It was the crew’s first night, we had just arrived, we were settling in. Kim Binsted, principle investigator on the HI-SEAS project, was preparing to leave for four months, nervous, I think, about launching this Mars mission, a project whose actualization was so uncertain throughout the buildup—NASA nearly pulled funding, there were delays in the construction of the habitat—that at times it almost seemed if any of us were to look down, we’d collectively run ourselves off the edge of a steep cliff. And yet here we were. In the shipping container attached to the dome, she and I stood surrounded by four months of shelf-stable food, hand tools, and mountains of toilet paper and paper towels. In the shipping container, I followed her gaze to an ax leaning against the wall. And then I heard her say, “Maybe I should take this with me.”I imagined what she might have imagined or maybe it was just what I imagined, which was the very bloody deaths of our crew at the hands of one of us who might not be as mentally sound under the pressures of isolation, or even at the hands of an intruder because, though our habitat was remote, we were still technically accessible. In any case, the fact of my isolation and vulnerability, the realization of it, and my voluntary removal of myself from life as I had known it, sharpened.The ax. All work and no play… does what to astronaut stand-ins? Binsted and I were quiet for a few seconds, and then, for unknown reasons, I insisted she not worry about it. We might need an ax if there were a fire, I said, or some other emergency. Also, if someone wanted to kill us, they could do so in many other ways, like pillow smothering, though I really did hope not to be murdered while pretending to live on Mars. She scowled and hesitated, then finally agreed to leave it. I still don’t know why I was so confident the ax wouldn’t be a problem—it wasn’t—but I do wonder about my instincts in this case.We were warned about the effects of isolation in small and large ways. The small ways: brief mentions during our pre-mission conference calls about tensions that arise between crew members and their friends, family, and mission support back home. Stories about small annoyances on previous analog missions—others’ chewing sounds, hurt feelings when movie night selections weren’t respected or worse, mocked, and the overall lack of privacy—thin walls and the fact that most space is shared space. We heard how these irritants had led to emotional outbursts on other simulated missions or how they’d been stuffed into sacks of silent grudges, to spill out upon return to Earth.The large ways in which we were warned: the multiple hours-long discussions to discover what our breaking points would be. Would we abandon the mission if we got a sudden job offer? If someone back home got sick? If someone died? If we got sick? How sick? Mentally? Physically? If we lost faith in our crewmates, or in the project entirely?And how did we plan to manage the well-documented challenges of isolation? These challenges included but were not limited to something scientists have called “third-quarter” syndrome, in which the itch to be anywhere but inside the dome with your five best friends flares hot when the end is in sight but not quite within reach. Diaries from Arctic and Antarctic expeditions suggest that it’s a special time, three-quarters into your mission. You’ve gotten used to your routines and found a rhythm, but the hard reality of being cut off from others, the demands of your duties, and the quirks of your crewmates have started to wear on you and the end to these low- to high-grade tortures is still not yet near. Other challenges include an alienation between the crew and those back home wherein intentions and tone are mis- interpreted in communications: the “crew-ground disconnect.” People’s feelings get hurt; information isn’t effectively conveyed; everyone gets frustrated. Productivity and mood can plummet.Challenges continue and can appear in the form of obsession with micro-stimuli. Small vexations—a crewmate’s favorite catchphrase, another’s tendency to take up too much space, the subtle and not-so-subtle slights—grow macro over time in an environment without much else going on.Here, I was guilty, somewhat predictably. As a writer, I tend to notice the little things. Minor, finely detailed irritants snuck up on me and then kept flicking the back of my head. The number of times in a row I replaced toilet paper in the first-floor bathroom. The cadence of a crewmate’s hard-soled sandals galloping down the stairs, remarkably consistent and always so loud. I also wondered why one of my crewmates kept swinging her crossed leg under the table at every meal so as to ever-so-gently tap me in the shin with her fuzzy slipper, seeming to reach across an incredible distance to make such slight contact, even after I’d tucked my legs well under my chair. But what I really wondered was why I couldn’t ask her to stop.Does all this make me sound a little unstable myself? Unsuited to live in an isolated environment with other people? Maybe. But I know I wasn’t alone. One crew member complained of another’s frequent throat clearing. Someone repeatedly expressed exasperation over the length of time it took some crew members to suit up for EVAs. And another suspected that his position on the chore chart was unfair because it gave him too many back-to-back heavy tasks. Then, when he traded with one of us and found himself in an even worse chore lineup than before, he became even more frustrated. In No Exit, Sartre wrote that hell is other people. But what about “other people” and you’re hurtling for eight months through the void of space in what amounts to a metal can on your way to a distant planet?From 1967 to 1968, Soviet researchers conducted a year-long medical-engineering experiment in which two male subjects lived in a space capsule just large enough for them and the two seats that held them. On a trip to Moscow to visit Kim Binsted in 2017, she and I spent time touring the very large facility that housed this capsule experiment as well as the Mars500 Experiment, the 520-day simulation of an entire Mars mission from “launch” to “surface expedition” to “trip back home.” When the tour guide mentioned the two men in a can, I wanted to know more. He didn’t go into detail, though he said that it was indeed an unpleasant experience for the subjects. After the year was up, both men still worked for the Soviet space program but, according to the guide, they never spoke to each other again.Our crew got along reasonably well—I’d say functionally most of the time and even jovially harmonious on occasion— but some personalities did clash. There were a couple of yelling bouts and some isolation-within-isolation events—that is, going to a room and staying there for a longer than culturally accepted period of time. We’d developed our own culture for what was socially expected, but for some of the crew whose personalities weren’t well-suited to the agreed-upon social interactions, this proved to be a strain. Most of us are still on good terms, though a couple of us don’t speak to others. One of us moved to New Zealand about a year after and hasn’t been in much contact since.Nothing quite matches the isolation that comes from being hundreds of millions of miles from Earth, cooped up with three to five other people, unable to have a real-time conversation with anyone else for two-and-a-half years. NASA couples the problem of isolation to the difficulties of confinement inside a small space. Tom Williams, element scientist for human factors and behavioral performance in the Human Research Program at NASA, says the isolation of long-duration missions is such a challenge because human beings are adaptive organisms. We’re ready to change to a changing environment, and we thrive when adapting. “What isolation does is sort of remove that context of adaptation because when we’re isolated, we’re not… able to engage our environment in as many different ways,” he says. “So it sort of creates this barrier to allowing us to be that adaptive resilient human.”In some ways it’s related to the boredom problem, the way certain aspects of your environment, daily schedule, and conversations smooth over, lose their texture. I distinctly recall sitting in a San Francisco beer garden with a friend shortly after my return from Mars. Then nearby and suddenly: a loud dog bark, a toothy lunge, and a pigeon quickly ascending with furiously clapping wings. I almost had a panic attack. I could barely believe the commotion while my friend, who had calmly looked on, couldn’t believe my dramatic response. But my senses hadn’t been so jarred in months.Williams also says that, socially, isolation challenges our ability to self-regulate “because we typically learn to respond to our environment in which other people may react to us.” How unsettled I felt in the first few days back, answering interview questions from news media and from people in general. It might sound strange, but I wondered who I could trust. I had spent more than four months building a particular and insular kind of camaraderie with my crewmates. Our mission depended on our faith in and understanding of one another, our conversational shorthands, knowing when we were serious and when we were joking, and the subtext and motivations behind it all. But how to be with other people? Outside that dome, suddenly I wasn’t so sure.We’ve all known discomfort, dislocation, sadness, loneliness, or the frustration of feeling isolated in some way or another. And here on Earth, there are many isolations, some torturous and immoral, some useful, some natural, some finite, others indefinite. Solitary confinement, for one. The separation of family members when they’ve migrated to the United States. The isolation of the sick in hospitals, the elderly in nursing homes, the mentally disabled in institutions of care. Being the only kid your age in a neighborhood. The woodland hermit, the friendless shut-in. Lonely spouses. Workers on a submarine or an oil rig or in a coal mine. New mothers, certain writers, graduate students toiling away in windowless laboratories.The word “isolation” can be traced to the Latin insula, which means “island”; it was also the word used to describe the four-story, block-long apartment complexes in Roman cities. “Isolation” as a word runs cool and clinical. Its appearance in English in 1833 is more recent than the comparable “solitude,” which appeared sometime in the 14th century. Isolation is more likely than solitude to be used in a scientific or medical context as in the isolation of a chemical compound or isolation as quarantine. And perhaps this is why the word carries a compulsory connotation, a sense of a forced seclusion. Solitude, in contrast, more readily allows the possibility of choice, eliciting thoughts of Thoreau at Walden Pond (laundry facilities and a warm meal just a short walk away), choosing for himself his own version of social detachment. Solitude, at least for writers and artists, can carry a positive meaning—a state in which deep thought and productive work can be achieved.In astronaut Michael Collins’ book Carrying the Fire, he describes his role as command module pilot, essentially dropping Neil Armstrong and Buzz Aldrin off on the moon and repeatedly circling the block before picking them back up.“I guess the TV commentators must be reveling in my solitude and deriving all sorts of phony philosophy from it, but I hope not. Far from feeling lonely or abandoned, I feel very much part of what is taking place on the lunar surface. I know that I would be a liar or a fool if I said that I have the best of the three Apollo 11 seats, but I can say with truth and equanimity that I am perfectly satisfied with the one I have… I don’t mean to deny the feeling of solitude. It is there, reinforced by the fact that radio contact with Earth abruptly cuts off at the instant I disappear behind the moon. I am now alone, truly alone, and absolutely isolated from any known life. I am it. If a count were taken, the score would be three billion plus two over on the other side of the moon, and one plus God only knows what on this side. I feel this powerfully—not as fear or loneliness—but as awareness, anticipation, satisfaction, confidence, almost exultation. I like the feeling.”I came across Collins’ book the summer between my junior and senior years of college. Though I was a chemistry major, attending a small liberal arts college in Kansas, that summer I lived in a dorm room at North Carolina State University, thanks to a National Science Foundation program that placed eager undergrads in physics labs around the country. My assigned project was to use a device called an ellipsometer to analyze the electrical properties of a semiconductor material that some people hoped might one day replace silicon in computer chips. It was a lonely summer. I talked little and walked a lot in Raleigh, a city with wide, busy streets and afterthought sidewalks. The local used bookstore, Reader’s Corner, was like an oasis. I picked up some Woolf that I didn’t read as well as Collins’ book, which I devoured. Never had I read anything by an astronaut that was so clear and unsentimental, so evocative and well written. I’d drifted away from my astronaut dreams in high school and college—it felt like kids’ stuff—but that summer, reading that book, I resolved to get my Ph.D. in physics, to recommit myself to going to space. “Your solitude will be a support and a home for you, even in the midst of very unfamiliar circumstances, and from it you will find all your paths,” Rilke wrote.Extracted from ONCE UPON A TIME I LIVED ON MARS: Space, Exploration, and Life on Earth by Kate Greene. Copyright © 2020 by the author and reprinted by permission of St. Martin’s Publishing Group.Read more at The Daily Beast.Get our top stories in your inbox every day. Sign up now!Daily Beast Membership: Beast Inside goes deeper on the stories that matter to you. Learn more.