Adaptive control of hypersonic vehicles in presence of aerodynamic and center of gravity uncertainties

The paper proposes a new class of adaptive controllers that are suited for command tracking in hypersonic vehicles (HSV) in the presence of aerodynamic and center of gravity (CG) uncertainties under cruise conditions. This class pertains to linear plants whose states are accessible with a partially known input matrix B. It is well known that standard multivariable adaptive controllers only yield local stability when the input matrix is completely unknown. In this paper, it is shown that when additional information regarding the structure of B is available, this difficulty can be overcome using the proposed class of controllers. In addition, a nonlinear damping term is added to the adaptive law to further improve the stability characteristics. The proposed adaptive controller is shown to be applicable for command following in HSV when subjected to a class of aerodynamic and center of gravity uncertainties. A model that accurately captures the effect of CG shifts on the longitudinal dynamics of a HSV is derived from first principles. Performance improvements are shown using simulation studies carried out on a full scale nonlinear model of the HSV. It is shown that the adaptive controller can tolerate larger CG shifts as compared to a fixed gain controller while tracking reference commands in velocity and altitude.