As I write this post, I’m struggling a little to put words onto the page. I didn’t sleep well last night, and my tiredness has taken its toll on my ability to concentrate. But at least I’m sat at my desk at home and not, say, in control of a massive hunk of metal filled with fuel and electronics, hurtling through space at thousands of kilometres an hour. Because a new study in Scientific Reports has found that astronauts need to get enough sleep too — and when they don’t, their performance suffers.
Erin Flynn-Evans from NASA Ames Research Center and colleagues studied people taking part in a spaceflight simulation on Earth. They weren’t actually astronauts, but “astronaut-like” participants, who all met NASA’s physical standards for space flight, as well as other criteria (such as having Master’s degree in a STEM subject). The participants lived in the Human Analog Research Exploration (HERA) habitat, a self-contained unit designed to mimic living and working conditions during space exploration. This paper included data from five separate “missions”, each of which involved four participants living together in the HERA habitat for 45 days (though one of the missions had to be cut short due to a hurricane).
Throughout each mission, the participants had a variety of tasks to complete, such as “extravehicular activities” and scientific work. Once every three days, at five points throughout the day, they also completed the psychomotor vigilance task, which simply involves watching a screen and pressing a button whenever a light randomly appears.
Importantly, each weekday participants were only allowed five hours of sleep; at the weekend they were allowed eight hours. They weren’t permitted to nap, and could only drink caffeine before 2pm. The researchers could therefore look at how performance on the psychomotor vigilance task changed across the course of the mission, as well as specifically on days when the “astronauts” got more or less sleep.
The team found that participants’ performance worsened as the mission went on, with reaction times on the task becoming slower. Interestingly, participants’ self-reported fatigue didn’t decline across the course of the mission, suggesting that tests like this may provide a better measure of performance than simply asking astronauts how they’re feeling. Participants were also slower and missed more of the lights in the task on days when they got only five hours of sleep, compared to days when they got eight hours.
Overall, the authors conclude, the findings “suggest that simply meeting the criteria required to be an astronaut is not in itself a determinant of resilience to chronic sleep restriction”. This isn’t entirely surprising — after all, astronauts are only human, and people in other professions with rigorous training requirements, such as pilots, are also adversely affected by lack of sleep.
Of course, there are some obvious limitations to the study: although it simulated a space mission, it was still conducted on Earth; similarly, the psychomotor vigilance task isn’t necessarily a good representation of the complex jobs astronauts need to perform. It’s also worth noting that the changes in reaction times on the task were pretty small, in the region of tens of milliseconds difference between the beginning and end of the missions, and there was lots of variation between participants. It would be interesting to explore these in more detail: are there particular characteristics that make astronauts’ performance more or less likely to suffer after a lack of sleep?
Still, the research does suggest that many days or weeks of poor sleep may build up to impair astronauts’ day-to-day functioning: an important insight given that this is the sort of time frame for future missions to the moon or beyond. And while NASA does allow crewmembers to sleep for eight hours per night on missions, astronauts themselves report actually sleeping for just six hours. So, the researchers say, it will be important to consider ways to promote better sleep while in space.