How difficult is it for Chang'e to fly to the moon? The game between major power

"On May 3rd, Beijing time, at 17:27, the Chang'e 6 probe was successfully launched by the Long March 5 Y8 carrier rocket from the Wenchang Spacecraft Launch Site in China, and then accurately entered the Earth-Moon transfer orbit, achieving a complete success in the launch mission."

01

Sampling on the Far Side of the Moon: Strategic Revelations of the Lunar Exploration Project

Over a month ago, the Queqiao-2 relay satellite mission achieved a complete success, winning a good start for China's fourth phase of the lunar exploration project. Now, Chang'e 6 has been successfully launched and completed the near-moon braking at 10:12 on May 8th, starting its lunar orbit, providing the necessary conditions for the subsequent lunar sampling, and the task process of sampling and returning from the far side of the moon is nearing half completion.

Chang'e 6 is a key link in China's fourth phase of the lunar exploration project, and its core mission is to complete the sampling and return from the far side of the moon, which is an important part of the construction of the basic type of the International Lunar Research Station. The International Lunar Research Station is a comprehensive scientific experimental facility jointly built by China and multiple countries, which will operate independently on the lunar surface and in lunar orbit for a long time, with short-term human participation, and is expandable and maintainable.

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The research station is mainly composed of five major infrastructures: the Earth-Moon transportation system, the long-term lunar operation support system, the lunar transportation and operation system, the lunar scientific research facility system, and the ground support and application system. It will carry out multidisciplinary and multi-target scientific research activities such as lunar exploration and utilization, lunar-based observation, basic scientific experiments, and technical verification.

Academician Wu Weiren, the chief designer of China's lunar exploration project and the director of the Deep Space Exploration Laboratory, pointed out that the International Lunar Research Station will be implemented in three stages: the first step is planned to be completed by 2028, mainly to carry out lunar environmental exploration and resource utilization test verification; the second step is planned to be completed by 2040, mainly to carry out the exploration of the space environment of the Sun, Earth, and Moon, and scientific experiments, and to build the Queqiao communication and navigation integrated constellation, serving manned lunar landing and deep space exploration of Mars, Venus, etc.; the third step is to build an application-type lunar research station, gradually upgrading from a research-type experimental station to a practical, multi-functional lunar base.

To build the basic type of the International Lunar Research Station, it is necessary to have an in-depth understanding of the lunar environment and the utilization of lunar soil resources, because this is related to the planning and design of the subsequent research station's work schedule, as well as the process of maintenance, supply, and other logistical support work. More importantly, it is closely related to the exploration direction of many subsequent scientific research activities and is also a prerequisite for the smooth progress of the second and third stages of research.

In 2020, the Chang'e 5 probe successfully landed with 1731 grams of lunar samples in the预定 area of Inner Mongolia's Siziwang Banner, and China's first lunar sampling and return mission was successfully completed, laying a solid foundation for human understanding of the lunar environment. However, due to the huge differences in the material composition, morphological structure, and rock age between the front and back of the moon, based on the in-depth study of the lunar samples brought back by Chang'e 5, we need to obtain lunar soil samples from the far side of the moon to analyze the lunar environment more comprehensively, which means that the success of the Chang'e 6 mission will add another important piece to the lunar exploration puzzle.The core mission of Chang'e 6 this time is to collect samples from the far side of the Moon and bring them back to Earth. Compared to the previous Chang'e 5 mission, which sampled on the near side of the Moon, Chang'e 6 faces greater and more complex challenges. In addition to continuously optimizing technologies such as lunar orbit braking, lunar orbiting, and soft lunar landing that have been mastered in previous missions, and consolidating the achievements of the "orbit, land, and return" three-stage strategy, Chang'e 6 also faces many tests that have never been encountered before.

On one hand, the far side sampling and return mission requires breakthroughs in technologies such as the design and control of lunar retrograde orbit, intelligent and rapid sampling on the far side, and the ascent from the far side. On the other hand, unlike the unobstructed sampling on the near side, the biggest difficulty in sampling from the far side lies in communication, as the Moon itself blocks the communication signals between Chang'e 6 on the far side and ground command. This is the issue that the previously launched Queqiao-2 relay satellite was designed to solve.

From the successful lunar near side sampling and return of Chang'e 5, to the relay communication services provided by the Queqiao-2 relay satellite, the smooth progress of Chang'e 6's far side sampling and return mission is based on the success of previous missions, and at the same time, it also helps to further the construction of the basic type of the International Lunar Research Station.

02

Exploring the Moon for 20 Years: Great Power Cooperation and Competition

In addition to the advancement on the technical front, another highlight of this launch mission is international cooperation. Since the China National Space Administration (CNSA) released the "Chang'e 6 Mission International Payload Cooperation Opportunities Announcement" in April 2019, it has collected and selected international payload proposals in two batches, ultimately confirming four international payload projects: the European Space Agency's lunar surface negative ion analyzer, France's lunar radon detector, Italy's laser retroreflector, and Pakistan's CubeSat.

On the launch day of May 3rd, about 50 international friends from space agencies and embassies of various countries such as Pakistan, France, Italy, as well as international organizations like the United Nations and the European Space Agency, participated in the Chang'e 6 International Payload Seminar held by the CNSA in Haikou, and together witnessed the launch of the Chang'e 6 mission.In fact, in the face of the arduous tasks, complex technologies, and numerous difficulties of space projects, international cooperation has become a consensus among countries. As early as the end of the last century, the space station project, jointly constructed by the United States, Russia, Japan, Canada, and the European Space Agency, had already begun to take shape; in 2017, the Russian State Space Corporation and NASA announced that the two countries would jointly create a lunar research station. However, the influence of factors such as faults and emergencies, as well as political maneuvering, has led to serious pressure on the decades-long cooperative relationship between the United States and Russia.

At the beginning of 2021, Russia officially withdrew from the plan to jointly build a lunar research station with the United States and stated that it would exit the International Space Station cooperation project by 2025 to build its own space station. In the same year, China and Russia signed a memorandum of understanding for the cooperative construction of an international lunar research station and issued a "Joint Statement of the China National Space Administration and the Russian State Space Corporation on the Cooperative Construction of an International Lunar Research Station."

Russia's resumption of its lunar exploration program is due to the strategic need to reshape its image as a major power, and the change in partners reflects the major power games and the reconstruction of the world order. At the same time, on the other side of the ocean, the lunar exploration approach centered around the "Artemis" program also plans to join hands with international partners and private enterprises to maximize the influence of national geopolitical strategy and economic fields.

It is true that lunar exploration is inevitably closely linked to the games of major powers. However, from the perspective of a community with a shared future for mankind, all technological breakthroughs will lead to the same destination, promoting the progress of human civilization in a way that is "peaceful use, equality and mutual benefit, and common development." This is also the original intention of China's proposal for the international lunar research station plan.

03

The Long Journey: Deep Space Exploration is a Long-term Task

As the outpost of deep space exploration, the moon has always been a key target for countries to conduct research. Continuously deepening our understanding of the moon can not only help humanity understand the formation and evolution of the solar system and the universe, the origin and evolution of life, but also guide the development of space activities. It also helps humanity to transfer experience and conduct research on more distant celestial bodies. In this process, new disciplines and technologies will be hatched, further advancing the development of frontier sciences.

The study of lunar soil by Chang'e 5 once became a hot topic on the internet due to the news term "moon cannot grow vegetables," making the "vegetable-growing gene engraved in the bones of the Chinese people" a hot topic. This not only demonstrates the unique agricultural civilization mark of the Chinese nation but also means that the mythological story of "Chang'e flying to the moon" is gradually entering the public and becoming closer to reality."Our journey is the stars and the sea."

— The resounding slogan still echoes in our ears, but looking back at our feet, the road to deep space exploration is still a long and arduous task.

Wu Weiren once said in an interview: "Compared to the universe, humans are insignificant, but the spirit of humans exploring the universe and space is great." It is this spirit of pursuing dreams and daring to explore that has allowed generations of Chinese space professionals to continuously break through technical barriers and move towards the dream of the moon.

Now, more than fifty years have passed since the successful launch of China's first artificial satellite, "Dong Fang Hong I," and China's lunar exploration project has also spanned a full twenty years. Where will the information from the lunar soil lead human deep space exploration? What difficulties and challenges will we face in the future?

04

How difficult is Chang'e's journey to the moon?

In the vast five thousand years of memory of the Chinese nation, the imagination of the moon has never ceased, which is Li Bai's "Ancient Rhapsody of the Bright Moon" with "When young, I did not know the moon, I called it a white jade plate," and it is also Du Fu's "Recalling My Younger Brother on a Moonlit Night" with "The dew is white tonight, the moon is bright in my hometown"... And since the Chang'e project was established in 2004, we have launched 8 times with a 100% success rate. According to the plan, the Chang'e project as a whole can be divided into three major steps of "exploration," "landing," and "residence," collectively referred to as the "three major steps," which respectively mean unmanned lunar exploration, manned moon landing, and long-term lunar residence.

Among them, the lunar exploration part is the currently implemented "Chinese Lunar Exploration Project," which is divided into three phases of "orbiting," "landing," and "returning," collectively referred to as the "three minor steps." After the basic completion of the three minor steps, the fourth step "survey" was proposed, which is the main character of our story today, "Chang'e 6."From Chang'e 1 to Chang'e 6

Steady and progressive technological iteration

Tracing the history of the Chang'e Project, it is clear to understand that Chang'e 1 to Chang'e 5 have completed the first of the three major steps, namely "lunar exploration." This process began in 2007 and came to a close in 2020. So, what have they specifically done?

According to the three-step plan, the theme of Phase I was "orbiting," completed by Chang'e 1 (2007) and Chang'e 2 (2010). They launched lunar orbiters/hard landers to orbit the moon at a height of 2000 kilometers above the lunar surface, conducting global lunar exploration.

The theme of Phase II was "landing," completed by Chang'e 3/Yutu (2013) and Chang'e 4/Yutu 2 (2018). They launched lunar soft landers/rovers to land on the lunar surface, releasing a lunar rover for detailed local exploration near the landing area. The landers also carried astronomical telescopes to observe the starry sky from the moon. During Phase II, the Queqiao relay communication satellite was also launched to prepare for communication during the far side of the moon landing.

The theme of Phase III was "return," completed by Chang'e 5's pathfinder (2014) and Chang'e 5 (2020). They launched a lunar automatic sampling returner, which, after landing on the lunar surface, used a mechanical arm to collect lunar soil and rock samples, and then sent them back to the returner. The returner brought the lunar samples back to Earth for related research.

The fourth phase of the project, "survey," actually marks the beginning of the second of the three major steps, the "ascend" plan. It starts with the launch of Chang'e 6 and the Queqiao II relay satellite in 2024, followed by Chang'e 7 and Chang'e 8. The theme of this phase is a comprehensive exploration of the lunar south pole, including a comprehensive survey and verification of the moon's topography, composition, and space environment, as well as the exploration of some technologies, in preparation for the future joint establishment of a lunar scientific research base by various countries.Landing on the Far Side of the Moon

The Big Test After Multiple Quizzes

According to plans, Chang'e 6 will collect 2 kilograms of lunar soil and rock samples from the Apollo crater in the South Pole-Aitken basin on the far side of the Moon and return them to Earth. This will be the first sample obtained from the far side of the Moon by humans. The South Pole-Aitken basin is the oldest known impact crater in the solar system, and it is currently believed to have formed in the early stages of the Moon's birth.

The Apollo crater is currently thought to have formed about 4 billion years ago. These two impacts allowed a large amount of lunar mantle material to reach the surface of the Moon. Therefore, the samples returned by Chang'e 6 will help in studying the history of the Earth-Moon system and the entire solar system. At the same time, Chang'e 6 will use other instruments it carries to obtain more scientific research data for the study of the lunar environment.

So, with a history of lunar landings spanning over 50 years, why hasn't the far side of the Moon been visited before? It's not because, as NASA administrator Nelson said, "the far side of the Moon is always dark." In fact, the far side of the Moon is illuminated by sunlight when the Moon is not full, and during a lunar eclipse, the entire far side can be fully illuminated.

The real key issue is communication, as the Moon's rotation speed is equal to its orbital speed around the Earth. Only one side always faces the Earth, maintaining a relatively balanced state of force, which is why from Earth, we always see only this one side of the Moon facing us. This final state of force balance is called "tidal locking." We know that electromagnetic wave signals travel in straight lines, which means we cannot communicate directly with the far side of the Moon from Earth. That's why we launched two Queqiao relay satellites to orbit in the Lagrange L2 Halo mission orbit, solving this problem.

In fact, Chang'e 6 is not the "first star" to make a soft landing on the far side of the Moon. As early as 2019, during the Chang'e 4 mission, we completed the world's first soft landing on the far side of the Moon and transmitted back the world's first close-up image of the far side through the Queqiao relay satellite. This was the world's first soft landing and inspection on the far side of the Moon, as well as the first landing at a high latitude polar region on the Moon, and the first relay communication between the far side and Earth.

Considering that Chang'e 4 has already visited the far side and Chang'e 5 has achieved lunar surface sampling, the fundamental purpose of Chang'e 6 this time is to integrate these two successful experiences, much like a student who, after undergoing multiple unit tests, finally faces the final exam...After completing the sampling on the far side of the Moon, the ascender will carry lunar regolith and take off from the far side to dock with the orbiter-returner combination. According to experts from the China Aerospace Science and Technology Corporation, Chang'e 6 uses the same rendezvous and docking technology as Chang'e 5. After the ascender takes off, it must perform four orbital maneuvers to reach the predetermined orbit. Then, the orbiter-returner combination gradually and steadily approaches the ascender, ultimately achieving rendezvous and docking. The process is completed by transferring the lunar samples from the ascender to the returner. Therefore, the biggest challenge throughout the entire process is how to control the stability.

The deep lunar crust and mantle composition are one of the key issues in current lunar science. They are of great significance for our understanding of the early differentiation of the Moon, and for exploring the dichotomy of the Moon, which includes the distinct differences in topography, structure, material composition, and distribution of the crust thickness between the near and far sides of the Moon. However, the far side also has a considerable area, and where to sample becomes a scientific topic.

As the oldest and largest impact basin on the Moon, the South Pole-Aitken Basin is the most likely basin to unearth mantle materials. Its peak ring, basin interior, and the impact melt layer and impact melt breccia of the ejecta blanket are all excellent areas for sampling mantle materials. Although the excavated mantle materials may be covered by regolith and basalt, later-formed impact craters can expose fresher mantle materials again. Therefore, the Aitken Basin is an ideal area for exploring and studying the deep lunar crust and mantle materials, and it has become the ultimate destination for Chang'e 6. It is expected to bring back a large amount of basalt, as well as some highland materials that have been splashed over by impacts. Scientists hope to understand the timing of volcanic activity and the composition of volcanic rocks on the far side of the Moon from these compositional information, as volcanic magma mainly comes from the mantle, and its compositional information can be used to infer the composition of the mantle.

In addition, the exploration of the Moon's interior is often achieved through the analysis of seismic waves. The seismometers from the Apollo era were all deployed on the near side of the Moon. However, the most representative terrain for the early differentiation of the lunar magma ocean is the pristine highlands on the far side of the Moon, as well as the largest and oldest South Pole-Aitken Basin in the solar system. Therefore, the far side of the Moon is the best place to study planetary evolution, which is also one of the reasons why Chang'e 6 chose this location.

Moreover, if we look at the second step of the entire lunar exploration plan, Chang'e 7 is planned to be launched around 2026, intending to continue landing at the South Pole of the Moon, with the main mission of conducting flying detection and striving to find water. Chang'e 8 is planned to be launched around 2028, with the purpose of conducting surveys on the material, environmental climate, and mineral composition of the South Pole of the Moon. At that time, the most critical step: the International Lunar Research Station will also be preliminarily established. Therefore, choosing the region with the greatest scientific significance for exploration is the most fundamental part of the Chang'e project.