A Long March-4C rocket carrying a relay satellite, named Queqiao (Magpie Bridge), launched on 21 May Description:Cai Yang/Xinhua/Eyevine

China is getting ready for a trip to the far side of the moon. On 21 May, the China National Space Administration launched a satellite that will relay information between Earth and a planned moon lander and rover, both set to launch in late 2018.

The satellite – called Queqiao, which means Magpie Bridge – launched from southwest China’s Xichang Satellite Launch Center aboard a Long March 4C rocket.

Chang’e 4, the moon lander, will be the first spacecraft ever to land on the far side of the moon, if all goes to plan. Because the far side always faces away from Earth, the lander will not be able to communicate directly with its operators – any commands sent to it, or data sent back, would be blocked by the moon itself.


To solve that problem, a satellite that sits in the line of sight both of the lander and Earth’s surface is needed to relay information back and forth. There is a special spot in space that’s ideal for that, called L2, which is about 64,000 kilometres past the moon. At that spot, the combined gravity of the sun and Earth counteract the forces that could tug an object out of orbit. It’s a perfect spot to park a spacecraft, because it can sit there without constantly firing its thrusters.

It’s also a place particularly well-suited for Queqiao. From L2, the satellite will have a view of the entire far side when the moon passes in front of Earth. Queqiao will be placed into a “halo” orbit that circles L2, so that it will still have a line of sight to Earth even when is the moon blocks out part of the planet.

Queqiao is expected to reach that orbit around 29 May, after which there will be a six-month testing period to make sure that all its systems are still working.

Read more: Chris Hadfield: We should live on the moon before a trip to Mars