Message-ID: <MZLZu9a00VcJ4Y0E5=@andrew.cmu.edu>
Reply-To: space+@Andrew.CMU.EDU
From: space-request+@Andrew.CMU.EDU
To: space+@Andrew.CMU.EDU
Date: Mon, 13 Nov 89 01:26:18 -0500 (EST)
Subject: SPACE Digest V10 #240

SPACE Digest                                     Volume 10 : Issue 240

Today's Topics:
	     Re: Radiation exposure for Apollo astronauts
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Date: 9 Nov 89 02:28:37 GMT
From: island!grenada!everexn!mike@uunet.uu.net  (Mike Higgins)
Subject: Re: Radiation exposure for Apollo astronauts


	Back when everyone was talking about O'Neil style space colonies in
the 1970's  (boy those were the days! :-).  I heard an interesing set of
numbers I call the 3 foot rule:  A naked human in space is virtually
transparent to cosmic rays: they pass right through all these big low density
organic molecules that we are made of most of the time.  To stop a cosmic
particle, you need lots of atoms packed closely together, like in a
solid piece of metal.  Problem is, cosmic particles are so energetic, they
cause a shower of slower particles when they hit the nuclius of a metal
atom.  These secondary particles are going slow enough that their cross-
sections allow them to hit our sparce organic molecules, and we get cooked!
So if you put a few milimeters of metal around yourself, (like, to hold the
air in, for example :^), your radiation dose goes way up.  As you put more
and more metal around you (or lunar ore slag) the radition goes higher and
higher, until you get about a foot thick.  At this point it starts to decrease
again as the inner layers absorb the secondary radiation from the outer.
At two feet thick, the radiation dose drops back down to what it was before
you started, and at 3 feet, you are as safe as you would be down here under
the atmosphere.  I don't know what they use for film safes or solar flare
protection on things like SkyLab:  there may be materials better at 
absorbing secondary radiation than lunar slag.  But the space habitat people
were looking for cheep bulk materials that might be available for shields.

	In case you havn't heard of this idea, there is a space suit design
based on this idea:  Wrap a human in some plastic mesh to help keep internal
pressure up. (Like a wet suit, only thiner and tighter).
Put a plastic buble over the head, and feed oxygen from a
plastic tank.  Make the mesh porus to water, and sweat seeps through and
regulates your temperature (you stay sweaty and uncomfortable all the time,
but if you have lots of water, it's otherwise a cheep system!).  Since
you made this suit out of low-Z materials, and you are made of low-Z materials,
the cosmic particles have cross sections too small to see you! Van-Allen
belts and solar flares are another can of worms, they are low energy
enough to get you, even when you are naked in space.

Mike Higgins                                       "Never trust a machine
...ucbvax!cogsci!well!fico2!everexn!mike            you can't program"
So many newsgroups...  so little time...

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End of SPACE Digest V10 #240
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