In case you haven’t seen this posted, NASA has a NASA cosmic ray challenge (with $29,000 prize) posted on Innocentive for ways to reduce the impact of cosmic rays on astronauts on extended space missions outside of Low Earth Orbit. This is a serious health concern for Mars missions, and traditional methods of radiation shielding (i.e. lots of lead) are too heavy for current mission parameters.
I’m not a material scientist, so the precise details are beyond me, but here’s roughly what I think the solution will ultimately look like (don’t worry, I’ve submitted this already!).
Picture three separate layers.
1. The outer-most layer is not intended to stop incoming particles, but rather to slow them down. As such, it will likely ablate away (or become damaged beyond use) over time. One possibility would be to take single-atom thick layers of carbon lattice, and then position millions of such layers in such a way that any incoming particle is virtually guaranteed to hit into something on the way in. The resulting material would probably only be millimeters thick, at most, with a consistency something like the insulating foam batting that goes into walls.
2. The middle layer will be designed to “tune” the types of radiation that will hit the inner-most layer. “Cosmic Ray” is actually a generic term for a wide variety of kinds of radiation, ranging from high-energy photons to massive particles (which can readily be stopped by a sufficiently dense material). I’m not sure exactly what material would be best for this – possibly hydrogen or helium gas, in pressurized tubes – by the idea is that light particles hit into the intermediate layer, and the resulting radiation that gets through tends to be larger, slower particles.
3. The inner-most layer would be a thin layer of dense material – say lead foil. This would be much thinner and lighter than if it were the primary radiation shielding, since the outer layers will have slowed down and filtered the forms of radiation that will ultimately hit it. Another alternative could be “active” magnetic shielding of some kind (necessitating a slightly different approach with the intermediate “tuning” layer).
Other secondary shielding could also include classic ideas, such as carefully positioning the crew’s drinking water around their living quarters, so as to provide additional layers of safety.