It is not easy to go to the back of the moon. A big problem is "communication". Tidal locking by the earth, the moon can only face the earth in the same direction forever. Not only have humans never seen the back of the moon on earth, but communication signals will also be blocked.

The Chang 'e IV mission itself is to go to the back of the moon for landing and patrol (lunar rover) detection. If all goes well, it will become the first international probe to land on the back of the moon. How to solve communication problems? The best way is to arrange a relay satellite at Lagrange L2, which can "see" both the back of the moon and the earth, and provide measurement and control support during the soft landing and lunar work of Chang 'e IV.

"Queqiao", a good name, is a bridge for transmitting signals and data between Chang 'e IV detectors on the back of the moon. We plan to launch the relay star "Queqiao" of Chang 'e IV to Lagrange, which is located at 2 o'clock on the extension line of the earth and the moon, about 60,000 to 80,000 kilometers away from the moon-this "pioneer" is related to the success or failure of the entire Chang 'e IV mission. Source: Baidu