Software carrier tracking of Chinese Chang'E-3 lunar explorer in the power descent phase

摘要

In Chinese Chang'E-3 mission, the lander finally succeeded landing on the lunar surface softly and released the moon rover. The power descent phase, which posed a great challenge to the newly developed receiver in the deep space station, also turns out to be the most challenging part in the whole mission as there would be no Doppler data to reconstruct the trajectory if the receiver had lost the lock with the downlink carrier. This paper has given the demonstration results of the Chang'E-3 Lunar Explorer signal tracking, using software phase-locked loop (SPLL) in the power descent phase. A new tracking scheme has been designed based on the combination of the open-loop signal recorder and the SPLL. A third order SPLL has been designed and tested based on the theory of the software-defined radio. The schedule of the tracking campaign has been laid out. The results show that the designed SPLL has successfully tracked the downlink carrier with signal phase estimation accuracy of around 2 degrees and this kind of off-line operation mode proves to be valuable for the challenging signal tracking campaign in the lunar and deep space explorations.