Two space simulation studies for the European Space Agency found that interpersonal tension increased in the beginning, around the middle, and toward the end of the confinement. This article reports data from a third study where this issue was further examined. Three subjects were confined in the MIR space station simulator in Moscow for 135 days. Communication analysis, peer rating, questionnaires, and interviews were used to assess crew tension. The temporal pattern found in this study corresponds to the previous findings. The beginning of the period was characterized by competition over leadership. Decreased crew cohesion and aggression toward the mission control marked the middle of the confinement. In the final weeks, open conflicts emerged, and one member was socially excluded. Joking occurred frequently in the first half of the confinement, whereas negative emotional expressions increased in the second half. These results might assist planners in anticipating behavioral problems during space missions.