Disturbance observer based control of a flexible Reusable Launch Vehicle

In this paper a disturbance observer based PD controller is proposed for a Reusable Launch Vehicle (RLV) in ascent phase. Disturbance observer based control is an effective way of achieving disturbance rejection and robustness to plant uncertainties. Here it is used for observing and stabilising the flexible mode in RLV. The disturbance observer makes the actual flexible plant dynamics similar to that of nominal rigid body dynamics within a limited frequency range. The classical gain stabilisation approach for stabilising bending mode is also presented. Both methods are compared and the advantages of disturbance observer based PD control over the gain stabilised PD control are discussed.