A mission to the dark side of the moon

While one side of the moon always faces Earth, the other side is always in shadow and largely unexplored.

China has launched a Chang’e-4 lunar probe to explore the dark side of the moon.

While one side of the moon always faces Earth, the other side is always in shadow and largely unexplored.

Chang’e-4, which includes a lander and rover, lifted off early Saturday morning from the Xichang Satellite Launch Center in southwest China’s Sichuan Province.

After a journey of almost four weeks, Chang’e-4 is set to land on the Aitken Basin of the south pole region, one of the largest and deepest impact craters in the Solar System at around 2,500 kilometers in diameter and 12 kilometers deep.

“The soft landing and exploration of the far side, which has never been done before, will result in first-hand information about the terrain and lunar soil components and other scientific data,” said Zhang He, executive director of the Chang’e-4 project.

“It will help enrich our understanding of the moon and the universe.”

The probe includes the first lunar low-frequency radio astronomy experiment, according to the China National Space Administration.

A mission to the dark side of the moon
Xinhua

China launches Chang'e-4 lunar probe in the Xichang Satellite Launch Center in southwest China's Sichuan Province, December 8, 2018.

The dark side has a clean electromagnetic environment, according to Zou Yongliao, head of the moon and deep-space exploration department under the Chinese Academy of Sciences. This makes it an ideal place for the study of low-frequency radio.

Astronomers believe the research will lead to new discoveries about solar eruptions, star formation and how galaxies evolve.

The probe will also study the environment of the moon’s dark side, including landforms, mineral composition, surface structure and radiation conditions.

The rocks on the Aitken Basin will be able to tell us more about the chemical composition of the moon and its evolution, Zou said.

Shanghai scientists have made great contributions to the project and there are several “made in Shanghai” aspects to the mission.

The country’s first lunar probe, Chang’e-1, was launched in 2007, making China the fifth country to develop and launch a lunar probe on its own.

Chang’e-2, launched in 2010, created a full lunar map with a resolution of 7 meters, as well as images of the Sinus Iridum, or the Bay of Rainbows, with a resolution of 1.5 meters, showing the details of the proposed landing site of Chang’e-3.

Chang’e-3, launched in 2013, was the first Chinese spacecraft to soft-land on and explore an extraterrestrial object.

1. The Ruler and Eye

The Shanghai Institute of Technical Physics of the Chinese Academy of Sciences’ laser range sensor works as the “ruler” of the lunar lander and rover.

When the lander is 15 kilometers above the moon, the newly developed “ruler” begins its work with two laser beams, one for short distances and the other for long.

“The moon’s far side has more craters than its near side and the terrain there is more rugged, so, the landing is more difficult,” said Cheng Pengfei, deputy researcher of the institute.

Cheng said the lander will rotate 90 degrees during landing, which requires the sensor to shift from using the long-distance laser beam to the short-distance one. For the Chang’e-3 probe, which landed on the moon’s near side, that happened when it was 3 kilometers above the surface. But the Chang’e-4 will operate at about 6 to 8 kilometers, which is more challenging.

The new sensor, with a detection range exceeding 40 kilometers and with superior range measurement accuracy, is designed for the extreme space environment.

After Chang’e-4 lands, the mirror-like Visible and Near-infrared Imaging Spectrometer, working as an “eye,” will start work. It will collect spectral information on the moon’s surface for analysis of its mineral composition.

“Compared with the VNIS used for the Chang’e-3 lunar probe, the new device has an optimized detection performance, and the data collection time is reduced to half,” said Xu Rui from the institute.

Xu said the technology was not just for the lunar probe. “It has a range of applications, such as exploration for minerals and the treatment of air and water pollution,” Xu said.

2. The GPS

Scientists around the world use Very Long Baseline Interferometry to track moving objects in space.

The Shanghai Astronomical Observatory of the CAS is using the most advanced version of the technology to track and position Chang’e-4 on its 380,000-kilometer journey.

The system gives scientists immediate access to Chang’e-4’s exact position. Within a minute, they can figure out whether it is on the right orbit or make adjustments. It took around 10 minutes to deal with data in the 2007 Chang’e-1 mission, said Hong Xiaoyu, the observatory’s senior researcher.

A mission to the dark side of the moon

The Very Long Baseline Interferometry.

China’s VLBI system is made up of a VLBI center and four telescopes in Shanghai, Beijing, Kunming in southwest Yunnan Province, and Urumqi in the northwest Xinjiang Uygur Autonomous Region.

The four telescopes together form one giant “telescope” with a diameter of more than 3,000 kilometers, spanning from Beijing in the north, Kunming in the south, Urumqi in the west and Shanghai in the east.

3. The Dress and Tights

Spacecraft are exposed to an extremely tough environment where temperatures can quickly swing from 100 degrees Celsius above zero to 100 degrees below zero.

Like spacesuits for astronauts, spacecraft also need “suits.”

Those for Chang’e-4 have been designed and made by the Shanghai Institute of Ceramics of the CAS.

As the probe prepares to land, its 7500N engines will fire, raising temperatures to around 1,400 degrees Celsius. To protect the probe’s electronic equipment, the institute designed a hood in the shape of the bustle dresses worn by women in the 1880s.

A mission to the dark side of the moon

The special “suits” designed for Chang’e-4.

“It is as thick as one centimeter and it can cover an area of 4 square meters,” said Yu Yun, a researcher at the institute. “It creates a barrier.”

On the moon, temperatures can range from over 100 degrees Celsius to 200 degrees below zero. Sensing components such as detectors wear “tights” to enable them to work in freezing temperatures and burning-hot conditions. The “tights” ensure the temperatures remain within the safe operating limits.

4. The Sunscreen

Not all parts on Chang’e-4 can wear “suits” or “tights.” So, they wear “sunscreen,” or thermal control coatings.

“The coatings are tailor-made to meet the different demands in temperatures of different parts of the Chang’e-4,” said Zou Yongjun, senior engineer at the Shanghai Institute of Organic Chemistry of the CAS.

Besides protecting Chang’e-4 from extremely chilly or scorching conditions, the coatings have been upgraded.

“To ensure that cameras take clear photos of the moon, we designed coatings that can eliminate stray lights,” Zou said. “Also, to protect some fragile core components, we upgrade to resist static electricity.”

A mission to the dark side of the moon

Thermal control coatings.

5. The Scanner

A 3D laser scanning device is being used to work out where the probe should land.

When Chang’e-4 is around 100 meters above the moon’s surface, the device will start to work. Within a second, it can emit 50,000 laser beams and figure out whether the area is suitable.

“Cameras usually take 2D photos which just show whether there are pits or rocks,” said Liu Yuan, senior engineer at the Shanghai Institute of Optics and Fine Mechanics of the CAS. “But 3D laser scanning can tell us how deep a pit is. It is of vital importance for Chang’e-4 to make the soft landing.”

Liu said the device had to be smart enough to find a suitable landing point in the limited time available.

“We can’t see what’s happening on the dark side of the moon and thus we can hardly offer a hand in time,” he said. “Also, the batteries will run out after a while.”

A mission to the dark side of the moon

The 3D laser scanning device

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