As any traveler knows, being a few time zones away from home can be brutal for your internal clock. Having jet lag when you’re aboard the International Space Station, where astronauts can watch the sun rise and set every 45 minutes, is even worse. Though the view is otherworldly, it’s not exactly conducive to a good night’s rest.
Astronauts have eight hours of sleeping time baked into their schedules, but pair that with an unfamiliar environment and erratic workloads — when the space shuttle docks, ISS crews switch to an extraterrestrial night shift — and you end up with some resource-depleted cosmonauts. Comb through astronauts' journals, as psychologist Jack Shuster did in 2010, and you’ll find snappy depictions of fatigue: “Our working day started at midnight," wrote one crew member, "just to make sure we were extra tired.”
Efforts to help astronauts achieve better sleep are vital to the well-being of both the current ISS crew and embarkees on future National Aeronautics and Space Administration missions to Mars, deep space and beyond. NASA research psychologist Erin Flynn-Evans, a circadian rhythm expert, is on the case. In the January issue of Nature Microgravity, Flynn-Evans and her colleagues write that astronauts experience circadian misalignment — that is, astronauts’ biological clocks were out of sync, preventing good sleep. In a 2014 Lancet Neurology report, she found that astronauts who try to combat this loss of sleep take a lot of prescription sleeping aids, but the drugs aren’t as effective in zero gravity as they are on Earth. All of Flynn-Evans’ research is in pursuit of a solution for sleeping in space. We spoke to her about the cause.
When astronauts are aboard the International Space Station, what are their sleep conditions like?
The sleep environment on the ISS now is actually pretty luxurious. There are individual quarters available to every crew member. They're really quite nice: Sound-attenuated sleep chambers that have no windows, which means there's no external light exposure; they're private and they have very carefully controlled air flow and temperature. They really provide a very optimized sleep environment.
Was it always like that?
No. Prior to that, the crew members had to sleep wherever they could. They had to experiment — so they might hook a hammock up to the side of a wall. We've heard reports of crew members sleeping sandwiched between water bottles. We've heard of crew members harnessing themselves to the floor. It’s changed quite a bit.
So if today's astronauts are fatigued, would it be fair to say it’s not the sleeping arrangements? Is there something else going on?
There likely is, yes, although it's important to note that the Lancet Neurology paper and the paper in Nature Microgravity both included a substantial amount of data from before the sleep stations were on the ISS.
In your Lancet study, you call the use of sleep aids in space “pervasive.” Why is that?
I think that the high prevalence of hypnotics used during spaceflight shows that astronauts recognize they're not getting enough sleep. They’re taking sleep medication because they want to be rested. The things that were notable about what we saw was they don’t seem to gain a whole lot from the use of hypnotics — there's not a big difference in the amount of sleep they get when they’re taking sleep medications versus when they’re not. They may fall asleep faster, and feel better about the sleep that they get. But there aren't really any objective differences in their sleep with or without medication.
In the more recent paper, the one we published in January, we found astronauts are more likely to take sleep medication when they’re circadian misaligned. That's a pretty important finding because it tells us that — just like shift workers — they recognize when they're out of sync.
Do you expect astronauts on Mars and deep space missions will take hypnotics with the same frequency as astronauts on the ISS?
It's an unresolved question. Radiation exposure degrades the quality and potency of medication. Any medication that would be brought along would be susceptible to degradation simply due to the conditions of space. In addition to that, the payloads are limited; every medication brought on a deep space mission will have to be very carefully planned. It’s unlikely that the astronauts will be able to take sleep medication at the rate they currently do.
Will sleeping on Mars be a problem?
The Martian day is about 40 minutes longer than the Earth day, so circadian desynchrony could be a major problem on Mars. We know that humans can adapt to a Mars day length. But we have to have a very structured schedule and very regimented light-dark cycle in order to facilitate that shift. Without that, humans on Mars could feel like they're continuously jet-lagged — which would not be a good thing.
If drugs aren’t as helpful as they could be — or out of the question for certain missions — what alternatives does NASA have?
Circadian misalignment is associated with a one-hour loss in sleep relative to sleeping during circadian alignment. That's very significant, to get a whole hour less when you're sleeping out of sync. If we can optimize their planned shifts, then we should be able to preserve their sleep a little bit better.
One of the ways we can do that is through exposure to blue light. We are sending up new solid-state lighting arrays, which have a LED array that can be tuned to different wavelengths of light. They can blue-enriched, which can facilitate shifting of the circadian rhythm. Blue light is a potent synchronizer of the human circadian system, and we can strategically use blue light to shift individuals to different types of schedule. So we can add blue light when we want them to shift, and we can take away blue light when we don't want them to shift.
Will we see these LEDs on Mars?
If the atmosphere of Mars was blue, then supplemental lighting wouldn’t really be necessary. The light that humans would get from the sun on Mars would reset their clocks. But because Mars has such a thin atmosphere, and because the planet is red, it’s almost like being in the dark. Red light is interpreted by the body as very similar to darkness; it has very little effect on human circadian physiology. Even though you would have enough light to visually explore, the light you synchronize with the clocks likely wouldn't be sufficient.
What else might work?
Light and darkness are the primary factors. The habitability of the sleep environment is obviously an important component in quality of sleep. Having a private, safe, comfortable sleep environment would be important. I'm doing a project right now where we’re evaluating habitability of the sleep environment for future space vehicles. We're looking at things like: What is the optimal temperature? What level of control should individuals have at controlling the microclimate within their sleep space? What variation between individuals allows for flexibility in making sleep environments suitable to good, quality sleep?
There’s still a lot to learn because we obviously have a limited number of people sleeping in space. In five years we'll know much more than we do now.
Is there a burning question you'd love to see answered?
There's tremendous intra-ocular pressure [within the eyes] during spaceflight. That could, potentially, lead to blindness. I'm interested to know the influence that pressure has on the human circadian rhythm — in order to stay synchronized to any day length, you need to have functional retinal ganglion cells.
I wouldn't say that anyone, including myself, knows how this system works in humans right now.