A novel saturated attitude controller for rigid body subject to bounded external disturbances

We propose a new smooth attitude controller for rigid body in the presence of input saturation and external disturbances. The controller is composed of three parts, i.e., the quaternion part, the saturated velocity part, and the bounded disturbance compensation part. The disturbance compensation part is derived from disturbance observers. The main contribution of the study is that the constructed observers can globally asymptotically track the external disturbances, given the disturbances are twice differentiable with bounded derivatives. Simulations are conducted to validate the effectiveness of the proposed controllers.