Burrowing inside an asteroid whose orbit carries it past both the Earth and Mars could protect astronauts from radiation on their way to the Red Planet. The idea is being investigated with funding from NASA.
A small population of asteroids pass by both the Earth and Mars in their orbits. So the idea is that a spacecraft containing Mars-bound astronauts could rendezvous with one of these objects as it goes by the Earth and travel with it until it nears the Red Planet.
In one version of the idea, the astronauts would actually dig a hole in the asteroid, put the spacecraft inside and cover it over with material from the asteroid. Within this protective burrow, the spacecraft would be shielded from cosmic rays during the six- to 10- month journey to Mars.
In a second version, the spacecraft would not contact the space rock. Instead, it would hover nearby, and astronauts or robots would visit it on spacewalks. “You’d have the astronaut actually go to the asteroid and begin to extract material,” Della-Giustina told New Scientist. The material collected could then be brought back and put into a hollow shell surrounding the spacecraft. The shell of rocky debris would make a radiation shield, she says. The plan has some potential hurdles, but nothing that seems to rule it out..