For manned long-duration missions to the Moon and Mars, there is a need for a Mission Execution Crew Assistant (MECA) that empowers the cognitive capacities of human-machine teams during planetary exploration missions in order to cope autonomously with unexpected, complex and potentially hazardous situations. MECA requirements are being derived via a cognitive engineering method, which addresses operational, human factors and technological aspects with their mutual dependencies. This method follows an iterative process of specification, evaluation and refinement to establish a sound - theoretical and empirical founded-set of requirements. It distinguishes three types of iterations: system-design review, scientific discourse and simulation-based evaluation. The first two iterations provided a set of requirements for distributed human-machine collaboration on the Moon or Mars. © 2006 IEEE.