A craft launched from China in May is preparing to land on the far side of the Moon - an unexplored place almost no-one tries to go. The Chang'e 6 mission aims to collect precious rock and soil from this region for the first time in history. The probe could extract some of the Moon's oldest rocks from a huge crater on its South Pole. But the landing is fraught with risks, because it is very difficult to communicate with spacecraft once they reach the far side of the Moon. Since launch