Research On The Control Of Spacecraft Rendezvous And Docking In An Elliptical Orbit

Spacecraft rendezvous and docking has always been considered as one of the hotspots in the aerospace field. Various kinds of aerospace missions depend on the successful rendezvous and docking between spacecrafts, such as on orbit assembly, supply of or-bital platforms, visitation of crew, etc. However, it remains a challenge to rendezvous with a non-cooperative target in an elliptical orbit at present. This dissertation focuses on the problems of the relative position and relative attitude control design for the space-crafts in an elliptical orbit. The main results are summaried as follows:First of all, the robust control problem of the relative position control for space-crafts in an elliptical orbit is discussed. On the basis of the Lawden equations, which are useful for the rendezvous and docking in an elliptical orbit, and the theory of input-to-state stability (ISS), a control law is designed to ensure that the relative distance and relative velocity of the spacecrafts are ISS with respect to disturbance acceleration. It is proved that, under the proposed control laws, the relative distance and relative velocity can converge to an arbitrary small neighborhood of zero by adjusting the design con-stants. Considering that, the presented control design is related to the orbit parameters of the target, such as orbit angular velocity, orbit angular acceleration and so on. These parameters are usually difficult to be measured real-timely. So the concept of input-to-state practical stability (ISpS) is introduced. A new control law, which is independent of these time-varying orbit parameters, is designed to guarantee that the closed-loop system is ISpS stable. Theoretical analysis and simulation examples are given to show the effectiveness of the proposed control schemes.Second, the relative position control for spacecrafts in an elliptical orbit with in-put saturation is considered. The input saturation phenomenon is described by a so-called dead zone operator model. Robust controllers are given, which guarantee the anti-saturation capacity and disturbance rejection capability of the whole system, based on the ISS and ISpS theory, respectively. The proposed controllers are independent of the real time information of orbit parameters of target spacecraft.Then, the rendezvous and docking problem in an elliptical orbit is discussed by us-ing inverse optimal method. A controller is designed for the Lawden equations without disturbance acceleration, which ensures that the relative distance and relative velocity of the spacecrafts are inverse optimal. The closed-loop system is asymptotically stable under the designed controller, and at the same time, is optimal with respect to a certain performance index incorporating a penalty on the relative distance, relative velocity and the control input. Then, the rendezvous problem with disturbance acceleration is con- sidered, and the inverse optimal controller is given, which ensures the ISS of the whole system.Sequentially, the sampled-data control problem for the rendezvous and docking system in an elliptical orbit is studied. The actual control process of rendezvous and docking can be regarded as a sampling-data control process. Based on the accurate but unknown discrete-time model of Lawden equations, a sampled-data contol law is presented, which guarantees the semi-global practical asymptotic stabilization (SPA) of the sampled-data system.Finally, discussing the attitude control problem for the rendezvous and docking system in an elliptical orbit. The attitude control process can be described as a track-ing process of a particular attitude maneuver. A robust control scheme is put forward, considering the uncertainty caused by the thruster nonlinearity, which ensures that the tracking error of attitude can converge to zero, asymptotically. Simulation examples are given to illustrate the proposed approaches.