The wisdom of the hottest chang'e-5 landing on the

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On December 1, 2020, the landing and ascent assembly of chang'e-5 probe successfully completed a soft landing in the predetermined area of the lunar surface through the stages of active deceleration, rapid adjustment, approach, hovering obstacle avoidance, slow descent and free fall

this light and steady landing contains the wisdom and efforts of countless astronauts

find the landing point while flying

for Chang'e V, there is only one chance to land on the moon, and it must be a success

compared with Chang'e 3 and Chang'e 4, Chang'e 5 has unprecedented requirements for the position accuracy and flatness of the landing site. As it involves the ascent taking off on the lunar surface after the completion of sampling, the process of selecting the landing point of Chang'e 5 is also the process of selecting the "launch site" for the subsequent ascent taking off on the lunar surface. There should be no too high bulges or too deep pits in the landing area, and the slope should also meet the task requirements

in short, it is like an autonomous "parachute jump" starting from 600 kilometers away and completed within 15 minutes

in order to achieve "correct site selection and accurate completion", Chang'e 5 adopted the "rough and fine relay obstacle avoidance" method that has been successfully applied on Chang'e 3 and 4. In this way, under the command of the guidance, navigation and control (GNC) system developed by the 502 Institute of the Fifth Academy of Aerospace Science and technology of China, the landing and ascent assembly first brakes and decelerates with high thrust, then quickly adjusts its attitude, takes photos of the terrain in the landing area where high molecular polymers are required to have necessary mechanical properties when they are intended to be used as materials, avoids large obstacles, realizes "rough obstacle avoidance", and then falls obliquely to the selected landing point, After flying directly above the landing site, it will change to vertical descent. When approaching the lunar surface, it will turn off the engine and land on the moon

eyes for exploring the path of the moon

gnc system cannot make decisions without various data support. The microwave range and velocity sensors developed by Xi'an Branch of the Fifth Academy of engineering, just like a pair of bright eyes, sense the path of Chang'e 5 to the moon and transmit information to the decision-making "brain"

according to Zhang Aijun, chief designer of the microwave range and velocity sensor of Xi'an Branch, it is completely different from the traditional chemical rocket. This radar starts when the landing and rising assembly is about 15 kilometers away from the lunar surface, and officially starts working when it is 6 kilometers away from the lunar surface

"the radar can detect the distance between the lander and the lunar surface, as well as the descent speed of the lander, and provide speed and distance information to the guidance, navigation and control system of the ascent, so that the lander can judge the landing point and speed." Zhang Aijun said

the moon landing engine has unique skills

the engine provides power guarantee for the safe landing of Chang'e 5. However, the mission of safe soft landing on the lunar surface cannot be completed by relying on ordinary aerospace engines

according to the sixth Institute of Aerospace Science and technology group, the moon is in a vacuum state and has no atmosphere, which means that air friction cannot be used to slow down. In order to complete the landing phase actions such as power descent and hover of the detector, the engine is required to have the ability to adjust the thrust depth

2006, the sixth Institute officially launched the key technology research of 7500 n variable thrust engine. After hard exploration, the development team has successively broken through three key technologies, namely, "high-performance and long-life thrust chamber", "accurate flow regulation and stability" and "engine system optimization and integration". The engine technical indicators basically meet the requirements of the detector, laying a solid foundation for subsequent development tasks

with the full support of 7500 n variable thrust engines, chang'e-3 spacecraft completed the first soft landing of extraterrestrial objects in China in December 2013; In january2019, chang'e-4 spacecraft realized the first lunar soft landing for humans. This time, it escorted chang'e-5 landing and ascending assembly to land on the moon smoothly

"brake commander" major

the engine shutdown in the final stage of Chang'e 5 lunar landing requires accurate instructions. Developed by China Aerospace Science and Industry Corporation γ The shutdown sensor is the "brake commander" in the process of falling the moon, which is very important

after the process of the moon falling, the γ The shutdown sensor measures the distance between the detector and the lunar surface in real time. When Chang'e 5 fell to a height less than 5 meters from the lunar surface, the equipment sent a shutdown command to shut down the orbit control and attitude control engines. This moment determines the success or failure of the landing mission. With the withdrawal of the reverse thrust of the engine, Chang'e 5 was able to fall to the moon

according to the introduction, γ X-ray has the characteristics of low interference from external environment and high accuracy, so it is used in manned spaceflight and lunar exploration missions with the highest requirements for accuracy and reliability. Previously, the γ The altitude control device has been successfully applied in the Shenzhou spacecraft mission to escort the astronauts back safely

the "legs" of Chang'e 5 were unusual

left the thrust of the engine, and Chang'e 5 landed in the form of free fall. Although the lunar gravity is small and the landing height is not high, a certain impact load will still be formed when it impacts the lunar surface

this requires the landing buffer system to play a role, absorb the impact load during landing, and ensure that the detector does not overturn or fall

the landing buffer mechanism, popularly speaking, is the "leg" of Chang'e 5, which is one of the technical difficulties in the moon landing link. The four "legs" of chang'e-5 are unusual. They integrate cushioning and support functions, inherit the perfect genes of chang'e-3 and chang'e-4, and are carefully designed by the institutional subsystem team of the Fifth Academy of Sciences

it is learned that the mechanism adopts the "offset retraction and self compression" scheme with completely independent intellectual property rights, which ensures simple retraction and reliable deployment, and can solve many problems such as landing buffer and landing stability

compared with the landing buffer design scheme of Chang'e 3, the landing buffer capacity of Chang'e 5 mission is increased by 30% due to the increased difficulty, but the weight index of the mechanism is reduced by 5%. The research team of the overall design department of the Fifth Institute finally solved this problem

exquisite design you don't know

there are some little-known exquisite designs in the process of Chang'e 5 falling into the moon

from the surface, it is the lander that "holds" the ascent to the moon. In fact, the GNC system on the lander works with the help of the central control computer and star sensor on the ascent

the central control computer is the "strongest brain" used by the ascent when it takes off on the lunar surface, and the star sensor allows the ascent to determine its attitude by "looking at the stars"

this kind of "cooperation" is a clever trick that designers have come up with in combination with the fact that "the ascent accompanies the lander throughout the whole process", which not only saves the cost, but also reduces the weight

in addition, when the lander approaches the lunar surface, the lunar dust aroused by the engine is easy to confuse the star sensor, thus affecting the subsequent ascent takeoff. The development team specially designed a cover to cover the lens of the star sensor at the final stage of the moon. They called it "please close your eyes after dark". Let the star sensor "open its eyes" after the moon sets and the dust clears

the bridge of Earth Moon communication

the output pull signal of Chang'e 5 control hydraulic cylinder, which has experienced the test of life and death at a distance of 380000 kilometers, worries Chinese people about every move at the upper and lower limits of high and low temperatures. Fortunately, through various antennas and data transmission means, the ground can keep in touch with Chang'e 5, understand its dynamics at any time, and send instructions to it

the ascender is equipped with a measurement and control antenna developed by Xi'an Branch, which, like the one carried by Chang'e 5, is the main support for measurement and control communication between it and the ground. The photos taken by the lander are sent back in real time by the data transmission system developed by the Institute to provide a basis for ground decision-making

compared with those on the ground, the communication distance between the earth and the moon is tens of thousands of times longer, and a special directional antenna to the ground is required for data transmission. The directional antenna designed by the overall design department of the fifth institute adopts a double axis drive mechanism, just like the human shoulder and elbow joints, which can make the reflector antenna radiator rotate flexibly and always aim at the ground. In order to meet the task requirements, the reflector antenna is designed to be extremely lightweight, and the weight is reduced by more than 40% compared with similar antennas

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