Robust flight control of a typical RLV during re-entry phase

Due to the inherent nonlinearities of Reusable Launch Vehicle (RLV) dynamics, its changing properties during flight and the engineering difficulties to predict its aerodynamics with high levels of fidelity, flight control requires strategies that allow to cope up with the non-linearity of the model and assure robustness in the presence of inaccuracies and changes in configuration. This paper presents a flight control strategy based on dynamic inversion controller which is designed for the re-entry phase of Reusable Launch Vehicle. In order to solve the robustness problem of regular explicit Nonlinear Dynamic Inversion (NDI) control law, the Incremental Nonlinear Dynamic Inversion (INDI) control law is proposed. Sensitivity to model mismatch is eliminated by feeding back state acceleration in INDI approach. The improved control law design is validated for re-entry phase of RLV for nominal and aerodynamic perturbation cases. Analysis of simulation results reveal that the robustness of the control law is increased.