Among the many hazards of manned missions to Mars (or pretty much anywhere else beyond LEO) is that of long-term exposure to cosmic rays – radiation isn’t something that the human body copes with well, and it’s a long ride out to the red planet. A research project at NASA has obviously been brainstorming with groups of classic science fiction fans, as they’ve come up with a plan that involves hitching a ride on an asteroid that passes both Earth and Mars, and burrowing the vehicle inside the rock to use it as a radiation shield. It may sound a little crazy, but no more so than a lot of the other ideas that have been suggested, and it has the merit of being a low-tech solution – less things can go wrong, and logistics people like that sort of thing.