Nonlinear attitude controller design based on variable structure control with sliding mode

Proposes a stabilizing control law for a nonlinear spacecraft´s attitude control system based on variable structure control with sliding mode. Taking the characteristics of the attitude system and the requirements of the control task under consideration, we conduct the controller design procedure in two steps. Provided that both the three body angular velocities and the three attitude angles can be offered directly by the spacecraft, angle errors are chosen as new state variables. A group of conditions which body angular velocities should satisfy when angle error equations are not only asymptotically stable but also decoupled is presented. Consequently the above group of conditions is used to construct a group of switch surfaces. The nonlinear attitude stabilizing control law is solved by variable structure control method. A numerical simulation for a spacecraft´s attitude control system is performed. Simulation results show that the control law designed in the paper is effective