The authors report the results of an ongoing study that investigates the effects of crew size, composition, mission duration, and mission interval on behavior and performance among polar and space expeditions. The standardized rates for a behavior/performance indicator constructed during the pilot study displayed distinctive patterns across different crew profiles and settings. Then, a further analysis over the missions in the pilot sample found compelling information suggesting that several factors created specific differentials between outside (baseline) groups (e.g., mission controllers, "folks back home") and groups in extreme environments. These differentials reflected how the passage of time was subjectivized by crews and how the expeditionary situation was otherwise defined differently from baseline. These analyses suggest that the definition of the long-duration mission, such as a mission to Mars, likely involves more than the issue of real-time duration. Also, crew size and composition of such ventures need to be examined in light of social and behavioral information that can be obtained from the expeditionary record. These analyses hold important implications for habitat and workplace design in extreme environments, such as those to be deployed for Mars surface operations.