Adaptive external torque estimation by means of tracking a Lyapunov function

A real-time method is presented to adaptively estimate three-dimensional unmodeled external torques acting on a spacecraft. This is accomplished by forcing the tracking error dynamics to follow the Lyapunov function underlying the feedback control law. Some stability analysis is provided for the case of external torques. The methodology can be generally applied to Lyapunov-derived control laws and is not specific to the control law used in this paper. The adaptive external torque estimation is very robust in the presence of measurement noise, since a numerical integration is used instead of a numerical differentiation. Spacecraft modeling errors, such as in the inertia matrix, can also be compensated for by this method. Several examples illustrate the practical significance of these ideas.

Adaptive external torque estimation by means of tracking a Lyapunov function Academic Article