Coordination of thrusters, reaction wheels, and arm in orbital robots

A fuel-efficient control strategy for a manipulator-equipped spacecraft is presented. The strategy uses the thrusters, the reaction wheels, and the arm drives in a coordinated way to limit the use of the thrusters and achieve ideally zero fuel consumption in contact-free maneuvering. The thrusters are activated automatically only after contact, to stabilize the inertial motion of the system. The controller regulates the translation of the center-of-mass (CoM) of the whole space robot, the rotation of the spacecraft, and the pose of the end-effector (EE) in a decoupled way, utilizing the thrusters to control the CoM translation only and the remaining actuators to control the rotation and end-effector coordinately. The method is validated experimentally using a hardware-in-the-loop simulator composed of a seven degrees-of-freedom (DOF) arm mounted on a 6DOF simulated spacecraft. Numerical simulations with discrete thrusters assess the fuel efficiency of the proposed strategy.