0337 Impact of Sleep Schedule Changes on the International Space Station

Abstract Introduction Astronaut crews have historically averaged six hours of sleep per night. In recent years, ISS crew have had more stable schedules, with consistent bed and wake times. Despite these improvements, there remain uncontrollable operational events that require crewmembers to shift their sleep. It is unclear what impact these acute schedule changes have on sleep and performance outcomes. The aims of this analysis are to characterize approaches to sleep shifting and to determine the impact on sleep outcomes and crew alertness and performance. Methods Crewmembers (n = 20) on the ISS were provided with actiwatches that they wore before flight, inflight, and immediately upon return. They were scheduled for 8.5 hours of sleep per day, between 2130-0600, unless operational events took place during the sleep episode. We characterized the impact of two types of sleep shifts, including splitting the daily sleep opportunity in two (“split sleep”) and shifting the entire sleep opportunity later, following the operational event. Results Ten crewmembers had 15 episodes of split sleep while inflight. These periods surrounded seven separate operational events that interfered with their nominal sleep window. The first sleep opportunity typically occurred before the disrupting event, while the second took place the following morning. Sleep duration was shorter (M1=2.60(0.80) vs. M2=4.11(1.51)) and efficiency lower (M1=74.72(13.94) vs. M2=82.50(8.99)) during the first sleep opportunity. When aggregating the two periods, the sleep opportunity lasted 7.08(1.06) hours. Thirteen individuals had 28 phase delayed sleep episodes following 11 disruptive events. These single sleep episodes were 5.99(1.05) hours long, sleep efficiency averaged 84.31(7.71), and the sleep opportunity was 6.85(0.67) hours. On remaining nights, crewmembers averaged 6.63(0.49) hours of sleep with a sleep efficiency of 82.51(3.41) and sleep opportunity of 7.45(0.51). Conclusion Scheduling astronauts for off-nominal operations came with some costs. When crew split their sleep, they slept longer than the average, while a delay reduced sleep. Crew had shorter sleep opportunities when forced to sleep outside of the nominal window, leading to improved sleep efficiencies. Further study is needed to determine the best scheduling approaches to accommodate uncontrollable operational events. Support (if any)