Anti-unwinding robust attitude control of spacecraft with limited states measurement

This paper proposes a control methodology for the attitude regulation of a rigid spacecraft without the measurement knowledge of angular velocities and is affected by parametric uncertainties and external disturbances. A non-singular terminal sliding manifold based controller is developed to regulate the orientation of spacecraft. The proposed controller uses the estimated value of angular velocity by using a finite time state observer. The overall system stability is theoretically proven by Lyapunov analysis which ensures the convergence of attitudes to their respective equilibrium point. Moreover, it shows that the proposed controller eludes the unwanted phenomenon of unwinding where the unnecessary large maneuvering path is taken by the spacecraft to reach the desired orientation. The effectiveness of the proposed controller is demonstrated by carrying out the numerical simulations for different initial conditions.