How Astronauts’ Sleep Tests the Limits of Human Space Exploration

We all know that androids probably dream of electric sheep, but real-life astronauts are probably dreaming of quieter pastures. “The ISS is really noisy,” Dr. Kris Lehnhardt tells Inverse. Lehnhardt is the professor of emergency medicine and the director of space medicine at the University of Texas Health Science Center at Houston, and he points out that if you’re the kind of person who falls asleep to the sound of a whirring fan or other household appliances, you’d have more of that than you could handle on the International Space Station.

Sleeping on the ISS is not all about peaceful Earth views and the gentle hum of a Star Trek-style spacecraft lulling you into a contemplative mindset. The truth is, sleeping in space is not just louder, but way more difficult in a variety of ways — and more important to boot. So how does NASA solve for it? The answer is more essential than you might think.

In The ISS, No One Can Hear You Scream

So just how noisy is the ISS? “All the fans and all the motors and all the other things up there all make sound,” Lehnhardt says. “So, one of the things that we actually have to do in space is we have to protect [the astronaut’s] hearing and their cognition, if you will, from the ambient noise of the ISS, which is very loud.”

You can readily find YouTube loops and other sources that will play the ambient noise on the ISS, and, at a reasonable volume level, a non-astronaut may find this white noise soothing. Again, this kind of thing is romanticized in science fiction and on sleep apps. One soundscape on the popular Calm app even simulates a fictional “Spaceship Engine Room,” echoing the comments of Brad Boimler (Jack Quaid) in Star Trek: Lower Decks when he commented that “Sometimes I hum warp engine sounds just to, you know, soothe myself.”

The gap between the gentle science fiction of astronaut sleep and the current reality is basically measured in decibels. “There is a pretty high decibel standard noise in ISS that the astronauts talk about a lot, and it's very disruptive to them,” Lehnhardt says. “One would say that the solution to that is simply hearing protection, and they do use hearing protection in a lot of different ways.”

But the issue is that the earbuds and earplugs used to block out the ISS cacophony can’t be totally noise-cancelling because astronauts need to be able to hear alarms. “There's a really fine line between how we deal with the background noise and how we make it quiet enough to sleep.”

Floating Past Bedtimes

As Lehnhardt points out, sleep that occurs in Earth orbit is a microcosm for what the future of all space travel might hold. For one thing, the further one gets out into space, the less we can agree upon the concept of “now.” Various time zones on Earth can produce horrible sleep deficits for travelers, but the jet lag on our planet is nothing compared to the round-the-clock schedule for those in orbit.

Jet lag on our planet is nothing compared to the round-the-clock schedule for those in orbit.

“The ISS lives on essentially Greenwich time, and that we do to coordinate with all of the international partners around the world,” Lehnhardt says. “But, because of orbital mechanics and timing of launches, sometimes you’ve got a vehicle coming up to bring cargo to the space station, and it’s the ‘middle of the night’ in space.”

This means that the astronauts have to be “sleep shifted” ahead of time, in order to make sure they meet their sleep quotas. The idea of a bleary-eyed spacer, just subsisting on coffee and stimulants to stay awake, is neither realistic nor practical. And, like many other aspects of space travel, astronaut sleep is heavily monitored and regulated.

But, other than it being noisy and on a script schedule, what is sleeping in space actually like? How is it fundamentally different from sleeping on Earth? Do you dream differently in space?

“Even in sleep and with your eyes closed, you may be seeing things in space that you wouldn't otherwise see on Earth.”

“A lot of the astronauts keep journals, and for a while, some of them were keeping journals and talking about sleep and dreams and space,” Lehnhardt says, pointing out that the practice of astronaut dream journals goes back to the Apollo days, and during those famous missions, “there are some interesting stories about different types of dreams in space or how they dream in space flight... the astronauts were describing how they could close their eyes and they would see little streaks of light with their eyes closed because the radiation was flying through the spacecraft and was hitting their retina and was giving them little flashes of light. So even in sleep and with your eyes closed, you may be seeing things in space that you wouldn't otherwise see on Earth. And who knows how that affects your brain in terms of dreams or your subconscious mind.”

Lehnhardt makes it clear that such unknowns are why some space missions make more sense for robots or other non-human explorers. But, he also points out that, as resilient, adaptable machines, human beings are still faster and more innovative than any bot we could send to the Moon or Mars. “Perseverance [the NASA rover that started exploring Mars on February 18, 2021] is an amazing vehicle, but the distance that Perseverance has currently covered, people could cover in a few days, and it's been up there for years,” Lehnhardt says. “It’s all about using the right tool for the right job.”

The further and further astronauts get away from Earth, the more challenging — and crucial — getting good sleep becomes. Right now, sleeping in orbit of Earth for long periods is difficult, but it may be easy compared to the challenges of astronauts sleeping for even longer periods on the Moon, Mars, or beyond.

Deep Space, Deep Sleep, Deep Problems

We might be testing these challenges soon. The planned lunar Artemis missions (Artemis II is set to launch no earlier than April 2026) could send astronauts to the south pole of the Moon, which would include locations in permanent shadow, an eternal night. Perhaps OK for a good night’s sleep, but not great for a human’s circadian rhythm. “We don't even know what will happen to people's brains when they can't see Earth anymore,” Lehnhardt says.

And we’ll need a lot more experience before we really know. Just like every star is different, and no two spaceflights are quite alike, it’s also true that the uniqueness of each person in space will determine exactly how well they do when trying to sleep under the stars.

“Some people love sleeping in space, and some people hate sleeping in space.”

“Some people love sleeping in space, and some people hate sleeping in space,” Lehnhardt explains. “It just depends.”

In talking to Lehnhardt, one can’t help but wonder not just about the ISS sleep problems, or the Moon sleep problems, or what the time zone in certain Mars neighborhoods will be relative to GMT. Instead, there are bigger questions: What about a version of humanity that has never slept on Earth, not once, ever?

If you leave the fantasy of Star Trek’s soothing warp cores behind, a lot of science fiction seems to suggest the only way for people to sleep well in space is to trick the mind into thinking you’re on terra firma. In Robert A. Heinlein’s 1963 novel Orphans of the Sky, a generation ship consisting of humans who believe that the known universe is only five miles long. This enclosed environment contains crops, houses, livestock, and an entire microcosm of the human experience. In the classic 1978 Battlestar Galactica, one of the last ships containing the seeds of humanity also contained a ship full of greenery and trees, allowing people to touch ground, even while on the run from murderous robots. Babylon 5’s titular space station, complete with rotating sections to provide artificial gravity, had a large Zen garden in its center, a place for reflection, and yes, plants.

Right now, the best Earthbound analogy for astronaut sleep schedules is to look at the way submariners sleep and get through the day. But none of that quite covers the far-future fantasy of living in space or on another planet, forever. “The challenges for the future of astronaut sleep will only get worse if we don't use all of our different means at our disposal to try and mitigate it,” says Lehnhardt. In other words, we need to take a close look at more astronauts sleeping in more situations in space. That’s the only way to create a good night’s sleep that might feel right at home — on Earth.