Six men spend 520 days sealed in a Moscow mock-up
Mars-500 ran a Mars mission at full length with nobody leaving the building. Four of the six crew came out with a sleep or behavioural disorder.
On 3 June 2010 a hatch closed on six men inside a set of windowless steel modules at the Institute of Biomedical Problems in Moscow. It opened again on 4 November 2011. Alexey Sitev, an engineer, commanded; Sukhrob Kamolov was the surgeon and Alexandr Smoleevskiy the physiologist. With them were Romain Charles, a French engineer, Diego Urbina, an Italian-Colombian engineer flying for ESA, and Wang Yue, an instructor from China's astronaut training centre. Nothing about the voyage was real except the confinement, and the confinement was complete.
Mars-500 remains the only time anyone has run a Mars mission at full duration. Roughly 550 cubic metres of sealed volume, all consumables loaded in advance, and radio traffic to the ground artificially held back to mimic the light-time lag — up to twenty minutes each way, so a question took most of an hour to answer. The crew flew out for 250 days, entered simulated orbit, and on 14 February 2011 Smoleevskiy, Urbina and Wang Yue suited up and stepped into a chamber dressed as the Martian surface. Two more Marswalks followed on 18 and 22 February. Then they climbed back aboard for a 240-day cruise home.
What the sensors recorded on the way is the useful part, and it is not flattering. Active wakefulness fell 7 percent across the mission: by the final quarter each man was spending 1.12 fewer hours a day awake and moving than at the start, while sleep rose 8.4 percent. One crewmember's body clock came loose from the 24-hour day altogether and free-ran near 25 hours, sending his sleep drifting all the way around the clock. Another averaged 6.54 hours a night, rated his sleep quality worst of the six, and accumulated errors on the reaction-time tests. Four of the six finished with a measurable behavioural disturbance or sleep disorder. One reported depression symptoms in 93 percent of mission weeks.
Ask who they fought with and the answer is uncomfortable. Over 520 days the crew logged 41 conflicts with mission control against 8 among themselves — five to one, aimed outward. Two crewmembers accounted for 85 percent of all perceived conflict. The failure mode was not cabin fever between bunkmates; it was the relationship with the ground, strained through a delay that made every misunderstanding take an hour to unpick.
What the experiment could not simulate matters as much. No weightlessness, no radiation, no possibility of dying, and everyone inside knew the hatch could be opened in minutes. A real crew has none of those exits and would reach the surface deconditioned rather than walking upstairs. Still, nobody quit and nobody was pulled out. Six people held together for the length of the trip — and the record shows exactly what it cost them.