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The Verge's This weekend, China embarks on a historic mission to land on the far side of the Moon says (near the end):

We know that the mission is set to launch on top of one of China’s Long March 3B rockets from the country’s Xichang Satellite Launch Center. And thanks to air closure notices, takeoff time is estimated to occur around 1:30PM ET on Friday, December 7th. China may only announce that the mission was a success after the spacecraft is on its way to the Moon, though Jones says we might hear earlier than that from other sources.

“It might be that the first indication we have of launch is that some poor soul near Xichang launch center is woken up thinking there’s an earthquake and complaining about it on social media.” Jones says.

If Chang’e-4 does make it to space, it will spend less than a month traveling to the Moon, likely touching down sometime in the first week of January. If that happens, China will have officially moved into its own elite group, as the only country to visit the side of the Moon we cannot see from Earth.

Question: Launch is tomorrow, so I'm wondering why it will take a month to get to the Moon? An easy explanation might be that it will reach lunar orbit in several days, and then take several weeks before it lands on the Moon, but there are lower energy orbits that take several weeks to get there, and Chang'e-4 is over a ton, so maybe the fuel saving compared to a "direct flight" is worth something in terms of delta-v.

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    $\begingroup$ I searched for a bit but China doesn't seem very forthcoming with mission details $\endgroup$ – Dragongeek Dec 8 '18 at 0:19
  • $\begingroup$ @Dragongeek planetary.org/blogs/emily-lakdawalla/2018/… and several links therein $\endgroup$ – uhoh Dec 8 '18 at 1:16
  • $\begingroup$ twitter.com/Yeqzids/status/1071140675901546496 $\endgroup$ – uhoh Dec 8 '18 at 1:22
  • $\begingroup$ "but there are lower energy orbits that take several weeks" What orbits are these? Bi-elliptics with several week trip times only save a negligible amount of delta V over a standard Hohmann. $\endgroup$ – HopDavid Dec 9 '18 at 4:18
  • $\begingroup$ @HopDavid Words like "lower", "several", "negligible" are malleable and so I'm not sure which direction your question is going. I'm thinking of something that takes maybe 4 to 40 weeks, and saves 4-14% (rough numbers). I'm not sure if you are challenging the existence of these solutions, or just saying that that much savings is "negligible" and unworthy of the term "lower". I'd read a lot about this but it was several years ago. In a folder full of old pdf's I pulled up link.springer.com/article/10.1007%2Fs10569-004-0406-8 randomly. Enlighten me if I've misrepresented the results. $\endgroup$ – uhoh Dec 9 '18 at 5:17
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According to Spaceflight Now (emphasis mine):

Chang’e 4 is expected to enter lunar orbit Tuesday [Dec 11 2018] after a series of course-correction maneuvers, then use braking rockets to descend to the moon’s surface, targeting a landing inside the 110-mile-wide (180-kilometer) Von Karman crater in moon’s South Pole-Aitken basin region in early January.

Your suggestion is correct - Chang'e 4 will enter Lunar orbit within a few days on a traditional transfer orbit. The good completion of the trans-lunar injection was announced by CASC (source in Chinese on Weibo) - the primary contractor for CNSA.

As to what Chang'e 4 will be doing in the intervening weeks, I haven't been able to find any information. However, since the exact landing date hasn't yet been revealed, it seems likely that details won't be forthcoming.

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I don't know the exact path, but I do know there's a path to the moon that takes about a month. The reason it's used is that it takes less energy.

The Apollo missions got there in three days but your economics are different when you are consuming supplies for every day in space.

See this question for more information: Low Energy Transfer within Earth-Moon system

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    $\begingroup$ @uhoh I was basically confirming your hypothesis. For an unmanned craft there usually no reason not to take the minimum energy path even if the savings are small. $\endgroup$ – Loren Pechtel Dec 8 '18 at 1:59
  • $\begingroup$ What is the month long path to the moon? A bi elliptic with a 600,000 km altitude apogee takes about a month. But saves less than .1 km/s. $\endgroup$ – HopDavid Dec 9 '18 at 4:25

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