Controller Design for Lateral Dynamics of Reusable Launch Vehicle by H-infinity Mixed Sensitivity approach

Abstract

Abstract During reentry flight regime of a typical Reusable Launch Vehicle (RLV), there is rise in dynamic pressure which increases the coupling between yaw (directional) and roll (lateral) dynamics. High uncertainty on aerodynamic coefficients due to less number of wind tunnel tests, makes it essential to use robust control design techniques to design a controller for any new aerodynamic configuration of RLV. Control system design during critical flight regime of RLV using 'H-infinity Mixed Sensitivity' approach is addressed in this paper. The main bottle neck in using H-infinity approach is the lack of guidelines in finding weighting functions to achieve required time and frequency domain specifications. It is seen that the solution process becomes easier if the coupling and damping requirements are first addressed by designing the aileron to rudder interconnect (ARI) gain and roll-yaw rate gains using classical approach and then applying the H-infinity procedure on the plant model, updated with the designed ARI and rate gains, to shape the sensitivity and complementary sensitivity functions. This is the main contribution of our paper. This approach has resulted in highly robust controller against plant parameter perturbations. The yaw-roll coupling, which is the main problem, could also be eliminated to a greater extent.