Physical agents such as robots are generally constrained in their communication capabilities. In a multi-agent system composed of physical agents, these constraints have a strong influence on the organization and the coordination mechanisms. Our multi-agent system is a satellite constellation, for which we propose a collaboration method based on incremental coalition formation in order to optimize individual plans and satisfy collective objectives. This involves a communication protocol and two coordination mechanisms: (1) an incentive to join coalitions and (2) coalition minimization. Results on a simulated satellite constellation are presented and discussed.