The six-strong crew of the European Space Agency's most gruelling mission yet will emerge from their capsule on Friday afternoon after an 18-month voyage that went, literally, nowhere.
The would-be spacefarers spent more than 500 days in windowless isolation in a simulated mission to Mars that played out in a complex of chambers at a research centre in Moscow. Once sealed inside the crew's only contact with the outside world was over the internet and by phone lines that carried a delay of up to 20 minutes to simulate the time it takes for radio signals to pass between Earth and Mars.
The crew of the $10m Mars500 project – three Russians, two Europeans and a Chinese man – return to the world safe in the knowledge that the medical, physical and psychological examinations they have endured for the last year and a half will prepare future astronauts for real journeys to far-flung planets.
"We are proud of them. They have been brave, enormously motivated and worked well as a team. It was never a given that it would work," Martin Zell, ESA's head of astronauts, said. "We have a lot of good science from the experiments and we learned about how to deal with a crew that is enduring this kind of mission." Asked how the crew found the experience, Zell answered: "To be blunt: long."
The crew will open the hatch of their capsule at 2pm local time on Friday, ending a voluntary incarceration that will be welcomed by family and loved ones, not least the wife of the commander, Alexey Sitev, a Russian marine engineer, who postponed his honeymoon after marrying two weeks before the mission began in June last year.
The rest of the crew are Sukhrob Kamolov and Alexander Smoleevskiy, who have medical backgrounds, engineers Diego Urbina and Romain Charles, and Wang Yue, who previously trained Chinese astronauts. The six men will go to hospital for three days of observation and quarantine before giving a press conference on November 8.
Of the more than 100 tests carried out on the men, a third involved their mental state. A team of psychologists studied their interactions during meals and their letters home to judge their psychological health.
The crew fought boredom by reading books, watching DVDs and playing Guitar Hero on a games console. They spent an hour in the gym each day, on equipment that would be taken on a mission to reduce muscle wastage. At Christmas the crew adopted the Apollo 13 spirit and fashioned decorations from wires and electrodes meant for electrophysiology tests.
Halfway through the mission three of the crew clambered into spacesuits and stepped into a sandpit in a mock expedition on to the surface of the red planet.
To keep the men on their toes, mission controllers faked emergencies, including a fire, a power outage and a two-day communications blackout.
Yury Bubeyev, the chief psychologist on the project, said his 10-person team noted no serious conflicts during the mission. The most serious problems were the laziness and boredom that afflicted the men after they "reached Mars" in February, he said.
"The most dangerous period came after their virtual walk on Mars, when the most interesting work had already been fulfilled and they were on the way home," Bubeyev said. "The objective had been reached, there was nothing new, the experiments had all been done several times, and they knew each other well. There was laziness and boredom and light fatigue."
During that time psychologists urged the men's family and friends to write more to their loved ones. They also sent new books and films, and recordings of sporting events. "We tried to make sure they always felt like one team, that they spent time together," said Bubeyev. "So we made sure if it was a Russian film, it would have English subtitles, or an English film with Russian subtitles."
Intercultural differences proved to be among the most difficult – the Italian and Frenchman, for example, could not understand why Russians devoted so much time to celebrating New Year and so little to Christmas, a Soviet legacy. And no one understood Wang Yue of China, Bubeyev said, so they were sent ebooks on Chinese culture.
"There were some moments of misunderstanding," Bubeyev said. "But then the Europeans and Russians asked him to teach them Chinese, and they can all write and speak it now.
"We didn't note any serious conflicts. It's a different question whether they'll continue to interact after the experiment. Maybe they're tired of each other."
ESA officials will speak to the crew about their plans for the future once they have settled back into normal life. "They don't have jobs yet. We didn't promise anything," Zell said.
2011 Six "aquanauts" lived inside an underwater laboratory to simulate a mission to visit and explore an asteroid. The Nasa-led assignment, designed to test new technologies, was delayed by bad weather and choppy waters.
2009 A six-man crew lived in isolation for 105 days in a forerunner of the Mars500 project at the Institute of Biomedical Problems in Moscow. The crew grew food such as salad leaves, radishes and cabbage to supplement astronaut-style packaged meals.
2005 Two dozen women stayed in bed for 60 days, with their feet a few degrees above their heads, to simulate the effects of prolonged weightlessness on the female physiology.
1999 A long mission simulated in Moscow descended into chaos when a Russian captain forced a kiss on a female Canadian crew member, and two other Russians had a drunken brawl that left blood spattered over the capsule walls.
1997 The Haughton-Mars field project began on Devon island, Canada, the world's largest uninhabited island. Volunteers continue to work in a Mars-like environment to develop technologies and procedures that could be useful for future missions to other planets.