Saturated attitude control for rigid body under input delay and pointing constraints

This paper designs the saturated attitude control law for the rigid body with constant input delay and pointing constraints. Specifically, a quaternion-based artificial potential function (APF) is proposed to encode the scalar fields about the desired attitude and pointing constraints. A time-delay-compensation-based controller is further developed and shows the uniform ultimate boundedness of system responses. Benefiting from the properties of the proposed APF and its gradient, the designer can assign the bound on the control a priori. Moreover, the local minima problem is excluded by the convergence of the Lyapunov-Krasovskii (LK) functionals rather than merely the convergence of gradient. The unwinding phenomenon associated with unit quaternion is avoided as well. Finally, numerical examples are furnished to show the effectiveness of the proposed method.