Radiation dangers on Mars missions are often exaggerated. In Mars orbit, we have data that indicates approx. 22 milirads a day. It should be a fair bit less on

Radiation dangers on Mars missions are often exaggerated. In Mars orbit, we have data that indicates approx. 22 milirads a day. It should be a fair bit less on the surface. That gives the colonists about 3 years of unshielded radiation exposure till they hit the radiation max that NASA recommends (remember, they should be shielded somewhat though) There is also a decent amount of recent evidence that chronic radiation exposure in this quantity is no where as near as dangerous as a concentrated burst.