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  Executive Summary Data that have been collected during space flight missions consistently indicate that sleep loss, circadian desynchronization, fatigue, and work overload occur, to varying degrees, for some individuals. Few studies of performance have been conducted in flight, however, and the findings that have been generated remain unclear as to how a crew member's performance during space flight is directly impacted by sleep loss. Extensive ground-based scientific literature, including controlled laboratory studies and data that have been gathered from industries, demonstrates that the degree of sleep and circadian disturbances that are often experienced by astronauts result in performance errors and may also impact long-term health.

Space flight evidence regarding sleep loss primarily includes data that were collected through controlled studies (Category II ) as well as through self-report (Category III). These evaluations, which have focused on short-duration (fewer than 30-day) missions, have provided data from astronauts' daily sleep logs, polysomnography, and actigraphy. These data have characterized sleep in space, overall, as shorter, less restful, and more interrupted than sleep on Earth. Circadian rhythms may also be misaligned due to scheduling constraints, with the result that fatigue (physical and mental) from work overload has been reported (Scheuring et al., 2007).

Questions, however, remain regarding the nature of sleep and circadian rhythms on long-duration space flight missions. Despite the fact that ISS construction has been under way for 9 years, systematic data collection to address this issue has only been undertaken recently. In light of ground-based evidence on sleep-loss-related performance effects, it is critical to understand the various factors that exist in the space flight and long-duration mission environment, and to identify ways in which sleep and circadian rhythms can be protected for crews who are flying on ISS and shuttle missions. NASA ground support personnel, as well as space flight crews, experience sleep loss, fatigue, circadian misalignment, and work overload. Ground teams that support robotic missions to Mars, as evidenced during the Mars Pathfinder, Spirit, Opportunity, and Phoenix missions, similarly face issues of sleep loss and circadian desynchronization.

As human space flight transitions from LEO (e.g., shuttle, ISS) to Exploration missions to the moon and Mars, and as NASA continues to support robotic missions to Mars and beyond, it becomes more important to characterize human risk factors accurately and adequately and to identify the ways in which to mitigate this performance risk safely and effectively. The first short-duration lunar missions, which will be similar to the shuttle missions, will seem to be fast-paced sprints as compared to the marathon-like races of later, longer lunar outpost missions (and ISS increments). Docking will require shifting of schedules for those in flight and for their support teams on the ground; the hurried schedule will likely include heavy workloads. Longer lunar missions will pose additional challenges to crews, including perpetual non-terrestrial day-night cues, environmental constraints, and extended periods of high-intensity workload. As the evidence reveals, crews on short- and long-duration lunar missions will need to be well-equipped and prepared for the potential performance and long-term health effects of sleep loss and circadian shifting.

To help characterize the kind of evidence that is provided in each of the risk reports in this book, the authors were encouraged to label the evidence that they provided according to the "NASA Categories of Evidence."

Category I data are based on at least one randomized controlled trial. Category II data are based on at least one controlled study without randomization, including cohort, case-controlled or subject operating as own control.

Category III data are non-experimental observations or comparative, correlation and case, or case-series studies. Category IV data are expert committee reports or opinions of respected authorities that are based on clinical experiences, bench research, or "first principles."