Revealed: Why is the thickness of the rocket shell only a few millimeters?

Seeing the Long March 5, a behemoth that is tens of meters tall, may give people a misunderstanding: the shell of this big rocket must be very thick to be strong enough. But in fact, the thickness of the commonly used rocket shell "skin" is only 1.2 mm to 2 mm, and the "skin" of the fairing is only 0.3 mm at the thinnest point. To make an analogy, if the rocket is compared to an adult and the shell is compared to the adult's outer coat, then this coat can be described as "as thin as a cicada's wing."

So, why is this so-called "skin" so thin?

The main material of the "skin" is aluminum alloy, which has high strength, corrosion resistance, light weight and low cost. It has the best comprehensive performance during the flight of Long March 3A series and Long March 2F rockets, and is the best choice for the "skin". More importantly, aluminum alloy is light and can reduce the weight of the rocket. People describe the rocket as "thin skin and big filling". If the "skin" is thin, more fuel can be loaded and "lift" heavier satellites.

The rocket shell is designed to be so thin mainly to reduce the weight of the rocket and increase the payload. If the weight of the rocket is reduced by one kilogram, the payload can be increased by one kilogram, and the weight of satellites and spacecraft can also be increased by one kilogram, providing more protection for astronauts and spacecraft to go to space. People usually describe rockets as "thin skin and big filling", and the main weight is the fuel in the belly of the rocket. But the fuel is "dead weight" and cannot be increased or decreased at will, so rocket designers put their minds on the outer shell of the rocket and made the outer shell of the rocket thinner, with the purpose of reducing the weight of the rocket.

Can it ensure the sturdiness of the rocket?

The outer shell of a rocket is actually composed of multiple parts. Including skin, stringers and frame rings. The frame ring and stringers form a cylindrical frame, which is combined with the skin through riveting. The skin is mainly used to maintain shape, transmit shear force, install instrument cables, etc.; while the stringers play the role of longitudinal main support. The relationship between stringers, frame rings and skin is like the bamboo strips in a lantern and the gauze cover outside. The "shell" of a rocket that we usually see is actually just its "skin".

The rocket "skin" is very thin and soft, but after scientific calculation and structural optimization based on force analysis, the "skin" and the frame are fixed with rivets. Each shell segment has thousands of rivets, which ensures the strength and rigidity of the overall structure. During the launch process, no matter which direction the external force is applied, it will not affect the flight of the rocket. However, if the "skin" is too thin, the strength of the shell will increase if the internal frame is continuously encrypted to ensure its strength, which will not achieve the expected effect. Therefore, the designers have to calculate the best ratio of the "skin" and the frame ring and stringers to ensure that the minimum material is used and the rocket body is strong and reliable.

The "skin" panel of the Long March 5 rocket fairing is only 0.3 mm thick. With the same rigidity, the weight of the rocket shell will be reduced by more than 10%. According to Li Cao, a rocket body structural designer, this way, the rocket can be loaded with more fuel and the payload can be smoothly sent into orbit while ensuring its firmness. Therefore, although the outer shell of the rocket is as thin as an eggshell, it can ensure that the rocket is strong enough during flight.

In addition, China's new generation of rocket tanks are also very thin, with a wall thickness of only 1 mm !

Yili, chief designer of the Long March 2F carrier rocket of the First Academy of China Aerospace Science and Technology Corporation, made a more intuitive analogy: the can of Coca-Cola that everyone drinks in their daily life must be considered very thin. If we want to make its carrying capacity the same as the tank of our rocket, the can of Coca-Cola can be made two-thirds thinner. Striving for excellence and perfection, the "ingenuity" of the Chinese people is behind the production of rockets. It is the hard work of countless outstanding aerospace talents that has led to the amazing achievements in the development of aerospace technology. The wisdom and courage of aerospace personnel have created the glory of China's aerospace industry and laid a solid foundation for the dream of mankind to explore the universe and chase the stars.