Chinese ground crews are standing by for the return of a lunar probe bringing back the first fresh samples of rock and debris from the moon in more than 45 years.

The Chang’e probe is expected to land in the Siziwang district of the vast Inner Mongolia region late Wednesday or early Thursday. It fired its engines early on Wednesday to put it on course before the orbiter separates from the return vehicle, with all systems functioning as expected, the China National Space Administration said.

Recovery of the return vehicle will be complicated by its small size, darkness and heavy snow, state media reported. Plans call for it to perform an initial bounce off the Earth’s atmosphere to reduce its speed before passing through and floating down on parachutes, making it difficult to precisely calculate where it will land, the official Xinhua News Agency quoted Bian Hancheng, a leader of the recovery crew, as saying. State broadcaster CCTV showed four military helicopters standing by Wednesday morning at a base on grasslands.