Sleep-Wake Actigraphy and Light Exposure During Spaceflight-Long (Sleep-Long) - 01.16.19

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Sleep-Wake Actigraphy and Light Exposure During Spaceflight-Long (Sleep-Long) examines the effects of space flight and ambient light exposure on the sleep-wake cycles of crew members during long-duration stays on board the International Space Station.
Science Results for Everyone
Would a bed-time story help?  Ten years of data show that astronauts normally do not get enough sleep, even though most take sleep medications during space missions. Recognizing that sleeping pills do not solve the problem helps researchers target further research on the effects of medication, and finding more effective ways, such as changing daily schedules or using sleep promoting light, to help astronauts sleep well.  Adequate sleep is essential for health, performance and safety, and a better understanding of how microgravity affects sleep and wake cycles could help not only astronauts, but the millions of people on Earth who suffer from insomnia.

The following content was provided by Charles A. Czeisler, Ph.D., M.D., Laura K. Barger, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Charles A. Czeisler, Ph.D., M.D., Harvard Medical School, Brigham and Women's Hospital, Boston, MA, United States
Laura K. Barger, Ph.D., Harvard Medical School, Brigham and Women's Hospital, Boston, MA, United States

Erin E. Flynn-Evans, Ph.D., MPH, Brigham and Women's Hospital, Boston, MA, United States
Joseph M. Ronda, M.S., Brigham and Women's Hospital, Boston, MA, United States
Kenneth P. Wright Jr., Ph.D., Boulder, CO, United States

NASA Johnson Space Center, Human Research Program, Houston, TX, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Information Pending

ISS Expedition Duration
September 2006 - March 2011

Expeditions Assigned

Previous Missions
Sleep-Short, a similar investigation was performed with short duration crew members during STS-104, STS-109, STS-111, STS-112, STS-113, STS-114, STS-121, STS-115, STS-116, STS-118, STS-120, STS-122, STS-123, STS-124, STS-125, STS-126, STS-127, STS-128, STS-129, STS-130, STS-131, STS-132, STS-133, STS-134, and STS-135.

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Experiment Description

Research Overview

  • Previous research performed on Space Shuttle crew members shows that sleep-wake patterns are disrupted on orbit. The Sleep-Long experiment examines whether sleep-wake activity patterns are disrupted during long-duration stays on board the International Space Station (ISS).
  • A wrist-worn Actiwatch records the activity of the crewmembers and the ambient light they experience.
  • Data collected from sleep logs is used to evaluate the crewmember’s subjective evaluation of the amount and quality of their sleep and alertness.
  • This investigation will help define light requirements, sleep-shifting protocols and workload plans for future exploration missions. The results of the study will determine if further countermeasures to sleep disruption need to be tested.

The success and effectiveness of manned spaceflight depends on the ability of crew members to maintain a high level of cognitive performance and vigilance while operating and monitoring sophisticated instrumentation. During short-duration space flights, crew members commonly experience sleep disruption and may experience misalignment of circadian (of or relating to biological processes occurring with a cycle of approximately 24 hours) phase during space flight. Both of these conditions are associated with insomnia, impairment of alertness, and cognitive performance.

There is little information on the effect of long-duration spaceflight on sleep and circadian rhythm organization. This experiment uses state of the art ambulatory technology to monitor sleep-wake activity patterns and light exposure in crew members on board the International Space Station (ISS). Subjects wear a small light-weight activity and light recording device (Actiwatch) for the entire duration of their mission. The sleep-wake activity and light exposure patterns obtained in-flight are compared with baseline data collected on Earth before and after space flight. The data collected increases understanding of how space flight affects sleep as well as aids in the development of effective countermeasures for long-duration space flight.

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Space Applications
The information derived from this study will lead to a better understanding of the effects of space flight on sleep-wake cycles. The countermeasures that may be developed based on the findings of this study, could improve sleep during missions, which in turn will help maintain alertness and lessen fatigue of the crew during long-duration space flights.

Earth Applications
A better understanding of insomnia is relevant to the millions of people on Earth who suffer nightly from insomnia. The advancement of state of the art technology for monitoring, diagnosing, and assessing treatment effectiveness is vital to the continued treatment of insomnia on Earth. This work has the potential to greatly benefit the health, productivity and safety of groups with a high prevalence of insomnia, such as shift workers and the elderly.

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Operational Requirements and Protocols
A total of 20 long-duration crewmembers are required as subjects for the experiment. Baseline data for each subject is collected for two weeks between Launch minus 120 (L-120) days and L–75, as well as from L-11 through L-0. Recovery in sleep patterns after space flight will be assessed from Return plus 0 (R+0) days to R+7.
Crew members put on the Actiwatches as soon as possible upon entry into orbit and wear them throughout the flight. Crew members maintain sleep logs; they are required to keep the log for seven consecutive days, every three weeks or during three separate weeks throughout the mission that meet specific schedule criteria. Crew members download data from the Actiwatches every 26 days and change the battery at the end of the increment. On the last day of the mission, crew members take off and stow the Actiwatches.

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Decadal Survey Recommendations

Behavioral and Mental Health B2
Behavioral and Mental Health B3

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Results/More Information

A comprehensive analysis of results, collected over a ten-year span, shows that Shuttle and International Space Station crew members have difficulty falling asleep and typically do not get the full amount of sleep recommended for them each night. Astronauts completing long-duration missions aboard ISS experienced sleep irregularity ~ 20% of days in flight, resulting in ~ 1 h loss in sleep per night. This occurred more often when a vehicle is docked with ISS. Sleep researchers studied diary entries and rest/activity monitor data of 78 individual crew members from 80 shuttle flights (from 2001 to 2011) and 21 ISS missions (from 2005 to 2011) and found that, on average, space travelers get about 6 hours of sleep per night while in space and only slightly more during the data collect interval scheduled about three months prior to launch. The intensity of the pre-flight training and travel schedule may have contributed to insufficient sleep in the pre-flight data collection interval. During space missions, roughly three quarters of shuttle and ISS crew members reported taking sleep-promoting medication. Shuttle crew members reported taking sleep-promoting medications on about half of their nights in space, including nights prior to performing extra vehicular activity (EVA) work the next day which were extra mentally and physically demanding. The sleep-aid drug Zolpidem (brand name Ambien) was reported as the most often taken by shuttle crew members. The high prevalence of sleeping pill use during spaceflight, despite chronic sleep deficiency and improved sleeping conditions and quarters on the ISS, may suggest that some other aspect of the space environment, such as microgravity itself, might contribute to sleep disturbance. The use of sleep-promoting medication did not significantly increase the amount of sleep that astronauts obtained and only increased the sleep efficiency of shuttle crew members by about one percent. The minimal sleep improvement on nights when sleep-promoting medications were used emphasizes the need for further investigation into the stability, absorption, and effectiveness of such drugs in-flight. Sleep and the use of sleep-promoting medications during spaceflight needs further investigation, including the effect of chronic sleep deficiency and hangover effects from sleep promoting medications on operational performance, to develop and recommend best practices for ISS crew members. The sleep duration of crew members aboard long duration ISS missions was similar to that of crew members aboard short-duration shuttle missions. Monitoring and assessment of sleep duration and timing should continue in future spaceflight missions as a medical requirement, including collection of baseline data before astronaut selection for flight to estimate more accurately individual baseline sleep duration. Development of other more effective countermeasures to promote sleep in-flight is crucial, and might include scheduling modifications, strategically timed exposure to specific wavelengths of light and behavioral strategies to ensure adequate sleep, which is essential for maintaining optimal health, performance, and safety. Further research of sleep is planned for the future 1-year ISS missions, twice the normal length of previous ISS missions, which might provide information on trends in sleep over longer durations, which is especially relevant for future exploration class missions beyond low Earth orbit.

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Results Publications

    Barger LK, Flynn-Evans EE, Kubey AA, Walsh L, Ronda JM, Wang W, Wright Jr. KP, Czeisler CA.  Prevalence of sleep deficiency and use of hypnotic drugs in astronauts before, during, and after spaceflight: an observational study. Lancet Neurology. 2014 September; 13(9): 904-912. DOI: 10.1016/S1474-4422(14)70122-X. PMID: 25127232.

    Flynn-Evans EE, Barger LK, Kubey AA, Sullivan JP, Czeisler CA.  Circadian misalignment affects sleep and medication use before and during spaceflight. npj Microgravity. 2016 January 7; 2: 15019. DOI: 10.1038/npjmgrav.2015.19.

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites
Sleep Medicine at Harvard Medical School

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image This image of an Actiwatch Activity Monitor next to a ruler to demonstrate the size of the Actiwatch. Image courtesy of NASA.
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image NASA Image: S104E5114 - Astronaut, Janet Kavandi on STS-104 wearing an Actiwatch on her right wrist for recording activities.
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image NASA Image: ISS014E05119 - The Sleep-Long Actiwatch is visible on the left arm of Astronaut Michael Lopez-Alegria the Expedition 14 Commander. The Actiwatch monitors light and activity patterns of crewmembers.
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image NASA Image: ISS014E12135 - Expedition 14 Flight Engineer, Astronaut Suni Williams, performs her daily tasks while wearing the Actiwatch device as seen on her left arm in the lower portion of this image.
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image NASA Image: ISS015E09441 - Expeditions 14 and 15 Astronaut and Flight Engineer (FE-2), Sunita Williams, is seen here entering data at a computer workstation for the Sleep-Wake Actigraphy and Light Exposure During Spaceflight-Long (Sleep-Long) experiment in the U.S. Laboratory/Destiny.
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