"Dr. O" wrote in message ...
http://www.nytimes.com/2003/12/09/sc...ce/09RADI.html

The thing I don't understand is that people have been spending much more
time in orbit than the round-trip to Mars. Although the upper atmosphere
does shield them somewhat, the majority of the radiation is still getting
through. Why are they so concerned then about radiation?

Also, lead shielding will have to be installed in any Mars spaceship anyway
because of the possibility of solar flares.

I always figured that shielding on a interplaneraty spacecraft should
use materials usable at other moments and for other purpose in the
mission. A dense outer shell should try not to stop the particules but
refract or reflect them. One might conceive a outer skin made of
hundreds of small panels (maybe a few centimeters accross) of light
materials on which incoming high-energy particules would skim accros
and mostly go back toward space, like a stealh fighter mostly reflects
radar (F-117), or an X-ray telescope focuses incoming photons.

For the particles which could not be be reflected due to their
incident angle, a second layer would absorb some of the energy. 15
centimeters of water could be used for that purpose. Only the water
would be kept as ice, providing some protection from hard impacts from
debris. When needed the water could be thawed back to liquid form.

Photodetectors could be installed in the ice shell, monitoring the
incoming radiation. But I think it would be best to try to provide a
space in which radiation would not be stopped, but directed away from.