Queqiao-2 relay satellite (Chinese: 鹊桥二号中继卫星; pinyin: Quèqiáo èr hào zhōngjì wèixīng; lit. 'Magpie Bridge 2 relay satellite') is the second of the communications relay and radio astronomy satellites designed to support the fourth phase the Chinese Lunar Exploration Program, after Queqiao-1 launched in 2018. The China National Space Administration (CNSA) launched the Queqiao-2 relay satellite on 20 March 2024 to an elliptical frozen orbit around the Moon to support communications from the far side of the Moon and the Lunar south pole. The name Queqiao (ch'wuh-ch'yow, "Magpie Bridge") was inspired by and came from the Chinese tale The Cowherd and the Weaver Girl.
Background and mission planning The initial phase of the International Lunar Research Station (ILRS), consisting of the Chang'e 7 and Chang'e 8 probes, was scheduled to be built in 2026 and 2028 on the southern edge of the South Pole–Aitken basin located on the far side of the Moon. While the Queqiao so far only had to connect with two probes on the far side of the Moon (Chang'e 4 lander and Yutu-2 rover), future mission would include more workload, with up to ten robots being active on the moon for the ILRS project, which requires a complex and sophisticated communication network. The Queqiao relay satellite was inserted in a halo orbit around the Earth-Moon L2 since 2018. China planned another relay satellite, called Queqiao 2, to support and supplement Queqiao-1. Originally, the idea was to design the relay satellite as an improved version of the Queqiao and launch it together with the Chang'e 7 probe. After a project revision, the Center for Lunar Exploration and Space Projects at the CNSA decided to launch it separately. This allowed the building of a larger variant of the relay satellite that could be launched earlier and used in the Chang'e 6 sample return mission that was also launched in 2024 to the Apollo crater on the far side of the Moon. Although the first Queqiao can provide the unique function of relaying constant communications to and from the far side of the Moon, aided by Chinese Deep Space Network, its halo orbits around the Earth-Moon L1 and L2 were inherently unstable and requires the satellite to consumes 80 g (2.8 oz) of fuel for a small orbit correction maneuver approximately every 9 days. Therefore, a frozen elliptic orbit around the Moon itself was chosen for Queqiao 2 due to its more stable nature. The frozen elliptic orbit can provide visual contact with the Moon for eight hours, i.e., two-thirds of its 12-hour orbit, since the point of its periselene lies above the side of the southern polar region facing away from the Earth. When Queqiao-2 reaches a position about 200 km from the lunar surface, it will perform capture braking and enter a lunar parking orbit of 200 × 100,000 km with a period of about 10 days. Eventually, Queqiao-2 will enter a large elliptical frozen orbit of 200 × 16,000 km with a period of 24 hours, which is inclined at 62.4° to the equator. No further orbit correction maneuvers are necessary for a period of 10 years, the assumed lifespan of the satellite. However, it did not enter that orbit and instead entered a 119.25° 254 × 16941 km retrograde orbit.
Design
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