So... Why not wrap the space-ships in sufficient amounts of rock or lead? Or thicker armour in lighter materials, like foamed lead or somesuch? Presumably there are engineering problems associated with the additional mass, but maybe it could be boot-strapped by construction on the Moon or somesuch? I mean, the Moon already lacks Van Allen belts, so it would be a good testing area as well as a good staging area. I hear it also has deposits of Helium-3 for rocket-fuel.