The world's first wooden satellite is about to be unveiled. Why do the United States and Japan use wood to build satellites?

In 2024, the United States and Japan will use the beauty of Northwestern Polytechnical University to build an artificial satellite. Does this sentence sound irrelevant? Don't worry, let me explain.

All students of Northwestern Polytechnical University know that our school flower is the white magnolia, which blooms all over the campus every spring and is so beautiful. The white magnolia is a plant of the genus Magnolia. Carpenters say that the wood of this kind of plant has excellent material, straight texture, and fine structure, making it suitable for making furniture.

Why would something suitable for furniture be used to make satellites? The logic is this:

We all know that humans are throwing more and more satellites into the Earth's orbit. After these satellites die, they will become space junk. In particular, the closer the orbit is to the Earth, the smaller the space is, and the greater the probability of colliding with other spacecraft. Fortunately, there is a characteristic of low-Earth orbit, that is, at this altitude, there is more or less air, which will very slowly slow down the spacecraft here. Therefore, the orbital height of the spacecraft here is actually gradually decreasing. After the low-Earth orbit satellites are scrapped, they will also gradually decrease in altitude and eventually enter the atmosphere and fall down.

Then the question arises again, if a satellite falls from the sky, are you afraid? What if it hits flowers and plants? Although the probability is very low because the earth is so big, if the frequency of satellite launches and satellite drops is high in the future, the probability of hitting densely populated areas will also increase. At this time, the advantages of wooden satellites are reflected. The high temperature generated by the interaction with the atmosphere during the return process will burn it cleanly, and the remaining metal parts will be very small, and they can also burn like a meteor, so the probability of hitting flowers and plants is much smaller.

So, what is the special feature of using wood to build satellites? The main thing is the mechanical properties. Wood has some experience in this regard, because the earliest aircraft of mankind was made of wood. However, compared with metal, wood's strength and stiffness are not superior. The so-called strength is the property of not being easy to break. For example, the tensile strength of aluminum alloy can reach 200-300 megapascals, while the tensile strength of the strongest wood is only more than 100 when it is pulled along the direction of its most medium. The so-called stiffness is the property of not being easy to deform. To put it bluntly, it is soft and hard. When wood is pulled along the wood grain, the elastic modulus is more than 10,000 megapascals, and the aluminum alloy is 70,000.

Fortunately, compared with airplanes, the structural strength requirements of satellites are not that high, because they do not need to bear aerodynamic loads, as long as they can withstand the overload and vibration during rocket launch, which is much smaller than the loads borne by key components of airplanes. In addition, the space environment is different from the earth environment. Under the torture of high vacuum and high radiation, the performance of wood is likely to be reduced.

I checked a paper published by Beijing Forestry University. The article proved through experiments that after being exposed to gamma rays, the cellulose of wood will degrade and some molecular chains will be broken, resulting in weakened tensile, bending, compressive and impact resistance. Therefore, magnolia wood was not determined to be a space wood from the beginning. Earlier in 22 years, it was taken to the International Space Station along with cherry wood and birch. After testing and selection, it was found that its performance changed the least in the space environment, and it was then established as a satellite material.

The first satellite he built was also experimental in nature. It was very small, only as big as a coffee cup. Just imagine, a small satellite means the structure on it bears less load, carries less test payload, and is cheaper to launch, so the cost is low. Even if it is destroyed after being launched into space, the loss is small, so it is relatively safe. How big a satellite can be made of wood in the future depends on its performance after it is launched into space tomorrow.

Hey, the school beauty has gone to space, when can I go there? I am Gou Sheng, bringing you hardcore and interesting aerospace knowledge. Just like and follow me and you can finish the get out of class.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Liang Yichen (Teacher Gou Sheng) Lecturer at Xi'an Aviation University

Reviewer: Han Wenbiao, Researcher at Shanghai Astronomical Observatory, Chinese Academy of Sciences

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.