Nonlinear adaptive control design for non-minimum phase hypersonic vehicle models with minimal control authority

The design of a nonlinear robust controller for a non-minimum phase model of the longitudinal dynamics of an air-breathing hypersonic vehicle is presented in this work. When flight-path angle is selected as a regulated output and the elevator is the only control surface available for the pitch dynamics, longitudinal models of air-breathing hypersonic vehicle dynamics exhibit unstable zero-dynamics. The approach proposed in this paper uses a combination of small-gain arguments and adaptive control techniques for the design of a state-feedback controller that achieves asymptotic tracking of velocity and flight-path angle reference trajectories in spite of model uncertainties. The method reposes upon a suitable redefinition of the internal dynamics of a control-oriented model of the vehicle dynamics and uses a time-scale separation between the controlled variables to manage the peaking phenomenon occurring in the system. Simulation results on a full nonlinear vehicle model illustrate the effectiveness of the methodology.