Robust Position and Attitude Control for Spacecraft Formation Flying

Abstract

An integrated approach combining a state-dependent Ricatti equation (SDRE) and an extended Kalman filter (EKF) is applied to spacecraft formation flying for robust orbital and attitude maneuvers. The formation flying considered in this study is a two-spacecraft formation with a bounded out-of-orbit plane relative motion. The chaser is required to simultaneously perform large position and angle maneuvers with sufficient accuracy. The chaser is then required to maintain a relative orbit expressed in the local-vertical-local-horizontal frame with respect to the target and align its attitude with the target attitude for more than one orbital period. The controls of the chaser are formulated as a nonlinear optimal regulator problem using their highly nonlinear dynamics. To test the robustness of this integrated approach, highly nonlinear dynamics, including external disturbances, are employed as the truth plant that is then used to generate the measurements for an EKF. The tracking error is then computed between the true plant and the desired state. A six degrees-of-freedom simulation of a two-spacecraft flying formation is used to demonstrate the robustness of this integrated approach to external disturbances and plant uncertainties. The integrated approach also has an effect well under the large uncertainty of the chaser moment of inertia.