For eight months, they had been crammed into a 1,200 sq. ft. geodesic dome situated on an otherworldly plain of red dust and tumbled rocks. They only left the module in protective suits and had no fresh food. Their communication with other humans came with a twenty-minute delay.

All of this is similar to the conditions humans will experience when they first arrive on Mars, a future milestone being plotted by groups including NASA, SpaceX, and China’s National Space Administration.

But the HI-SEAS crew didn’t spend their eight isolated months on Mars—they were on a volcanic slope in Hawaii. And while their routines included simulated science experiments such as geologic exploration and food cultivation, the real experimental subjects were the “astronauts” themselves.

HI-SEAS (Hawaii Space Exploration Analog and Simulation) is partly funded by NASA and run by a University of Hawaii professor. The goals of the mission that concluded Sunday included improving understanding of how teams work together in extreme conditions, and testing methods for managing crew stress and improving resilience. HI-SEAS is building on substantial previous research on teams working in isolation, including some based on the real-world example of crews on the International Space Station, and a 520-day simulated Mars mission called Mars500.

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When it comes to settling Mars, human questions are arguably as important as building rockets. Once crews reach the Red Planet, they’ll have little, if any, help from Earth, so they’ll need to know how to get along and solve problems on their own. And that moment is getting closer—SpaceX, for instance, has said it will start testing its first Mars-focused vehicle, the Falcon Heavy, this November.

The findings from HI-SEAS V haven’t been released yet. But the returning crew, including a computer scientist, an aeronautics engineer, and an astrobiologist, apparently made a beeline for the Earth food.