Today four Russians, a German and a Frenchman walked into a mocked-up spacecraft and swung the metal hatch shut behind them. If all goes as planned, that hatch won't open again for 105 days. The six men have volunteered to spend more than three months in isolation to simulate the experience of a manned flight to Mars. The crew will subsist on freeze-dried space rations and will clean themselves with wet wipes; they'll also go without smoking, alcohol, TV, and internet.