Effects of total sleep deprivation on performance in a manual spacecraft docking task

Sleep deprivation and circadian rhythm disruptions are prevalent among shift workers and astronauts, significantly impacting cognitive performance and increasing the risk of occupational accidents. Fatigue is a major concern in high-performance environments, including spaceflight, where even minor performance decrements can have catastrophic consequences. Astronauts often experience chronic sleep deprivation due to environmental and psychological factors inherent to space travel, and irregular sleep-wake cycles exacerbate these effects. Previous research has shown that sleep deprivation impairs various cognitive functions, including psychomotor control, problem-solving, and attention. In astronauts, insufficient sleep correlates with impaired sustained attention and mood. Manual spacecraft docking, a mission-critical task, requires sophisticated cognitive and motor skills. While the relationship between cognitive performance and docking performance has been explored, the impact of sleep deprivation on this complex operational task remains unclear. This study aimed to determine the effect of total sleep deprivation on manual spacecraft docking performance and to investigate the role of sustained attention in this impairment, using the PVT as a sensitive measure of sustained attention. The hypothesis was that both docking accuracy and progression through varying task difficulty levels would deteriorate after sleep deprivation compared to a well-rested control condition.

Numerous studies demonstrate the negative effects of sleep deprivation on performance across various professions, including healthcare, transportation, and military. In aviation, sleep-deprived pilots show degraded psychomotor control and attention. Spaceflight presents unique challenges, with astronauts experiencing reduced sleep duration and quality due to environmental factors (noise, altered light cycles, hypoxia, hypercapnia) and psychological factors (isolation, confinement, stress). Studies have linked sleep deprivation in astronauts to impaired sustained attention and mood. The 1997 Progress space shuttle crash, during a manual docking maneuver, highlighted the potential risks of fatigue in space. Existing research on sleep deprivation's effect on complex tasks like simulated docking has produced mixed results, possibly due to small sample sizes or the absence of control groups. Some studies reported no performance decrement, possibly attributing this to the novelty and motivational aspects of the tasks. However, the impact of sleep deprivation on spaceflight-relevant operational performance requires further investigation with larger and more controlled studies.

Sixty-six healthy participants (62 after exclusions due to missed sessions or technical issues) aged 18-39 (mean 24.84, SD 4.69), with a balanced gender distribution (28 women, 34 men), participated in a randomized, counterbalanced crossover study. Participants were screened for pre-existing sleep problems, extreme personality traits, and depression. They were required to maintain a regular sleep schedule (23:00-07:00 h) for at least one week prior, monitored via actigraphy and sleep diaries, and caffeine consumption was restricted. Participants spent five days and four nights in the laboratory, undergoing two test sessions (control and sleep deprivation) on days three and five. The control condition involved an 8-h sleep period (23:00-07:00 h) before the 13:00-15:00 h testing. In the sleep deprivation condition, the 07:00-09:00 h testing followed approximately 24 h of continuous wakefulness. The main tasks were a 6 degrees-of-freedom (6df) manual docking simulation and the PVT. The 6df simulation, based on the Russian TORU system, used an adaptive version with eleven docking task designs across five difficulty levels. Participants received instructions and feedback after each trial, with difficulty level adjusted based on performance (accuracy ≥ 0.85 for success). The PVT involved a 10-minute reaction time task with varying inter-stimulus intervals (2-10 seconds). Response speed (reciprocal reaction time) and the number of lapses (response time >500 ms) were recorded. Data analysis involved linear mixed models (docking accuracy and PVT) and the Wilcoxon signed-rank test (highest level achieved in 6df). Susceptibility to sleep deprivation was assessed by comparing PVT performance between conditions, with interaction effects examined. The study was approved by the relevant ethics committee and registered with the German register for clinical studies.

Sleep deprivation significantly increased self-reported sleepiness (KSS) and impaired PVT performance, with reduced response speed and increased lapses. Docking accuracy decreased significantly after sleep deprivation, but only at higher difficulty levels (levels 4 and 5). There was no significant difference in the highest difficulty level successfully completed between conditions. The linear mixed model showed significant main effects of difficulty level, session (improvement from first to second session), and condition (lower accuracy after sleep deprivation). A significant interaction between level and condition indicated that the sleep deprivation effect was most pronounced at higher difficulty levels. Men showed significantly higher docking accuracy than women, and accuracy decreased with age. Including PVT response speed susceptibility in the model removed the main effect of condition on docking accuracy, but the interaction between level and condition remained significant, indicating that individuals more susceptible to sleep deprivation on the PVT showed greater impairment in docking accuracy at higher difficulty levels. The interaction with the number of lapses on the PVT was not significant.

The study demonstrates a detrimental effect of total sleep deprivation on manual docking performance, particularly at higher difficulty levels. This contrasts with some previous studies, potentially due to methodological differences (smaller sample sizes, lack of control group). The lack of significant difference in the highest level reached might be due to limited variation in the task's difficulty. The improved performance from the first to the second session suggests a learning effect that occurred even under sleep deprivation. The finding that PVT response speed susceptibility to sleep loss explained the main effect of sleep deprivation on docking accuracy highlights the importance of sustained attention in this complex task, although it doesn't fully account for the observed impairments. The motivational aspect of the task, especially at easier levels, may have compensated for sleepiness to some extent. The study acknowledges the limited age range and the potential influence of gaming experience on performance.

This study demonstrates that total sleep deprivation impairs performance in a complex manual docking simulation, particularly at higher difficulty levels. This impairment is partially explained by reduced sustained attention, as measured by the PVT. While the engaging nature of the task may compensate for sleepiness at easier levels, even small performance decrements can be critical in safety-critical operations. Future research should explore the impact of exhaustive training on susceptibility to sleep loss and the use of operational performance measures to assess astronaut readiness for duty.

The study's adaptive task design, while allowing assessment in untrained participants, resulted in varied numbers and difficulty levels of completed tasks, making comparisons challenging. The lack of prior training with the docking simulation might have increased performance variability, potentially masking some effects. The sample, primarily young students, might not fully represent the astronaut population. The order effect observed, although addressed by the counterbalanced design, is a potential limitation. The study didn't directly quantify learning under sleep loss. Finally, the difference in testing times between conditions suggests the possibility of circadian phase effects, although these are expected to be small given the timing of testing.