This research derives from a 60-day isolation study realized for the European Space Agency (ESA) as a simulation of space flights. Three goals were pursued in this study: (a) to study individual and group responses to the stress factors specific to the simulation; (b) to make a critical comparison of a variety of tools and methods used for this purpose; and (c) to express recommendations for future research. Direct methods (questionnaires, tests) and indirect methods (observation) were used in an individual and a whole group assessment. The group did not show important stress manifestations during the isolation period. It maintained its cohesion by opposing the external authority. Some tools were more efficient than others: The qualitative and indirect methods have revealed much more information than the quantitative or direct methods that reinforced one's defense to avoid criticism.