Sleep, circadian rhythms, and fatigue management in space flight operations

Abstract

Early in the history of human space flight, scientists realized that several factors in the space environment may adversely affect human function and performance. Among the principal concerns expressed were potential disturbances in circadian rhythms and the subsequent effects on performance and well-being. In addition to environmental changes such as microgravity and a sunrise and sunset every 45 minutes in low Earth orbit, several operational reasons were cited for the possible development of sleep disturbances and fatigue during space flight. Over the years, spaceflight investigations have confirmed that sleep disruption and circadian desynchrony are regular occurrences before and during missions, while terrestrial studies have increasingly shown that circadian desynchrony and sleep disruption carry serious health and performance implications. As a result, serious potential consequences remain associated with these risks. Recent efforts on behalf of flight medical operations, behavioral health and performance psychologists, psychiatrists, and researchers, mission planners, and habitability designers, as well as crewmembers themselves, have yielded fatigue prevention and sleep health initiatives across the United States and international space agencies. This chapter is intended to provide a description of sleep and circadian rhythms in space and relevant health and performance outcomes based on terrestrial evidence; operational strategies for risk mitigation; and current and future research oriented toward the assessment and treatment of fatigue on orbit.