04 January 2019
A lander, rover and relay satellite named Queqiao jointly completed the landing, and now serve to communicate between the Moon and Earth, said Sun Zezhou, chief designer of the Chang'e 4 probe, from the China Academy of Space Technology. The mission has conquered at least three difficulties so far.
The first was to position the Queqiao relay satellite at the second Lagrangian (L2) point of the Earth-Moon system, about 79,000 km from the Moon and 40,000 km from Earth, where it can see both Earth and the Moon's far side.
The second, Sun said, was to guarantee the accuracy and reliability of the relay satellite for Moon-Earth communication and to access the probe's control system. The third was the safe landing of the probe in the designated area, which has many geological features, said Wu Weiren, the Chief Designer of China's lunar probe programme. “If the probe couldn’t find a safe landing area, it would have kept adjusting itself until a relatively safe spot was found,” Sun introduced.