Attitude Tracking of Uncertain Flexible Spacecraft Systems Subject to Unknown External Disturbances

In this paper, we investigate the attitude tracking problem of uncertain flexible spacecraft systems subject to external disturbances. In sharp contrast to existing results, the dynamics of flexible spacecraft systems and external disturbances are allowed to be unknown. To deal with the challenges by these unknown factors, we develop a class of nonlinear internal models which converts the attitude tracking problem of uncertain flexible spacecraft systems into a regulation problem of an augmented system. Furthermore, to overcome the difficulties caused by the unmeasurable modal variable, the uncertainty introduced by the internal model, and the cross-coupling of the uncertainties with the system state, we design an auxiliary dynamic system for auxiliary stabilization, a dynamic compensator for dynamic compensation, and a linearly parameterized transformation for adaptive regulation in sequence. By introducing a series of coordinate and input transformations, we propose an adaptive dynamic control law to achieve regulation of the augmented system and thus leading to the solution to the attitude tracking problem. In addition, we analyze the convergence issue of the estimated parameter to its true value by the persistently exciting condition. Finally, the effec tiveness of the developed approach is verified by its application to the attitude manoeuvre of a flexible spacecraft system in the presence of external disturbances.