How many steps are needed to keep a spacecraft “neither hot nor cold” in the universe?

When we imagine space

You might think of the vast stars.

Fascinating nebulae and mysterious black holes

But do you know?

Space is actually an extremely cold environment

The average temperature is about -270℃

However, not every place in space has such low temperatures. The temperature in space varies greatly, depending on whether an object is exposed to radiation from a star. For example, the side of a space station facing the sun will be very hot, with a surface temperature of up to 150°C, while the side facing away from the sun will be very cold, with a minimum temperature of less than -100°C. The reason for such a big difference is that the heat transfer method in space is very different from that on Earth.

Chinese Space Station

We know that there are three basic ways of heat transfer: heat conduction, heat convection and heat radiation.

Heat conduction refers to the transfer of heat between objects through contact; thermal convection refers to the transfer of heat through the movement of fluids (liquids or gases); thermal radiation refers to the transfer of heat by objects through the emission or absorption of electromagnetic waves.

In the terrestrial environment, all three methods can be carried out effectively. However, in space, since there is no air or other media, conduction and convection are almost non-existent, and there is only radiation as a heat transfer method. This means that in space, objects can only regulate temperature by emitting or absorbing electromagnetic waves.

This is a huge challenge for spacecraft, because spacecraft will generate a lot of heat during operation and will also receive radiation from the sun. If the heat cannot be dissipated in time, it will cause the spacecraft to overheat or even be damaged.

At the same time, the spacecraft must also avoid radiating too much heat, especially when it is on the dark side of the sun, to prevent the temperature from being too low. Therefore, the spacecraft needs to design an effective temperature control system to maintain the appropriate temperature required for the normal operation of the instruments and equipment on the spacecraft.

During the development of a spacecraft, there is also a crucial test - the thermal vacuum test , which simulates the space environment and conducts comprehensive tests on the spacecraft and its systems. The purpose of this process is to ensure that the spacecraft can operate normally in the real space environment and complete the intended mission.

Thermal vacuum testing on the ground is the main means of verifying the performance of spacecraft in space. Its importance is self-evident. It is related to the safety of spacecraft and the success of the mission. Thermal vacuum testing can also test the performance and function of products on spacecraft, verify the rationality of product design, and expose potential defects in components, materials, processes and quality. Practice has proved that the reliability of spacecraft in orbit after thermal vacuum testing will be greatly improved.

Navigation satellite undergoes thermal vacuum test at KM7

The spacecraft thermal vacuum test needs to be carried out in a dedicated space environment simulation device. The space environment simulation device is an important ground test equipment in the spacecraft environment simulation project, which is mainly composed of a vacuum container, a vacuum system, a liquid nitrogen system, a measurement and control system , etc.

Vacuum system

The main task of the vacuum system is to provide a vacuum background for the spacecraft. The air molecules in the vacuum container are extracted through a combination of a vacuum pump and a cryogenic pump to obtain and maintain the high vacuum environment required for the thermal vacuum test of the spacecraft.

At present, my country's spacecraft thermal vacuum tests generally require that the vacuum degree in the container is no higher than 6.5×10-3Pa, and may even be as low as 1.3×10-3Pa, which is equivalent to one billionth of the normal atmospheric pressure on our ground.

Liquid nitrogen system

The main function of the liquid nitrogen system is to use liquid nitrogen to cool the heat sink in the vacuum container, making the heat sink temperature lower than -173°C, and use the heat sink to simulate the cold black background in space.

Measurement and control system

The main function of the measurement and control system is to accurately control the temperature of the spacecraft during the test.

In space, a spacecraft experiences extreme temperature changes from high temperatures in the direct sun to low temperatures in the shadows. This happens once every time a spacecraft orbits the Earth.

Low temperature is mainly achieved by using a liquid nitrogen system to construct a cold background to absorb the thermal radiation of the spacecraft; high temperature is achieved by using an infrared cage or infrared lamp as a heating method and electric heating. Ultimately, the temperature of the spacecraft is accurately controlled through a balance between the two, thereby simulating the temperature changes of the spacecraft in space.

Commonly used heating methods in spacecraft testing (infrared lamp array, infrared cage, thin film electric heater)

With the development of aerospace models, my country has successively developed various types of space environment simulation equipment, which have made great contributions to the development of my country's spacecraft. my country's largest thermal vacuum test equipment is KM8, with a diameter of 17 meters and a height of 35 meters, equivalent to a 10-story building. It is also the third largest space environment simulator in the world and the largest in Asia.

KM8 space environment simulation equipment

By simulating the thermal vacuum environment in space, we can discover possible problems in advance and repair them. In this way, when the spacecraft actually enters space, we can explore this mysterious and beautiful universe with greater confidence.

author:

Li TaoMember of Beijing Refrigeration Society, technician and engineer of China Academy of Space Technology

Liu Yuan is a member of the Beijing Refrigeration Society, and a branch secretary and researcher at the China Academy of Space Technology.

Zhou Yuege, member of Beijing Refrigeration Society, deputy director and senior engineer of China Academy of Space Technology

Editor: Dong Xiaoxian