Lunar sampling faces high temperature challenges, and "Chang'e" has its own cooling "artifact"!

□ Zhu Rongkuan

On May 3, the Chang'e-6 probe was launched from the Wenchang Launch Center in Hainan aboard a Long March 5 Yao-8 carrier rocket, thus starting the world's first 53-day journey to collect samples from the back of the moon and return.

The Chang'e-6 probe and the Long March 5 Yao-8 carrier rocket combination photographed on May 3 (Source: Xinhua News Agency)

When digging on the lunar surface with a temperature of over 100 degrees Celsius, the small "Chang'e" does not have enough heat dissipation area. At this time, it is the turn of our independently developed heat dissipation artifact "water sublimator" to make a shining appearance.

So, why can this water sublimator dissipate heat? When we use a fan in the hot summer, the sweat on our body evaporates and we feel much cooler.

Although there is no air on the surface of the moon and no wind can form, water evaporates in a vacuum environment and sublimates after freezing, taking away a large amount of heat.

The water sublimator is mainly composed of four parts: a porous plate, a water storage tank, a water pipe, and a control valve. When the surface temperature of "Chang'e" is too high, the water sublimator will receive a signal to start working, the control valve will open automatically, and the water stored in the water storage tank will flow into the porous plate through the water pipe. One side of the porous plate is exposed to the vacuum environment of the moon, so the water molecules close to this side will evaporate immediately, requiring a large amount of heat absorption to freeze the water close to "Chang'e" in the plate into ice. The pressure in the vacuum environment is very small. Once the solid water molecules in the ice lose their restraints, they can easily run out and become active gas. This is sublimation. Sublimation will absorb more heat, and the temperature of "Chang'e" will drop. Don't underestimate the heat taken away by this ordinary 5 kilograms of water. It can allow "Chang'e" to work 20 more hours under the scorching sun.

The principle of sublimation heat dissipation does not sound complicated, but it is not easy to ensure a balance between water supply and water consumption: if too much water is supplied at one time, the water that does not have time to freeze will spray out of the porous plate; if too little water is supplied, not enough ice can be condensed and the heat cannot be dissipated.

As the person responsible for quality first, designers need to consider all possibilities.

The question most often asked by Academician Yang Mengfei, chief designer of Chang'e-5, is "why". If anyone can withstand his "seven whys", it proves that he has a thorough understanding of the technology, products and processes.

"Chinese astronauts will never bring questions into space." Through repeated rejections and debates, they have polished out safe and high-quality plans, innovated in the face of challenges, and overcome difficulties under great pressure. Countless efforts have been made to build the ladder for space exploration and the moon.

(The author is a spacecraft thermal control designer at the Beijing Space Vehicle General Design Department and the winner of the first prize of the 10th National Science Popularization Explanation Competition)