The three astronauts of Shenzhou-17 returned to Earth on April 30, ending a six-month space flight journey, just in time for May Day. Before returning home, the Shenzhou-17 spacecraft needs to be evacuated from the Chinese space station assembly, and then begin to circle the Earth for about five times before re-entering the Earth's atmosphere. Since the number of circles around the earth has been greatly reduced, the time for the Shenzhou 17 spacecraft to return to the earth has also been shortened, which is the technology of rapid return.
Although we can accurately calculate the launch window of the spacecraft and the return time of the spacecraft, and can quickly achieve the autonomous rendezvous and docking of the spacecraft with the space station assembly, and can also quickly return to the earth from the space station, our current technology cannot make the Shenzhou 17 spacecraft land 100% accurately to the pre-selected landing site.
Because after the spacecraft is evacuated from the space station, it also needs to carry out a series of operations, including the adjustment of flight attitude, the separation of the module, and re-entry into the atmosphere, and in the process of re-entering the atmosphere, it will be affected by air resistance, especially when there are almost 10 kilometers from the ground, the parachute will be opened, and the area of the parachute will reach 1200 square meters.
In the process of descending, such a large parachute will be affected by objective factors such as airflow, temperature, and wind at the landing site, resulting in the actual landing site cannot be accurately controlled. However, you don't need to worry about whether the spacecraft will drift far away during the descent, or within the range of the Dongfeng landing field.
It is precisely because the spacecraft is affected by many objective factors when returning to the sea that it cannot land accurately, and every time the Shenzhou manned spacecraft returns to Earth after a flight mission, all aspects of the search and rescue forces at the Dongfeng landing site will carry out relevant joint exercises and drills to prepare in advance for the triumphant return of the Shenzhou spacecraft. When the spacecraft returns, the search and rescue teams in the air and on the ground will set off in advance to find the spacecraft. Under normal circumstances, when the spacecraft's return capsule slowly descends with a huge parachute, the search and rescue helicopter has already arrived nearby.
After entering the era of the space station, the Shenzhou manned spacecraft landed at the Dongfeng landing site, and the area of the Dongfeng landing site is as high as 20,000 square kilometers, and the terrain is very complex, not only deserts, Gobi deserts, but also mountains, etc., plus after the spacecraft opens the parachute during the return to the earth, it will be affected by the wind and deviate from the pre-selected landing site, how did these search and rescue teams quickly find the Shenzhou manned spacecraft?
There are Beidou's navigation terminals in the spacecraft's return capsule, so even if the spacecraft is flying in space, we can also grasp the precise position and flight speed of the spacecraft. During re-entry, the temperature outside the re-entry capsule rose sharply to one or two thousand degrees Celsius due to the strong aerodynamic heating effect. Under such high temperatures, the gas molecules on the outside of the spacecraft's return capsule and the ablated materials on the surface of the spacecraft are ionized, and the spacecraft will enter a "black barrier area", at which point it will lose contact for a short time.
However, this loss of contact did not last long, that is, for a few minutes, and within these minutes, the spacecraft return capsule could not get in touch with the ground command center. When the altitude of the spacecraft continues to decrease, the aerodynamic heating effect becomes weaker and weaker, the external temperature becomes lower and lower, the communication is restored again, and the spacecraft return capsule contacts the ground command center again, at this time the staff can also grasp the flight situation of the spacecraft, including the descent speed and specific location.
Although the spacecraft will briefly lose contact when entering the black barrier, the staff of the ground command center also have a lot of technology to track the spacecraft's return capsule. For example, the staff of the ground command center will use radar to track the flight of the return capsule, so as to predict the approximate location of the spacecraft's landing site to the air and ground search and rescue teams at the Dongfeng landing site.
When the spacecraft return capsule descends to almost 10 kilometers above the ground, the parachute will be opened, because the parachute area reaches 1,200 square meters, which is very large, the helicopter air rescue team has come to the vicinity of the landing site in advance according to the forecast of the ground command center. When the spacecraft descends within range, the helicopter flying in the air will also track the descent of the spacecraft's return capsule in real time, and share the actual situation with the command center and the search and rescue vehicles on the ground.
When the spacecraft's return capsule landed on the ground, the search and rescue teams in the air and on the ground had actually come to the vicinity of the landing site, ready to carry out search and rescue work at any time. In addition, after landing, the Beidou navigation terminal inside the capsule will also continue to send out signals, and search and rescue personnel can also quickly find the return capsule according to this signal.
Why is the return capsule dark and not autumnal?
When the spacecraft return capsule lands on the ground, the ground staff will check the situation of the spacecraft, and also learn some information about the astronauts in the spacecraft. After making preparations, the crew will open the hatch to help the astronauts get out, and the astronauts will not immediately stand up and walk after leaving the capsule, but will be carried by the staff, and then sit on special chairs to rest, and slowly restore the gravity environment on the ground.
I believe that many friends have seen the appearance of the return capsule of the Shenzhou 17 spacecraft after landing on the ground, and the previous Shenzhou manned spacecraft and the Chang'e-5 probe returner, the exterior of the return capsule of this spacecraft is also dark, and it feels like it has been scorched. In fact, this is also the case, and the spacecraft did withstand high temperatures of up to 1000-2000°C on the way back to Earth.
This is because the spacecraft are flying very fast when they are flying around the Earth, almost close to the Earth's first cosmic speed of 7.9 kilometers per second, after all, only if the flight speed is fast enough, it will not fall. It is precisely because the spacecraft flies quite fast that when it returns to the Earth and enters the Earth's atmosphere, the aerodynamic heating effect will be very strong, and the external temperature will rise sharply to one or two thousand ° C. Under such high temperatures, the ablative material on the surface of the spacecraft return capsule will fall off and take away the heat, which is why the exterior of the spacecraft return capsule will be burned black and unrecognizable.