Decentralized fault-tolerant control for multiple electric sail relative motion at artificial Lagrange points

This paper establishes a distributed fault-tolerant control framework for E-sail relative motion at Sun-Earth artificial Lagrange points, capable of accounting for unexpected E-sail actuator fault like effectiveness loss and bias error. The E-sail relative motion problem is formulated on the linearized dynamics, and the steering control is conducted by suitably adjusting the sail attitude and sail lightness number. The proposed control strategy facilitates the E-sail relative distances to evolve within a bounded range and to synchronously converge to the desired values, while collision avoidance of the relative motion is ensured as well. In particular, the locally shared information among the E-sails is assumed to be characterized by their relative distances only, thus extending the existing results where the inter-sail communication capability is static. The concept of distributing multiple E-sails in cluster flight is useful for the deep-space formation missions such as the DARWIN mission, in which a multi-point measurement of the space environment is required. Illustrative examples show the validity of the proposed method in a typical mission scenario.