The conditions weren't nearly as harsh as they would be on Mars, of course, but there were strict limitations. Participants could only leave the dome if they had a spacesuit on, for instance, and they had to survive on simple food (usually canned or powdered). Entering the dome was, psychologically, much like leaving Earth -- they were cut off from the luxuries of home for much longer than your average camping trip.

This isn't the last HI-SEAS mission. NASA has offered grants that will keep the experiment going through 2019, and recruiting is already underway for the next two stays. Even so, this extra-long test (there were previous 4- and 8-month stays) is already a big confidence booster. Its data will help NASA tweak its strategies for supporting long-endurance space missions, whether it's the mix of supplies they need to bring or a choice of personalities that mesh well together.