But we rarely hear about the degree of emotional strength and dedication it takes to become an astronaut, work as an astronaut, and, moreover, come to terms with not being an astronaut anymore after dedicating years of one’s life to space exploration.

Life’s trials are no walk in the park for most Earthlings, and astronauts aren’t immune to the everyday strains of emotional distress, loneliness, anxiety, and fear. But from the start of their careers, astronauts also face a grueling training program that tests the limits of their bodies, minds, and spirits.

According to NASA, astronaut candidates must complete a rigorous two-year program that includes water survival training, advanced robotics, aircraft flight readiness, extravehicular activity training, and Russian language courses. The program is extremely selective. Only 0.065% make the cut, as of 2017. It’s about a hundred times easier to get into Harvard than to become an astronaut.

To prepare astronauts assigned to work on the International Space Station, NASA provides preflight education on the common psychological risks associated with long-duration missions. “In the early flights, it’s not like you’re going to this destination that has this structure in place already,” says retired astronaut and artist Nicole Stott, whose 2009 piece The Wave made history as the first canvas painting created in space, “You’re really facilitating it all along in every evolution of the mission.”

High-stress work, with consistent pressure to perform without fault, can put any and all kinds of workers at risk of experiencing severe emotional distress. According to the DSM-V, high-risk individuals (including military employees—like pilot astronauts) have 3% to 58% chance of developing Post-Traumatic Stress Disorder, an alarming increase when compared to the general population’s 1% to 14% chance. With PTSD comes a slew of additional symptoms and disorders, including a 84% chance of alcoholism, 42% chance of drug abuse, 68% chance of depression, and 26% chance of antisocial personality disorder.

By no means do these statistics suggest most astronauts develop serious emotional trauma. However, one troubled team member can threaten an entire mission. From 2010 to 2011, the Russian Academy of Sciences executed and completed the Mars500 psychological isolation experiment, a project meant to simulate the effects of a 520-day-long mission to Mars. The two astronauts in the study with the highest observed levels of stress were involved in 85% of all team conflicts.

One individual can truly have a ripple effect. In 2007, former astronaut Lisa Nowak drove from Houston, TX to Orlando, FL, allegedly planning to kidnap fellow astronaut Colleen Shipman. She arrived at the airport with an elaborate arsenal, complete with latex gloves, a black wig, pepper spray, a drilling hammer, garbage bags, rubber tubing, and an 8-inch folding knife. The incident resulted in Nowak being charged with attempted murder and caused NASA to develop new behavioral health screenings in the wake of Nowak’s psychotic break, including a series of 20-30 minute psychological and cognitive assessments occurring once astronauts returned to Earth.

Not all teams experience conflict. For some, the pressure during missions can create a stronger bond. As recalled by Mike Massimino, there have been plenty of good memories along the way. “The best friendships I’ve ever had were with my crewmates. It’s like a hybrid of family and friendship,” he explained. “because you spend so much time with each other, you get to love each other, but you also get to work together, and you care for each other so much. That’s really the most important thing about it.”

It’s clear that the sheer sight of our planet, vibrant with life and wonder, has a profound emotional impact on those who are lucky enough to see it. “There’s really no way to prepare yourself for it,” says Massimino, “Just seeing the beauty and wonder of it.”

Seeing the Earth from space can fundamentally change an astronauts outlook on life, society, and the human experience. Some, including Massimino and Apollo astronaut Edgar Mitchell, have referred to this experience as the Overview Effect, a shift in global awareness and perception of our own world. Former astronaut Ron Garan shared in his book, The Orbital Perspective, that his first glimpse of Earth from the International Space Station in 2008 caused him to experience this very phenomenon.

“As I approached the top of this arc, it was as if time stood still, and I was flooded with both emotion and awareness,” writes Garan. “Seeing Earth from this vantage point gave me a unique perspective—something I’ve come call the orbital perspective. Part of this is the realization that we are all traveling together on the planet and that if we all looked at the world from that perspective we would see that nothing is impossible.”

Eventually, astronauts have to come home, and some experience personal difficulties adapting to not being in space anymore. According to a 2017 study conducted by the US National Library of Medicine, the average age of retirement for astronauts is approximately 48 years old.

The oldest active astronaut, Story Musgrave, was terminated from duty with NASA at age 62. In an interview with AARP Bulletin, Musgrave recalls, “I had six flights. I could have done a lot more there. I was the lead person to fix the telescope. But after my last flight, they told me: No more, that was it. They didn’t offer me anything else.” With plenty of life left to live, many astronauts face the prospect of a major career shift. Transitioning to civilian life, after making a living out of the extraterrestrial, is not without its challenges.

“I was an astronaut with NASA for 18 years,” remarks Massimino, whose journey to working for NASA took three applications before he finally landed the job. “The time before that, I had done other things, but I was basically trying to get myself to NASA. All the sudden, you’re ready to do something else. I think making a change after doing anything that long as you’re getting older is just difficult.”

Massimino’s experience with career change, aging, and emotional well-being is not unique. According to researchers at the Yale School of Medicine, although few studies on older adults and emotional health exist, the probability of exposure to potentially traumatic events (i.e. witnessing deaths, natural disasters, war conflict) is between 74.2% and 96.1% for adults over age 55.

Still, these former astronauts have a lot of advice to offer their successors. “Think about what you can control and what you can’t control,” says Massimino. “You can control your training; you can control becoming a better astronaut. You can’t always control policies, decisions—that’s not our job. So, concentrate on what you can control and make yourself the best astronaut you can be. Don’t squander this opportunity.”

But our future generation of astronauts will be forced to overcome a specific, unique hurdle. As space exploration continues to advance into uncharted territory, astronauts may quickly find themselves without that view of our planet, which kept their predecessors emotionally tethered to humanity here on Earth.

Missions to space are only going to increase in distance and duration, with NASA researchers determined to mount a human mission to Mars by the 2030s. During a mission to Mars, astronauts would be subjected to a two-way 20-minute delay in communications, meaning they could wait up to 40 minutes for a reply from mission control. We know practically everything about our space explorers while they are whizzing around our planet; what emotional stresses will they face without that lifeline, and without the Earth so close?

“Think about it,” says Stott, “Nine months on a relatively small spaceship to go to Mars. At some point, you don’t have that stunning view of Earth out the window anymore.”

Stott, who has in recent years used the arts and space to provide therapeutic services to children in hospitals through the Space for Art Foundation, maintains a fair warning for those who may be the first to journey to our red neighbor. “With these longer missions on the space station, we may be learning some things about our bodies, and I think there is some psychological aspect to it too,” Stott says.