The Earth and Moon imaged by a Saudi camera on the Chinese Longjiang-2/DSLWP-B microsatellite, a part of the Chang'e-4 mission. Harbin Institute of Technology
China will launch the Chang'e-4 spacecraft on Friday, December 7, to make the first ever attempt at a landing on the far side of the Moon.
Here are the details on the launch, landing site, science objectives and more to provide what you need to know about the pioneering mission.
When will it launch
The lander and rover are due to launch atop a Long March 3B rocket from the Xichang Satellite Launch Centre in southwest China on Friday between 18:15-18:34 universal time/GMT (13:15-13:34 Eastern Time), which is 02:15-02:34 Beijing time Saturday.
Unfortunately it looks unlikely that China will be providing live coverage of the launch, in which case the first official news after liftoff may only come once the spacecraft have successfully entered lunar transfer orbit.
Preparations for the November 2017 launch of the Beidou-3 M1 and M2 satellites via Long March 3B from Xichang, Sichuan Province. beidou.gov.cn
Why the far side of the Moon?
Chang'e-4 was originally a backup to Chang'e-3, launched in December 2013. When this succeeded, it allowed scientists to consider repurposing CE-4 for something more ambitious.
The vast majority of the far side of the Moon never faces the Earth due to tidal locking, and humanity's first of that hemisphere of our celestial neighbour did not come until the Soviet Luna 3 mission sent back imagesin 1959, and the Apollo 8 astronauts in 1968.
Surprisingly it looks very different to the near side, with greater visible crater coverage and few of the mare, or dark basaltic 'seas' created by lava flows that we can see with the naked eye on the near side. Why this is so remains a mystery and the answers will help our understanding of the Moon's history and even the development of the solar system.
Images of the near (left) and far side of the Moon. NASA
Relay satellite for communications
A lunar far side landing is unprecedented because, as noted above, that hemisphere cannot be viewed directly from the Earth, meaning innovative solutions are needed to facilitate communications for sending commands to the spacecraft and aiding landing, and receiving telemetry and the all-important science data.
From here will be able to simultaneously contact tracking stations on Earth and the spacecraft on the far side of the Moon and relay communications with its huge parabolic antenna.
A rendering of the Queqiao Chang'e-4 lunar satellite performing its communications relay functions beyond the Moon. Chinese Academy of Sciences
Landing sites and date
The mission will target an area within the South Pole-Aitken Basin (SPA), a huge, ancient and scientifically significant impact crater on the far side of the Moon. It has a diameter of around 2,500 kilometres and could contain exposed material from the Moon's mantle.
The SPA basin, which stretches from the south pole to Aitken crater, is of huge interest and a target for most proposed missions to visit the lunar far side. A number of candidate landing sites have been analysed for Chang'e-4.
A preliminary monochrome mosaic of the moon from the Lunar Reconnaissance Orbiter (LRO) Wide Angle Camera (WAC), centered in the middle of the South Pole-Aitken basin. NASA/GSFC/Arizona State University
The 186-km-diameter Von Kármán crater is currently understood to contain the sel ected landing site, according to a papers published by Huang Jun et al in the American Geophysical Union’s Journal of Geophysical Research: Planets, with other publications also analysing sections of this crater as potential sites.
The white box indicates the Chang'e-4 landing area with the Von Kármán crater, according to a paper from Huang Jun et al, 2018. Huang et al, 2018.
The Von Kármán crater offers a relatively flat area on the far side, which is much more topographically variable than the near side. The landing will still pose new challenges for China's space engineers.
No official news on the landing date has been released, but with sunrise over Von Kármán late in December, the landing is currently believed to be scheduled for around January 3, 2019.
The lander and rover are very similar to the Chang'e-3 spacecraft which landed on Mare Imbrium five years ago, with the lander at around 3,800 kilograms and the rover at 140 kg. The rover will descend from atop the lander a few hours after setting down.
The lander will carry a Landing Camera (LCAM), Terrain Camera (TCAM), a Low Frequency Spectrometer (LFS) with three 5-metre-long booms, and the Lunar Lander Neutrons and Dosimetry (LND), with the latter developed in Germany.
A render of the Chinese Chang'e-4 lunar lander designed to set down on the South Pole-Aitken Basin on the far side of the Moon. CNSA
The rover will be equipped with a Panoramic Camera (PCAM), a Lunar Penetrating Radar (LPR), a Visible and Near-Infrared Imaging Spectrometer (VNIS) and, from Sweden, an Advanced Small Analyser for Neutrals (ASAN).
The rover was, like its predecessor Yutu (Jade Rabbit), to be named via a public contest and voting. A top three from a shortlist of ten nameswas decided by online voting, with the final selection to be declared by a committee in late October. However, the name has yet to be announced, with rumoursthat a completely new name will be sel ected.
A photo of Yutu (Jade Rabbit) taken by the Chang'e-3 lander in December 2013 on the surface of the Moon. Chinese Academy of Sciences
The far side of the Moon offers several unique opportunities for science. With the Moon shielding the spacecraft from Earth's interference, Chang'e-4 will be able to carry out unprecedented radio observations at low frequencies not possible on Earth due to its atmosphere.
The imaging spectrometer will allow an analysis of the composition of the lunar surface, while the radar will be capable of bringing insights into the layers, and therefor the history, and other geological features below the surface. Chang'e-3 used a similar instrument to reveal a complex history under Mare Imbrium.
The Swedish ASAN instrument will tell scientists about how the solar wind interacts with the Moon, and the German LND payload will help in understanding processes on the lunar surface mixing processes while also being sensitive to possible lunar water.
The cameras will meanwhile return clear, high-resolution images from the lunar far side, comparable to those from Chang'e-3 on the near side.
A view of Mare Imbrium taken by China's Chang'e-3 mission. Chinese Academy of Sciences
Mini biosphere experiment
Another science payload, chosen from around 200 submissions to a student contest to place an experiment on Chang'e-4, will see potato and arabidopsis seeds and silkworm eggs sent to the Moon in a 'mini biosphere' to test photosynthesis and respiration in the low-gravity lunar environment.
The 3-kg tin will also contain water, a nutrient solution and air, and a small camera and data transmission system.
While there have been many experiments in low-Earth orbit and analogue studies, this will be unprecedented.
A prototype of the mini lunar biosphere experiment for the Chang'e-4 mission, launching in late 2018. CNS
Chang'e-4 side quests
Aside from the lander and rover, the Chang'e-4 mission has been packed with innovations and surprises.
The Queqiao relay satellite carries the Netherlands-China Low-Frequency Explorer (NCLE) was developed by Radboud University in Nijmegen and other institutions in the Netherlands which will attempt to look into the cosmic 'dark ages' after the lander and roving section of the mission.
The Longjiang-1 and -2 (aka DSLWP-A/B) microsatellites launched to the Moon with the Queqiao Chang'e-4 lunar relay satellite on May 20 UTC, 2018. Harbin Institute of Technology
Launched along with Queqiao were two microsatellites, known as Longjiang-for pioneering VLBI astronomy and amateur radio experiments.
While Longjiang-1 was lost after trans-lunar injection, two cameras, one developed in Saudi Arabia and another by students at Harbin Institute of Technology in Northeast China, have returned images from Longjiang-2 lunar orbit.
An image of the Moon and distant Earth downloaded fr om Longjiang-2/DSLWP-B on October 10, 2018. Harbin Institute of Technology
China's extended lunar plans
Chang'e-4 is just one step in China's lunar exploration plans. As early as late 2019 China will attempt its first sample return mission with Chang'e-5, targeting the near side of the Moon. Its backup, Chang'e-6, could attempt a far side or polar landing and return.
While China is the only country to have soft-landed on the Moon since the Soviet Luna 24 mission in 1976, NASA, with its Lunar Gateway, India with Chandrayaan-2, the European Space Agency, Russia and private space companies are all part of a wave of renewed interest in the Moon.
The first Long March 5 rocket being rolled out for launch at Wenchang in late October 2016. Su Dong China Daily
The payload fairing for Chang'e-4 has logos from international mission partners. Visible here are the @DLR_en , @KACST and a Dutch space logo, as well as CNSA and CLEP (China lunar exploration project).
Right then, we might be in (some sort of) luck. Here's an unofficial live stream from Xichang showing the Long March 3B on the pad for the Chang'e-4 Moon mission, launching in around 90 minutes. https://www.douyu.com/1963680