WENCHANG: China on Friday launched the Chang’e-6 spacecraft to collect and return samples from the moon’s mysterious far side — the first endeavor of its kind in the history of human lunar exploration.
A Long March-5 rocket, carrying the Chang’e-6 spacecraft, blasted off from its launchpad at the Wenchang Space Launch Site on the coast of China’s southern island province of Hainan at 5:27 p.m. (Beijing Time).
Approximately 37 minutes after liftoff, the Chang’e-6 spacecraft separated from the rocket and entered its planned Earth-moon transfer orbit, which had a perigee altitude of 200 kilometers and an apogee altitude of about 380,000 kilometers, according to the China National Space Administration (CNSA).
The launch of the Chang’e-6 spacecraft was a complete success, the CNSA announced.
“Collecting and returning samples from the far side of the moon is an unprecedented feat. Now we know very little about the moon’s far side. If the Chang’e-6 mission can achieve its goal, it will provide scientists with the first direct evidence to understand the environment and material composition of the far side of the moon, which is of great significance,” said Wu Weiren, an academician of the Chinese Academy of Engineering and chief designer of China’s lunar exploration program.
“However, the mission is very difficult and risky. We are looking forward to its success,” Wu said.
The Chang’e-6 spacecraft, like its predecessor Chang’e-5, comprises an orbiter, a lander, an ascender and a returner.
After it reaches the moon, it will make a soft landing on the far side. Within 48 hours after landing, a robotic arm will be extended to scoop rocks and soil from the lunar surface, and a drill will bore into the ground. Scientific detection work will be carried out simultaneously.
After the samples are sealed in a container, the ascender will take off from the moon and dock with the orbiter in lunar orbit. The returner will then carry the samples back to Earth, landing in north China’s Inner Mongolia Autonomous Region. The entire flight is expected to last about 53 days, the CNSA said.
MOON’S TWO FACES
As the moon’s revolution cycle is the same as its rotation cycle, the same side always faces Earth. The other face, most of which cannot be seen from Earth, is called the far side or “dark side” of the moon. This term doesn’t refer to visible darkness, but rather the mystery shrouding the moon’s largely unexplored terrain.
Remote-sensing images show the moon’s two sides are very different. The near side is relatively flat, while the far side is thickly dotted with impact craters of different sizes and has much fewer lunar mares than the near side. Scientists infer that the lunar crust on the far side is much thicker than that on the near side. But why that is so remains a mystery.
An impact crater known as the Apollo basin, located within the South Pole-Aitken (SPA) Basin on the far side of the moon, has been chosen as the primary target landing and sampling site for the Chang’e-6 mission, according to Wang Qiong, deputy chief designer of the Chang’e-6 mission.
The colossal SPA Basin was formed by a celestial collision over 4 billion years ago and has a diameter of 2,500 kilometers, equivalent to the distance from Beijing to Hainan, and a depth of about 13 kilometers. It is the oldest and largest impact crater on the moon and in the solar system, and it may provide the earliest information about the moon, scientists say.
The huge impact of the celestial collision that formed the SPA Basin may have ejected materials from the depths of the moon. If those materials can be collected and returned to Earth for study, they would provide new insights into both the early impact history of the solar system and the geological evolution of the moon, said Zeng Xingguo, a scientist at the National Astronomical Observatories of the Chinese Academy of Sciences (CAS).
“First-hand, direct samples from the moon’s far side are essential to giving us a deeper understanding of the characteristics and differences of the two sides of the moon, and to revealing the secrets of the moon,” Zeng said.
More than 300 kilograms of lunar samples have been retrieved over the course of 10 missions carried out by the United States, the Soviet Union and China, and all were collected from the moon’s near side, said Yang Wei, a researcher at the CAS Institute of Geology and Geophysics.
“Our understanding of the formation and evolution of the moon comes almost entirely from the study of lunar samples, and this study is also necessary for future deep space exploration,” Yang added.
NEW CHALLENGES
“The whole mission is fraught with numerous challenges, with each step interconnected and nerve-wracking,” Wang said.
In order to realize communication between Earth and the probe on the far side of the moon, China sent the Queqiao-2 relay satellite, whose name translates to “magpie bridge-2,” into a highly elliptical lunar frozen orbit earlier this year.
Although the Chang’e-4 mission achieved the world’s first soft landing on the far side of the moon in 2019, Chang’e-6 still faces significant risks as the rugged terrain of the moon’s far side poses great challenges for its landing, space experts say.
The Chang’e-6 mission needs to see new technological breakthroughs in such areas as lunar retrograde orbit design and control, rapid intelligent sampling, and takeoff from the far side of the moon, Wang said.
The design of the Chang’e-6 probe is similar to that of the Chang’e-5 probe, which collected samples from the northern hemisphere of the near side of the moon, said Huang Hao, a space expert from the China Aerospace Science and Technology Corporation (CASC).
But Chang’e-6 will land in the southern hemisphere of the moon’s far side, so the mission will use a lunar retrograde orbit to adapt to its sampling task, Huang added.
As the Queqiao-2 relay satellite orbits the moon, the Chang’e-6 probe will be unable to communicate with controllers on Earth for some time during its operations on the moon’s far side, said Deng Xiangjin, another expert from CASC.
“We conducted a comprehensive analysis of data from hundreds of ground experiments, and used artificial intelligence to improve the design of the spacecraft to enhance its autonomous control abilities and improve its sampling efficiency,” Deng said.
“The amount of samples that Chang’e-6 can collect is uncertain and cannot be estimated accurately at present. Our goal is to collect 2 kilograms,” Deng added.
BEYOND BORDERS
The Chang’e-6 mission is carrying four payloads developed through international cooperation, providing more opportunities for the world’s scientists and merging human expertise in space exploration.
Scientific instruments from France, Italy and the European Space Agency (ESA)/Sweden are aboard the Chang’e-6 lander, and a small satellite from Pakistan is aboard the orbiter.
After the Chang’e-6 spacecraft enters lunar orbit, the small satellite will be released to carry out in-orbit imaging tasks. A laser retro-reflector developed by Italian scientists will be used for positioning and distance measurement in future lunar missions, Wang said.
A lunar surface negative ion analyzer developed by the ESA/Sweden will be used to detect negative ions and study the interaction between plasma and the lunar surface. And a scientific instrument developed by French scientists will detect radon isotopes and study the transmission and diffusion mechanisms of volatile compounds in the lunar environment, Wang said.
China adheres to the principles of extensive consultation, joint efforts and shared benefits in its international cooperation on lunar exploration, and is willing to engage in multiple levels and types of cooperation with countries and international organizations around the world, on the basis of equality and mutual benefits, said Ge Ping, deputy director of the CNSA’s Lunar Exploration and Space Engineering Center.
China has opened applications to borrow and study the lunar samples obtained by the Chang’e-5 mission to the international community, and welcomes scientists from around the world to participate in its future lunar and planetary exploration projects, Ge added.
Qamarul Islam, a professor at the Institute of Space Technology of Pakistan, expressed great appreciation for the collaboration experience with China. He said the relatively small countries who are not able to go into space on their own should be given the opportunity to do some space research.
“We are very proud to be part of this historic mission,” said Pierre-Yves Meslin, Detection of Outgassing RadoN Principal Investigator from France, adding that he is looking forward to further space cooperation between the two countries.
“The very nature of space exploration encourages us to think of our planet as one, and encourages us to think of humanity together. It is absolutely key for us to continue our young journey out into the cosmos by working together,” said Neil Melville-Kenney, Negative Ions on the Lunar Surface Technical Officer of ESA.
