The six-member crew emerged yesterday from a dome in Hawaii, on the barren northern slope of the Mauna Loa volcano, where they were studied as part of the US space agency's mission to send people to Mars by the 2030s.
In addition to insufficient stimulation, isolation and a lack of fresh food and air were the toughest challenges during the yearlong experiment, known as the Hawaii Space Exploration Analog and Simulation (HI-SEAS) - the third and longest of its kind.
"We were always in the same place, always with the same people," said French astrobiologist Cyprien Verseux in a Periscope interview by organizers posted on Twitter.
The crew lived inside a structure 36 feet (11 meters) in diameter and 20 feet tall, emerging only if outfitted in spacesuits, never breathing the outside air or eating fresh vegetables.
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Despite describing the monotony as the hardest part, Verseux said the experiment shows that "a mission to Mars in the close future is realistic.
The experiment did not test the process of growing food, but was aimed primarily at the psychological study of the crew.
"The technical and psychological problems can be overcome," Verseux said.
Video footage of the team as they emerged shows the three men and three women looking a bit bewildered as they met visitors and well-wishers and posed for selfies. Organizers gave them fresh fruit and vegetables.
In interviews, the crew was upbeat but made passing references to arguments and growing tired of seeing the same faces.
Another mission member, American Tristan Bassingthwaighte, agreed, urging future participants to bring "lots of books."
Bassingthwaighte said that team members engaged in hobbies such as salsa dancing and playing the ukelele to stave off the boredom.
"If you can work on something that is self developmental... You will not go crazy," he said.