  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.
