Nonlinear optimal control of spacecraft approaching and tracking a non-cooperative maneuvering object

In the space operation tasks of a non-cooperative target, it is crucial for the chaser to approach to the target and observe it in a specified close position. In this paper, for the six degrees of freedom control of approaching and tracking the non-cooperative target, the model of attitude and orbit coupled dynamics is set up based on the orbit dynamics described in the line-of-sight coordinate frame and the attitude dynamics described in the relative error of quaternion in the body coordinate frame. IN view of nonlinearity, time-variability and computational speed, the θ-D control method is employed to control the attitude and orbit coupled dynamics for approaching and tracking. In order to reduce the control error of the target with orbit and attitude maneuver, Lyapunov min-max approach is used to design the θ-D controller so that when the non-cooperative target is maneuvering and tumbling, the control accuracy can be improved. The simulation results confirm the validity of this model and the good tracking performance of the proposed controller.