How was a soft landing on the far side of the moon successfully achieved?

Because the moon rotates synchronously as it orbits the earth, people in the past knew almost nothing about the conditions on the far side of the moon. It is said that in 1822, when the 84-year-old William Herschel was dying, he told the priest that it would be the greatest happiness in his life if he could see the back of the moon. Unfortunately, no one could satisfy his request at that time. In order to solve this eternal mystery, the former Soviet Union launched the "Lunar 3" automatic interplanetary station on October 4, 1959, after the "lunar 2" accurately hit the moon and achieved a hard landing. It is 1.3 meters long, 0.96 meters in diameter and weighs about 279 kilograms. On October 6, it began to orbit the moon and eventually became an "artificial asteroid." At about 6:30 a.m. on the 7th, it successfully circled to an altitude of about 7,000 kilometers on the far side of the moon. During the 40 minutes of flying over the back of the moon, it took many photos at different scales, immediately processed them automatically (including correcting the distortion caused by perspective), and then sent the data back to the earth, making it the first time for humans to do so. See the real situation on the far side of the moon. Although the clarity of these photos was not ideal due to the technical conditions at the time, they were undoubtedly a group of extremely precious photos. After that, "Lunar 3" flew away from the moon and became an artificial asteroid.

The success of "Moon 3" has won praise from all over the world. However, humans are not satisfied and they continue to work hard. Because to achieve human landing on the moon, a hard landing or a miss will not work. It must descend slowly on the moon like an airplane. This requires turning on the brake rocket before landing and jetting forward to gradually reduce the speed and implement a "soft landing". Obviously, a soft landing is much harder than a hard landing.

But there is still a question: Can the detector be supported on the lunar surface? In the past, some people believed that due to the continuous bombardment of meteorites over billions of years, a deep layer of fine dust-like quicksand was formed on the surface of the moon. After landing, the spacecraft would fall into a "sand pool" just like the Red Army passed through the grass during the Long March. , causing the falling object to be submerged. Therefore, soft landing can explore the actual conditions of the lunar surface and is an indispensable step before humans land on the moon.

The first soft landing on the moon was still the former Soviet Union's probe - "Moon 9", which was also mankind's first "automatic station". It was launched on January 31, 1966, with a take-off weight of 1,583 kilograms. On February 3, it reached 75 kilometers above the moon, and then a "lunar module" weighing about 100 kilograms automatically separated from the rocket and slowly descended to the west of the Procellarum. After the lunar module landed safely (it weighed only about 16 kilograms on the lunar surface), it automatically opened its protective cover and the camera began to work. It worked on the lunar surface for 75 hours, allowing humans to obtain the first batch of photos of the sky and its surface taken from the moon, giving people an immersive feeling. The desolate and peculiar scenery on the moon left a deep impression on people. Four months later, the American "Surveyor 1" also landed safely in the Oceanus Procellarum, not far southeast of the former Soviet Union's "Moon 9".

The weight of the American "Surveyor" probe when it took off was between 1 and 1.5 tons. The lunar module weighed about 280 kilograms and contained many instruments. For example, in addition to a television camera, Surveyor 3 also carried a special small excavator for lunar surface sampling. After it landed on the lunar surface on April 19, 1967, according to the order of the ground command, it dug the first artificial trench in the "Sea of ??Consciousness", which was 20 centimeters deep. The excavated lunar soil was sent to the lunar module for testing and analysis. One week after landing on the lunar surface, "Surveyor 6" rose 4 meters high from the lunar surface again under the command of the ground, moved 2.5 meters, and landed again on the lunar surface 8 seconds later. "Surveyor 7" used laser to measure the distance between the moon and the earth with an error of only ±15 centimeters, with an accuracy of four parts per 10 billion! If you use it to measure the distance from Nanjing to Beijing, the error will be within a hair.