Robust Model-based H∞ control for Free-floating Space Manipulator Cartesian Motions

During on-orbit tasks, when space manipulator systems (SMS) need to handle captured unknown objects accurately, robust control for compensation of uncertainties and disturbances is required. To avoid fuel consumption and/or sudden end-effector impacts with the object, the SMS is in free-floating mode, i.e., the base is not actuated. In this work, a robust Cartesian-space controller is developed for a free-floating SMS during object capture. The controller consists of a model-based part, which linearizes the dynamics globally and guarantees specific performance, and of a linear H-infinity part, that assists by adding robustness in the presence of parametric uncertainties and/or disturbances. It is shown that the developed controller minimizes tracking errors and attenuates sensor noise. The sensitivity of the developed controller to uncertainties is studied by Monte Carlo simulations; the resulting tracking errors are an order of magnitude smaller than those obtained without H-infinity compensation. The control method applies to spatial systems and is demonstrated by a planar example.