Author: Guo Chaokai

　　At 23:11 on December 1, Beijing time, after a week of earth-moon transfer, near-moon braking, and a round-the-moon flight journey, the Chang'e-5 probe successfully landed on the front of the moon at 51.8 degrees west longitude and 43.1 north latitude. The pre-selected landing zone near the distance, and return the landing image map.

　　As the final battle of the three-step "circle, fall, and return" of the Chinese lunar exploration project, the Chang'e-5 mission will collect about 2 kilograms of lunar samples from the moon and return to the earth.

Where does the Chang'e-5 probe softly land on the moon?

How does the detector land steadily?

How will "digging" operations be carried out after landing?

Where did it fall?

　　According to the China National Space Administration, at 22:57 on December 1st, the Chang'e-5 lander and ascender combination began a power reduction from about 15 kilometers away from the lunar surface. The 7,500-Nine variable thrust engine was turned on and the probe was gradually turned on. The relative lunar speed dropped from about 1.7 km/s to zero.

The landing image of the Chang'e-5 probe taken on December 1.

Photo by Xinhua News Agency reporter Jin Liwang

　　During this period, the Chang'e-5 probe made rapid attitude adjustments and gradually approached the moon surface.

After that, automatic obstacle detection was carried out. After the landing site was selected, the obstacle avoidance and slow vertical descent began, and the land steadily landed in the area north of the Rumk Mountains in the storm ocean on the front of the moon.

During the landing, the landing camera equipped with the lander took an image of the landing area.

　　After the successful landing, the lander under ground control has carried out the state inspection and setup work such as the deployment of the solar wing and the directional antenna, and will officially start the lunar surface work lasting about 2 days, and it is expected that about 2 kilograms of lunar samples will be collected.

　　Previously, the US Apollo planned to bring back more than 380 kilograms of lunar samples from the moon. The Soviet Union relied on unmanned aerial vehicles to obtain more than 300 grams of lunar soil in three times; however, spacecraft from the United States, the Soviet Union and other countries have not visited Rümm. Near the mountain range.

　　Ouyang Ziyuan, an academician of the Chinese Academy of Sciences and the first chief scientist of the Chinese Lunar Exploration Project, once said that the landing site chosen by China is thousands of kilometers away from the landing site of the Apollo program, which will usher in new phenomena and discoveries.

　　Pang Zhihao, the chief science communication expert of national space exploration technology, told China News Agency that the frontal storm ocean on the moon is relatively young, rich in radioactive elements such as uranium, thorium, and potassium, and there are basalts about 1.3 to 2 billion years ago. These young basalts are obtained. The isotope age of, will help advance the understanding of the lunar volcanic activity and evolution history.

It can fill an important gap in the study of lunar volcanic activity by scientists.

　　"According to lunar scientists, previous studies of lunar soil samples obtained by the United States and the Soviet Union showed that volcanic activity on the moon peaked 3.5 billion years ago, then weakened and stopped. However, observations on the lunar surface found that certain areas may contain The volcanic lava formed only 1 to 2 billion years ago is similar to the age of the Chang'e 5 landing area. If the samples recovered by Chang'e 5 can confirm that the moon is still active during this period, it will rewrite the history of the moon." Pang Zhihao Say.

Image taken by the landing camera of the Chang'e-5 probe after a soft landing Source: National Space Administration

How to fall?

　　After selecting the area north of the Rumke Mountains as the landing site, how does the Chang'e-5 landing ascent assembly complete a series of moves with a high degree of difficulty in a short time and land steadily on the surface of the moon?

　　Experts from the Fifth Academy of China Aerospace Science and Technology Corporation told reporters that after active deceleration, rapid adjustment, approach, hovering avoidance, slow descent, and free fall, the steady fall of Chang'e 5 seemed light and relaxed, but it contained scientific research. Many wisdom and accumulation of personnel.

There are four things to watch for this Chang'e 5 landing moon.

Aspect 1: "Quick site selection and stable settlement"

　　The setting moon of the Chang'e 5 mission is the same as the braking of the recent moon. There is one chance and only one success.

Since it involves the lunar takeoff of the ascender after sampling, the process of the Chang'e-5 landing on the moon is also to select the "launch site" for the subsequent lunar takeoff of the ascender.

　　Compared with Chang'e-3 and Chang'e-4, Chang'e-5 has unprecedented high requirements for the location accuracy and flatness of the landing site. This requires no too high bumps, no too deep pits, and gradients in the landing area. To meet the task requirements.

　　In order to achieve "correct site selection and accurate settlement", Chang'e 5 adopts the "coarse and fine relay obstacle avoidance" method used on Chang'e 3 and 4 where 502 of the Fifth Academy is located.

The landing and ascent assembly will hover once when it reaches 100 meters from the lunar surface. By taking pictures of the selected area, the landing point can be accurately identified and selected.

After that, the landing ascending assembly flies diagonally downwards, paying attention to avoiding obstacles while descending, flies directly above the selected landing site and then descends vertically, shuts off the main engine in advance when it is closer to the lunar surface, and then uses the landing legs. Buffer to achieve a soft landing.

Aspect 2: Landing buffer "shows their talents"

　　The key to the falling moon lies in the word stability.

When the Chang'e 5 landing ascending assembly hits the lunar surface, it will cause a large impact load. It is necessary to design a corresponding landing buffer system to absorb the impact load of landing to ensure that the probe does not tip over or sink. This is the falling moon. One of the technical difficulties.

The landing buffer mechanism, in layman's terms, is the "leg" of Chang'e-5.

　　Compared with the landing buffer design scheme of Chang'e-3, due to the increased difficulty of the mission, the landing buffer capacity requirements of the Chang'e-5 mission have been increased by 30%, but the agency weight index has been reduced by 5%.

The "legs" of Chang'e 5 inherited the good genes of Chang'e 3 and Chang'e 4. It has a completely independent intellectual property rights of "biased close, self-tightening" scheme, which guarantees simple folding and reliable deployment, and solves the landing buffer. Various issues such as landing stability ensure that Chang'e-5 can complete its "close embrace" with the moon in a stable and reliable manner.

Aspect 3: "Please close your eyes at dark"

　　During the landing process, when the Chang'e-5 landing ascending assembly is close to the lunar surface, the main engine will arouse moondust, which will easily trigger the moondust to pollute the star sensor, which will affect the subsequent lunar takeoff of the ascender.

　　In order not to let the moon dust "fascinate the beautiful eyes of the ascender", the researchers specially designed a cover.

Cover the lens of the star sensor at a certain height from the moon surface. After the moon is set, the moondust will dissipate, and the star sensor will be notified to open the cover. Between the opening and closing, the lander and ascender are combined. Has successfully landed on the moon.

This process is affectionately called "close your eyes when it's dark" by researchers.

Aspect 4: Directional antennas "a thread"

　　The falling moon affects the hearts of Chinese people.

What test is Chang'e 5 going through at a distance of 380,000 kilometers?

All information needs to be transmitted through a small "pot" of the landing and ascent assembly to transmit telemetry data.

This "small pot" is a directional antenna-a transmission conversion device that transmits data from the detector to the ground.

　　To send data from the moon back to the earth, the communication distance is tens of thousands of times farther than ground mobile phone communication, which requires a special ground directional antenna to send data.

The directional antenna designed by the researchers includes a reflective surface antenna radiator and a biaxial drive mechanism.

In order to reduce the weight of the whole device, this reflector antenna has an extremely lightweight design, which is more than 40% lighter than similar antennas, which is both light and reliable.

　　Experts from the Fifth Academy of China Aerospace Science and Technology Corporation said that the dual-axis drive mechanism is like a human shoulder joint and elbow joint. It drives the reflective antenna radiator to rotate flexibly, ensuring that the "small pot" is always aligned with the ground and transmitting the Chang'e-5 landing to the earth. Telemetry data.

Chang'e 5 has a combined body simulation diagram.

Photo courtesy of Beijing Flight Control Center

How to "dig soil"?

　　The Chang'e-5 mission is one of China's most difficult space missions with the most complicated system composition.

After successfully landing on the moon, the Chang'e-5 probe will carry out about 2 days of lunar surface work, "do all it takes" to collect about 2 kilograms of lunar samples, and realize China's first extraterrestrial celestial body sampling.

　　Researchers have meticulously designed two "digging" modes for Chang'e-5: drilling and surface extraction.

The detector carries "artifacts" such as drilling and sampling devices, surface sampling devices, surface sampling primary packaging devices, and sealed packaging devices. Deep drilling, shallow drilling, and shoveling, digging, and clipping will be used. Collect about 2 kilograms of "lunar soil" and seal and package them.

　　"Our goal is two kilograms. After demonstration, two kilograms are not small in quantity and can be achieved in engineering." said Pei Zhaoyu, deputy director of the China National Space Administration's Lunar Exploration and Space Engineering Center and spokesperson for the Chang'e 5 mission. But as an assessment of this mission, our goal is to sample and return. If we collect samples and return to Earth, we will succeed. No matter how many we bring, we will succeed."

　　According to the movement relationship between the sun, the earth, and the moon, as well as the various constraints of the project, the total period of the Chang'e 5 mission is 22 to 23 days, with all links interlocking.

This task will create five "China No. 1".

　　"The first is the sampling and packaging of extraterrestrial objects, the second is the takeoff of extraterrestrial objects, the third is the lunar orbital rendezvous, the fourth is the high-speed earth reentry with samples, and the fifth is the analysis and research of lunar samples. This is the first time in my country. ." Pei Zhaoyu said.

　　From launch to successful landing, it took 380,000 kilometers, arrived in 7 days, and descented in more than 800 seconds. The performance of the Chang'e-5 probe was almost perfect.

　　This is the third successful soft landing of a Chinese probe on the surface of the moon, which is a big step forward from the dream of sampling and returning from the moon.

Looking forward to the "Five Girls" of Chang'e successfully completing the "earth excavation" work and returning to the earth smoothly!