Anti-disturbance nonlinear optimal controller design for RLV

The reentry attitude control of the reusable launch vehicle (RLV) is challenging due to disturbances. Therefore, an anti-disturbance nonlinear optimal controller (ADNOC) design scheme is presented. Firstly, a fast and slow dual-loop control system is designed based on time-scale separation principle. The linear transformation of attitude angular rate is developed. By the optimization of state dependent Riccati equation (SDRE), the nonlinear optimal control law is designed to generate optimal control commands. Then the nonlinear disturbance observer (NDO) is implemented in order to estimate the unknown disturbances. The estimation of disturbances is utilized for compensation in the controller. Simulation results show that the ADNOC obtains good tracking performance and can be able to suppress the disturbances effectively.