Nonlinear Control of Motion Synchronization for Satellite Proximity Operations

This paper considers the problem of motion synchronization of free-flying robotic spacecraft and serviceable floating objects in space. The synchronization maneuvers are a combination of relative position tracking and attitude reorientation. Control laws are developed that ensure that the relative position vector between a pursuer and target spacecraft is always directed toward the docking port of the target. The tracking-error reference signals are generated based on a novel "virtual target" construction. Also, the attitude reorientation of the pursuer is achieved by constructing a desired attitude from the virtual target, and the control law seeks to nullify the errors between the current and desired attitude parameters. The control law synthesis proceeds along familiar, established procedures motivated by feedback-linearization-based approaches. Disturbance torques due to gravity gradient and other unknown but bounded disturbances are accounted for using an adaptive control formulation. The stability of the control laws are demonstrated via Lyapunov analysis and Matrosov's theorem. Numerical simulations are performed to demonstrate the efficacy of this control formulation. [PUBLISHER ABSTRACT]