Nested zero-dynamics redesign for a non-minimum phase longitudinal model of a hypersonic vehicle

The paper presents a novel approach to control design for a minimally-actuated longitudinal model of a hypersonic vehicle that exhibits exponentially non-minimum phase behavior. To circumvent the instability of the zero dynamics with respect to the regulated output (airspeed and altitude), a redefinition of the altitude tracking error as a function of the states of a dynamic controller is pursued. The proposed controller stabilizes the internal pitch dynamics while ensuring zero steady-state tracking error. Central to the approach is the definition of two separate nested zero-dynamics subsystems corresponding to successive redefinitions of the regulated output.