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A recent Chinese book published by the CLEP program has confirmed that there was indeed a problem associated with Chang’e 4 between launch and landing (which might explain the aloof/tense coverage back then in Dec. 2018 - Jan. 2019). (1/6)
One of the two fuel tanks on the lander was found to be leaking propellant far faster than expected 7 hours after launch on Dec. 7. Not only fuel loss was concerning (it was once believed that it was lacking 10 kg of fuel reserves), there was also problems w/ shifted COG. (2/6)
In the end the LOI and pre-landing orbit changing plans were changed. Instead of entering straight into a 100 km circular lunar, the LOI was performed on Dec. 12 to enter a 200 x 400 km (one say 100 x 400, needs checking) orbit w/ the 7500N main engine. (3/6)
After LOI the spacecraft made at least one (some say two, needs checking again) burns w/ its 150N RCS thrusters to eventually lower the orbit back to 15 x 100 km on Dec. 30 before landing on Jan. 3. All engine burns used the not leaking fuel tank to shift back its COG. (4/6)
This new plan (which also risked problems with its main engine since a planned short test firing of the main engine during cruise to the Moon was cancelled) eventually left it with 3 kg of fuel to spare & a 19 s shift in the landing time, good enough for a safe landing. (5/6)
The book I mentioned is apparently available as free e-book, but I don’t have the app to read it (no, I’m not a user of the Chinese Penguin Kingdom). If someone can download & share it please do! It also has some good lunar far side surface photos. https://weread.qq.com/web/reader/334324d07218bc823345170 … (6/6)
Here's a summary of the mission from amateur perspective. Note at the time we relied on state media announcements for orbital guesses seed elements. But period measurements were solid as well as how the Doppler would have fitted. The mission spent ALOT of time in ground lock.
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