When the spacecraft returned to earth after completing its mission, it was faced with severe friction with meteorites entering the atmosphere and air. How did the spacecraft solve this problem?

On a clear night, looking up at the bright stars, sometimes you will see dazzling meteors, which are fleeting. Why does it shine? It turns out that this is the light emitted by the high-speed flying meteorite entering the atmosphere and violently rubbing against the air and violently burning. When the spacecraft returned to Earth after completing its mission, it faced a living environment as cruel as a meteorite. The research shows that when the speed of spacecraft reaches 3 times the speed of sound, its front end temperature can reach 330℃; When the flight speed is 6 times the speed of sound, it can reach 1480℃. When the spacecraft returns from the invitation to travel in space and reaches 60-70km above the ground, its speed is still more than 20 times of the speed of sound, and its temperature is above 10000℃, which is high enough to turn the spacecraft into a fire. It seems to be an insurmountable obstacle that high speed leads to high temperature. People call this kind of obstacle thermal barrier. Obviously, the thermal barrier did not stop mankind from advancing into the universe, so how did scientists overcome the thermal barrier and let the spacecraft go home safely?

The magical experience of meteorites reaching the earth through space has given scientists special inspiration. By analyzing the composition and structure of the meteorite, it is found that although the surface of the meteorite has melted, the internal chemical composition has not changed. This shows that the surface of the meteorite melted at a high temperature of several thousand degrees due to the friction heat during the falling process, but the heat could not reach the interior of the meteorite because of the short time of passing through the atmosphere. Wearing an "armor" made of ablative materials on the spacecraft head can consume the heat generated by friction in a series of physical and chemical changes such as melting and gasification of ablative materials, so as to achieve the purpose of protecting the spacecraft.

An astronaut described the spectacular scene of the spacecraft breaking through the thermal barrier: when the spacecraft entered the atmosphere, it first saw smoke through the porthole, then colorful flames appeared and crackled at the same time. This is the burning of ablative material on the spacecraft head. They sacrificed themselves to keep the temperature inside the spacecraft at room temperature and protect the spacecraft from returning to the ground safely.

As an ablative material, it requires large gasification heat, large heat capacity, good thermal insulation and strong heat dissipation function. There are many kinds of ablative materials, among which ceramics are the best and fiber reinforced ceramic materials are the best choice. In recent years, many high-strength materials have been successfully developed. Fibers with high elastic modulus, such as carbon fiber, boron fiber, zirconium carbide fiber and alumina fiber, are used to manufacture carbide and ammoniated composite ceramics, which are excellent ablative materials and become unbreakable armor of spacecraft.