A tool mounted on a servicer satellite for fuelling an unprepared or partially prepared client satellite. The tool includes a robotic arm mounted on the servicer satellite and a valve tool configured to be releasibly gripped by the robotic arm. The valve tool includes a housing with a support frame and a wrench mechanism mounted on the support frame. The wrench mechanism is configured for removing and replacing the first access valve cap on the first fill-drain valve and coupling a first propellant fill line to the first propellant tank optionally removing and replacing the second access valve cap on the second fill-drain valve on the second propellant tank and coupling a second propellant fill line to the second propellant tank, and actuating the valve actuation nut on the first fill-drain valve, and optionally actuating the valve actuation nut on the second fill-drain valve.