The Shenzhou-17 astronauts have successfully returned to Earth! The three astronauts, Tang Hongbo, Tang Shengjie, and Jiang Xinlin, have safely left the return capsule and returned to the embrace of the motherland! The flight time of the Shenzhou-17 astronaut crew in space has reached 188 days, breaking the record for the duration of a single manned space mission on the mainland.
Like previous Chinese space station missions, Shenzhou 17 also landed at the Dongfeng landing site. Before returning to Earth, mainland aerospace researchers had already set a theoretical aiming point for Shenzhou-17 and let the spacecraft land in the target area of the landing site. This is like drawing a target and a bullseye on the ground, allowing the Shenzhou spacecraft to fly from space to the target on the ground, which is a great test of the mainland's prediction and guidance accuracy of the spacecraft.
After the ignition and braking of Shenzhou 17 was completed, the flight control hall of the ground flight control center issued the first landing point forecast coordinates of the Shenzhou spacecraft. According to the coordinates of the fourth landing point forecast, the distance between the two places is about 4190 meters.
This accuracy is already very high, and Shenzhou 17 can accurately hit the "target". It is extremely difficult for the Shenzhou-17 manned spacecraft to accurately land in the predetermined area from space, which shows the strong prediction and guidance capabilities of mainland aerospace.
Shenzhou-17 flies at a speed of up to 28,000 kilometers per hour in space, and its kinetic energy is extremely high. Moreover, the orbital altitude of Shenzhou 17 before returning can reach 390 kilometers, so its gravitational potential energy is still very large. Therefore, if Shenzhou 17 wants to return to Earth safely, it will have to find a way to consume its huge kinetic energy and gravitational potential energy.
The Shenzhou-17 manned spacecraft consists of three modules: the orbital module, the return module, and the propulsion module, and the astronauts stay in the return module. After the separation of Shenzhou-17 from the space station, two attitude adjustments will be made successively. During this time, the orbital module will be detached and it will remain in orbit.
The combination of the propulsion module and the return module will activate the thrust reverser rocket engine to brake and slow down the spacecraft, a process that lasts from two and a half minutes to three minutes. After braking, the push-back combination derails and enters the return orbit inertial coasting, and the altitude continues to decrease, flying towards the theoretical aiming point.
During the unpowered free fall, the flight control hall issued the first landing point forecast for Shenzhou 17: the longitude of the landing point is 100°04'47" east longitude, and the latitude of the landing point is 41°34'03". After a few minutes of free fall, the height of the push-back complex quickly dropped to 145 km.
Immediately afterwards, the propulsion module of Shenzhou-17 will also be separated, and the astronauts will embark on the final journey back to Earth in the return module. At this time, the re-entry capsule is about to re-enter the atmosphere, and the establishment of its re-entry attitude angle is very critical, and it must be controlled at about 1.6 degrees. Otherwise, if the angle is too large, the re-entry capsule will plunge headlong into the atmosphere, which will produce extremely high temperature and overload, and if the angle is too small, the re-entry capsule will be bounced back into space by the atmosphere and will not be able to re-enter the atmosphere normally.
At this stage, the second landing point forecast coordinates of the Shenzhou-17 return capsule were issued: east longitude 100°04'51", north latitude 41°34'03". As you can see, the longitude is very different from the first forecast, and the latitude is exactly the same as the first forecast.
When Shenzhou-17 drops to almost 100 kilometers at an altitude of about 100 kilometers per second, its speed can reach 7 kilometers per second, and it begins its official re-entry. During the high-speed flight, the front of the re-entry capsule will be strongly compressed, forming a high temperature of more than 1,000 degrees, which will burn the outer surface of the re-entry capsule into a fireball, forming a plasma shell that can block radio communication. In this way, the capsule entered the "black barrier zone", at which point it was about 80 kilometers above the surface.
When the altitude drops to 40 km, the re-entry capsule leaves the black barrier area and restores communication with the ground. When the altitude of the re-entry capsule is further reduced to 10 km, the parachute opens one by one, allowing the re-entry capsule to slow down further. Soon after, the third forecast coordinates of the return capsule were issued: 100°04′01" east longitude, 41°35′44" north latitude". This forecast is still very close to the second one.
As the re-entry capsule gradually approached the ground, its motion state has become basically stable, and the final landing location has been determined, at this time, the flight control hall issued a fourth and final landing point forecast: 100°03′47" east longitude, 41°36′11" north latitude.
It can be seen that Shenzhou-17 ended up very close to the initial forecast point, and the two were about 4.19 kilometers apart. A slight deviation in the final landing point may be related to the wind force in the air after the parachute is opened. Tang Hongbo said in the return capsule at the time: "It's a bit like my feeling of swinging a thousand autumns. ”
At an altitude of 1 meter above the ground, the Shenzhou-17 return capsule activated the four thrust reverser rocket engines at the bottom, allowing it to land safely and smoothly at a speed of 2 meters per second. When the capsule reached the ground, rescue helicopters and vehicles arrived.
The entire return process of Shenzhou-17 was completed under the accurate prediction and guidance of mainland aerospace scientific researchers. Judging from the results, the landing time and place of Shenzhou-17 are highly consistent with the forecast, which once again demonstrates the accurate prediction and guidance ability of the mainland's aerospace.