Page:Risk of performance errors due to sleep loss, circadian desynchronization, fatigue, and work overload.pdf/22



Long-duration lunar missions will be marathon-like events that are similar in nature to the current ISS increments. During these missions, both ground and flight crews will experience high-tempo operations and shift work. As was noted above, unfamiliar day-night cues could affect the circadian system and the subjective need to sleep. As a result, for long-duration lunar missions, it is estimated that human performance errors due to sleep loss, fatigue, extended work shifts, circadian desynchronization, and work overload could occur.

For a Mars mission, this risk remains relevant and important, although certain aspects of the risk may vary for the different mission phases. The initial transit to Mars is anticipated to be similar to the ISS long-duration experience with regard to sleep loss, extended work durations, and workload. It is anticipated that this transit will exclude the slam shifting and high-tempo schedules that are similar to the dockings and critical mission activities that were experienced during the building of the ISS.

On the surface of Mars, work activities may consume a large part of crew time; the slam shifting that can lead to circadian desynchronization should be absent from a Mars scenario as the crews will, of necessity, manage their own timelines. It is suspected, however, that daylight is not bright on the surface Mars; the sunlight on Mars is about one-half of the brightness of that seen on Earth, and the martian sky does not appear blue but pink due to suspended dust, which means that the surface of Mars is, in fact, darker than what is experienced on Earth (Murphy, 1997). The spectrum of light wavelengths is also different on Mars than on Earth. This difference in light exposure may complicate the entrainment of circadian rhythms, since the circadian system is most sensitive to blue wavelengths (Brainard et al., 2001), which are less prevalent on Mars than on Earth (Murphy, 1997).

Additionally, Mars has a day-night cycle (lasting 24 hours 39 minutes) that differs from that on Earth, which, as evidenced by recent ground studies, may pose challenges to performance. Sleep disruption and subjective decrements in alertness and performance were reported to be very burdensome to the scientists and engineers at the NASA Jet Propulsion Laboratory who lived on a Mars sol schedule while working on the Mars exploration rovers (MERs) (Bass et al., 2004; Czeisler et al., 2001). A study by DeRoshia et al. (2007) on self-report findings from MER operations personnel showed increased fatigue levels among 82% of the participants, as well as increased levels of sleepiness and irritability. Reduced levels of concentration and energy were also reported by most of the participants. The degree to which the physiological challenge of living on the Mars sol can threaten the success of a mission is described further in the appendix of the DeRoshia et al. report.

Subjects who were living on a laboratory-simulated Mars sol schedule experienced sleep disruption and decrements in alertness and performance (Wright et al., 2006; 2001). Most humans cannot adapt to this non-24-hour day without adequate countermeasures (Gronfier et al., 2007). Performance and circadian entrainment data have just been collected from the Mars Phoenix scout lander (MPSL) mission (May 25–Sep 1, 2008) ground crew who were living on a Mars sol (L Barger, unpublished results, 2008). From these previous studies and a preliminary review of the MPSL data, it is expected that future crews who are traveling to Mars and the ground crews who will support the Mars missions will experience similar decrements in sleep, circadian alignment, performance, and alertness. As a result, for Mars missions, it is estimated that human performance errors that are due to sleep loss, fatigue, extended work shifts, circadian desynchronization, and work overload could occur.