Variable Swarm Strategy for small spacecraft

Recently, the concept of controlling a large group of spacecraft has been studied extensively in literature for different applications. Swarms of microsatellites are an attractive alternative to traditional large spacecraft due to the resulting enhancement in robustness of the overall mission architecture while reducing the cost of each platform. The Guidance, Navigation & Control (GNC) subsystem of the space system is required to drive and keep the satellites formation towards multiple different configurations, which are imposed by the mission objectives. It is relevant to investigate low computational effort algorithms enabling spacecrafts to achieve and keep a formation by ensuring obstacle avoidance. The Artificial Potential Field (APF) method provides simple and effective collision-free path planning for practical terrestrial robotics control. This thesis objective is the design of an APF based method to guarantee the creation of a spacecrafts swarm formation, where each spacecraft is equidistant from each other. The performance of the proposed method are evaluated combining the APF with a Proportional Derivative (PD) controller, and by means of extensive simulations. Each spacecraft, starting from a random initial position, moves to achieve the formation centered in the desired position. These simulations were conducted both considering the spacecrafts as the only entities in orbit and also considering both fixed and moving obstacles. The capability of the swarm to rearrange the formation according to spacecrafts number is also analyzed. In this case, once the formation has been created, one of the spacecrafts is considered inoperative and the remaining ones should rearrange themselves in a different configuration whose mean position is driven to the desired one. Finally, a proximity operation scenario was considered to evaluate the maximum dimension of the obstacle that the swarm of spacecrafts is able to avoid during the formation acquisition maneuver. The results verify the effectiveness of the algorithm to guide the spacecrafts towards the desired configuration while avoiding obstacles using minimum computational effort.