ADAPTIVE EXTERNAL TORQUE ESTIMATION BY MEANS OF TRACKING A LYAPUNOV FUNCTION

A real-time method is presented to adaptively estimate three-dimension al unmodeled external torques acting on a spacecraft. This is accompli shed by forcing the tracking error dynamics to follow the Lyapunov fun ction underlying the feedback control law. Some stability analysis is provided for the case of external torques. The methodology can be gene rally applied to Lyapunov-derived control laws and is not specific to the control law used in this paper. The adaptive external torque estim ation is very robust in the presence of measurement noise, since a num erical integration is used instead of a numerical differentiation. Spa cecraft modeling errors, such as in the inertia matrix, can also be co mpensated for by this method. Several examples illustrate the practica l significance of these ideas.