Maintaining intact cognitive performance is a high priority for space exploration. This review seeks to summarize the cumulative results of existing studies of cognitive performance in spaceflight and analogue environments. We focused on long-duration (>21 d) studies for which no review has previously been conducted. There were 11 published studies identified for long-duration spaceflight (N = 42 subjects) as well as 21 shorter spaceflight studies (N = 70 subjects). Overall, spaceflight cognitive studies ranged from 6-438 d in duration. Some 55 spaceflight analogue studies were also identified, ranging from 6 to 520 d. The diverse nature of experimental procedures and protocols precluded formal meta-analysis. In general, the available evidence fails to strongly support or refute the existence of specific cognitive deficits in low Earth orbit during long-duration spaceflight, which may be due in large part to small numbers of subjects. The studies consistently suggest that novel environments (spaceflight or other) induce variable alterations in cognitive performance across individuals, consistent with known astronaut experiences. This highlights the need to better quantify the magnitude and scope of this interindividual variability, and understand its underlying factors, when predicting in-flight cognitive functioning for extended periods.

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The ability of the participants to adapt successfully to the Mars day suggests that future missions should utilize a similar circadian rhythm and fatigue management program to reduce the risk of sleepiness-related errors that jeopardize personnel safety and health during critical missions.

Carbon Dioxide (CO 2 ) removal is one of the primary functions of the International Space Station (ISS) atmosphere revitalization systems. Primary CO 2 removal is via the ISS's two Carbon Dioxide Removal Assemblies (CDRAs) and the Russian Carbon Dioxide removal assembly (Vozdukh); both of these systems are regenerable, meaning that their CO 2 removal capacity theoretically remains constant as long as the system is operating. Contingency CO 2 removal capability is provided by Lithium Hydroxide (LiOH) canisters, which are consumable, meaning that their CO 2 removal capability disappears once the resource is used.With the advent of 6 crew ISS operations, experience showing that CDRA failures are not uncommon, and anecdotal association of crew symptoms with CO 2 values just above 4 mmHg, the question arises: How much lower do we keep CO 2 levels to minimize the risk to crew health and performance, and what will the operational cost to the CDRAs be to do it? The primary crew health concerns center on the interaction of increased intracranial pressure from fluid shifts and the increased intracranial blood flow induced by CO 2 . Typical acute symptoms include headache, minor visual disturbances, and subtle behavioral changes. The historical database of CO 2 exposures since the beginning of ISS operations has been compared to the incidence of crew symptoms reported in private medical conferences. We have used this database in an attempt to establish an association between the CO 2 levels and the risk of crew symptoms. This comparison will answer the question of the level needed to protect the crew from unacceptable risk of acute effects. As for the second part of the question, operation of the ISS's regenerable CO 2 removal capability reduces the limited life of constituent parts. It also consumes limited electrical power and thermal control resources. Operation of consumable CO 2 removal capability (LiOH) uses finite consumable materials, which must be replenished in the long term. Therefore, increased CO 2 removal means increased resource use, with increased logistical capability to maintain necessary resources on board ISS. We must strike a balance between sufficiently low CO 2 levels to maintain crew health and CO 2 levels which are operationally feasible for the ISS program. Nomenclature BMD