmsc.lockheed.com (news) writes:
>
>>Solar sailers are only good near a star, they won't work in interstellar space
>>No light, no solar wind to move them.  The biggest problem with high speed 
>
>You also can only move into one direction using sails: away from the
>sun. Sailing against the wind, like it's possible on the ocean isn't
>possible.

Hardly a problem, as the Sun's gravity should provide you with a (considerably
more powerfull) force toward it. All you need do is to fold your sails (or
turn them in a right angle toward the sun) - and inward you go. In fact, the
imbalance is so severe that only a heroic design (i.e. *very* thin, wide area
sails) would allow solar wind (with effect proportional to sail area) to 
out-power gravity (with effect proportional to mass) - and even that, to a
very small extent.

>>interstellar travel is fuel.  The Bussard ram get that uses interstellar
>>hydrogen to power it is an interesting solution.  Anti-mater is a compact
>>way to store fuel but expensive to produce.  Finding an anti-matter planet
>
>And dangerous to store. A strong magnetic field would be the safest so-
>lution. But the anti-matter has to be magnetic for that. And all you
>need is still a very small high-velocity projectile to make the whole
>thing some bomb.

I think anti-matter is defenitely the fuel of choice (in fact, it is not so
outlandish even with current technology!).

It is NO more dangerous than just about any other matter-based fuel one can
think of. Any matter-based fuel is in a highly energetic state and readily
convertable to useable energy. A failure of the fuel container would lead to
a catastrophic consumption of all the fuel in a short period (i.e. explosion).
It matters not if the fuel was in the form of miligrams of antimatter, or
hundreeds of tons of cryogenic hydrogen - all the fuel would be consumed
at once. Normally, one would not expect spacecraft to survive the catastrophic
consumption of all their fuel (but SF spacecrafts might exist under rules that
allow such events).
If Anti-matter is used, the containment structure might be more massive than
the fuel itself, but that's an acceptable trade-off to allow for such a potent
fuel.

As for being expensive to produce, price could go down with mass production /
new technology. Anyway, considering that (with today's technology), the balk
of spacecraft fuel is merely used to lift just more fuel up - the use of
nearly massless fuel (even if a containment structure must be lifted along)
might justify the higher costs. I would suspect that if anti-matter could be
produced with, say 0.01% efficiency, it would be economical to lift space loads
with it.

I am not a Treky, but I was under the impression that "DiLithium crystals"
were supposed to be naturally occuering crystals where anti-matter is imbedded
securely in the structure and is thus available for exploitation. (Perhaps
some true Treky can correct me on this). While the idea is far fetched (in
particular, that such crystals might occuer naturally), the possibility that
crystal structures might secure unstable quantum states (such as matter -
antimatter proximity) is not dismissed out of hand. The possibility that
crystal structures might catalyse nuclear reactions is an even more distinct
possibility (say, the contraversial "cold fusion")

>>would be like gold to a space fareing people.

Anti-planets are unlikely in matter-galaxies. Asteroids, debrees, solar winds,
etc. that regulary smash into planets would explode with considerable fury
hurtling chunks of the planet into space. With the planet taking the shape of
a hazy cloud (or an asteroid belt), it's "cross section" would become much
larger, speeding up the process of capturing matter - until the whole planet
was anhilated. Anti-asteroids or Anti-rocks would suffer a similar fate at the
hand of micro-asteroids. Inter-stellar space (let alone inter-planetary space)
is just too populated to allow anti-matter structures to survive. It is
speculated that anti-galaxies, and anti-black-holes might exist - as not enough
matter would come in from inter-galactic space to foster the disintegration
process. It might even be possible that some matter galaxies and anti-matter
galaxies collide (are colliding now?) with an energetic light (gamma) show.

Well, I don't know if a distant anti-galaxie is such a gold mine afterall.

>Unless nothing falls onto the surface, that is. And there's still the
>problem of mining the stuff.

True.


>May the Anti-Cool Be with You!
>
>(C)OOL mcmxcii


Dan Shoham               shoham@ll.mit.edu
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