The Inspiration Mars Foundation's audacious plan for a private manned mission to Mars has more than a few challenges to overcome before its 2018 launch date, and it turns out the solution to one problem — dangerous cosmic rays — comes in the form of feces. The current plan calls for the two astronauts aboard the 1166-cubic-foot spacecraft to defecate into bags which would be used to line the walls of the ship (after extracting as much water as possible from the waste for reuse). At launch, the ship would be lined with bags containing food and water, and as the 501-day mission progressed they would be swapped out for bags containing solid waste as resources are used up. Inspiration Mars' Taber MacCallum told New Scientist about the plan, saying that "it's a little queasy sounding, but there's no place for that material to go, and it makes great radiation shielding." In addition to lining the ship with solid waste, food, and water, the upper stage of the launch rocket and an aluminum shell would help shield the astronauts from radiation.