Compliant Spacecraft Capture via a Nonlinear Disturbance Observer-based Impedance Controller

This paper proposes the use of a nonlinear disturbance observer-based impedance controller for the compliant capture of free-flying spacecraft using a free-flying robot. First, the dynamics for a free-flying spacecraft are derived. An existing nonlinear disturbance observer that can be used to determine the end-effector disturbance for a fixed-base manipulator without knowledge of the second state derivatives is then extended for use with a free-flying robot. The observer is shown to be asymptotically stable. The observer is then paired with an impedance controller, and the proposed technique is successfully experimentally validated at Carleton University’s Spacecraft Robotics and Control Laboratory, where a robotic manipulator achieves the compliant capture of a free-floating spacecraft.