Shenzhou 13 has successfully landed at the Dongfeng Landing Field! The three astronauts, Zhai Zhigang, Wang Yaping and Ye Guangfu, finally returned to Earth safely! This is another milestone in the history of China's manned spaceflight, and the complete success of the Shenzhou 13 mission will open the curtain on the comprehensive construction of the Chinese space station.
The three astronauts lived and worked on the space station for 183 days, the longest manned space mission in China's space history. After half a year, the three astronauts finally returned to the earth and returned to the embrace of the motherland.
The Shenzhou XIII return capsule withstood the test and brought the three astronauts back safely. Some parts of the outer surface of the return capsule looked black and dark, and were burned at high temperatures on the occasion of return. But when launched, the Shenzhou spacecraft will not go through such a process, why is this? What kind of thrilling test did the spacecraft go through when it returned?
When Shenzhou XIII was launched from the ground, it was an acceleration process that began at zero speed. The Long March 2F YaoXIII rocket used to launch the spacecraft can take off with a takeoff weight of up to 497 tons. Coupled with the fact that the atmosphere near the Earth's surface is very dense, it is very difficult for rockets to accelerate.
When the rocket flies in the atmosphere, it is not so fast, and the interaction with the air is not so strong that it does not make the spacecraft burn. And outside the spacecraft, there is also the protection of the fairing, which can prevent the aerodynamic heating effect from affecting the spacecraft.
About 120 seconds after the rocket was launched, the escape tower separated, at which point the rocket's altitude was about 39 km and the speed was about 1.65 km/s. At an altitude of 80 kilometers, the rocket left the dense atmosphere. When the altitude exceeds 110 kilometers, the spacecraft crosses the edge of the atmosphere into space, the fairing is thrown away, and the spacecraft is directly exposed to space.
When flying in the atmosphere, the speed of the rocket did not exceed 3 km / s. After entering space, the air resistance becomes very weak, at this time the 4 boosters have separated, the first and second stages have separated, and the rocket that consumes a lot of fuel has become much lighter, so the rocket can continue to accelerate to 7.7 km / s, and finally enter the orbit.
When Shenzhou XIII returned, the spacecraft first separated from the space station. After evacuating the space station, the Shenzhou spacecraft made its first attitude adjustment, and then the orbital module was separated and the return-propulsion module assembly continued to advance. Thanks to the fast return technology, the spacecraft only needs to make a few turns around the earth to find the time to return.
After the second attitude adjustment, the engine ignites and brakes, and the spacecraft slows down, disengages from its original orbit, and begins to enter the return orbit. The spacecraft descended from an orbit nearly 400 km high, and when it descended to 145 km, it adjusted its posture again, and then the propulsion module was separated. The return module carries the astronauts to continue descending, establishing the correct re-entry attitude angle and preparing to re-enter the atmosphere.
The re-entry angle of the return capsule is critical, if the angle is too small, the return capsule will be bombed into space by the atmosphere and cannot be returned, which is like a stone floating on the water. If the angle is too large, the re-entry speed of the return capsule is too fast, and it will produce too high a temperature, resulting in the possibility of the spacecraft being burned down.
The re-entry module enters the atmosphere at a re-entry angle of about 1.6°, at a speed of 7.9 km/s. The re-entry capsule travels through the atmosphere at such a fast speed that it compresses the air in front of the flight, creating a huge aerodynamic heating effect that raises the temperature on the surface of the re-entry capsule to thousands of degrees.
In order to cope with such extreme heat, the outside of the return capsule is covered with honeycomb-like heat-proof materials, which will take away huge heat after ablation at high temperatures, so that the temperature of the inner surface of the return capsule is only about 30 ° C, and astronauts wearing spacesuits in the capsule will not feel much heat.
During this time, the outside of the return module was a high-temperature plasma, and astronauts were able to see a spectacular sight through the portholes. At this point, the spacecraft's communication with the ground is interrupted by the interference of plasma, which is the so-called "black barrier zone" and lasts for about 4 minutes.
After sufficient deceleration of the atmosphere, the speed of the return capsule is reduced to 200 m/s. At an altitude of 10 kilometers, the guide parachute, deceleration parachute and main parachute of the return capsule are opened in turn, and the heat-proof outsole is thrown away. Under the action of the main parachute, the return capsule continues to decelerate until it is reduced to 3.5 m/s. At a distance of 1.2 meters from the ground, the reverse thrust rocket was activated and the return capsule landed on the ground at a safe speed.
Some people may say, why not let the parachute turn on and slow down in the first place? There are two reasons, on the one hand, the speed of the re-entry of the return capsule is too fast, the air is relatively thin at the beginning, and the parachute does not play much deceleration.
On the other hand, after the return capsule and the air have a violent interaction, it will also produce thousands of degrees of high temperature, if you open the parachute early, it will undoubtedly be burned, and it will not be able to slow down the return capsule at all. Only when the atmosphere is dense enough and the temperature and speed of the return capsule are low enough, can the parachute play an effective deceleration effect.
Finally, let us warmly welcome the three astronauts of Shenzhou 13 home!