You can't really shield against galactic cosmic rays (too high energy, would require far too much mass), which make up approximately 95% of the dose. https://s

You can't really shield against galactic cosmic rays (too high energy, would require far too much mass), which make up approximately 95% of the dose. https://science.sciencemag.org/content/340/6136/1080.abstract https://science.sciencemag.org/content/340/6136/1080.abstrac... *Edit - but the comment higher up isn't right either, that most Mars-bound astronauts will have decreased lives. The paper linked above estimates 3% of astronauts to die from cancer caused by the trip (assuming no exposure on the surface of Mars, meaning they're in the ground).