Comment by m4rtink

There more ways than just brute forcing massive shielding. If you know where the radiation is coming from & is directional (Sun, nuclear reactor) you can put the shielding some way from you & put the hab module in the shadow created by the shield - AKA a "shadow shield".

Some types of radiation can be deflected by strong magnetic fields - based on the technology and power source of your craft, this might end up lighter than pure mass based shielding.

Or you can just have your crewed ships go as fast as possible, reducing exposure & avoiding some radiation sources all together - zipping through radiation belts & doing fast transits in the quiet part of the solar cycle.