Zhongxin Wanghai, June 6 Question: How important is the last meter? "Count" to see the landing of the "Shenzhou XV" return module

Reporter Zheng Yingying Ma Shuaisha

According to the China Manned Space Engineering Office, at 2023:6 Beijing time on June 4, 6, the Shenzhou 33 manned spacecraft return module successfully landed at the Dongfeng landing site, and the on-site medical supervision and medical insurance personnel confirmed that astronauts Fei Junlong, Deng Qingming and Zhang Lu were in good physical condition, and the Shenzhou <> manned mission was a complete success.

The return of the spacecraft goes through four stages: braking deceleration, free glide outside the atmosphere, re-entry into the atmosphere, and recovery landing. Among them, recovery landing is the final step in manned spaceflight, and there are many key nodes in the process.

It is about 35 km above the ground

After the re-entry module enters the dense atmosphere, it is the most hostile stage of the return process. As the altitude decreases, the density of the air becomes more and more, and the friction between the surface of the spacecraft and the atmosphere generates huge heat, resulting in the return module not receiving the radio signals sent by the ground, and the ground cannot receive the radio signals sent by the return module, this area is called the radio "black barrier area".

The landing search beacon is located at the bottom of the return module and is one of the devices for communication between the spacecraft and the ground. According to the 804 Institute of the Eighth Academy of China Aerospace Science and Technology Corporation, the landing search beacon machine began to work after leaving the "black barrier area", and continued to send beacon signals outward to ensure that when the return module was about 35 kilometers away from the earth and the black barrier disappeared, it would re-contact the ground as soon as possible and give the target information. After that, the landing search beacon continued to work, marking its position until the return module search and rescue mission was completed.

It is about 10 km above the ground

During the return landing of the spacecraft, reducing the speed and slowing the impact is the key to ensuring the safety of astronauts. When the return module is about 10 kilometers above the ground, the guidance parachute, deceleration parachute and main parachute are opened one after another, and the speed of the return module is reduced from 200 meters per second to 7 meters per second.

But the speed of 7 meters per second is still very dangerous for astronauts, and landing at this speed is very likely to cause damage to the astronauts' spine. In order to ensure the life safety of astronauts and let them still have a good ride feeling at the last moment of landing, the landing thrust reverser engine needs to start the "key escort" before landing.

About 1 meter above the ground

When the return module descends to about 1 meter above the ground, the four landing thrust reverser engines installed at the bottom of the return module begin to "brake precisely", further reducing the rappelling speed on the basis of parachute deceleration. After receiving the command, the four landing thrust reverser engines ignite simultaneously within 4 milliseconds to achieve the purpose of slowing down the landing speed.

According to the 806 Institute of the Eighth Academy of China Aerospace Science and Technology Corporation, the ideal cushioning effect of the return module is when the landing thrust reverser engine is turned off, which is exactly the landing time of the return module. Therefore, the technical difficulty in the development of landing thrust reverser engines lies in "precision" and "synchronization": not only simultaneous ignition, but also accurate thrust performance in an accurate time. Any one of the landing thrust reverser engines working abnormally may endanger the safety of astronauts in the return module.

The four landing thrust reverser engines are each about 4 kg and less than 10 cm in diameter. Don't look at their size and weight, each can produce about 30 tons of thrust when working, and 3 units work together to have nearly 4 tons of thrust. These four landing thrust reverser engines are "small and complete", and "extremely powerful", steadily helping astronauts go home for the last 12 meter. (End)