I’d always wanted to visit Mars. Instead I got Hawaii. There, about 8,200 feet above sea level on Mauna Loa, sits a geodesically domed habitat for testing crew psychology and technologies for boldly going. I did a four-month tour at the NASA-funded HI-SEAS—that’s Hawaii Space Exploration Analog and Simulation—in 2013, and a new 8-month mission is scheduled to start in October. It’s a long time to be cooped up, “so the psychological impacts are extremely important,” habitat designer Vincent Paul Ponthieux says. The key to keeping everybody sane? A sense of airiness. Yep—even on Mars, you’re going to need more space.