Chang'e-6 returns triumphantly, bringing back "local specialties" from the far side of the moon! 1935.3 grams! This is the first time that humans have returned lunar samples. Don't be fooled by the fact that this is just nearly 4 pounds of "soil", its value is even more valuable than gold. Scientists have high hopes for these treasures from the moon, as they hold the secrets of the moon's past and present, and even the solar system. Each one could be the key to unlocking new knowledge. We have too much curiosity and expectation for this lunar soil. Since the 1950s, humans have conducted more than 100 explorations of the moon and 10 samples have been collected and returned from the front of the moon. The United States has carried out 6 manned moon landings through the Apollo program, bringing back a total of 381.7 kilograms of lunar samples; The Soviet Union collected 326 grams of lunar samples in three stages through a lunar probe; In 2020, Chang'e-5 carried out China's first unmanned lunar sampling and return mission, bringing back 1731 grams of lunar samples. So, since the Chang'e-5 mission has been successfully completed, why does the backup Chang'e-6 still have to fly to the moon to 'dig soil'? Because for lunar research, the diversity of these samples is far from sufficient. The surface area of the moon is close to 38 million square kilometers, only slightly smaller than the area of Asia, and current sampling research is very limited Yang Yuguang, Vice Chairman of the Space Transport Committee of the International Astronautical Federation, said that there is a significant difference in terrain and landforms between the far and near sides of the moon, and the formation process has its own particularities. More samples are needed to support research on its geology, volcanic activity, and other aspects. Previous studies have also shown that the moon has a binary nature, with significant differences in composition and structure between the front and back sides. The thickness of the lunar crust on the near side of the moon is approximately 30 to 50 kilometers, and the distribution area of basalt is over 30%; On the far side of the moon, the thickness is about 60 to 80 kilometers, and the distribution area of basalt is only about 3%. Due to direct exposure to space, the far side of the moon acts as a shield, blocking a large number of small celestial bodies from directly impacting the Earth. Therefore, unlike the relatively flat and open front of the moon, the far side of the moon is covered with gullies, canyons, and cliffs. A very obvious feature is that more than 90% of the low-lying and flat areas on the surface of the moon are located on the front side of the moon, which is called the lunar mare. Chang'e-5 landed in the largest lunar mare on the front side of the moon - the Mare Imbrium. However, there are almost no large lunar mare on the far side of the moon except for the Moscow Sea, "said Yang Yuguang. Due to the "tidal lock" of the moon, its rotation period and revolution period are equal, and the strong gravity of the Earth always causes the moon to face the Earth in the same direction. Humans can only see the front side of the moon from Earth. For humans, the far side of the moon can be described as a 'secret realm within a secret realm'. It can be said that in terms of lunar sampling, Chang'e-5 has completed this ring in time because it has collected the youngest lunar soil with a geological age of about 2 billion years on the front side of the moon, while Chang'e-6 has completed this ring in space, "said Yang Yuguang. What is the difference between the "soil" on the far side of the moon and the "earth" on the front side of the moon? Collecting samples from the far side of the moon, especially from the South Pole Aitken Basin that we have chosen, may result in significant differences in mineral chemical composition compared to samples from the near side Li Chunlai, the deputy chief designer of Chang'e-6 mission and a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, believes that studying these samples will help reveal the unique geological structure and material composition differences on the back of the moon, and more comprehensively understand the geological evolution history of the moon. Li Chunlai analyzed that the sampling point of Chang'e-6 is located in a huge impact basin, which was ejected by early impact events and is likely to excavate deep materials. The Antarctic Aitken Basin is a massive impact crater that provides an opportunity for studying early impact history, and even early impact processes on Earth. It helps to understand and judge the early evolutionary history of the solar system, and promotes comparative planetary studies. During the sampling process, we felt that the lunar soil on the far and near sides of the moon was different. The lunar soil on the near side was more delicate and loose, while the state on the far side seemed to be different. Therefore, we have higher expectations and hope that scientists will make new discoveries Hu Hao, the chief designer of the Chang'e-6 mission, said. 1935.3 grams, each gram represents a technological breakthrough in 53 days, 11 stages, 1935.3 grams! Starting from May 3rd, the Long March 5 Yao-8 carrier rocket successfully launched the Chang'e-6 probe into its designated orbit. It went through stages such as Earth Moon transfer, near moon braking, separation of the four spacecraft, smooth lunar landing, surface sampling, lunar takeoff, rendezvous and docking, sample transfer, lunar orbit waiting, lunar ground transfer, and re-entry and recovery. Finally, Chang'e-6 returned to Earth with full achievements. Looking back on this journey to explore the moon, it was not easy to find the "local specialties" on the back of the moon. Where is the difficulty? The terrain and landforms on the back of the moon are complex, there is only one chance for the moon to fall, and "digging soil" is like "opening a blind box"... Sampling and returning on the back of the moon has no precedent to follow, facing many new situations and problems. This mission is more challenging than the Chang'e-4 lunar landing and the Chang'e-5 lunar surface sampling Yang Yuguang believes that one of the major difficulties faced by Chang'e-6 is that "landing, sampling, and takeoff on the far side of the moon all require relay satellites for measurement and control, and the entire process cannot be directly monitored through ground stations." "Chang'e-6 was originally a backup of Chang'e-5, and executing the far side mission is a new challenge to the backup." In Hu Hao's view, the challenges come from multiple aspects such as quality and reliability, changes in technical status, and planning arrangements. What should I do? Before the Chang'e-6 mission, researchers conducted in-depth analysis on the quality and reliability of both space and ground products, making the entire system more robust, healthy, and reliable; Many changes have been made to adapt to the landing sampling on the far side of the moon; In just over a year, we started developing the Magpie Bridge 2 relay satellite from scratch and carried out extensive testing and verification work... "The fact proves that we have successfully addressed various challenges and successfully completed the mission," said Hu Hao. Difficulties are constantly being overcome, and there are new breakthroughs in key core technologies. There are many highlights Yang Yuguang introduced that the Chang'e-6 mission has achieved three key technological breakthroughs. ——Breakthrough in the design and control technology of lunar retrograde orbit. The basic status of Chang'e-6 and Chang'e-5 is the same, the difference is that Chang'e-6 landed on the far side of the moon, and the landing location changed from the northern hemisphere to the southern hemisphere. If we continue to use the lunar prograde orbit scheme of Chang'e-5, it means that many devices are facing in the opposite direction. The retrograde lunar orbit scheme adopted by Chang'e-6 has brought certain difficulties to the orbit design, but it avoids significant adjustments to hardware equipment and achieves the optimal performance of the entire system. This is a well-designed measure that can effectively reduce costs. ——Breakthrough in moon back intelligent sampling technology. The lunar back sampling of Chang'e-6 can only rely on the support of the Queqiao-2 relay satellite. Once problems arise, the task becomes difficult, especially for surface sampling. Due to the fact that the path of the robotic arm is not unique, it is very difficult to complete the task independently without human intervention. The researchers have upgraded the Chang'e-6 sampling and packaging subsystem, designed control algorithms and sampling strategies suitable for sampling on the far side of the moon, further improved the intelligence and automation of sampling, and enhanced sampling efficiency and capabilities. ——Breakthrough moon back takeoff and ascent technology. Chang'e-6 will take off from the far side of the moon and perform intelligent autonomous control with the assistance of the Queqiao-2 relay satellite. The sampling and return of Chang'e-6 spacecraft adopts the method of lunar orbital rendezvous and docking, which requires the ascent vehicle to enter the same orbital plane as the orbital return combination, and then achieve close range rendezvous and docking through adjustment. The ascent spacecraft flies at a speed of approximately 1700 meters per second in lunar orbit, which means that even small deviations in the orbital plane can lead to rendezvous and docking failures. The Chang'e-6 mission is the most technologically advanced lunar exploration mission in China's space history to date, and also the fourth successful soft landing on the lunar surface in China. This will lay a solid foundation for future larger and deeper lunar and deep space exploration activities Yang Yuguang said. On June 28, 2016, the handover ceremony of Chang'e-6 lunar sample was held in Beijing. The National Space Administration handed over the Chang'e-6 sample container and sample certificate to the Chinese Academy of Sciences. This marks the official transition of the Chang'e-6 mission from the engineering implementation phase to a new stage of scientific research. How to manage lunar samples, where particles are precious? Actually, there are rules to follow. In 2021, the National Space Administration issued the "Management Measures for Lunar Samples" to standardize the preservation, management, and use of lunar samples, in order to maximize their scientific research value and social benefits. In principle, lunar samples are divided into four basic uses: permanent storage, backup permanent storage, research, and public welfare. The Lunar Sample Laboratory is the 'first stop'. Both Chang'e-5 and Chang'e-6 lunar samples need to be unsealed, stored, and distributed here. The lunar sample laboratory is divided into three rooms from the outside to the inside. The first room is used to unseal samples, the second room stores Chang'e-5 lunar samples, and the third room is prepared for Chang'e-6 lunar samples. In the laboratory, staff classify and store existing Chang'e-5 lunar samples based on whether they have been in contact with the atmosphere. Zhou Qin, deputy chief designer of the ground application system for the Chang'e-6 exploration mission, introduced that the lunar samples that have been in contact with the atmosphere are divided into two parts: one is some rock samples selected at that time, and the other is some returned samples released to the public. The primitive lunar samples that have not been exposed to the atmosphere will be stored in a nitrogen sealed glove box. In addition, Zhou Qin also introduced the preservation method of resin embedding - making small rock debris particles or lunar soil into resin light strips, and researchers can directly use these light strips for isotope and chemical composition analysis. This method can maintain the original shape of the sample particles, facilitating research. At the same time, in the sealed state, the sample is not easily broken, which is conducive to long-term storage and use. To save well, it is even more important to use it well. Previously, the National Space Administration had distributed 7 batches of 85.48 grams of Chang'e-5 lunar samples to 131 research teams in China. Bian Zhigang, Deputy Director of the National Space Administration, revealed that Chinese scientists have discovered the sixth new mineral on the moon, "Chang'e stone," from lunar samples collected by the Chang'e-5 mission; The study also proved that magma activity still existed on the moon 1.96 billion years ago, extending the known geological lifespan of the moon by 1 billion years. The entry of lunar samples into the "Chang'e era" has greatly enriched human understanding of the moon and even the universe. With the deepening of research on lunar samples from Chang'e-5, more mysteries of the moon are being uncovered. Pang Zhihao, the chief scientific communication expert of national space exploration technology, stated that according to the mission plan, the main scientific tasks of Chang'e-6 are focused on searching for new minerals and rocks, searching for deep lunar materials, searching for ancient materials, and unraveling the mystery of the formation of norite. To uncover the truth, we still need to wait for researchers to complete the analysis and research of the samples, but we can look forward to the possibility that the Chang'e-6 lunar samples may contain the following components: rock fragments, which come from rocks on the lunar surface; Mineral particles, including feldspar, pyroxene, ilmenite, etc., are the main components of the lunar surface; Glass material, formed by impact melting; Trace elements such as copper, gold, etc. are very helpful for studying the formation and evolution of the moon; helium