On March 27, NASA astronaut Scott Kelly and Russian Cosmonaut Mikhail Kornienko were launched into space, embarking on a mission at the International Space Station that will assess how a year in zero-gravity affects the human body. Scientists have already established that spending four to six months — the average duration of these expeditions — can cause changes in the eyes, muscle atrophy, and loss of bone density, but what else happens? How does a year isolated in space affect their behavior, their psychology, when cabin fever easily strikes some of us who voluntarily spend a weekend at home?

No human has ever spent a year in space, and because of that, the answer to those questions is still forthcoming. Both Kelly and Kornienko have each spent about six months on their own space missions and returned psychologically unscathed, qualifying them to go on this year-long journey. To become qualified, however, both astronauts were required to undergo rigorous — and somewhat mysterious — mental health training, building on the their innate, strong psychological foundation.

What's In An Astronaut's Mind?

Potential astronauts undergo multiple rounds of interviews with NASA officials and psychiatrists; they weed out people with mental health disorders or anything else that’s grounds for disqualification. NASA looks for qualities that are “pretty much what you’d expect from any individual whose job it is to work very closely in very risky environments, and isolated environments,” said Jamie Barrett, a psychologist on the astronaut selection panel, at a meeting of the American Psychological Association in August 2014. These people should make a “good neighbor,” exhibiting good social skills, an easygoing attitude, and resilience, all of which are crucial to a long stay in an enclosed space about the size of a four-bedroom house.

When it comes to those qualities, social skills and a good attitude will help both astronauts stay positive on the ISS, but it’s their resilience that keeps them strong.

Flying to the edge of space can be incredibly nerve wracking. Some of the first people to get there spoke of a phenomenon known as “break-off,” which describes the “notion that you would feel disconnected from the Earth when you were above it, particularly when you were in orbit,” Dr. Larry Young, Apollo program professor of astronautics at the Massachusetts Institute of Technology and an advisor for NASA’s Innovative Advanced Concepts program, told Fast Company. This phenomenon can be caused by anything from being isolated so high up, to a person’s own psychology, to the ergonomics of the plane. For some pilots, being so detached from earth produced such emotional extremes that they felt detached from reality altogether. Others felt sudden anger toward their fellow pilots.

Surely, Kelly and Kornienko dealt with these emotions in their previous flights and gotten over them. But that feeling of detachment most likely remains for the entire time an astronaut is in the ISS. In space, astronauts are away from their families and friends — in fact, the last time Kelly was on the ISS, his sister-in-law, former Arizona Rep. Gabrielle Giffords, was shot. They can no longer feel the sun’s warmth or a cool breeze, and water appears only as misshapen floating orbs. In an interview with the Associated Press, both astronauts said they would miss nature the most. Kornienko said he would miss flowing water to swim in, while Kelly said he’d miss the outdoors of his Houston home. It’s no coincidence that being in nature promotes wellbeing and reduces stress.

“[The weather] never changes on the space station,” Kelly told The Washington Post in March. “Even though it’s a pretty nice environment, I guess it’s like living in Southern California, people get sick of it … after a while.”

The Psychological Effects Of Long-Term Spaceflight

While on the ISS, both astronauts will undergo up to 10 medical and psychological evaluations each day. They’ll also write in journals, which psychologists will review once they return. These will determine whether we’re prepared for longer flights into the universe.

Though it’s unclear exactly what they’ll experience, previous studies on the long-term effects of spaceflight have shown they’re at risk of anxiety, depression, and psychosomatic symptoms. In addition to these, they may also experience emotional problems related to the stage of the mission — it’s easy to experience sadness or even depression when realizing half the mission is over but there’s still another half — as well as post-flight personality changes. Interpersonal tension and decreased cohesiveness aren’t uncommon either. All of these effects could then be exacerbated by sleep problems, an alteration in time sense, homesickness, changes in perceptual sensitivities, and having too much free time.

The astronauts’ training prepares them for battling these effects. Though NASA wouldn’t divulge whether astronauts are put through stress tests or other challenging situations, Barrett said these forms of training “would probably be a useful thing to do.” They also undergo inter-cultural sensitivity training, which teaches them better ways to understand each other — some American astronauts can even live with a Russian family before launch.

In addition to training, future missions may also provide onboard assistance to those who still develop mental health issues. That assistance would come in the form of a computer program currently being developed to help astronauts find solutions to their problems and fight any disorders, Pacific Standard reported. The program would also keep no record of who used it, thus allowing astronauts to feel comfortable getting help, and avoiding any fear of being disqualified from future flights.

Positive Psychological Effects

There's a good chance the astronauts will come back with positive psychological effects, too. Other astronauts dating back to the Apollo missions of the 60s and 70s have already spoken about these: “You develop an instant global consciousness, a people orientation, an intense dissatisfaction with the state of the world, and a compulsion to do something about it,” Apollo 14 astronaut Edgar Mitchell once said. “From out there on the moon, international politics look so petty. You want to grab a politician by the scruff of the neck and drag him a quarter of a million miles out and say, ‘Look at that, you son of a bitch.’”

In another review of long-term spaceflight, published in the journal Acta Astronautica, researchers wrote that isolated environments such as space may also give people an opportunity for spiritual growth. “For example, people in polar environments or space may experience increased fortitude, perseverance, independence, self-reliance, ingenuity, comradeship. … Some astronauts and cosmonauts in space have reported transcendental experiences, religious insights, or a better sense of the unity of mankind as a result of viewing the Earth below and the cosmos beyond.”

Kelly and Kornienko still have over three-quarters of their flight left. While we wait for their return, you can follow Kelly’s journey on the ISS through his Twitter account.