Since the summer of this year, the highest temperature in many places in China has broken the historical extreme value and experienced the strongest hot summer day once in decades. Facing the high temperature, we can cool off the heat by turning on the air conditioner on earth. How does the Chinese space station in space maintain a comfortable temperature? Today, let’s reveal how the thermal control system of China Space Station makes our space home "like spring all the year round".
Space environment: ice and fire
China Space Station is located in a space environment about 400km from the ground. Without the protection of the atmosphere, the surface temperature of the space station can reach above 150℃ under the direct sunlight, and below -100℃ on the back side. In this "ice and fire" space environment, in order to ensure that astronauts can have a space station environment suitable for work and life, a thermal control system is needed to control the temperature.
Thermal control system is an important system to ensure the normal operation of space station equipment and the comfort of astronauts’ space life. The thermal control system is like our air conditioning system on the ground. By reasonably organizing the heat exchange process inside and outside the spacecraft, the temperature of all parts of the space station is always within the range required by the mission, which provides a good temperature environment for the normal work of space station equipment and the life of astronauts.
Different from the previous manned space missions, all spacecraft in the space station period need to fly in orbit for a long time, and astronauts also need to live in orbit for a long period of time, so higher requirements are put forward for temperature control. Facing the mission characteristics and requirements of China Space Station, the thermal control team has carried out a lot of technical research and carried out a number of technological innovations to create a comfortable "space home".
Thermal control mode 1
Create "Central Air Conditioning"
"Central Air Conditioning" in Thermal Control System of Space Station — — The fluid loop is the core of the thermal control system of the space station, and it is distributed in every corner in the Tianhe core module and the experimental module. The fluid loop can evenly wrap the important parts of the space station. Through the reciprocating circulation of special liquid in the pipeline, the heat generated by the equipment in the cabin and the life of astronauts is collected and brought to the corresponding equipment and structures through the loop to dissipate heat to the overheated place and heat to the supercooled place, so as to realize the functions of heat dissipation and heat supplement. At the same time, it can accurately control the temperature of different "rooms" of the space station and keep the temperature uniform and stable, which can be described as a tailor-made "central air conditioner".
The candlestick experimental module is the largest spacecraft with the heaviest load and the most test loads in China. There are many test loads installed in the module, and various exposure test loads with high heat consumption are arranged outside the module, which requires higher thermal control. The development team has developed three sets of liquid cooling systems for the experimental cabin of the space station, which can collect and radiate the heat generated by various equipment or test loads to outer space, and can support the heat dissipation of test loads above several kilowatts. One of them is a heat dissipation circuit specially designed to ensure the temperature of the extravehicular test load. The four-way valve technology is developed for the first time, which solves the influence of the installation state of the extravehicular test load on the loop system and is superior to the multi-valve control technology used by the International Space Station in weight.
Thermal control mode 2
Apply "space sunscreen"
In addition to building a "central air conditioner" to adjust the heat and cold of the space station, it can also passively insulate the spacecraft, and the thermal control coating is one of the passive thermal control. Since Shenzhou XII, the Shenzhou series of spaceships have been coated with a new silvery coating, which is a magical "space sunscreen" — — Low absorption-low emission thermal control coating.
In the construction stage of the space station, shenzhou spaceship is faced with the difficulty of cabin temperature control under long period and large temperature difference. When the space station assembly flies, the shenzhou spaceship may be continuously blocked by other cabins, resulting in the spacecraft being in an extremely low temperature environment where the sun cannot shine for a long time, and the lowest temperature is even lower than -100℃. However, when the space station assembly forms some configurations, the local area of the spacecraft will continue to be irradiated by the sun, with the highest temperature exceeding 100℃, which brings severe tests to the normal work of spacecraft equipment and the living environment of astronauts.
In order to solve this temperature control problem, the research team designed and developed a low absorption-low emission thermal control coating. Low absorption, as the name implies, is that the coating material itself has low solar absorption characteristics, which can effectively reduce the temperature rise caused by solar irradiation. Low emission means that the coating has low infrared emissivity, which can effectively block the radiation heat leakage from the interior of the spacecraft to the external cryogenic environment and avoid the continuous decrease of the temperature in the cabin. The thermal control coating is like a layer of "sunscreen", which effectively ensures the operation of the spacecraft in the long-term extremely high and low temperature environment and keeps the cabin in a suitable temperature range.
Thermal control mode 3
Put on an insulated "coat"
Another kind of passive thermal control is to put a thermal insulation "coat" on the spacecraft. Take Tianzhou-4 as an example. Tianzhou-4 runs in an orbit about 400 kilometers from the ground, and it takes about 90 minutes to circle the earth. Sometimes it is in the shadow of the earth and sometimes it is exposed to the direct sunlight. It needs to experience 14 such "ice and fire" every day. Therefore, the developers put on special heat insulation materials to resist the harsh environment and maintain a comfortable internal temperature.
The choice of fabric for spacecraft "coat" is very particular, which is carefully designed according to scientific principles. The fabrics with different characteristics meet the different needs of spacecraft. The "coats" of the cargo cabin and propulsion cabin of Tianzhou No.4 were designed in two different colors, gray and white. The cargo cabin needs to provide a temperature suitable for astronauts’ life, which is relatively high, so it is put on a gray "coat" to absorb more sunlight heat. The propulsion cabin is mainly equipment, which needs lower ambient temperature, so put on a white "coat" to reflect more sunlight heat.
In addition, the interior of Tianzhou No.4 "coat" adopts the design of multi-layer heat insulation components, which has a strong warm-keeping effect. It is composed of a film with high reflectivity and a polyester net supporting the film, which can be repeatedly superimposed to form a multiple structure. The heat inside is reflected by the reflective film layer by layer, and it is difficult to seep out of the surface, thus forming a high thermal resistance and preventing heat loss.
Through the cooperative work of air conditioning, sunscreen and thermal insulation clothing, the research team has built the China Space Station into a comfortable "space home" and kept it "like spring all the year round". The thermal control system seems to be the "big housekeeper" who controls the heating and cooling of the space station, ensuring the comfort of the space station in the harsh space environment and caring for the space station to travel safely in the sky.
