After a long, hard day, who doesn't long for the comfort of a soft mattress and the embrace of a good night's sleep? Still, for many people, a full-night's rest is a rather elusive thing. Factors ranging from stress to competing priorities often prevent us from going to bed early enough to get the proper amount of sleep we need. This reality also is true for astronauts living and working in space, and some of them have trouble sleeping in space.

Rest is a fundamental necessity for most species, and humans are no different. As NASA prepares to send humans farther into space than ever before, we need to understand fully the impacts of long-duration spaceflight on our astronauts, including the health, performance and behavioral challenges they will face along the journey.

Understanding the effects of spaceflight on sleep is critical to ensuring crew members are appropriately rested, alert and focused on their missions as they explore asteroids and eventually Mars. Gaining this insight is just one of the myriad reasons humans have been living and working in space for more than 13 years aboard the International Space Station.

Although the agency has been aware for decades of sleep deficiency in some astronauts, results of a recent NASA-funded study published in The Lancet Neurology journal show just how much sleep deficiency astronauts may experience in the weeks leading up to and during spaceflight.

The results from this study will help inform our doctors as they identify and implement countermeasures that can ensure astronauts are able to get the same quality and quantity of sleep in space as they do on Earth.

"The study provided us valuable data and insights into incidence and severity of sleep deficiencies in space and has driven the development of countermeasure approaches that are already being tested aboard the space station," said Bill Paloski, manager of the Human Research Program.

"We have similar studies in progress and plan to address multiple other risk areas aboard the space station, and we expect to fully utilize that valuable platform in this endeavor for as long as it remains aloft."

Researchers from Brigham and Women's Hospital, Harvard Medical School, Boston, and the University of Colorado, Boulder, studied the sleep patterns of 64 astronauts on 80 space shuttle missions and 21 astronauts aboard the space station before, during and after spaceflight. Although the crew members' schedules allowed for 8.5 hours of sleep per day, the astronauts who participated in the study averaged only about six hours of sleep while in space.

NASA's Human Research Program (HRP) funded this study to understand better the levels of sleep deprivation experienced by astronauts during spaceflight and its potential to impact crew health and performance during the mission.

"This study is the latest result from our long-term research into sleep, fatigue and performance in astronauts," said Mark Shelhamer, HRP's chief scientist.

"Appropriate countermeasures and interventions had already been implemented based on preliminary findings from this work. HRP continues to study these issues, including the correlation of sleep impairment with potential performance deficits. In high-performing individuals in a demanding environment, we explore every possible avenue in order to maintain performance and the ability to respond to anomalies."

NASA scientists and NASA-funded external researchers, including those involved in this study, have investigated issues related to astronaut sleep deprivation for decades. No single reason has been found as to why astronauts may sometimes go without a good night's sleep in space.

Several factors may contribute to difficulty sleeping including disrupted circadian rhythms. The circadian rhythm is a 24-hour cycle that tells our bodies when to sleep and regulates many other physiological processes. It is also possible that because of the effects of microgravity people need less sleep in space.

"NASA studies are helping us better understand individual differences in response to sleep loss, biomarkers for detecting those differences, and monitoring tools and countermeasure strategies to mitigate sleep problems," said Lauren Leveton, NASA element scientist for Behavioral Health and Performance in the Human Research Program.

"Efforts are planned to understand more fully the spaceflight environment and the role that other factors may play in reducing or promoting sleep, including microgravity and various psychological stressors such as levels of workload, stress and adequate sensory stimulation. Research is looking toward more individualized countermeasures to ensure sleep quality and quantity for future spaceflight missions," added Leveton.

Astronauts work in harsh, complex environments where they are sometimes subjected to uncomfortable and high stress situations. There are many professionals on Earth in similar work environments. This research into sleep deficiency and deprivation also has benefits to people on Earth including airline pilots and professional drivers who spend hours behind the wheel.

What we're learning from astronauts in space as we work to prepare for human exploration missions into deep space can help prevent fatigue in commercial airline cockpits; it can prevent accidents caused by drowsy truck drivers on highways and it can ensure that doctors are completely focused in operating rooms around the world.

NASA continues to work on countermeasures against sleep and circadian rhythm disruption. Future developments in medicine and technology should soon help astronauts in space rest easier.