Six volunteers on Friday stepped out into the outside world after spending the last one-and-a-half-years locked away in an isolation module in Moscow to simulate the effects of a return trip to Mars.
The multi-national crew showed no ill effects after emerging from the capsule where they had lived and slept for the last 520 days but were clearly delighted they had completed their earth-bound "journey" to the Red Planet.
After the pressure in the capsule was equalised with the outside, a researcher broke the seal and then opened the door of the module. All six crew members, dressed in blue overalls, walked out one-by-one in good health.
Looking slightly dazzled by their first encounter with other human beings for 18 months, the crew of one Chinese, one Italian, one Frenchman and three Russians lined up in a row to receive the congratulations from scientists.
"The international crew has completed the 520 day mission," commander Alexei Sityov, one of three Russian participants in the experiment, told Russia's space bosses in formal military style.
"The programme has been fully carried out. All the crew members are in good health. We are now ready for further tests," he added in comments broadcast by Russian television and the European Space Agency (ESA).
Italian Diego Urbina, who clenched his fists with delight as he finally stepped out of the capsule, said it had been an honour to have been involved in the programme.
He said he hoped that the experiment would help humans reach "a distant but reachable planet". Fellow "Marsonaut", Frenchman Romain Charles, said the crew were ready to "embark on the next spaceship" that would go to Mars.
Chinese participant Wang Yue put it simply: "After 520 days, we are finally back."
They were each presented with a flower by young female researchers in white coats as a reward for their endeavours.
But they were then immediately ushered away by scientists from Moscow Institute of Biomedical Problems (IMBP) for several days of medical and psychological tests. They are next due to appear in public for a news conference on Tuesday.
The unprecedented experiment has simulated the duration and isolation of a return journey to the Red Planet, even including "walks" on a replica of the Martian surface and 20-minute time gaps in communication with outside.
Yet ever since the crew were first locked up back on June 3, 2010, their 180-square-metre (1,900 square foot) module has stayed firmly rooted to the earth in a car park outside the Moscow research facility.
While there were some titters when the volunteers donned space suits for their "space walk" in a glorified sandpit at the halfway point, scientists insist the experiment was vital preparation for an eventual voyage to Mars.
"I welcome the courage, determination and generosity of these young people who have devoted almost two years of their lives to this project, for the progress of human space exploration," said ESA director general Jean-Jacques Dordain.
The deputy head of the Russian space agency, Vitaly Davydov, said a manned voyage to Mars was being considered sometime in the mid-2030s, although he noted that humans would have to return to the Moon first.
"The end of Mars-500 is not only the start of serious preparation for a real voyage to Mars," he told the ITAR-TASS news agency. "The results are going to be used in the bio-medicine sector and will be used in the national space programme up to 2030."
Controversially, the experiment did not include a woman, with researchers clearly wanting to avoid it degenerating into a scientific version of television's sexual tension-filled "Big Brother".
Each of the participants is receiving three million rubles (around $100,000) for his work, the Interfax news agency quoted the head of the project Boris Morukov as saying.
Initially, the Russians were to receive less but the sum was increased once ESA revealed how much its two volunteers were being paid, Interfax said.
(c) 2011 AFP