Ellipse detection-based visual servo control for capturing upper-stage rocket body

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Ellipse detection-based visual servo control for capturing upper-stage rocket body

Kojima, Hirohisa / Okawara, Taku / Trivailo, Pavel M.

Abstract The quantity of space debris in orbit around the Earth including separated rockets, malfunctioning satellites, and small particles is continuously increasing. One such type of space debris is the upper stage of the H-series rockets, which has a joint, called the Payload Adapter Fitting (PAF), where the satellite to be deployed is connected. Because the PAF is circular, it offers a natural and desirable target marker for detecting the rocket stage attitude and capture the stage using image processing. Traditional visual servo control based on a single elliptical image of a circular feature cannot determine the normal direction of the PAF and is unable to maintain the imaged ellipse inside the camera field of view as the motion in the optical axis direction may exceed the desired speed. To overcome these problems, a method of control gain switching in visual servo control based on two elliptical images of two circular features of the PAF is proposed, in which the convergence of the projected ellipse to a circle is prioritized, followed by forward motion to adjust the relative distance. A 1/10 scale PAF model and a six degrees-of-freedom robotic manipulator equipped with a camera on its end-effector were used to validate the proposed control method. The experimental results show that the convergence time for the proposed method is shorter than that without control gain switching.

Highlights • PAF is treated as the natural target maker for capturing space debris. • Control gain switching visual servo control is proposed. • The convergence of the projected ellipse to a circle is prioritized. • Forward motion is executed after the convergence of the projected ellipse to a circle. • Convergence time for the proposed method is shorter than that without control gain switching.