Fixed-time observer-based filtered hierarchical backstepping control for a gun-launched coaxial rotor vehicle

This paper presents an improved fixed-time control strategy for path tracking of autonomous gun-launched coaxial-rotor micro aerial vehicles (MAVs) operating under unknown aerodynamic forces. The proposed algorithm combines a filtered fixed-time hierarchical backstepping (FTHB) method with a fixed-time disturbance observer (FDO). Using a coordinate transformation, the complex dynamics of the MAV are decoupled into fully actuated and underactuated subsystems. The novelty of this work lies in two key contributions: (1) the design of a fixed-time hierarchical backstepping controller for the nominal system, ensuring fixed-time stability, with fixed-time filters employed to estimate virtual control inputs and thereby reduce the complexity of the backstepping design, and (2) the integration of fixed-time observers to estimate unknown disturbances in fixed time, effectively addressing the challenges posed by aerodynamic uncertainties affecting the entire system. The effectiveness of this control strategy is rigorously demonstrated through fixed-time stability analyses. A comprehensive comparative assessment, covering both qualitative and quantitative evaluations, is carried out through extensive simulations comparing the proposed controller with a fixed-time controller, a finite-time controller, and a disturbance observer-based controller. This evaluation clearly underscores the robustness and superior performance of the proposed control strategy.