MAUNA LOA >> A year ago six volunteers of different nationalities and personalities — some chattier than others, some neater and cleaner — entered a modest dome two-thirds of the way up this desolate volcanic slope, where they had agreed to spend the next 365 days confined together to study potential effects on crews for future missions to Mars.

On Sunday all six crew members emerged from their dome habitat and felt the chill Mauna Loa mist for the first time in a year. They looked a bit pasty and in need of some sun but otherwise appeared in good spirits.

“I’m looking forward to pineapple,” Andrzej Stewart, chief engineering officer of the latest NASA-funded Hawaii Space Exploration Analog and Simulation, or HI-SEAS, mission, said moments before he and his crew mates feasted on fresh fruits and vegetables outside the dome.

Stewart and his col-leagues had just made history, having completed the longest-running space simulation on U.S. soil, as scientists and researchers continue to plan and prepare for an eventual manned expedition to Mars. The previous record-holder was the eight-month mission in the HI-SEAS dome that wrapped last year.

Since 2013 some 24 specialists chosen from about 800 applicants have put their lives on hold to simulate extended missions to Mars atop Mauna Loa.

They’ve missed births, weddings, funerals and other significant moments to live with hardly any privacy in the dome’s close confines, documenting their days and their moods as researchers away from the dome took down additional information.

Meanwhile the HI-SEAS project has steadily compiled massive amounts of what could be invaluable data on crew cohesion and other subjects to help plan manned trips to Mars.

“We now have 24 months of 24/7 data,” HI-SEAS Principal Investigator Kim Binsted said Sunday, moments before the crew exited. “This is really a whole portfolio of studies. We’re going to be digging through data for years.”

The project, affiliated with the University of Hawaii at Manoa, has also steadily gained more attention since 2013. The crowd of friends, family and media on hand to greet the crew as they re-enter the world has grown with each mission.

About 50 people welcomed them Sunday, including international reporters and film crews. Now that HI-SEAS has completed four missions, including three on crew cohesion, “we’re actually respected now,” Binsted said.

For this mission there were too many people on the rocky slope to allow access to the small interior dome. Reporters were briefed to give crew members space in case they were overwhelmed by the crowd and the attention after a year in isolation. The crew members stayed to speak with visitors Sunday.

Eventually, NASA could use the Hawaii missions’ findings on crew cohesion, as well the crews’ use of water and other resources, to help the space agency plan expeditions to the red planet. NASA officials say the nation’s space agency has at least a $3 billion annual budget dedicated to future Mars missions.

The agency has invested more than $2 million to fund the missions on Mauna Loa, including two future eight-month simulations, according to Binsted, who’s a UH researcher.

Crew members said Sunday they were happy to step outside the dome without having to wear a spacesuit to simulate life on the red planet. Stewart, a self-described “military brat” who moved frequently growing up, said he felt mixed emotions on leaving the habitat. “If you live somewhere long enough … kind of where you live becomes home after a while. I’m going to miss the place.”

Winter was tough

Much of the crew agreed that the hardest time they spent in isolation was during winter, when it was really “cold and dark,” as Chief Medical and Safety Officer Sheyna Gifford put it. The habitat, which includes composting toilets and showers, relies on solar power.

During the yearlong mission crew members conducted their own research and projects. They also used virtual-reality equipment to view family and friends, and to study, if that helped boost their morale better than conventional video messages. The missions have an approximately 40-minute communications delay to simulate the distance to Mars.

The HI-SEAS researchers are just starting to unpack their data on crew cohesion from the past three missions. (The first, four-month mission studied food choices and its effect on crew morale.) So far, “what seems to be most important is resilience,” Binsted said Thursday.

Some conflict will be inevitable on a two- to three-year mission — but what’s key is to select resilient crew members who can rebound from that conflict as quickly as possible and return to normal and the mission at hand, she said.

Binsted and those running HI-SEAS select “pretty low-drama” crew members. Astronauts tend to be “stoic” and “positive,” so the challenge then becomes to detect the conflicts among crew members who are pretty easygoing by nature, she said.

“If there’s problems brewing, you don’t tend to find out about them until they’re real issues,” Binsted said Thursday. The latest crew wore special sensors that showed where they were most of the time, so the HI-SEAS researchers could study the members’ distance from one another, Binsted said. Researchers can then compare the sensors’ distance data to the crew’s logs of how well they got along with their colleagues, to see whether there’s a connection, she added.

Gifford said the crew members had very different personalities.

“I’m a talker. Commander (Carmel Johnston) is not a talker. I’m from California and Boston. Two of the members are from Montana, and when you say, ‘Good morning,’ they say, ‘Mm.’ That’s actually ‘good morning’ in Montana.”

“The cultural difference and the aesthetic difference of whether you like it clean or neat or busy or quiet: vast,” Gifford added. “It’s compromise. Flexibility and compromise get you through.”

Christianne Heinicke, the crew’s German chief scientific officer, quipped that she doesn’t talk much, but her American colleagues in the dome “talk all the time.”

NASA doesn’t want crews that get along so well that they become too independent of mission control back on Earth, Binsted said. That scenario played out in the 2015 film “The Martian,” in which a tightknit crew leaving Mars defies NASA’s orders to return to Earth. Instead, in an act of mutiny, they return to the red planet to rescue a stranded astronaut, played by actor Matt Damon.

The space agency could send astronauts on a two- to three-year mission to orbit Mars and return to Earth as early as the 2030s, said Bill Hill, NASA’s deputy associate administrator for exploration systems development. Mars is “the next logical step” for human exploration, and crew cohesion is “really important,” he said.

Any Mars-bound crew will “spend the better part of five years together training,” Hill said. Today astronauts similarly train before their lengthy trips aboard the International Space Station, he added.

On Mauna Loa the latest crew also had to problem-solve, most notably with its water supply. At one point the habitat’s plumbing broke, so the crew relied on buckets to use water and bathe.

They also kept close track of their water use, restricting it to about 4 gallons a day per member, Stewart said. In July the HI-SEAS support staff truck broke down and couldn’t bring more water up the mountain.

The crew had an emergency tank of water but didn’t know whether it was safe to use because “it hadn’t been touched in years,” according to Gifford. The crew solved the problem by boiling the water into steam and then collecting it as purified water, she wrote.

Crew members said Sunday they never felt forced or trapped in the dome, but they felt obligated to stay for all the effort that went into the research. They said it was important to take breaks from work for their mental health.

“In the known Universe, people are the unknown. A machine can only break in so many ways,” Gifford wrote on her website weeks before entering the dome. “People are constantly inventing new ways to break themselves and each other.”