China started bringing back the world's first lunar samples from the far side of the moon on Tuesday as part of the Chang'e-6 mission, according to the China National Space Administration (CNSA).

The ascender of the Chang'e-6 spacecraft took off at 7:48 a.m. (Beijing Time) from the moon's surface to dock with the orbiter-returner combo and will eventually bring the samples back to Earth. The 3000N engine operated for about six minutes and successfully sent the ascender into the designated lunar orbit.

The Chang'e-6 lunar probe was launched on May 3. Its lander-ascender combo landed on the moon on June 2. The probe spent 48 hours and completed intelligent rapid sampling in the South Pole-Aitken Basin on the far side of the moon and then encapsulated the samples into storage devices carried by the ascender according to plan.

Intelligent sampling

Intelligent sampling is one of the key stages of the Chang'e-6 mission. The probe withstood the high temperatures on the far side of the moon and successfully collected lunar samples by two methods: surface sampling with a robotic arm and drilling.

Researchers at the ground laboratory used data sent back by the Queqiao-2 relay satellite to simulate the geographic model of the sampling area and the sampling process, providing important support for sampling decisions.

Jin Shengyi with the China Aerospace Science and Technology Corporation knows the process well. He said the first step to successful sample gathering is having exact replicas made of the probe's work area, some 380,000 kilometers away.

He explained that when the lander lands on the lunar surface, it needs to first have perceptual imaging of the location. So, his team on the ground analyzed the data and built a digital model of the location. Then they built a physical replica based of the digital model that resembles the lunar surface environment 1:1.

"We place a sample-gathering mechanism in this replica environment, which is also tuned to the same status as the one on the moon," Jin said. "In this reconstructed physical environment, we select sampling points and establish sampling strategies and also verify them in this reconstructed environment."

'An extremely difficult mission'

China obtained samples from the near side of the moon during the Chang'e-5 mission in 2020. Although the Chang'e-6 probe builds on the success of China's previous lunar sample return mission, it still faces some big challenges.

Deng Xiangjin with China Aerospace Science and Technology Corporation said it has been an "extremely difficult, extremely honorable and extremely challenging mission."

After landing, the Chang'e-6 probe worked on the southern latitude of the moon's South Pole, on the far side of the moon. Deng said the team hopes it can stay in the most ideal state.

He said in order to make its lighting, temperature and other environmental conditions as consistent as possible with the Chang'e-5 probe, the Chang'e-6 probe adopted a new orbit called the retrograde orbit.

"In this way, our probe will maintain similar working conditions and environment, whether on the southern or northern latitudes; its working condition would be good," he told CGTN.

The Chang'e-6 probe works on the far side of the moon, which is always invisible from Earth. So, the probe is invisible to Earth during its entire lunar surface working process. To ensure its normal operation, the Queqiao-2 relay satellite transmitted the signals from the Chang'e-6 probe to Earth.

Even with the relay satellite, during the 48 hours that the probe stayed on the lunar surface, there were some hours when it was invisible.

"This requires our entire lunar surface work to be significantly more efficient. For example, we now have the rapid sampling and packaging technology," Deng said.

"On the far side of the moon, the landing position of the Chang'e-6 probe cannot be measured by the ground stations on Earth, so it must identify the location on its own. The same problem arises when it ascends on the far side of the moon, and it also needs to take off from the moon autonomously," he added.

Payloads on the probe

The lander, equipped with payloads such as a descent camera, a panoramic camera, a lunar soil structure detector and a lunar mineral spectrometer, has successfully powered on and conducted scientific exploration as planned.

These instruments played a crucial role in scientific missions, including the detection and study of lunar surface morphology and mineral composition, as well as the exploration of the moon's shallow subsurface structure.

Before the probe drilled for samples, the lunar soil structure detector analyzed and assessed the subsurface structure of the sampling area, providing data for the sampling process.

Scientific goals of the Chang'e-6 mission

Professor Zuo Wei with the National Astronomical Observatories of Chinese Academy of Sciences, also the chief designer of the ground application system for the Chang'e-6 mission, said the mission would fill the gaps in lunar sample studies as part of the mission's scientific significance and its scientific goals.

Zuo said there are two main scientific goals for the Chang'e-6 mission.

"One is the analysis and research of the geological background of the lunar far side landing area, and the other is the analysis and research of its lunar samples."

The mission is the first in which lunar samples from the far side of the moon have been collected. Zou said this would fill a gap in lunar sample collections.

All 10 lunar sample collections before the Chang'e-6 mission were conducted on the near side of the moon. The research on the moon and the study of its evolutionary history were also established from the near side.

The pre-selected landing area of the Chang'e-6 probe, the South Pole Aitkin Basin, is the biggest, oldest and deepest impact structure known on the moon.

"The Chang'e-5 mission has already changed human's understanding of the moon," Zuo said. "This time, we hope to collect samples from different areas and different ages. We hope to have even older lunar samples and have new understanding of the early thermal evolution of the moon."

Chinese national flag on the far side of the moon

The probe's lander displayed a physical Chinese national flag for the first time on the far side of the moon after its successful sample collection.

Professor Zhou Changyi with the National Space Science Center of Chinese Academy of Sciences, also the chief designer of the effective payload system of Chang'e-6 probe, told CGTN that the flag could stay on the moon for 10,000 years.

"Previously, we used a type of polymer fiber for the Chang'e-5 flag. This time, we used basalt rock from the Earth," said Zhou.

The stone came from north China's Hebei Province. It was pulled into extremely thin threads, which went through spinning, weaving and printing to become the flag it is.

Zhou said the material can withstand temperatures up to 700 degrees Celsius and could be made into functional clothing, for example, for firefighters on the ground. But trying out this new material on the moon could mean more because the moon also has basalt.

"Going ahead, such basalt fiber may also be used on the moon to make other things. We hope to use the basalt on the moon to make building materials. And, perhaps, even make some contributions to the future moon base," Zhou said.

(CGTN's Sun Ye also contributed to the story.)