Human Health and Performance Risks of Space Exploration Missions
Chapter 3
As previously detailed in this report, space flight evidence shows that astronauts lose sleep during flight, and ground-based evidence shows that sleep loss, fatigue, extended work shifts, circadian desynchronization, and work overload lead to performance errors, injuries, and accidents. A possible qualitative likelihood scale for performance errors during certain mission operational scenarios is Level 1 will most likely not occur Level 2 could occur Level 3 will most likely occur
Using this scale, the risk of performance errors due to sleep loss, fatigue, circadian desynchronization, and work overload is considered a Level 2 risk for ISS, lunar sortie, lunar long, and Mars missions. As this section addresses risk in the context of Exploration mission operational scenarios, the Level 2 risk for ISS will not be addressed.
Early, short-duration lunar missions will be fast-paced "sprints" that are similar in nature to current shuttle missions. Representatives from MOD anticipate that crew rotations and schedule shifting will still be required during lunar sortie missions, particularly at the beginning and end of a mission when rendezvous between vehicles (the crew exploration vehicle and the lunar lander) will need to occur (S Curtis, personal communication). While shifting should not be prevalent for the duration of the lunar sortie stay, crews will be required to shift while they are conducting critical mission tasks (S Gibson, personal communication, 2008).
In addition, the day-night cues on the surface of the moon will be different than the day-night cues on Earth. The elevated portions on the rim of Shackleton crater, which is a proposed landing site that is near the South Pole of the moon, may be exposed to light as much as 90% of the time (flight surgeon R Scheuring, personal communication, 2007). Anecdotal reports of individuals conducting 2- to 3-week exploration missions in the Arctic, where light exposure is, as it is on the moon, close to continuous, indicates that exposure to constant light may result in an individual being unable to detect a need for sleep and/or rest (flight surgeon R Scheuring, personal communication, 2007). If daily EVAs are conducted on the lunar surface, this level of sunlight exposure may stimulate the same physiological response as are experienced during Arctic expeditions. The high-tempo operations of multiple EVAs on the lunar surface could lead to work overload, extended wake durations, cumulative sleep loss, and excessive fatigue.
If the landing site is not at the lunar poles, however, but is at more equatorial locations, the day-night cycle on the moon involves 2 weeks of light exposure and 2 weeks of darkness. Either way, the natural lighting conditions will not be the same as those experienced on Earth due to the 24-hour clock. This means that astronauts will not be able to depend on natural lighting cues to help with their circadian rhythms.
Additional factors that are associated with sleep and circadian issues in the current space flight environment—e.g., high-tempo workloads and adaptation to the space flight environment—will remain risk factors on lunar sortie missions. Subsequently, performance errors remain a plausible risk during the short-duration missions to the moon and could occur during the lunar sortie mission scenario.
Risk of Performance Errors Due to Sleep Loss, Circadian Desynchronization, Fatigue, and Work Overload
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