In the first half of this year, the mainland has several space projects worth everyone's expectation, one of which is the Chang'e-6 probe landing on the moon and returning samples to Earth. The probe is expected to be launched in the first half of this year, and the Chang'e-6 mission is in the spotlight because the Chang'e-6 probe is located on the far side of the moon, an area where humans have not retrieved lunar samples before.
Because the Moon is tidally locked, the far side of the Moon is always facing away from the Earth, so it is more difficult to land on the far side of the Moon to take samples and return to Earth. The Queqiao-2 relay satellite, which was launched earlier, can help the Chang'e-6 probe communicate with the ground command center.
Now the Queqiao-2 relay satellite has arrived in its scheduled orbit and is waiting for the arrival of the Chang'e-6 probe. Just when everyone is looking forward to the Chang'e-6 probe to retrieve samples from the far side of the moon as soon as possible, the Chinese space station has a new mission, that is, the launch of the Shenzhou-18 spacecraft.
Shenzhou-18 was launched at the right time
At the end of this month, our space station will have two important missions, one of which is the launch of the Shenzhou 18 spacecraft, and the other is the return of the Shenzhou 17 spacecraft.
As the first manned spacecraft to go to China's space station this year, the Shenzhou-18 spacecraft is about to be launched. On April 17, the Shenzhou 18 spacecraft and rocket assembly have been transferred to the launch area, which actually means that the Shenzhou 18 spacecraft will be launched in the next few days and will start a six-month space mission.
In this 6-month period, the astronauts of the Shenzhou 18 spacecraft will complete a series of tasks, although the official has not yet announced the specific tasks of Shenzhou 18, but it can be known that there will be many normalized tasks, including the daily care of the space station, out-of-cabin activities, etc. And in May, a new round of extravehicular exposure experiments will be conducted.
Speaking of extravehicular exposure experiments, I believe many friends still remember that last month, the Shenzhou-17 astronaut crew successfully completed the retrieval of the first batch of extravehicular exposure experimental material samples. A total of 407 samples of the first batch of extravehicular exposure experimental materials will be installed by the astronauts of Shenzhou 15 on March 8, 2023, and these materials will soon return to Earth with the Shenzhou manned spacecraft.
Countdown to the return of Shenzhou 17
From the point of view of time, the launch of the Shenzhou 18 spacecraft is expected to be a matter of the next few days, when the Shenzhou 18 spacecraft is launched and arrives at the Chinese space station, the two astronaut crews will be handed over in orbit, this process will last about a few days, and after the handover is completed, the Shenzhou 17 spacecraft will return to Earth.
Previously, the official has also announced that the return time of the Shenzhou 17 spacecraft will be at the end of this month. Therefore, now not only the launch of the Shenzhou 18 spacecraft has entered the countdown stage, but the return of the Shenzhou 17 spacecraft can also be said to have entered the countdown stage.
Although the principle of the spacecraft returning to Earth from outer space seems very simple, that is, after a series of orbit changes, braking and deceleration, it lands on the ground, but the actual process is actually very complex and full of all kinds of thrills. When the spacecraft re-entry capsule landed on the ground, we could see that the outside of the spacecraft re-entry capsule was black and unrecognizable.
I believe many netizens have seen the simulation of the Perseverance rover landing on Mars before, when the probe broke into the Martian atmosphere at high speed, it was like a burning fireball flying over quickly.
When the burning phenomenon is over, the Perseverance rover lander will open its parachute to further slow down, and finally slowly lower the Perseverance rover to the surface of Mars through an "aerial crane".
The process of the spacecraft returning to Earth is actually similar to that of the probe landing on Mars, when it enters the atmosphere at high speed, it is like a burning fireball, the outside temperature is very high, and the parachute will be opened to further slow down after the combustion phenomenon is over.
In the final landing stage, different countries will have different ways, and the return capsule of our Shenzhou manned spacecraft will turn on the thrust reverser engine at the bottom at the moment of landing, and then land on the ground. The American manned spacecraft, on the other hand, do not need to turn on the thrust reverser engine, because their spacecraft chooses to land in the sea, because the sea surface itself can also act as a buffer.
And the situation of the probe when it lands on the moon is not so complicated, and there will be no violent burning. This is because the moon has no atmosphere, and when spacecraft and probes land on the moon, they are completely braked and slowed down by the engine. It is also because the moon has no atmosphere, so probes and spacecraft will not become black and unrecognizable when they land on the moon.
Therefore, one of the reasons why spacecraft and probes will burn violently when they return to the earth is that they fly very fast, and the earth has a dense atmosphere, and after breaking into the earth's atmosphere at high speed, the aerodynamic heating effect is very strong, and the external temperature rises sharply.
Spacecraft returning to Earth in low-Earth orbit will face a high temperature of one or two thousand °C, while spacecraft returning to Earth from the Moon or Mars will be faster, the aerodynamic heating effect will be more intense, and the outside temperature will be higher, reaching or approaching 3,000 °C.
Under such high temperatures, ordinary spacecraft are unbearable, so many satellites and cargo spacecraft will re-enter the atmosphere in a controlled manner after the end of their missions, and then burn violently in the atmosphere and turn into ashes to avoid occupying limited orbital resources.
The manned spacecraft return capsule needs to bring the astronauts back to the ground safely, so it cannot burn up in the atmosphere like satellites and cargo spacecraft. Although the spaceship's return capsule will not be burned, there are still some changes on the outside under such high temperatures, that is, the surface of the spacecraft, which was originally very clean and tidy, will be burned black.