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Abstract-This paper describes the design of a nonlinear robust/adaptive controller for an air-breathing hypersonic vehicle model. Due to its complexity, a high fidelity model of the vehicle dynamics derived from first principles is used only in simulations, while a simplified model is adopted for control design. This control-oriented model retains most of the features of the high fidelity model, including non-minimum phase characteristic of the flight-path angle dynamics and strong couplings between the engine and flight dynamics, whereas flexibility effects are regarded as a dynamic perturbation. A nonlinear sequential loop-closure approach is adopted to design a dynamic state-feedback controller that provides stable tracking of velocity and altitude reference trajectories and allows to impose a desired trim value for the angle of attack. Simulation results show that the proposed methodology achieves excellent tracking performances in spite of parameter uncertainties.

Abstract-This paper presents the design of an adaptive flight control systems for constrained air-breathing hypersonic vehicle models. The proposed architecture comprises a robust adaptive nonlinear inner-loop controller, and a self-optimizing guidance scheme that shapes the reference to be tracked in order to avoid the occurrence of control input saturations. The scheme is explicitly designed to account for the presence of a state-dependent input saturation on the control loop for the vehicle longitudinal velocity, arising from physical limitations in the propulsion system. The approach is based on the integration of a previously-developed adaptive controller with a self-tuning pre-filter which shapes the reference command to maintain the control signal within feasible values. The reference command are left unaltered whenever there is sufficient control authority for stable tracking. Simulation results are provided to show the effectiveness of the method.

Longitudinal rigid-body models of air-breathing hypersonic vehicle dynamics are characterized by exponentially unstable zero-dynamics when longitudinal velocity and flightpath angle (FPA) are selected as regulated output. To enable application of stable dynamic inversion methods (and their adaptive counterparts), previous studies have considered the addition of a canard control surface to eliminate the occurrence of the unstable zero; however, the addition of a canard may negatively impact the design of the thermal protection system. In this paper, we present a methodology for robust nonlinear control of the rigid-body longitudinal hypersonic vehicle dynamics which employs only the elevator as aerodynamic control surface. The method reposes upon a nonlinear transformation of the equations-of-motion into the interconnection of systems in so-called feedback and feed-forward forms that allows the combination of high-gain and low-amplitude feedback, achieved through the use of saturated functions. Simulation results using the flexible vehicle model are presented to illustrate the effectiveness of the method.

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