Compliant Floating-Base Control of Space Robots

This letter presents a compliant feedback controller of an arm-equipped spacecraft, which does not enforce requirements on the spacecraft position and attitude. The controller is applicable to the pre-contact, contact, and post-contact phases of a robotic operation. In contrast to conventional floating-base strategies, the controller eliminates the instability of the system during a steady contact, and thus can be used in realistic applications. The controller uses an external-internal transposed-Jacobian control for compliant regulation of the end-effector, together with regulation of the whole-body Center-of-Mass (CoM) and angular momentum for achieving post-contact stability, and force feedback for achieving a stable contact phase. The method is validated experimentally using a hardware-in-the-loop simulator composed of a seven degrees-of-freedom (DOF) arm mounted on a 6 DOF simulated spacecraft. Numerical simulations further validate the method considering a realistic thrusters system, measurement noise, and time delay.