Attitude controller for reentry vehicles using state-dependent Riccati equation method

XIE Dao-cheng(谢道成), WANG Zhong-wei(王中伟), ZHANG Wei-hua(张为华)

(College of Aerospace Science and Engineering, National University of Defense Technology,
Changsha 410073, China)

Abstract:To get better tracking performance of attitude command over the reentry phase of vehicles, the use of state-dependent Riccati equation (SDRE) method for attitude controller design of reentry vehicles was investigated. Guidance commands are generated based on optimal guidance law. SDRE control method employs factorization of the nonlinear dynamics into a state vector and state dependent matrix valued function. State-dependent coefficients are derived based on reentry motion equations in pitch and yaw channels. Unlike constant weighting matrix Q, elements of Q are set as the functions of state error so as to get satisfactory feedback and eliminate state error rapidly, then formulation of SDRE is realized. Riccati equation is solved real-timely with Schur algorithm. State feedback control law u(x) is derived with linear quadratic regulator (LQR) method. Simulation results show that SDRE controller steadily tracks attitude command, and impact point error of reentry vehicle is acceptable. Compared with PID controller, tracking performance of attitude command using SDRE controller is better with smaller control surface deflection. The attitude tracking error with SDRE controller is within 5°, and the control deflection is within 30°.

Key words:reentry vehicle; attitude controller; nonlinear control; state-dependent Riccati equation; Schur algorithm; tracking performance