Design and Verification of TT&C System for Queqiao-2 Relay Satellite

The Queqiao-2 relay satellite operates in a frozen lunar orbit, its onboard, its tracking, telemetry, and command （TT&C） system is not only responsible for the TT&C communication tasks between the relay satellite and ground stations, but must also ensure reliability under more severe radiation environments than those encountered by Earth satellites. In situations where ground stations cannot directly measure lunar probes in the far side or polar regions of the Moon, the relay satellite’s T&C system can act as a relay node to enable the ground station to perform orbit determination and positioning of the lunar probe. Under the existing T&C system and the Earth-Moon distance, it is difficult to improve the telemetry rate and measurement accuracy. Therefore, it is necessary to verify a new TT&C system under deep-space conditions. In response to these mission requirements and challenges, the TT&C system of the relay satellite was designed as follows: A unified S-band carrier system was adopted to perform routine TT&C tasks between the satellite and the ground station, with the transponder designed with a heterogeneous backup configuration. A four-way measurement link （ground station-satellite-probe-satellite-ground station） was designed to enable real-time measurement of lunar probes that are not visible from the ground station. Additionally, a GMSK + PN TT&C transponder was configured for application verification. Since the in-orbit launch of the “Queqiao-2” relay satellite, the TT&C system has consistently and stably performed TT&C and communication tasks. Simulation results of the four-way lunar measurement demonstrate that it can achieve meter-level positioning accuracy for the lander. Estimations of the new T&C system indicate that it can achieve centimeter-level ranging accuracy at the Earth-Moon distance.The actual operational performance and simulation verification results demonstrate that the TT&C system design of the relay satellite meets the mission requirements and can provide references for the design of TT&C systems for future deep space exploration and lunar exploration missions.