These scientists sleep in the world’s most extreme environments. Here’s how they get a good night’s rest

There’s no shame in an elaborate sleep setup. A weighted blanket, pillows of varying density and squish factor, dueling humidifiers and dehumidifiers, and soft LED lighting can help carry someone to dreamland.

But sometimes, one needs to sacrifice the comfort of a curated bedroom in pursuit of, say, science and adventure. Exploration leads researchers to some of the planet’s most extreme climes, from tundras to mountaintops to outer space. In these unfamiliar environments, investigators must relearn how to doze. Sleep is essential for human survival, after all. With a little practice, a good night’s sleep can come even to those far from a bed — or civilization. Inverse spoke to three experts about how they get a decent slumber deep in caves, high in the treetops, and even in orbit around Earth. Here’s what they had to say, as told to Elana Spivack.

Deborah Buecher, bat biologist and founder of Buecher Biological Consulting

I met my husband in 1970 in a cave. He was the trip leader, and it was my first cave. I fell in love with caving, and we got married. He passed away after 48 years of marriage, but we caved our entire married life.

One night, we set up base camp in Ghost Town, a cavern in New Mexico’s Lechuguilla Cave. The chamber was maybe 300 feet wide by 100 feet high, and was covered in big, 20-foot-high stalagmites. They were kind of creamy white, so they looked like ghosts. I think that’s why it got named Ghost Town.

When you turned the lights out, you saw nothing. It’s the most dark you're ever going to see. You can’t see your hand in front of your face. Your eyes and brain have trouble with that. And sometimes if people are left in a cave for a while, they swear they start to see some lights. That’s maybe because their brain needs to supply what it wants.

This happened to me, too. I would wake up and see a room and colored lights. It wasn’t real. I think it was my brain creating it. I remember seeing some of those stalagmites. It wouldn’t be just the cream of the formations and the brown of the mud. It had more blues and purples. We weren’t “on” anything except macaroni and cheese!

Hiking through caves is really strenuous, so you sleep very well. You want to pack as light as possible. The cave temperature was about 67 degrees [Fahrenheit], but it’s 100 percent humidity. We would sleep in maybe fleece pants, a fleece or polyester top, and a balaclava or a winter hat.

For a self-experiment, French scientist Michel Siffre went into a French cave, and researchers never gave him a hint of what time it was. He would call in, and they would have a conversation, and he would report body temperature and all of that. But they wanted to know, without the stimulation of the sun, how human circadian rhythm might shift.

When we were caving, we did shift. We might get back to camp after a day of work at 10 pm and be just ready for dinner. And then we might sleep until 9 am but then go hiking for a really long time. What was on our watch didn’t make a difference unless we were doing science and we needed to report it. The time of day did not drive our activities. If we were hungry, we’d have a snack. We might eat just a little bit more throughout the day and then have a big dinner and a big breakfast. We found that our internal clocks shifted — and we were happy with that.

Tim Kovar, founder and owner of Tree Climbing Planet, a recreational tree climbing school

The most consecutive nights I’ve spent up in a tree is four. There was one year I spent over 200 nights in hammocks outside.

When camping in trees, it’s important to make sure the tree is solid and safe. Make sure you’ve done your tree inspection and you have the proper climbing and camping gear. Water is a big one, and so is a proper sleeping apparatus. I use a specially designed treetop hammock called the Treeboat.

You also need a spirit of adventure, and a big-old pocket full of patience too, because things do go astray. That sense of adventure and wanting to be there is probably the biggest tool in the toolbox. There is always one other person camping with you in the treetops — and his name is Murphy, as in Murphy’s Law. He’s always present, him and his relatives the knot gnomes. They tie up all your ropes.

In 2000, I slept up in the Stagg tree in California alone. It’s about 2,000 years old, and the top was blown out probably 500 years ago, so you could sleep inside the trunk, 240 feet up. I remember laying down on the duff, with hundreds of years of debris, leaves, and bark falling down, looking out through that opening of that cave up there. Oh, my gosh, it was one of the most beautiful and memorable experiences of my life.

I usually sleep in the hammock. John Muir went up and tied himself in with his belt to try to sleep. I attempted that once. I didn’t make it all night. It was so uncomfortable.

When you’re sleeping in trees, it gets cold up there. We have insulating pads that we put around the hammocks to help trap that body heat. Sometimes, you find those perfect branches that are nice and stout and very solid, at least 4 inches in diameter. The tree dances as a living organism and parts of the tree move one way or the other. It feels like you’re on a boat.

When you're in the treetop you also hear the birds around you. You’re in this vortex of this bird symphony. Once, while I was in Panama, I was laying in my hammock, enjoying the birdsong. I was living in the moment, and then I felt this tugging on the rope. I looked down, and there was a howler monkey climbing up my rope, like he found the ultimate vine. I’m like, “Oh, that’s cute.” A second later, I was like, “Wait, that’s coming straight to me.” I grabbed the rope and one strong tug and he let go and took off.

When you’re sleeping in the treetops, anything becomes free game as a highway for the insects. I learned that the hard way. One of the first nights staying up there, I woke up with all these ants inside my hammock. This is the jungle; I can’t just go down because then I’m on the ground in the middle of the night and that’s an hour hike back to the base camp.

The only lucid dreams I’ve ever had were in the treetops. Either you get no sleep at all or you get these deep little lucid dreams going on. And that’s pretty special.

I would love to sleep in the baobab trees in Madagascar. I haven’t been there yet, so that’s on the bucket list. They’ve got a pretty wide crown where I imagine the starry nights would just be spectacular.

Getting back in bed after staying in trees was more comfortable, but I felt claustrophobic sleeping within walls and the ceiling and not having the openness. It felt a little staler. It didn’t feel as alive and vibrant — and honestly, it didn’t feel as natural.

Thomas Marshburn, NASA astronaut and physician who has taken multiple trips to the International Space Station

Zero-gravity sleep is some of the best I’ve ever had. Your head, your neck, your torso all get into their natural position when not being pulled on by gravity. You don’t get a crick in your neck; you don’t sink into the bed as you fall asleep. Your soft palate and all the soft tissue around your throat, which is what makes people snore on Earth, lift and open up when you fall asleep under zero gravity. With the airway a little more open, the air can move more easily.

Sleep is scheduled into a crew member’s day on the ISS, and there are nine hours of it. That’s not to say we all sleep nine hours. It depends on sleeping habits before you launched. But people will sleep anywhere from five to nine hours. That’s rarely intruded upon for operations. If it is, then time has to be given back. Sleep in space is absolutely restorative and absolutely essential, just like it is on the ground.

If you’re tired, you can take a cat nap by just relaxing your muscles wherever you are. Hopefully your feet or some part of your body is restrained, or you’ll slowly float across a cabin. At night, we have our own individual crew quarters that are about the size of a phone booth.

It’s quiet, at least from the spacecraft noise. You have a fan on you all the time. You also have a sleeping bag, but not for warmth — it’s for restraint. You get into this thin sleeping bag and Velcro yourself in or zip it up. There are arm holes so your arms can float in front of you. There’s also straps, so if you’d rather cuddle yourself, you can ball up inside the sleeping bag and strap yourself down tight.

There’s a very deliberate attempt to make a break from the intense work day, so you’re ready for sleep. After we’ve had our final conferences with the ground, even if you have a little bit of work left, we’ll all get together, talk out the day, share some excitement, have a good dinner. We turn down the lights — they have LED lights throughout the station. You can go from this light blue bright light to a sunset orange glow light. I typically get a little bit of work done and maybe a little email, read a little bit, and slowly go off to sleep.

When you are sleeping, there’s a lot of airflow around you from the fan because you’ve got to get rid of the carbon dioxide that builds up around your head. That doesn’t float away like it does on Earth from buoyancy effects. Without gravity, you can’t have buoyancy, so the CO2 sticks in your face.

The human body is under an alert state the whole time you’re in space. The base of your brain knows this is a dangerous place. Not to mention the stress of going through a tight timeline. Crew members use meditation apps, read, or have some other activity they use before they go to sleep.

For me, it usually takes a week or so to figure out how to sleep in that environment, then the zero G makes it very pleasant. If you get a feeling like you’re falling when you’re asleep, you wake up. Well, when you are up there, you really are falling because you’re in orbit around the Earth on the International Space Station, so your brain interprets it accurately. I’d keep jumping awake for the first few nights, but then I’d adapt. After that, it starts to be smooth sailing.

When I do dream, being able to fly around in the dream is really nice. Typically dreams center around my family, whom I miss while in space.

We have 16 sunrises and sunsets a day on the ISS. We’re going around the Earth every 90 minutes. When I see a certain angle of the sun and the clouds, I want to pull out the paper, start reading the news, get a cup of coffee, and my body starts to reset. Similarly, I get that same feeling when I wake up and it’s sunset outside. If I’m trying to sleep, I avoid looking at the Earth when it’s in daylight.

THE FUTURE OF SLEEP reveals what science currently knows about what sleep is, why we need it, and if we can hack our own slumber. Read the rest of the stories here.