Second-order Terminal Sliding Mode Control for Near-space Vehicles Based on Disturbance Observer

For a class of affine nonlinear near space vehicle system, a second-order terminal sliding mode control with double-power reaching law is designed to make the attitude angle tracking command signal. Double-power reaching law is selected to ensure that the tracking error can move to the sliding mode surface for a finite time and keeps moving along the sliding mode surface until the tracking error converges to zero. Nonlinear disturbance observer is proposed to estimate the external disturbances and the parameter uncertainty. Lyapunov theory proves the validity of this method. Finally, simulation results show the feasibility of the control scheme.