Chang’e-4 release of Yutu-2 rover shown in artwork.
Credit: China Central Television (CCTV)/China National Space Administration (CNSA)/Screengrab/Inside Outer Space

China’s Chang’e-4 mission to the farside of the Moon has garnered a number of new China Central Television (CCTV) interviews, revealing details of the pioneering effort and those involved in the undertaking.

Safe on the farside, Chang’e 4 set down somewhere in this NASA Lunar Reconnaissance Orbiter LROC image obtained July 17, 2010. The lines connect craters seen in the Chang’e 4 descent image (CNSA/CLEP) with the same craters seen in the LROC image.
Credit: NASA/GSFC/Arizona State University

China’s Yutu-2 (Jade Rabbit-2) lunar rover, which on January 3 (Beijing time) made a historic touchdown on the farside of the Moon together with the Chang’e-4 probe, has a strong all-terrain mobility to safely trundle across the treacherous lunar surface, said its design director.

Image of Yutu-2 on the Moon’s farside during deployment from lander.
Credit: China Central Television (CCTV)/China National Space Administration (CNSA)/Screengrab/Inside Outer Space

Six-wheel drive

The rover’s cross-country ability is supported by its six-wheel drive system and four-wheel-steering system, said Shen Zhenrong, design director of Rover of Chang’e-4 Probe Project, fifth institute of China Aerospace Science and Technology Corporation (CASC).

“The rover has all of its six wheels drivable, and at its four trundles there is a steering wheel, which allows the rover to make a pivot turn, thus comes the six-wheel drive and four-wheel steering systems,” he said.

In addition to the special drive system, the rover also features light body weight and a unique wide mesh wheel design that not only enhances its payload capacity but also avoids lunar dust accumulation on the wheels.

Pre-launch prepping of Yutu-2 rover.
Credit: China Central Television (CCTV)/China National Space Administration (CNSA)/Screengrab/Inside Outer Space

Terramechanics

“We did some terramechanics tests to come up with this elastic mesh wheel design. The width of the wheels enhances the rover’s payload capacity to some extent, and the mesh sifts through the fine dust on the Moon, which lightens the burden on the wheels,” said Shen.

With such a design, the rover is able to climb a slope of up to 20 degrees, said Shen.

Originally a backup plan for the rover of Chang’e-3 probe, the Yutu-2 is actually more than just a simple replica of its predecessor the Yutu lunar rover, according to Shen. 

Credit: China Central Television (CCTV)/China National Space Administration (CNSA)/Screengrab/Inside Outer Space

Upgraded version

The Yutu-2 rover is an upgraded version of its predecessor in terms of software and hardware.

“For different purposes of scientific exploration, we removed the X-ray detector and installed at its head a neutral atom detector, which is jointly developed by China and Sweden. Other loaded devices such as the infrared spectrograph, the built-in panorama camera, and the lunar exploration radar, remain unchanged in comparison with that of (the rover of) the Chang’e-3,” said Shen.

On a roll. China’s Yutu-2 rover on the Moon’s farside.
Credit: CNSA/CLEP

Another subtle change on the Yutu-2 is better cable enclosure, which leaves almost no single cable unprotected on the body.

“Because on the lunar surface, the cables could scratch on the rock’s edges and trigger short circuit. So we adopted a new method to enclose the Chang’e-4’s cables and then tested the enclosure with some stability, reliability and duration tests,” said Shen.

The Chang’e-4 lander/rover spacecraft are now expected to study the mineral composition and shallow lunar surface structure of the Moon’s farside, as well as perform low-frequency radio astronomical observation.

Yutu-2 rover moves toward crater inspection.
Credit: CGTN/CNSA/CLEP

Chang’e-4 touched down at a preselected landing area at 177.6 degrees east longitude and 45.5 degrees south latitude on the farside of the Moon at 10:26 (Beijing Time), the China National Space Administration announced.

The process was recorded by the camera on the lander and the images were sent back to Earth via the relay satellite “Queqiao” (Magpie Bridge), which operates in the halo orbit around the second Lagrangian (L2) point of the Earth-moon system, about 65,000 kilometers  from the Moon, where it can see both Earth and the moon’s far side.

Relay satellite for handling farside operations.
Credit: CNSA’s Lunar Exploration and Space Engineering Center (CNSA-LESEC)

Stern challenges

Engineers and scientists overcame various obstacles before succeeding in developing the Chang’e-4 probe and Yutu-2 rover.

One of the stern challenges is taking on the day/night changes in temperature on the Moon’s surface.

“We have adopted a new temperature control technology to keep an ideal temperature inside the probe on the Moon, day and night. It may sound quite easy but we encountered many obstacles, including the two-phase fluid system. When conducting the experiment on ground, we found that the heat-transfer capability of the system was not what as we expected,” said Sun Zezhou, chief designer of the Chang’e-4 probe, China Academy of Space Technology.

He explained that it was because they couldn’t perfectly simulate the gravity of the Moon on the Earth. After tons of work and by introducing innovative measures, the team finally managed to pull it off and build a reliable heat control system.

Chang’e-4 carrying out low-frequency radio astronomical studies.
Credit: CCTV/Screengrab/Inside Outer Space

The sustainability and reliability of the rover in negotiating the changing terrains is crucial.

“So we were sure we could accomplish the designated targets, that is, the rover must move at least 10 kilometers on different terrains. Just as what I mentioned, we made the lifespan of the rover at least four times that of the original under the simulated high and low temperatures and the topography of the moon surface,” said Zhang Xiao, executive director of Chang’e-4 probe, China Academy of Space Technology.

Visualization program

Chinese engineers have developed a system to visualize the abstract data of Chang’e-4’ lunar exploration.

“With this visualization program, we created a lunar rover in the virtual world and established a coordinate system of moonwalk. We can observe where the rover walks to with the real ratio. Also our rover, the conditions of the lander can be displayed to our scientists in a visualized way,” said Zhang Kan, engineer of software office of the Beijing Aerospace Control Center (BACC).

The first close-up photo of the Moon’s farside, taken by a monitoring camera on the Chang’e-4 lander showed the direction the rover would drive on to the lunar surface. Top of image shows the rails the rover will use to access the surface.
Credit: CNSA/CLEP

The exploration process is displayed in the form of animation, but without a predesigned script. All the development is decided by the real time data sent back from the Chang’e-4 probe.

Lunar tour

“After we received the data, we start all parts of our three-dimensional visualized program, like the angle of rotation and lunar tour. Our real time reflection of the rover’s gesture and position is of great importance,” said Zhang.

The system can also help scientists and engineers tell whether the probe is in good condition and detect any mistake it may have during lunar exploration, according to Zhang.

“If any mistake occurs, the system can reflect on our rover and lander in real time. If any part is out of order, or the data is wrong, the system can reflect in real time. Therefore the scientists and engineers can notice immediately and analyze and track down which part went wrong,” said Zhang.

Credit: China Central Television (CCTV)/China National Space Administration (CNSA)/Screengrab/Inside Outer Space

One small roll

Chang’e-4’s rover, named “Yutu-2” (Jade Rabbit-2), rolled onto the floor of the moon’s Von Karman Crater in the South Pole-Aitken Basin at 22:22 Beijing Time (14:22 GMT) about 12 hours after the probe’s soft-landing on the moon’s uncharted side, which is never visible from Earth.

“The separation process of Chang’e-4’s rover was smooth and perfect. The rover rolled only a small step onto the moon, but it represented a huge stride for the Chinese nation. It is a crucial step for us in exploring space and the universe,” said Wu Weiren, the chief designer of China’s lunar exploration program.

Radio clean environment

The probe will conduct low-frequency radio astronomical observations, survey the terrain and landforms, detect mineral compositions and shallow lunar surface structures and measure the neutron radiation and neutral atoms to study the environment on the far side of the moon, according to the China National Space Administration.

“The probe will detect various physical phenomena dating back to the formation of the universe. The farside of the Moon has a clean environment with low noise, which is very helpful for our research. It is of great scientific significance to reach the farside in terms of a deeper understanding of the Moon,” said Ye Peijian, an academic from the Chinese Academy of Sciences.

Germany’s scientific payload is a “Lunar Lander Neutron and Dosimetry” instrument, developed by Kiel University.
Credit:
Kiel project manager. Jia Yu

Dose rate

The Chang’e-4 is installed with payload Lunar Lander Neutrons and Dosimetry. Jointly developed by Chinese and German scientists, the project is expected to overcome some of these concerns.

“Our instrument measures the dose rate or the radiation which astronauts would experience on the moon. If you were on the moon, both the neutral and the charge dose rate, and that’s something which is important because that’s the only risk, once an astronaut has come back from the moon, that’s the only risk that remains,” said Robert F. Wimmer-Schweingruber, a professor with Kiel University in Germany who took part in the Lunar Lander Neutrons and Dosimetry project.

“This instrument also plans to measure whether there is water on the farside of the Moon’s surface, and its quantity. We hope to measure the quantity as precisely as possible,” said Zhang Shenyi, Chinese co-principal investigator of the Lunar Lander Neutrons and Dosimetry project.

Particle analyzer

Another payload, the Advanced Small Analyzer for the Neutrals, developed by Chinese and Swedish scientists, has taken on a different responsibility.

“The payload will measure two kinds of particles – the ones brought by solar winds, which may be charged with electrons and later produce a hydrogen atom, and the other, original particles of the Moon, such as sodion, oxygen ion,” said Zhang Aibing, co-principal investigator of Chang’e-4 Advanced Small Analyzer for Neutrals.

This instrument was jointly developed by Chinese and Swedish Scientists back in 2015.

“It is very important to understand what happens when the solar wind crashes into the lunar surface, and it interacts there and spread particles around. And these particles form the extremely thin atmosphere like gases environment of the moon surface,” said Johan Kohler, head of the Space Situational Awareness of Rymdstyrelsen Swedish National Space Agency.

Credit: NASA/GSFC/Arizona State University

Open data policy

The Low-Frequency Explorer was installed on the relay satellite Queqiao. It was jointly developed by scientists from China and the Netherlands.

“It (exploring the low frequency) aims to understand how that planet is rotating, what is the major cause of such activity. Whether all of these movements inside the solar system will affect human being’s lives is also a question,” said Ping Jinsong, co-principal investigator of the Low-Frequency Explorer.

Over the next few months, scientists from around the world will receive first-hand data from their instruments. They say they will study and share their findings with other global experts in accordance with an open data policy.

Go to these informative videos about the Chang’e-4 mission:

https://youtu.be/1_rCTxTSQn8

https://youtu.be/aW7f3cyKD9Y

Note: Leonard David is author of Moon Rush: The New Space Race to be published by National Geographic in May 2019.

To pre-order Moon Rush: The New Space Race, go to:

https://shop.nationalgeographic.com/products/moon-rush

https://www.barnesandnoble.com/w/moon-rush-leonard-david/1129287265?ean=9781426220050

https://www.amazon.com/Moon-Rush-New-Space-Race/dp/1426220057

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