A real threat to astronauts are cosmic rays, these are very high energy charged particles originating outside of our solar system which can pass straight through a spaceship and astronauts possibly giving them cancer or even radiation sickness. It is actually quite possible that if we could get astronauts to Mars by the time they got there they would be so damaged by the radiation there would be no point in sending them.
If you are on the ground you are protected by the atmosphere and the earth's magnetic field. Astronauts on the Space Shuttle or International Space Station are still protected by the earth's magnetic field, but as soon as you get beyond this you are in much more danger.
An engineer called Ram Tripathi from the Langley research centre in Virginia may have the solution. Make the spaceship look like one of the table decorations made from a pineapple surrounded by cherries on cocktail sticks.
The idea is to charge up the cherries (which would be made of metal) to enormous voltages some positive some negative , this means that the cosmic ray particles which are charged will be attracted to the cherries and hit them rather than the astronauts.