The crew of an isolation experiment to simulate a 520-day mission to Mars are in the final countdown before the opening tomorrow of the hatch on the windowless cells in which they have been locked away since June last year.
The $15-million 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.
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.
Space officials say space technology is still decades away from being able to land astronauts on the Red Planet, more than 56 million kilometres (35m miles) away across the solar system.
