Swarms of spacecraft are an idea that has been growing in interest in the last few years. This work focuses on the strategies and costs for the maintenance of a swarm of a large number of spacecraft in a close neighborhood (in our case represented by an sphere but any other confining geometry could be considered) for long periods of time. One of the main issues that one encounters when optimizing the sequence of control maneuvers for a large group of spacecraft is the huge number of variables and constraints. Our methodology considers a hierarchical structure that accounts both for collision avoidance and degradation of the con- finement region of the spacecraft swarm. In an strobe way, usually counted in one or few orbital periods, a few spacecraft of the set are selected and a suitable and efficient control procedure is applied to them, assuring this way computational efficiency