Fault detection and recovery of spacecraft formation flying using nonlinear observer and reconfigurable controller

• A novel scheme for fault detection and recovery of spacecraft formations.
• The proposed scheme is based on a state observer and a reconfigurable controller.
• The state observer is designed based on the super twisting sliding mode technique
• The reconfigurable controller is developed using the sliding mode technique.
• Theoretical proofs along with simulation results validate the proposed scheme.

This paper addresses fault tolerant spacecraft leader–follower formation control through the development of a fault observer and a re-configurable control law. Using carrier-phase differential GPS measurements for relative position and velocity, an estimate of the true thrust output on all three axes of the follower spacecraft is accomplished using a pair of super twisting sliding mode observers. Modifications on the ‘broken’ super twisting observer are applied in order to accommodate additional sensor feedback inputs for relative position and velocity between the leader and the follower spacecraft. A fault observer estimating the true thrust output of the follower spacecraft is developed which functions in parallel with a re-configurable control law capable of formation maintenance in the event thrust in the along-track and radial axes are no longer available. Simulation results show fault reconstruction and recovery with formation stabilization even in the presence of external disturbances which are unknown to both the controller and the observer.