Cosmic radiation will be a significant problem en route to Mars, and unless resolved could put the whole “colonize the red planet campaign” out of action fairly quick.
(Space Travel) Among the gravest risks of a manned flight to Mars ranks the possibility that massive amounts of solar and cosmic radiation will decimate the brains of astronauts, leaving them in a vegetative state, if they survive at all.
Dubbed “Risk 29” by NASA’s Mars scientists, the cosmic radiation risk remains a show-stopper because shielding a spacecraft from all radiation could make it too heavy to reach Mars, which, at its closest, is 38 million miles from earth.
Although scientists are working on experiments to determine how tolerant the human mind is to deadly radiation, working on radiation tolerance level may not convince the public to travel off world.
What scientists and engineers need to do is figure out a way to make a lighter shield around the space craft to insure that solar radiation does not hamper future colonists as there will probably be no chemotherapists around to treat cancer on that world.
They could also perhaps have construct a “detachable” shield around the craft, which they can discard once arriving on Mars.
If no radiation safe ways are developed for traveling to the red planet (among other worlds) then we can expect perhaps only a few thousand souls living on other worlds, instead of the hundreds of millions necessary to colonize our solar system.