Via Assymetrical Information comes this Discover article on just how Earth-bound we may be as a species, because of the damage caused by cosmic rays.
Planetside, here, we're protected by the Earth's magnetic field, but out in space, we don't have that gigantic damping field. Metal shields made of lead or iron turn out to make the problem worse, because when cosmic rays collide with them, they release a cascade of charged particles that can cause the same kind of damage as the cosmic rays themselves.
In 1950, brilliant science fiction writer Cordwainer Smith wrote a haunting short story, Scanners Live in Vain, which all hinged on the fact that traveling through space caused irreversible dementia -- much like the kind of brain damage the article discusses as a distinct possibility.
I wonder if Adam Stone's solution to the problem in "Scanners" could work for us? It's certainly worth looking into. I'm sure the oysters won't mind.