Wu Weiren, chief designer of the lunar exploration program, presents the Chang’e-4 rover.
Credit: CCTV/Screengrab

China is set to launch on December 8 the first farside lunar landing mission in history, headed for a touchdown within the South Pole‐Aitken (SPA) basin following a 27-day flight.

The scientific instruments of China’s robotic Chang’e-4 lander/rover will analyze both surface and subsurface of this region. Both the lander and the rover were designed as a backup for the successful December 2013 Chang’e-3 lander and Yutu rover mission.

Credit: New China/Screengrab/Inside Outer Space

As prelude to the upcoming Moon mission, China launched the Queqiao relay satellite last May. It is now positioned in an Earth-Moon L2 Lagrange point – a place in space where the spacecraft can handle communications between ground controllers and the farside lander/rover mission.

Credit: New China/Screengrab/Inside Outer Space

Biological experiment

According to an earlier Xinhua news agency story, the Chang’e-4 will carry a tin containing seeds of potato and arabidopsis, a small flowering plant related to cabbage and mustard. It may also tote along silkworm eggs to conduct the first biological experiment on the Moon.

This “lunar mini biosphere” experiment was designed by 28 Chinese universities, led by southwest China’s Chongqing University, The cylindrical tin, made from special aluminum alloy materials, weighs roughly 7 pounds (3 kilograms).

Candidate landing region of China’s Chang’e-4 lander within Von Kármán crater in SPA basin.
Credit: Jun Huang, et al.

Lander, rover payloads

The Von Kármán Crater in the Moon’s Aitken Basin is the anticipated landing site for Chang’e-4.

In a recently published paper – “The scientific objectives and payloads of Chang’e-4 mission”, led by Yingzhuo Jia of the University of Chinese Academy of Sciences in Beijing, details are offered regarding the forthcoming lunar exploration goals of the lander/rover. Jia is also with the State Key Laboratory of Space Weather, National Space Science Center of the Chinese Academy of Sciences.

Swedish Institute of Space Physics Advanced Small Analyzer for Neutrals (ASAN) instrument for Chang’e-4 rover.
Credit: Institutet för rymdfysik, IRF

The Chang’e-4 mission totes six kinds of scientific payloads.

On the lander, it carries the Landing Camera (LCAM), the Terrain Camera (TCAM), and the Low Frequency Spectrometer (LFS). There are three kinds of payloads on the rover, the Panoramic Camera (PCAM), the Lunar Penetrating Radar (LPR), and the Visible and Near-Infrared Imaging Spectrometer (VNIS).

That Low Frequency Spectrometer is newly developed for Chang’e-4 lander; the other payloads are inherited instruments from Chang’e-3 lunar mission.

There are also three international joint collaboration payloads within the Chang’e-4 explorer mission:

  • Germany’s Lunar Lander Neutrons and Dosimetry (LND) installed on the lander
  • Sweden’s Advanced Small Analyzer for Neutrals (ASAN) installed on the rover
  • Netherlands-China Low-Frequency Explorer (NCLE) installed on the relay satellite

Overall, the scientific objectives for the Chang’e-4 are:

  • Low-frequency radio astronomical study on the lunar surface
  • Shallow structure investigation at the lunar farside within the roving area
  • Topographic and mineralogical composition studies of the lunar farside within the rover’s patrol area

The Chang’e-4 mission carrying out low-frequency radio astronomical studies on the lunar surface is intriguing.

The lunar farside blocks the Earth’s ionosphere, human-made radio frequency interference, and the auroral kilometric radiation noise. Additionally, also blocked is the solar radio emission during the night time.

“Hence, the lunar farside has been believed as the best place for the low-frequency radio astronomical observation,” the paper notes. The Low Frequency Spectrometer on the lander and the Netherlands-China Low-Frequency Explorer installed on the relay satellite are slated to carry out joint low frequency radio astronomical observations.

Group shot…China’s Chang’e 3 lander and Yutu rover in December 2013 mission.
Credit: Chinese Academy of Sciences

Penetrating look

Another aspect of the Chang’e-4 rover is use of a Lunar Penetrating Radar, able to detect the lunar subsurface structure on the robot’s patrol route, and to detect the thickness and structure of the lunar regolith. The device is a nanosecond impulse radar with bistatic antennas.

A similar device was utilized on the Chang’e-3 rover, Yutu.

It works like this: An ultra-wideband nanosecond impulse is produced by a transmitter, sent through the transmitting antenna down to lunar surface. The receiving antenna receives the reflected signal. The echo signal from the underground target is received by the receiving antenna, amplified in the receiver and then restored as data record.

South Pole-Aitken (SPA) basin.
Credit: NASA/Goddard

Impact basin

The SPA basin is the largest and oldest impact basin of the Moon. Although the terrain is low, this region is not filled with mare basalts as other Moon basins, Yingzhuo and colleagues note, suggesting its special thermal history and unique evolution features. The materials in the region are likely to be of great significance to reveal the compositions of the crust and even the mantle of the Moon. All kinds of lunar exploration data show that SPA basin possesses unique geochemical characteristics.

China’s next lunar probe, Chang’e-5, is designed to bring select samples from the Moon back to Earth. It builds upon a progression of Chinese Moon explorers: Chang’e-1 and Chang’e-2 orbiters in 2007 and 2010, respectively, and the Chang’e-3 lunar lander/rover mission in December 2013.

To access the paper, “The scientific objectives and payloads of Chang’e-4 mission,” go to the Planetary and Space Science journal, Volume 162, 1 November 2018, Pages 207-215 at:

https://www.sciencedirect.com/science/article/pii/S0032063317300211?via%3Dihub

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