Hypersonic Missile Adaptive Sliding Mode Control Using Finite- and Fixed-Time Observers

Finite- and fixed-settling time differentiators utilizing a nonrecursive higher order sliding mode (HOSM) observer are studied. Fixed convergence time estimation is achieved independent of initial conditions of the differentiation errors. The corresponding convergence/settling times are estimated. The finite- and fixed-time HOSM differentiators' performance is compared against the Levant recursive one via a hypersonic missile control simulation case study during the missile's terminal phase of flight. A continuous adaptive HOSM control is utilized. The double-layer adaptive algorithm is based on an equivalent control concept and does not allow overestimation of the control gains that mitigates control chattering. The robustness and high-accuracy output tracking in the presence of matched and unmatched external disturbances and missile model uncertainties is demonstrated for both the differentiators and the controller.