Before space travel became a thing, it wasn't clear if astronauts would be able to sleep after lift-off. Why? Well, as a recent review paper published in the journal Sleep Science explains, humans spent millions of years evolving to survive under earthly conditions. Life on the third planet from the sun comes with a non-negotiable physical reality, including 24-hour days and gravitational pull towards the center of the planet. Not so much elsewhere in the solar system.
But, as humans are really good at innovating our way out of our inabilities, we tried and succeeded. Space missions taught us that humans could, in fact, log Zzzs in space. Unfortunately, those Zzzs aren't exactly grade-A. Over the years, American astronauts, as well as space journeymen from Russia, China, Europe and elsewhere, have filled us in on their in-flight sleep habits. And they consistently report shorter, more disturbed nights of rest. Objective sleep tests, though few and far between, support subjective their sleep assessments. One late-'90s Russian study, for example, showed more disturbed sleep and wonkier circadian rhythms in cosmonauts at the Mir space station, compared to earth-bound humans.
In a lot of cases, poor sleep is a function of opportunity: People are too time-strapped or physically unhealthy to fall into uninterrupted blocks of deep, cyclical rest. But astronauts are in peak physical condition (not a lot of sleep apnea in those taut, iron-stomached bods), log 8.5 hours of designated sleep-time each night, per Mission Control guidelines and take measures to keep their bodies on a regular schedule sans gravity.
Their sleeping environments have also gotten an upgrade over the years. Back in the day, beds were something of a DIY project. Today, astronauts doze in spiffy, customized sleep pods fastened to the wall or the ceiling. Yet, they remain under-slept.
We can't (or shouldn't) dismiss their sleeping troubles, because the astronaut life demands long hours of mentally and physically taxing work. And fatigue leaves people prone to cognitive misfires, including judgment errors, carelessness and weakened memory and focus. Mission tasks don't require single cognitive tasks; they require flexing multiple mental muscles on a near-constant basis, while simultaneously performing precise psychomotor skills and handling considerable psychological stress. (Soaring to the moon isn't a vacation, per se.) Not to mention, circadian misalignment (common among shift-workers and people with Delayed Sleep Phase disorders) is linked to health issues, including cardiometabolic disease, depression, diabetes symptoms and general brain-fog.
All evidence, the paper says, "point[s] to the conclusion that, compared to sleep on earth, the duration in human sleep in space is shorter, averaging about six hours. In addition to changes in the sleep/wake cycle, other changes such as neurobehavioral, physiological (changes in endocrine and thermal physiology, muscle tonicity and bone consistency) also occur."
Fatigue-related errors likely contributed to at least two space-travel accidents, according to the paper. Human error, potentially caused by sleep loss and early-a.m. shiftwork, may have contributed to human error underlying the 1986 Challenger crash. And, it's thought that operator fatigue played a role in 2003, when the Columbia shuttle nearly launched with 18,000 fewer pounds of oxygen than necessary. Additionally, we have a spate of examples for earth-bound travel disasters related to poor or disordered sleep, across trains, planes and automobiles (and ships).
In short: We want our astronauts to stay in tip-top shape for the sake of fruitful, safe space exploration. It's not that astronauts don't take measures to sleep better — they throw back Ambien, too. But, prescription sedatives come with risks and Ambien might not work on the next frontier of space travel: Mars, where late-sleepers might rest easier than early risers, according to one mice study. So far, our future on Mars is full of "mights."
Apparently, countermeasures are being developed to improve space sleep quality and duration, and facilitate circadian rejiggering. As we reported in January, the National Space Biomedical Research institute issued a grant for a company to develop a sleep mask to combat the issue of time zone change; earlier this year, NASA scientists tasted various light setups to determine what wavelengths could help align astronauts biological clocks better.
But, we need to do more. For example, the paper mentions programs for "training and implementation of preflight circadian adaptation," both for astronauts and their families. That, along with the vomit comet, should be required practice for all astronauts-in-training.