Design of a Robust Block Backstepping Controller for 6-DOF Circular Parachute

This paper presents a robust block-backstepping control framework for precision landing of an underactuated, canopy-tilting circular parachute based on a coupled 6-DOF parachute-payload model. Unlike prior approaches that rely on simplified lateral dynamics or strong wind prediction assumptions, the method preserves translational-rotational coupling and reformulates horizontal dynamics into a block-structured strict-feedback form for Lyapunov-based design. A two-step block backstepping controller is developed to stabilize horizontal position and velocity tracking errors, with an added diagonal robust term to counter bounded wind disturbances and modeling uncertainties under a matched-disturbance assumption. High-fidelity MATLAB/Simulink drop simulations, incorporating noise, latency, actuator delays, and parameter uncertainties (20 trials from 3,000 m with random initial offsets), demonstrate significant performance gains over a tuned PID baseline. The approach reduces mean landing error from ~50 m to ~0.125 m and decreases CEP radius from 60.294 m to 0.1129 m, confirming substantial improvements in accuracy and dispersion.