Queqiao: China's lunar relay satellite

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How China's lunar relay satellite arrived in its final orbit
Luyuan Xu • June 15, 2018

http://www.planetary.org/blogs/guest-blogs/2018/20180615-queqiao-orbit-explainer.html

After a 24-day journey, Queqiao, the relay satellite for China's Chang'e 4 lunar mission, successfully entered its Earth-Moon L2 halo orbit. A normal mission to lunar orbit usually takes four or five days, but Queqiao took much longer due to its special orbit. Here's a guide to the spacecraft's long and complicated journey.

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Qeqiao used a lunar swing-by transfer orbit with an apogee of about 400,000 kilometers from Earth. This transfer orbit usually needs 2 or 3 trajectory correction maneuvers (TCMs) and takes about 4 or 5 days to arrive at the Moon. On May 22, Queqiao made its first TCM, and that turned out to be the only one necessary.

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http://www.planetary.org/blogs/guest-blogs/2018/20180615-queqiao-orbit-explainer.html

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Longjiang-2: Earth images from lunar far side

After launch and en route to the Moon on May 21, Queqiao deployed two microsatellites called Longjiang-1 and 2. Four days later on May 25, both satellites were supposed to perform a braking maneuver to enter lunar orbit. Unfortunately, only Longjiang-2 was confirmed to successfully enter lunar orbit, with a perigee of 350 kilometers and an apogee of 13,700 kilometers.

Longjiang-2 (also called DSLWP-B) was tracked by amateur radio operators. Its onboard camera, developed by Saudi Arabia, began operating on May 28 and successfully sent back images of the Moon the Earth.

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NASA completed its feasibility of using the lunar halo orbit in 1968. But since all Apollo launch sites were facing the Earth, they never use their resesarch.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680015886.pdf