I believe that many friends have seen the picture of the Shenzhou 17 spacecraft returning home, from entering the black barrier state when re-entering the atmosphere and briefly losing contact, to opening the guidance parachute, deceleration parachute, and main parachute, and finally at the moment of landing on the ground, there was a dazzling fire at the bottom of the spacecraft, and the scene suddenly appeared in the situation of smoke and dust.
This kind of situation also appeared when the previous Shenzhou manned spacecraft returned, and the fire appeared at the moment of landing, and with the appearance of the fire, the dust at the landing site was also lifted. And such a scene did not exist when the American spacecraft returned. What is going on here? Could it be that the technology of our spacecraft returning to the home is inferior to that of the people and not as advanced as that of the United States?
In the history of human spaceflight, there have been two types of manned spacecraft, one of which is the Shenzhou manned spacecraft, the Soyuz manned spacecraft, the manned Dragon spacecraft, and the other is the space shuttle that has been decommissioned. From the point of view of the design concept, the space shuttle does have a lot of obvious advantages.
The first advantage is that the space shuttle has a very strong load capacity, which can send more than 20 tons of payload into space, and the famous Hubble telescope was transported to space by the space shuttle, and during the operation, the space shuttle also carried out in-orbit repair and maintenance of the Hubble telescope many times.
The second advantage is that the shuttle can not only be reused, but can glide through the air like a fixed-wing aircraft on the return to Earth and then land on the runway. A return technology such as the Space Shuttle will not have a flash of fire, nor will there be smoke and dust.
However, due to various reasons, the space shuttle was retired more than 10 years ago, and now the manned spacecraft of China, the United States, and Russia have gone through a series of compartment separation, re-entry into the atmosphere, opening parachutes, and finally landing at the landing site when returning home. The difference is that the US manned spacecraft choose to land in the sea, while the Chinese and Russian manned spacecraft land on land.
How did the ship get back?
When the Shenzhou manned spacecraft, the Soyuz manned spacecraft, and the Manned Dragon spacecraft are launched, they are all vertically launched with high-thrust carrier rockets, and then the orbits are adjusted after entering orbit, and then rendezvous and docking with the space station assembly. In the case of return, it is not a vertical return to home like a launch, and the whole process is still more complicated.
As a first step, the spacecraft will not return to Earth immediately after it is evacuated from the space station assembly. Taking the Shenzhou 17 spacecraft as an example, it needs to fly around the earth 5 times, and then adjust the flight attitude, the first time is that the entire spacecraft rotates 90 degrees counterclockwise, changing to lateral flight, at this time, the orbital module will be thrown away, leaving only the return capsule and the propulsion module combination.
The return capsule and propulsion module assembly also need to make a flight attitude adjustment, continue to rotate 90 degrees counterclockwise, and after two attitude adjustments, the propulsion module of the return capsule and propulsion module combination is already in front of the spacecraft, and the engine of the propulsion module can be started.
The engine of the propulsion module is used to brake and decelerate, and the flight speed of the combination of the return capsule and the propulsion module is reduced. As the flight speed of the re-entry module and propulsion module group decreases, so does their altitude, and the next step is to start preparing for re-entry.
In the second step, the flight altitude of the return capsule and the propulsion module assembly is lowered from a circular orbit of about 400 kilometers to an orbit of 140 kilometers under the condition of braking and deceleration, and the return module will be separated from the propulsion module, and the propulsion module will also be thrown away and left in the low-earth orbit, while the return module will continue to descend in altitude.
In the third step, when the re-entry capsule descends to an altitude of about 100 kilometers, it will begin to enter the atmosphere. Although the braking deceleration of the propulsion module, the descent speed of the re-entry capsule is still very fast, and the aerodynamic heating effect on the outside of the re-entry capsule is very strong during the high-speed re-entry into the earth's atmosphere, so the temperature outside the re-entry capsule will continue to rise. The entire ship's re-entry capsule was surrounded by flames. During this period, the spacecraft's return capsule will also be temporarily lost.
Fourth, as the re-entry capsule continues to descend in altitude, it is getting closer and closer to landing, and because the re-entry capsule descends quite quickly, a series of decelerations are required to achieve a safe landing. There is a parachute in the re-entry capsule, and when there are still about 10 kilometers above the ground, the parachute is opened. I believe many friends have seen the scene of the return of the Shenzhou spacecraft, the huge red and white umbrella above the spacecraft is the main umbrella of the return capsule, its area reaches 1200 square meters, almost equivalent to the size of 3 basketball courts.
And this huge main parachute does not open all at once, but first opens the guide parachute, and then the guide parachute pulls out, and the parachute can reduce the speed of the return capsule descent from 200 meters per second to 90 meters per second.
At this time, the return capsule also descends to an altitude of almost 8 kilometers from the ground, and the deceleration parachute will be thrown away, and the main parachute with an area of 1,200 square meters will be opened, and under the action of the main parachute, the speed of the re-entry capsule will drop from 90 meters per second to 8 meters per second. This is basically the limit of parachute deceleration, which is still a bit fast.
Therefore, the researchers installed four thrust reverser engines at the bottom of the spacecraft's return capsule, and when the return capsule was about 1 meter from the ground, the four thrust reverser engines would be started to provide an upward thrust to the return capsule, and the final deceleration process would be carried out, reducing the descent speed of the return capsule to 1-2 meters per second to complete the landing buffer. The fire and smoke that you can see from the picture are actually the thrust reverser engine working.
Previously, we shared that Chinese and Russian spacecraft all land on land, while American spacecraft land on the sea. If the Shenzhou manned spacecraft does not start the thrust reverser engine for the final braking and deceleration in the final stage, and the spacecraft return capsule lands at a speed of 7-8 meters per second, the impact on the astronauts will be relatively large. Therefore, the start of the thrust reverser engine is also very critical.
The American spacecraft is still a little fast in the process of parachuting, but they do not need to install thrust reversers, because their spacecraft falls directly to the surface of the sea, and the sea itself can act as a buffer. Since the American spacecraft was not equipped with thrust reverser engines, there was no flash of fire at the moment of landing.
Bring home 31.5 kilograms of space specialty
The Shenzhou-17 astronauts traveled to space for six months, during which the three astronauts completed a series of tasks, including two out-of-cabin activities and extravehicular repair of the solar wing of the Chinese space station. In addition to this, they have conducted a series of scientific studies.
When returning from the Shenzhou-17 spacecraft, he also brought back 31.5 kilograms of space "specialty": the sixth batch of space science experiment samples of China's space station. According to reports, the samples brought back this time involve 23 scientific experiments, including 32 samples of life experiments and 18 samples of materials.