Indirect adaptive control for attitude tracking of spacecraft with unknown reaction wheel friction

This paper examines attitude tracking problem with unknown friction torque of reaction wheels and external disturbances. A robust adaptive controller with parameter update law is proposed and analyzed. An indirect (nonregressor-based) approach to dealing with the effects of unknown friction torque and external disturbances is explored. This is done by not focusing on friction torque and external disturbances themselves, but on their bound, which allows the core information on friction torque and external disturbances to be extracted and used for control design. It is shown that the proposed controller guarantees not only stability of the resulting closed-loop system but also transient performance. Numerical simulations are presented to show the effectiveness of the proposed attitude tracking approach.