The most costly and tricky part of any manned space mission is providing life-support for its human crew: food, oxygen, and protection from radiation and other hazards of space travel. On a human mission to Mars, most of the cost—some 80 percent of it—would involve returning the crew. Rather than quintuple the cost, those funds could go toward building a permanent settlement. After several unmanned missions drop supplies at a base station on the Red Planet, two spacecraft carrying two humans each would be sent on the six- to eight-month voyage to Mars to begin the first human colony on another planet.