Dual Disturbance Observers Based Control for Relative Position and Attitude Coupled Spacecraft

When approaching non-cooperative target at rendezvous, servicing spacecraft is not only disturbed by environmental conditions, but also by flexible appendages such as sails. In addition, spacecraft with manipulator is also disturbed by the moment of manipulator. In this paper, the position and attitude tracking control of spacecraft in the process of approaching non-cooperative target at rendezvous is investigated under the multi-disturbance of manipulator and flexible appendages. Aiming at attenuating the modeled disturbance and the manipulator disturbance, two disturbance observers are designed for feed forward compensation of the elastic vibration and the manipulator disturbance. Then a composite controller with a hierarchical architecture by combining DDOBC(dual disturbance-observers-based-control) and H
_∞
control is designed, where DDOBC is used to reject the disturbance from the manipulator and vibration from the flexible appendages. Simulations are conducted to demonstrate the effectiveness of the proposed composite hierarchical control law.