The business function in charge of realizing the Space Systems and their sub parts is the A.I.T Function. It deals with the planning and the execution of the Assembly, Integration and Test activities. In the business context of Sitael s.p.a. that aim to the qualification of a modular satellite platform, suitable both for the realization of constellations and for the application in different missions, the thesis work aim to analyze the AIT activities flow. For each activity input, output, resources and constraints are examined in order to coordinate them to the logic and actors foreseen by the V-Model for System development and to the milestones baselined by the ECSS for the Space Project realization.