Queqiao (Change′e 4 Relay, CE 4 Relay)

Launch data:

Spacecraft data:

Mission details:

• China′s Queqiao deep-space communications relay satellite was launched on May 20, 2018. It will unfurl a 4.2m dish antenna. After a 100 km lunar flyby on about May 25 it will take up station in a 13000-km-wide ′halo orbit′ around the Earth-Moon L2 point, 64445 km behind the Moon, to provide farside radio communications to support the planned Chang′e 4 farside lander.
• Earth-Moon L1 and L2 (EML1, EML2) are on the lunar Hill sphere that marks the approximate point where lunar gravity dominates over Earth gravity. Don′t confuse them with Sun-Earth L1 and L2 (SEL1, SEL2) on the 1.5-million-km radius Earth-Moon system Hill sphere which marks the point at which the Earth′s gravity (with the Moon′s help) dominates over the Sun. (that′s the point at which it′s a better approximation to pretend you&primere in orbit around object A rather than object B). SEL1 and SEL2 have been used a lot since ISEE-3 went to SEL1 in 1978. EML1 and EML2 are much less well known. They were explored by Japan′s Hiten probe in 1990; the ARTEMIS P1/P2 spacecraft and the Chang′e-5FTD vehicle also visited them, but this will be the first time a probe has used either EML location as its primary mission destination.
• Queqiao made a 100 km lunar flyby at 1340 UTC May 25, 2018 and made a braking burn close to perilune to put it on course to reach EML2.
  The CZ-4C third stage made a 9900 km lunar flyby at 1403 UTC May 25, and ended up in a 16910 x 444000 km x 14.5 deg Earth orbit.
• The CZ-4C also deployed two 45 kg DSLWP (Discovering the Sky at Longest Wavelengths Pathfinder) small astronomy satellites, Longjiang-1 and 2 (DSLWP-A and B). The two satellites also made lunar encounters on May 25, 2018. Longjiang-2 is confirmed to have successfully entered lunar orbit; initial orbit parameters were around 350 x 13800 km x 21 deg.
• Contact was lost with Longjiang-1 on May 21, 2018; if it failed to make the insertion burn it will probably end up in an orbit similar to the third stage.

External links:

• Satellite tracking (n2ya.com): Real time satellite tracking