After entering the era of science and technology, human beings soon realized their dream of flying to the sky, walked out of the earth and began to explore the universe. If astronauts want to go into space, they need the boost of rockets, and the speed should be very fast, that is, the first cosmic speed and the second cosmic speed that we often hear. First, the speed of the universe is 7.9 kilometers per second. Only when we reach this speed can we overcome the constraints of the earth’s gravity and enter the orbit around the earth.
To move around the sun, we need to reach the second cosmic speed, which is 11.2 kilometers per second. When astronauts complete their missions in space, they need to return to the earth by spacecraft. However, with the current science and technology of human beings, they do not have the ability to easily and freely enter the earth as in science fiction. Our spacecraft now need to take great risks to return to earth.
Some people may ask such a question: is the spacecraft accelerating or decelerating when it returns to earth? Some people may say, isn’t this bullshit? If the spacecraft returns to the earth to accelerate its motion, the final impact on the ground will be very powerful, and the spacecraft and its astronauts will be spared? Only decelerating motion can ensure the safety of astronauts landing, so is the real situation like this? In fact, many people’s understanding is wrong.
It is a complex process for spacecraft to return to earth from space, which needs to go through three stages. In the first stage, the speed of spacecraft in space is very fast, which is basically at least the first cosmic speed. At such a speed, the spacecraft can not cut into the earth’s descending orbit, so to return to the earth, the spacecraft first needs to give a reverse force to make the spacecraft’s speed fall below the first cosmic speed.
After the spacecraft’s speed drops, it can be pulled to the atmosphere step by step by the gravity of the earth. At this time, the spacecraft has just entered the atmosphere, the speed is very fast, and it will continue to accelerate. Some people may say, open the parachute quickly to slow down. In fact, at this position, because the atmosphere is very thin, the parachute cannot be opened normally.
The second stage is that the spacecraft leaves the rarefied atmosphere area and enters the black barrier area, which is also the most dangerous period of time. At this time, the atmospheric density continues to rise, and the speed of the spacecraft is still very fast, mainly at the bottom. The ionosphere is generated on the surface of the spacecraft, and the communication with the outside world is interrupted. At this time, if the parachute is opened, the instantaneous force on the parachute is huge, which is very likely It’ll tear, it’ll crash.
Although the black barrier area is the most dangerous area for spacecraft, it is also a very important area, because before the parachute is opened, the spacecraft has to rely on this area to decelerate completely. At this time, the atmosphere acts as the “parachute” of the spacecraft, and the spacecraft continues to “brake” under the atmospheric resistance until the altitude from the ground drops about 10000 meters For “sonic” or “subsonic”, the spacecraft has consumed about 99% of its kinetic energy.
The third stage is the landing stage. After the spacecraft passes through the black barrier area, the speed has been greatly reduced due to the continuous friction of the atmosphere in the previous stage. At this time, the spacecraft is about 10000 meters away from the ground. At this time, the atmospheric density is large enough to open the parachute. This is also the last step of deceleration. Whether the spacecraft can land safely and successfully depends on this last step of deceleration.
Under normal circumstances, as long as the parachute can be successfully opened in the third stage, the spacecraft can successfully and safely land at a speed of 10 meters per second. From the above three stages, we can see that the whole process of spacecraft returning to the earth has experienced deceleration, acceleration and deceleration. It’s not a simple deceleration movement, let alone a full acceleration.
In fact, the risk of astronauts returning to earth by spacecraft is far greater than entering space. Human rocket technology is very mature, astronauts into space are basically no risk, can safely go to heaven. However, the human space return technology is not really strong. It is still a dangerous thing for astronauts to return to earth.
Generally speaking, when a spacecraft returns to earth, the safest landing area is the ocean, because the ocean itself is a deceleration effect. If the spacecraft does not slow down well after entering the atmosphere, resulting in a very high landing speed, then the astronauts in the spacecraft will be in great danger. When a spacecraft falls into the ocean, it can decelerate effectively, instead of directly breaking up like land.
Of course, with the continuous progress of human science and technology, the current spacecraft return technology has been greatly improved, and the safety of direct landing on land is also very high. China’s astronauts return to the ground is a safe landing on land.
So will future spacecraft return to earth in this way? Of course not. In fact, the current space technology of mankind is poor after all. Entering space needs the boost of rockets, and returning to earth can only passively rely on the atmosphere to slow down. The real space technology is that the spacecraft can go in and out of the earth freely. It doesn’t need the atmosphere to slow down, and it completely depends on the power of the spacecraft.
Of course, it will take a long way for human beings to realize this kind of space technology. Perhaps only after the real realization of anti gravity technology can our spaceship return to earth without any difficulty, as described in science fiction movies. Moreover, anti gravity is also the key for human beings to enter the interstellar age. Only with the strength of anti gravity technology, can human beings really become an interstellar civilization and be able to go out of the solar system and explore other galaxies. We are looking forward to that day.
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