Control of Asteroid-Hovering Spacecraft with Disturbance Rejection Using Position-Only Measurements

This paper addresses the control of spacecraft hovering about uniformly rotating asteroids using only position measurements. The highly uncertain dynamical environments and the absence of velocity feedback make it a challenging issue. To overcome the difficulties, an extended state observer is designed to estimate the spacecraft velocity and uncertain perturbations simultaneously. It ensures ultimately bounded estimation errors, irrespective of the control law applied. A velocity-free hovering controller is then obtained by driving a full-state feedback controller with estimates from the observer. The observer and controller design accounts for both measurement errors and unknown perturbations, and a Lyapunov analysis shows that the resultant control scheme globally stabilizes the spacecraft trajectory to the vicinity of the desired hovering state. Furthermore, autonomous hovering operations, implemented by either continuous or on-off thrusters, in both the body-fixed frame and the inertial frame are simulated with sensor noise and multiple unknown disturbances to demonstrate the effectiveness of the proposed methods.