From: The Low Golden Willow (phoenix@ugcs.caltech.edu)
Date: Mon Mar 03 1997 - 15:30:18 MST
===(David Cary)===
I've heard an interesting study in which it was claimed that, in some
cases, *no* shielding was better than any reasonable amount of
shielding. The argument was that, with no shielding, a high-energy
cosmic ray would hit and utterly destroy one DNA molecule in an
organism. However, with "small" amounts of shielding, the high-energy
cosmic ray would hit the shield and generate lots and lots of low-energy
particles, which would spread out and damage many, many cells of the
organism. The authors argued that the amount of shielding which would be
thick enough to catch all these low-energy particles was totally
unreasonable.
===
I've been reading O'Neill's _2081_ and _The High Frontier_. He said
about 2 meters of outer crud would be necessary to block radiation. You
need much less to block solar alpha particles and the like, but then the
high energy cosmics cause the above problem, so you end up with the
larger number. (Actually, you don't need much to block normal solar
alphas, but those solar storms get nasty.) It seems to me that a fair
depth of soil, plus heavy meteor shielding, should handle the radiation
problem anyway for colonies. Getting around is a different problem; I
hope storms are short enough that one can wait them out.
This looks like an incentive to have large manned ships.
Another thing is that the inner solar system is usually considered the
place to be for energy and communications. But after reading O'Neill's
ideas for deep space colonies, basically involving a very large mirror,
it struck me that the outer system might be more desirable. Or that the
biozone for habitats is wider and farther out than usually thought.
Because while energy is richer close to the sun, so is radiation. _If_
large but thin mirrors aren't too unwieldy to make and maintain, then by
doubling your distance you need to quadruple your collectors but can cut
your shielding by 3/4, because the mirror _doesn't_ focus the radiation
-- if it did shielding wouldn't be a problem in the first place. So
there should be some range where the mass of shielding saved makes up
for the mass of a larger mirror.
Of course shielding can be crud, whereas the mirror presuably has some
material requirements. I don't know what they're usually thought to be
made of, though. Ag? Al? Chromium? Sheets of conducting graphitics?
Merry part,
-xx- Damien R. Sullivan X-) <*> http://www.ugcs.caltech.edu/~phoenix
"And honesty means never having to say 'Please don't flush me down the
toilet.'" -- Scott Adams, "Dilbert", Bob the dinosaur
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