The all-male crew of a mock spaceship played a video action game to cool down when tensions rose during a 17-month isolation study simulating a voyage to Mars.
In their cramped, windowless module at a Moscow research facility, the earthbound pioneers split into teams -- three Russians against two Europeans and one Chinese -- and put their trust in Counter-Strike, said Russian Alexander Smoleyevsky, 32.
We know that flies can turn into elephants in space so whatever conflict arose, we tried to nip it in the bud, said Rustamovich Sukhrob, 37, his blue jumpsuit hanging loosely on his frame after months of food rations.
The six crew members, all of whom lost weight, looked weary but relieved on Tuesday when speaking to reporters for the first time. They had spent three days in quarantine since the end of their mission on November 4.
The $15 million (9 million pounds) Mars500 experiment aimed to answer one of the big unknowns of deep-space travel: can people stay healthy and sane while spending 520 days rocketing to the Red Planet and back in a small spaceship?
The study volunteers were never weightless, but scientists tried to make their isolation mimic the mental and physical strain of a real flight to Mars as closely as possible.
They ate astronauts' rations, rarely showered, took blood and urine samples and slept plastered with electrodes, all the while being under constant video surveillance -- a touch that earned the study comparisons to a reality TV show.
Each man was paid 3 million roubles ($98,300), Mars500 project director Boris Morukov told Reuters.
I was shaky when I came out, I hadn't seen anybody else other than my five friends for so long my heart was beating like crazy, my legs were trembling... I was so excited, Italian-Colombian participant Diego Urbina told Reuters.
It was very hard, I am not going to lie, he said. At his lowest ebb he dreamt of daily life on Earth only to suddenly wake up in this dark chamber knowing you have so long to go.
French crewmate Romain Charles said he missed a good croissant in the mornings. To break the monotony, he taught his crewmates to play Home Sweet Home and Rocket Man on the guitar.
A previous 420-day experiment in 2000 ended in drunken disaster when two participants got into a fistfight and a third tried to forcibly kiss a female crew member.
But Mars500, the first fully-fledged simulation, is being hailed as a success and brought a welcome flood of publicity for the European Space Agency, struggling against waning interest in space exploration among crisis-hit tax payers.
We rarely finish these long-term experiments and we did it as a team, said China's Yue Wang, the youngest crew member at 27, flashing a wide grin.
We are family members, we built a very close, solid relationship, We trust each other.
Morukov and others warned the crew may struggle to adapt to normal life outside their 550-cubic-metre module.
The hardest, riskiest part is over but the experiment is not. We will continue to study the crew ... we are responsible for the long-term consequences, said Anatoly Grigoryev, of the Institute of Biomedical Problems, which ran the study.
Russian space officials have floated a plan to run a similar study on the International Space Station, even though technology is decades away from being able to power humans to Mars and land them unharmed by radiation.
(Reporting by Alissa de Carbonnel; Editing by Robert Woodward)