The Queqiao-2 relay satellite supports the fourth phase of China’s lunar exploration mission to land probes on the Moon. Its primary function is to facilitate communication between lunar surface exploration missions (Chang'e-6, Chang'e-7 and Chang'e-8, etc.) and ground stations, particularly for missions to the Moon’s far side and polar regions. The relay communication payload is one of the most critical and core components of Queqiao-2 relay satellite. The mission features, design and key technologies of Queqiao-2 communication relay payload are analyzed and introduced. A full digital modulation and demodulation function is developed for the forward and return links, considering factors like communication techniques, long-distance transmission, compatibility with multiple lunar probes, and engineering feasibility. This, combined with the ability to update software in orbit, makes the communication relay payload highly flexible and innovative. A key challenge is detecting and tracking multiple targets from high-dynamic signals of the return link. This is addressed by creating a dedicated algorithm to ensure stable communication. Since its launch in March 2024, the communication payload has been operating well in orbit with high reliability, which establishes a leading role in system technical performance around the world. It has provided stable and reliable relay communication for the Chang’e-6 lunar probe for sampling and return mission, successfully completing the world’s first lunar sample return mission from the far side of the Moon. The Queqiao-2 relay satellite's communication payload has played a significant role in China's deep space exploration, generating substantial economic and social benefits. It has laid a solid foundation for future deep space exploration, human spaceflight programs, lunar exploration projects and international cooperation.
