Queqiao: The bridge between Earth and the far side of the moon

China's Chang'e-4 probe marked the first soft-landing of a spacecraft on the far side of the Moon, which always faces away from Earth. To communicate with ground stations, Chang'e-4 relies on Queqiao, a relay communication satellite that orbits a point behind the Moon and bridges Earth and Chang'e-4. In a recent review, researchers explain the design of Queqiao and depict the future of lunar relay communication systems.