When I was a child, whenever I saw planes flying in the sky, I would be fascinated by them, and my mind couldn't help but be full of questions: how did they fly? What would it feel like to fly into the sky? How would I do it if I wanted to land? For a little guy who is full of infinite yearning for the unknown world, this is undoubtedly an exciting mystery.
Time flies, and now our aerospace technology is changing with each passing day, and it is not only airplanes that shuttle back and forth in the sky, but also spaceships that go to the vast sea of stars. Have you ever been fascinated by their majestic presence, curious about how they fly and what their mysteries are?
First of all, I have to admit that I was quite surprised when I first saw the capsule fall from the sky like a dazzling meteor during re-entry. Thanks to the explanation of the concept of "pneumatic heating", I have a new understanding of this commonplace scene. However, this raises a new question: why didn't the spacecraft suffer so much heat when it took off?
On closer inspection, I think the key may lie in the fact that the spacecraft interacts with the surrounding air in completely different ways. Imagine that when the spaceship lifts off like an arrow, it is faced with a gradually thinning atmosphere, and the speed is increasing step by step. When it returned, the spacecraft was flying straight into the thick atmosphere, and the speed was even higher. It's like a person splashing water in front of a waterfall and waving his arms in a swimming pool.
A little comparison will show that when the spacecraft is at an altitude not far from the ground, because the air is still dense and the speed is not so fast, even if there is "aerodynamic heating", its heat will not be particularly high; as the altitude increases, although the speed increases, the surrounding air becomes thinner and thinner, and it is naturally difficult for heat to accumulate. As a result, the spacecraft will not be exposed to dangerously high temperatures throughout the liftoff.
On the other hand, the process of returning to Earth requires the spacecraft to dive all the way back into the atmosphere from almost a vacuum, so it must defy the Earth's gravity at a considerable speed. When the spacecraft enters the dense air, this huge kinetic energy is instantly converted into heat, which triggers a violent "aerodynamic heating". Without proper protection, the ship will be burned. It's like a refrigerator door suddenly opening and the cold air rushes into the room, and you feel a bitter chill in your face.
One might ask, "Then why can't we slow down the spacecraft before entering the atmosphere and let it slowly pass through the dense air area, so that it doesn't generate too much heat?" However, it should be understood that when the spacecraft re-enters the atmosphere, its speed is so fast that it is difficult to play a role when the air is thin if it is only used by the power of the parachute, and once it enters the dense area, the surface of the umbrella will be burned by the high temperature in an instant. As for the thrust reverser, the amount of fuel it requires is also astronomical, and it is undoubtedly a self-burdening burden to carry so much extra load.
Therefore, the current approach adopted by human beings is to let the spacecraft first go all the way in the atmosphere, use the air resistance to gradually slow down, and after the speed is reduced to a low level, and then finally land smoothly with the help of a deceleration parachute and thrust reverser. To use a popular metaphor, it is like a person jumping from a high place into a pool, although there will be a huge splash when falling into the water, as long as you continue to swim, you will eventually reach the shore safely.
At this point, we have not only understood the nature of things, but also experienced the joy of scientific exploration. Who says cold concepts have to be boring? With clever explanations, vivid metaphors and appropriate illustrations, abstract things can be concretized. It's like coating a beam of light with color, making it more vivid and attractive. I hope that this explanation is not too boring, but will give everyone a further understanding and love for the mysteries of the universe. May we always be curious and continue to explore this unknown world!
Disclaimer: The information in this article comes from the Internet, which is not guaranteed to be completely correct and is for reference only.