Thread by @AJ_FI

China's complex Chang'e-5 lunar sample return mission is set to launch between 20:00-21:00 UTC (3-4 pm ET (04-05:00 am local tomorrow). It will seek to return the first lunar samples since the 1970s. Thread on the launch, spacecraft, science and more.

First, launch coverage is ongoing here, in Chinese:
Alternatives and updates likely to be posted by @Nextlaunch

https://twitter.com/Nextlaunch/status/1330818000233041922

The rocket for the launch is China's largest (57m, 860 tonnes), the Long March 5, which was designed with the Chang'e-5 mission in mind. The failure of its 2nd launch in July 2017 delayed CE-5 by 3 years. But now it's on the pad.

The mission is to last around 23 days from launch til landing in Inner Mongolia, where reentry craft from China's crewed Shenzhou missions land. This image from the Chang'e-5-T1 test mission (2014) which tested the high-speed reentry from the Moon, inc. bounce off the atmosphere.

The ~850-tonne Long March 5 is launching to 8.2-tonne Chang'e-5 towards the Moon in order to bring back ~2 kgs (upper limit 4 kg) of samples. The vast of majority of this mass is fuel for overcoming gravity.

The Chang'e-5 spacecraft itself consists of four modules: service module for propulsion; lander; ascent vehicle on the lander for getting back into lunar orbit; and a reentry vehicle for atmospheric reentry. See this overview of the mission profile: planetary.org/space-missions…

This complex mission profile involving lunar orbit rendezvous and docking (like Apollo rather than the direct return of Soviet Luna missions) indicates China has its eyes on even more ambitious missions like putting astros on the Moon and a Mars sample return.

There's little info at this point on the mission timeline. My estimate based on old journal articles, press statements and guesswork is:
- 112 hours/4.6 days to Moon
- Sunrise over Mons Rümker landing area late-ish on Nov 27.
- Lunar orbit insertion: 200 km orbit mid Nov. 28...

Landing attempt sometime between November 29 and Dec 2, depending on the orbit of the spacecraft and light conditions at the landing site. This info points ~20:30 UTC on November 29

https://twitter.com/Cosmic_Penguin/status/1330561964041388033

The landing attempt will target Mons Rümker in Oceanus Procellarum in the northwest of the near side of the Moon. It hopes to collect material much younger (1-2 bn years) than samples ever collected before (3 bn years + for Apollo/Luna missions)

The lander will use a 7500N variable thrust engine used for the Chang'e-3 & 4 landings in 2013 and 2019 for the propulsive landing. This is part of the mesmeric, almost fractal CE-4 landing on the lunar far side in January 2019.

The sampling operations will last ~48 hours. A drill will bore as far down as 2 metres to take samples while a scoop will take surface regolith. Below is a drill test with regolith simulant (CCTV).

The ascent vehicle on top of the lander will then blast off (a first liftoff from another planetary body for China & a huge challenge) into a ~15 x 180 km orbit. There is a window of 3.5 hours at the end of a period of two days for the ascent vehicle to dock with service module.

This is a simulated docking test from a few years back. China has performed rendezvous & docking in low Earth orbit between Tiangong and Shenzhou & Tianzhou spacecraft, but this time is 380,000 km away & light delay. A big challenge.

The samples will then transfer from ascent module to reentry vehicle. The service module remains for 6 days in lunar orbit before starting the 112-hour journey back home. The reentry vehicle separates 5,000 km from Earth for a skip reentry.

The landing site will be Siziwang Banner, Inner Mongolia sometime Dec 15-16. The sealed samples will then be transferred to a lunar sample lab in Beijing for processing, analysis and storage.

In terms of science, the geologically 'young' samples CE-5 aims to grab will give insight into the evolution of the Moon how recently it was geologically active. Was there volcanism much more recently than previously thought? 1971 image of Mons Rümker from Apollo 15 astronauts

Why is this area, named Procellarum-KREEP Terrane, rich in radioactive elements? Did that play a role in late-stage volcanism?

There is a backup to Chang'e-5 if anything goes wrong. CE-6 was manufactured at the same time. It will provide another shot at this complex mission if anything goes wrong. And if it succeeds, CE-6 can make an even more ambitious landing at the lunar south pole.