Predictive guidance and robust fault-tolerant control for RLVs

Abstract:

A joint design based on improved predictor-corrector guidance and robust fault-tolerant attitude control was proposed to realize the re-entry accurate guidance and robust fault-tolerant control for reusable launch vehicles (RLVs). First, an improved predictive guidance law with modified magnitude model of bank angle and corridor function of track angle was designed. Combined with the nominal profile of the angle of attack, the input command of the attitude system was calculated online. Then, a modified tracking differential disturbance observer was presented to estimate the system uncertainty/disturbance and the actuator faults. The estimation accuracy of compound disturbance was further improved by adding feed-forward term to the observer. Finally, an auxiliary anti-saturation system was designed to tackle the problem of the saturation of control surfaces, and a sigmoid saturation function was utilized to enhance the control performance of the backstepping method in the angular rate loop. Simulation test on 6 degree-of-freedom (DOF) guidance control system shows that the RLV was capable of tracking attitude angle commands precisely in the presence of the compound disturbance of attitude system, the actuator faults and saturation, and the RLV trajectory reached the re-entry terminal area with satisfying constraints. Thus, the proposed method can realize the re-entry guidance accurately and solve the problems of attitude system uncertainty, actuator faults and saturation, indicating its satisfactory robustness and fault-tolerant capability.