An astronaut asleep in the microgravity of Earth orbit-continual free-fall around the earth, inside the pressurized module Harmony node of the International Space Station in 2007
Sleeping in space is an important part of space medicine and mission planning, with impacts on the health, capabilities and morale of astronauts.
Human spaceflight often requires astronaut crews to endure long periods without rest. Studies have shown that lack of sleep can cause fatigue that leads to errors while performing critical tasks. Also, individuals who are fatigued often cannot determine the degree of their impairment.
Astronauts and ground crews frequently suffer from the effects of sleep deprivation and circadian rhythm disruption. Fatigue due to sleep loss, sleep shifting and work overload
could cause performance errors that put space flight participants at
risk of compromising mission objectives as well as the health and safety
of those on board.
Mission Specialist Margaret Rhea Seddon, wearing a blindfold, sleeps in SLS-1 module (STS-40)
Overview
Sleeping in space requires that astronauts sleep in a crew cabin, a small room about the size of a shower stall. They lie in a sleeping bag which is strapped to the wall. Astronauts have reported having nightmares, dreams, and snoring while sleeping in space.
Sleeping and crew accommodations need to be well ventilated;
otherwise, astronauts can wake up oxygen-deprived and gasping for air,
because a bubble of their own exhaled carbon dioxide had formed around their heads. Brain cells
are extremely sensitive to a lack of oxygen and brain cells can start
dying less than 5 minutes after their oxygen supply disappears; the
result is that brain hypoxia can rapidly cause severe brain damage or even death. A decrease of oxygen to the brain can cause dementia and brain damage, as well as a host of other symptoms.
In the early 21st century, crew on the ISS were said to average about six hours of sleep per day.
On the ground
Chronic
sleep loss can impact performance similarly to total sleep loss and
recent studies have shown that cognitive impairment after 17 hours of
wakefulness is similar to impairment from an elevated blood alcohol
level.
It has been suggested that work overload and circadian
desynchronization may cause performance impairment. Those who perform
shift work suffer from increased fatigue because the timing of their
sleep/wake schedule is out of sync with natural daylight. They are more prone to auto and industrial accidents as well as a decreased quality of work and productivity on the job.
Ground crews at NASA are also affected by slam shifting (sleep shifting) while supporting critical International Space Station operations during overnight shifts.
In space
Flight engineer Nikolai Budarin, uses a computer in a sleep station in the Zvezda Service Module on the International Space Station (ISS).
Cosmonaut Yury Usachov in his sleeping compartment on Mir, called a Kayutka
During the Apollo program, it was discovered that adequate sleep in the small volumes available in the command module and Lunar Module
was most easily achieved if (1) there was minimum disruption to the
pre-flight circadian rhythm of the crew members; (2) all crew members in
the spacecraft slept at the same time; (3) crew members were able to
doff their suits before sleeping; (4) work schedules were organized –
and revised as needed – to provide an undisturbed (radio quiet) 6-8 hour
rest period during each 24-hour period; (5) in zero-gravity, loose
restraints were provided to keep the crewmen from drifting; (6) on the
lunar surface, a hammock or other form of bed was provided; (7) there
was an adequate combination of cabin temperature and sleepwear for
comfort; (8) the crew could dim instrument lights and either cover their
eyes or exclude sunlight from the cabin; and (9) equipment such as
pumps were adequately muffled.
NASA management currently
has limits in place to restrict the number of hours in which astronauts
are to complete tasks and events. This is known as the "Fitness for
Duty Standards". Space crews' current nominal number of work hours is
6.5 hours per day, and weekly work time should not exceed 48 hours.
NASA defines critical workload overload for a space flight crew as
10-hour work days for 3 days per work week, or more than 60 hours per
week (NASA STD-3001, Vol. 1). Astronauts have reported that periods of high-intensity workload can result in mental and physical fatigue.
Studies from the medical and aviation industries have shown that
increased and intense workloads combined with disturbed sleep and
fatigue can lead to significant health issues and performance errors.
Research suggests that astronauts' quality and quantity of sleep
while in space is markedly reduced than while on Earth. The use of
sleep-inducing medication could be indicative of poor sleep due to
disturbances.
A study in 1997 showed that sleep structure as well as the restorative
component of sleep may be disrupted while in space. These disturbances
could increase the occurrence of performance errors.
Current space flight data shows that accuracy, response time and
recall tasks are all affected by sleep loss, work overload, fatigue and
circadian desynchronization.
Factors that contribute to sleep loss and fatigue
The most common factors that can affect the length and quality of sleep while in space include:
- noise
- physical discomfort
- voids
- disturbances caused by other crew members
- temperature
An evidence gathering effort is currently underway to evaluate the
impact of these individual, physiological and environmental factors on
sleep and fatigue. The effects of work-rest schedules, environmental
conditions and flight rules and requirements on sleep, fatigue and
performance are also being evaluated.
Factors that contribute to circadian desynchronization
Exposure
to light is the largest contributor to circadian desynchronization on
board the ISS. Since the ISS orbits the Earth every 1.5 hours, the
flight crew experiences 16 sunrises and sunsets per day. Slam shifting
(sleep shifting) is also a considerable external factor that causes
circadian desynchronization in the current space flight environment.
Other factors that may cause circadian desynchronization in space:
- shift work
- extended work hours
- timeline changes
- slam shifting (sleep shifting)
- prolonged light of lunar day
- Mars sol on Earth
- Mars sol on Mars
- abnormal environmental cues (i.e.: unnatural light exposure)
Sleep loss, genetics, and space
Both
acute and chronic partial sleep loss occur frequently in space flight
due to operational demands and for physiological reasons not yet
entirely understood. Some astronauts are affected more than others.
Earth-based research has demonstrated that sleep loss poses risks to
astronaut performance, and that there are large, highly reliable
individual differences in the magnitude of cognitive performance,
fatigue and sleepiness, and sleep homeostatic
vulnerability to acute total sleep deprivation and to chronic sleep
restriction in healthy adults. The stable, trait-like (phenotypic)
inter-individual differences observed in response to sleep loss point to
an underlying genetic component. Indeed, data suggest that common
genetic variations (polymorphisms)
involved in sleep-wake, circadian, and cognitive regulation may serve
as markers for prediction of inter-individual differences in sleep
homeostatic and neurobehavioral vulnerability to sleep restriction in
healthy adults. Identification of genetic predictors of differential
vulnerability to sleep restriction will help identify astronauts most in
need of fatigue countermeasures in space flight and inform medical
standards for obtaining adequate sleep in space.
Computer-based simulation information
Biomathematical
models are being developed to instantiate the biological dynamics of
sleep need and circadian timing. These models could predict astronaut
performance relative to fatigue and circadian desynchronization.
