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).
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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.
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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.
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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.
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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.
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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.
weread.qq.com/web/reader/334…
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weread.qq.com/web/reader/334…
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