Ground testing and training cannot be separated from simulation technology and simulation equipment. To understand simulation technology and simulation equipment, one must first understand the manned spaceflight environment.

(1) Vacuum environment and simulation

At an orbital altitude of 500 kilometers for manned spacecraft, the vacuum degree in space is around 10-6 pascals; At an orbital altitude of 1000 kilometers, the spatial vacuum is around 10-8 Pa.

When conducting thermal simulation tests on spacecraft and extravehicular spacesuits in space environment (mainly thermal vacuum tests and thermal equilibrium tests), the main concern is the influence of vacuum environment on the thermal characteristics of the specimens. When the vacuum degree reaches 10-2 Pa or above, radiation heat transfer has become the main form of heat transfer, and the effects of convection and conduction heat transfer can be ignored. Therefore, the vacuum degree simulated by space simulation equipment reaches the order of 10-3 Pa, which can simulate the heat exchange effect of spacecraft flight orbit vacuum environment more realistically, without the need to pursue higher vacuum degrees. Only some special tests, such as vacuum dry friction and cold welding tests, require higher vacuum testing equipment.

(2) Sun irradiation environment and simulation

The sun radiates tremendous energy into space at all times, and the wavelength of sunlight covers a wide area from 10-14 meters (gamma rays) to 104 meters (radio waves). Different wavelengths of sunlight also radiate different amounts of energy. Visible light radiation has the highest energy, with visible and infrared radiation accounting for over 90% of the total solar radiation energy.

During orbital flight, spacecraft and extravehicular spacesuits primarily receive three types of radiation energy: energy from visible and infrared radiation from the sun, energy from reflected solar radiation from the Earth, and thermal radiation from the Earth's atmosphere. The energy absorbed by spacecraft and extravehicular spacesuits affects their temperature and distribution, and the amount of energy absorbed depends on their structural shape, surface material properties, and flight orbit. Ultraviolet radiation with a wavelength less than 300 nanometers, although only accounting for a very small portion of the total solar radiation energy, can cause significant changes in the optical properties of the material surface. The ultraviolet radiation effect is mainly manifested as photochemical effect and photoquantum effect.

The solar radiation simulation experiment can simulate the solar spectral thermal and photochemical effects generated by the solar radiation environment on spacecraft and extravehicular spacesuits. If only simulating thermal effects, it is called out of space heat flow simulation. There are two methods for simulating heat flux outside space, one is the jet simulation method, also known as the solar simulation method; Another type is the absorption heat flow simulation method, also known as infrared simulation method. For specimens with complex shapes and surface materials, it is advisable to use solar simulation method; For specimens with regular appearance and a single surface material shape, infrared simulation method can be used. If it is necessary to simulate the photochemical effects of UV irradiation environment, a UV irradiation simulator can be used.

(3) Space Cold and Black Environment and Simulation

The equivalent temperature of the cold black environment in space is about 3K, with a thermal absorption rate of 1, which can be regarded as an ideal blackbody without thermal radiation and reflection. When there is no solar radiation, the universe is a completely 'cold' and 'black' space. In this cold and dark environment, all the heat energy emitted by objects is completely absorbed, hence it is also known as a heat sink environment. The cold black environment has a significant impact on the thermal performance of spacecraft and extravehicular spacesuits. To develop spacecraft and extravehicular spacesuits, sufficient thermal vacuum and thermal balance tests must be conducted in simulated cold black environments to verify whether their thermal design and performance meet the requirements.

In order to simulate a cold and dark environment in space, components made of aluminum, copper, or stainless steel materials are usually used. The inner surface is coated with a specially designed black paint with high absorption rate, and liquid nitrogen is introduced into the interior of the component. This device is called a heat sink. At present, various aerospace countries around the world use this heat sink with liquid nitrogen as a cold source to simulate the cold black environment in space. Thermal analysis theory calculations and experimental data analysis show that using a heat sink with a temperature of 77K liquid nitrogen and an absorption rate of 0.9 or above to simulate the cold black environment in space has a simulation error of only about 1%, which fully meets the requirements of cold black environment simulation experiments. In addition, pursuing lower temperatures is unnecessary and will greatly increase the technical difficulty and investment in simulation equipment.