China's lunar exploration project is divided into three phases: "circling", "dropping" and "returning". The Chang'e-3 probe, which consists of a lander and a rover, will achieve the first soft landing of an extraterrestrial body for our country's spacecraft, with the proportion of newly developed technologies reaching more than 80%.
"The thrust of Chang'e-2's braking rocket is relatively small, and its orbit changes are carried out step by step, one at a time, finally allowing it to run smoothly in an orbit around the moon at an altitude of 100 kilometers." Li Jisheng said, " The thrust of Chang'e-3's brake rocket is very large. Once it changes orbit, it will change to an orbit of 100 kilometers around the moon. Therefore, the accuracy of determining parameters such as the attitude, speed, and orbit position of the satellite is very high. If the error is large, , after the orbit change, it will deviate from the previously designed orbit."
Li Jisheng said that the first soft landing will be another challenge to the ground control system. There is no air on the moon, and it is impossible to use a parachute to slowly land the return capsule on the ground like a manned space return capsule. If the lander adopts a hard landing, the lander will be damaged, so a soft landing method must be adopted, that is, a thruster is used to generate thrust in the opposite direction to the moon's gravity to support the landing zone and slowly descend from a high altitude. When it is far away from the moon, the gravity is small.
The closer to the moon's surface, the greater the gravity. Therefore, the thrust is not a constant thrust, but a variable thrust. There are strict matching requirements between the descent height and speed of the lander, and the matching between the descent speed and altitude is designed. During the landing process, the lander will automatically control the thrust to match the descent speed and altitude. However, considering that unexpected or emergency situations may occur, the ground must have the ability to control it and monitor what it drops to on the ground. high? What's the speed? If the match does not match, the ground will send some instructions to control it to make it match. In this way, it can slowly and safely land on the moon instead of falling directly. This is the first time we have tried this control process. Technology The requirements are very high.
In addition, the remote control of China's first lunar rover "Yutu" is also a new attempt for this Chang'e-3 mission. "Under normal circumstances, the lunar rover can navigate independently without ground control. But when an unexpected situation occurs, or the ground wants to change the route of the lunar rover, it must send instructions to control the movement of the lunar rover." Li Jisheng said, "This It is a very new technology for us and needs to be tested in practice." (Yang Lei and Wang Nannan)