Uplink Radio Frequency Signal Fluctuations

KAGUYA was a Japanese large lunar explorer that orbited and observed the moon from 2007 to 2009. During in-orbit operation, unexpected fluctuations and lock-offs of KAGUYA's uplink radio frequency telecommand signal were sometimes observed. To investigate the cause of the fluctuations, archived telemetry data were surveyed, and the telemetry data that showed the fluctuation were extracted. According to fault tree analysis of the telemetry data, multipath interference from the lunar surface and the spacecraft structure was deemed the most probable cause. This finding was verified by geometrical analysis of multipath interference. On the basis of the analysis results, the fluctuation map for a lunar polar orbiter was presented for the first time. This map was used to avoid the telecommand operation failure of KAGUYA. This lesson can be generally applied to operations of planet and lunar orbiters.