Six cosmonauts travelled 70 million miles to Mars and back over 520 days, but without leaving a couple of rooms in Moscow.
The Moscow Mars 500 project began on 3 June 2010 and finishes today (4 November).
Mission controllers sealed the six volunteer crew members in three windowless steel capsules. The ultimate test of a long meeting with no natural daylight finally saw the Russian captain Alexei Sitev, led his crew back into the world again after 17 months without any other business other than simulating the effects of being cooped up for the equivalent time a mission to Mars would take.
Social media was allowed, and Italian crew member Diego Urbina tweeted extensively about the experiment.
Video conferencing was also used extensively, albeit with a 20-minute delay to simulate real broadcast conditions in space.
Russian mission controllers said the project had proved that a crew could survive the inevitable psychological isolation involved with a trip to the Red Planet.
Patrik Sundblad, a scientist at the European Space Agency, which ran the project with the Moscow Institute, said: “Pscyhologically, we can do it”.
Picture of Mars 500 courtesy of RIA Novosti
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