The crew of an isolation experiment to simulate a 520-day mission to Mars are in the final countdown before the opening on Friday of the hatch on the windowless cells in which they have been locked away since June last year.
The $15-million (9 million pound) Mars500 experiment aims to answer one of the big questions of deep-space travel: could people endure the stresses of a voyage of more than six months to the Red Planet?
The six male volunteers from Europe, China and Russia are not exposed to weightlessness or solar radiation, but in just about every other way life inside the 550-cubic-metre mock spaceship in Moscow resembles that of a real space flight.
Clothed in blue jumpsuits, the would-be astronauts take daily urine and blood samples, eat rations like those of real astronauts and do not shower often.
Communication with the outside world comes with a 20-minute lag and the crew have faced power outages and other impromptu glitches.
Halfway through, two crew members donned 32-kg (70-pound) spacesuits to clomp about in a dark sand-filled container meant to imitate the surface of Mars.
The research we have points to levels of high stress, said Igor Ushakov, the head of the Russian Institute for Biomedical Problems which runs the spaceship.
The most difficult thing for them was being starved of information.
Psychologists fear a return to the noise and activity of ordinary life will come as a shock to the crew, and plan a period of rehabilitation.
The key principle is to take it step by step to return them to the world which they left, Ushakov told Reuters.
A previous 420-day experiment ended in drunken disaster in 2000, when two participants got into a fistfight and a third tried to forcibly kiss a female crew member.
But Mars500 is being hailed as a success. The emergency exit remained sealed and it proved an unexpected publicity coup for the European Space Agency, a collaborator on the project.
It was not designed to be a PR thing but I think it naturally evolved to be quite a positive and comprehensive advertisement for what we might eventually do next, ESA's head of human space flight operations Martin Zell told Reuters.
HOW REAL IS IT?
With video cameras tracking the crew everywhere but the toilets, Mars500 has been likened to a scientific reality show.
To kill time, China's Wang Yue practised calligraphy, France's Romain Charles strummed his guitar and together the crew, aged from 28-38, played karaoke, chess and Nintendo Wii.
The elaborate pretence of their imaginary spaceflight includes four days' quarantine after they return.
Folks who get close to us will need to go through a small medical examination, so we don't catch a cold! Italian Diego Urbina tweeted earlier this month.
In another tweet, he said he most yearned for family, calling my friends, bumping into strangers, going to the beach.
Over 100 different experiments have crowded in on the Mars500 project, with researchers of every stripe interested in scrutinizing the men.
Space officials say space technology is still decades away from being able to land astronauts on the Red Planet, more than 35 million miles (56 million km) away across the solar system.
NASA unveiled $10 billion plans last month to build a huge deep-space rocket to carry astronauts beyond low-Earth orbit after 2017, but space-faring nations are still debating whether to target a mission to the Moon, an asteroid or Mars.
Among real-life astronauts, support for Mars500 has been tempered by some scepticism.
Space veteran Sergei Krikalyov, who has spent a record 803 days in orbit, told Reuters: It's useful but, sitting here on Earth, it won't solve real problems of long human exposure in space.
But the crew has won praise. I can't help but applaud the fact that six people would go ahead and do something like this, said U.S. astronaut Mark Polansky, who heads NASA operations at Russia's Star City training centre outside Moscow.
It's really giving up a lot to pretend that you are on your way to Mars.
(Reporting by Alissa de Carbonnel; editing by Andrew Roche)