What happens to your sleep in space

What changes and why

Our internal body clock (the circadian rhythm) runs on a cycle of about 24 hours and is set mainly by daylight [1][2]. In orbit, almost everything that keeps it on time is missing or scrambled:

• The Sun rises every 90 minutes. The International Space Station circles Earth about every 90 minutes, so crews see 16 sunrises and sunsets in 24 hours [3].
• Indoor light is weaker than daylight. The day–night cycle made by artificial lighting is not as effective as natural daylight at setting the clock [2].
• Schedules shift. Station time follows Greenwich Mean Time, with a planned day of at most 10 hours of work and an 8-hour sleep period [4]. But arriving spacecraft, repairs and spacewalks often move bedtimes [4][2]. When crew have to sleep at the “wrong” biological time, sleep suffers (see below) [5].
• The bedroom is unusual. Astronauts sleep floating in a sleeping bag strapped to the wall [1]. The station is noisy, because life-support equipment is fitted with cooling fans [2]. The U.S. space agency, the National Aeronautics and Space Administration (NASA), lists noise, temperature, vibration and light as things that disturb sleep in space [6].

On average, sleep is short. In the largest study, astronauts slept an average of about 6 hours a night: 5.96 hours on Space Shuttle missions and 6.09 hours on the space station, measured with a wrist activity monitor [7].

Timeline: days to a Mars mission

1. Before launchFinal weeks of training

   Short sleep starts on the ground. In the 11 days before launch, crews averaged 6.04 hours (Shuttle) and 5.86 hours (station) [7].

2. First days and weeksShort missions

   On Space Shuttle missions, which lasted days to weeks, sleep averaged 5.96 hours a night, and 61 of 78 crewmembers (78%) used sleep medicine, which was taken on 52% of the 963 nights logged [7].

3. About 6 monthsTypical station stay

   Sleep averaged 6.09 hours [7]. In 21 station astronauts, the body clock was out of step with the sleep period on 19% of nights in flight (13% before flight). Those nights were shorter (5.4 versus 6.4 hours), rated worse, and sleep medicine was used more often (24% versus 11%) [5].

4. Mars-length missionsAbout 2 to 3.4 years (730–1,224 days)

   In a 520-day ground simulation of a Mars mission with six crew, people moved less over time, spent more time sleeping and resting, and got less light. Most had problems with sleep quality, alertness or the timing of their sleep, suggesting their body clocks drifted [8]. NASA rates this risk as one that requires mitigation for Mars missions [9].

5. Back on EarthFirst week after landing

   Sleep improves. In the first week after landing, astronauts slept more: 6.74 hours after Shuttle missions and 6.95 hours after station missions [7].

What crews do about it

• A planned, regular schedule. NASA requires crew schedules to protect body-clock alignment, with consistent sleep timing from day to day and a recommended 8.5-hour sleep period [10]. In 2014 the head of the European Space Agency (ESA) space medicine office said the structured routine usually makes sleep medicines unnecessary, and that melatonin may be suggested for jet lag [4]. In NASA studies, however, most crew reported using sleep medicines at some point: 75% of station crew in one study [7] and 71% in another [11].
• Light at the right time. ESA notes that blue light could make the body more alert, while red light might help bring on sleep [4]. In 2023 an ESA astronaut set up a lamp to glow red at bedtime and blue on waking, as an experiment [1]. NASA lists a flexible lighting system on the station as a promising countermeasure, not yet in routine use, with research under way to test how well it works [9].
• A good place to sleep. NASA calls for individual, separate sleeping quarters, with personal control of the sleep environment, eye masks, ear plugs and light blockers [6].
• Medicines, used carefully. Sleep aids were used about 10 times more often during station missions than in ordinary adult outpatient medicine [12], and 71% of station crewmembers reported using them [11]. ESA notes that side effects such as drowsiness on waking are a concern, because crew must be able to respond to emergencies [4]. Changes to schedules and lighting could reduce the need for a sizable share of all medicine use in flight [12].

After landing and recovery

• Sleep gets longer in the first week after return [7].
• Why it matters long term. NASA notes that ground studies link chronic short sleep and body-clock disruption to poorer performance and mood in the short term, and to long-term conditions including Alzheimer’s disease, heart and blood vessel disease, some hormone-dependent cancers and diabetes [9]. These links come from studies of people on Earth, not from astronaut data.

What it means for clinicians on Earth

These points are general education for clinicians, not advice about any individual patient. Coordinate with the person’s flight surgeon (the physician responsible for crew health) where there is one.

• Ask about sleep medicines used in flight. Sleep-medicine use in space is common [7][12], so a medication history after a mission should include them.
• Body-clock misalignment, not just “stress”, is linked with shorter sleep. In astronauts, sleeping at the wrong biological time was linked with about an hour less sleep and more medicine use [5]. ESA compares it to jet lag; the space programs’ main tools are consistent sleep timing and light, with medicines as an option if those fail [10][4].
• Short sleep often starts before launch [7]. In anyone preparing for a flight, including spaceflight participants, the weeks of training are worth asking about too.
• Persistent problems deserve the usual assessment. In the largest study, sleep improved in the first week after landing [7], so ongoing insomnia or daytime sleepiness later on should be assessed as it would be in anyone else.
• Think long term. Chronic sleep loss and body-clock disruption are associated with long-term health risks in ground studies [9].