Robust Integral Trajectory Tracking of the Controllable Aerial Towed Drogue

This paper proposed an anti-disturbance trajectory tracking controller for the flexible cable towed aerial drogue even under the towing aircraft's trailing vortex and continuous gust disturbance, by effectively integrating robust integral of the sign of the error (RISE) control with the model-assisted linear extended state observer (LESO). Inspired by the established modeling of hose-drogue aerial refueling systems, the towed flexible cable-drogue's multi-body dynamics with finite variable length links and joints are formulated, together with the towed drogue's 3 degrees of freedom (DOF) motion model. Then, the unmeasurable tensions acting on the drogue by the cable are viewed as a kind of disturbances of the dynamics and are estimated with the model-assisted LESO. With the compensation of these estimated disturbances, the RISE based feed-back trajectory controller is constructed for the aerial towed target under complex airflow disturbances. This combined method takes advantage of both the disturbance observer-based control and disturbance suppression-based RISE control. The simulation results show the proposed method's effectiveness for the aerial towed drogue's trajectory control from both control accuracy and anti-disturbance property perspectives, even under the trailing vortex and continuous gust.