“Right now, the psychological risks are still not completely understood and not completely corrected for,” said Kimberly Binsted, a professor of information and computer sciences at the University of Hawaii at Manoa and the principal investigator for the project. (She is not in the dome.) “NASA is not going to go until we solve this.”

Isolation can lead to depression. Personality conflicts can spin out of control over the months.

“How do you select and support astronauts for a mission that will last two to three years in a way that will keep them healthy and performing well?” Dr. Binsted said. Or as Mr. Scheibelhut put it:

“I’m so interested to see how I react. ‘I don’t know’ is the short answer. I think it could go a lot of different ways.”

Several mock Mars missions have been conducted in recent years. A simulation in Russia in 2010 and 2011 stretched 520 days, most of the duration of an actual mission. Four of the six volunteers developed sleep disorders and became less productive as the experiment progressed. The Mars Society, a nonprofit group that promotes human spaceflight, has run short simulations in the Utah desert since 2001 and is looking to do a one-year simulation in the Canadian Arctic beginning in 2015.

Hi-Seas has already conducted two four-month missions, and next year, six more people will reside for one year inside the dome, a two-story building 36 feet in diameter with about 1,500 square feet of space. It sits in an abandoned quarry at an altitude of 8,000 feet on Mauna Loa.

To simulate the operational challenges, the crew members in the Hi-Seas dome are largely cut off. Their communications to the world outside the dome are limited to email, and each message is delayed by 20 minutes before being sent, simulating the lag for communications to travel from Mars to Earth and vice versa.