The prospect of interstellar migration

With the development of human science and technology, people are no longer satisfied with limiting the pace of expansion to land, sea and air on the earth, and then explore the unknown and vast space field.

From the first unmanned probes to the manned rocket spacecraft, the rise of human space industry has promoted people's cognition and research on the universe, and learned that such a vast universe is full of radiation magnetic fields and countless celestial bodies and nebula dust run in wonderful laws.

Space is dominated by vacuum, without oxygen and gravity; And the temperature is extremely cold, generally around MINUS 270 degrees Celsius. Such an environment is totally unsuitable for human survival. If humans enter space without any protective measures, they will lose consciousness due to extreme hypoxia, and at the same time, their blood will lose pressure and boil, completely lose their ability to act and suddenly die.

Moreover, after leaving the protection of the earth's atmosphere, the human body will be attacked by all kinds of cosmic rays and radiation, which will cause a devastating blow to the human body. But these difficulties can't stop human beings from exploring space themselves.

In order to cope with the harsh environment in space, space scientists invented special protective spacesuits to protect astronauts from the damage of space rays, and at the same time provide oxygen for astronauts and maintain temperature. But the spacesuit is far from meeting the needs of human beings to explore space. After wearing a spacesuit, although personal safety is guaranteed, because there is no gravity in space, the actions of astronauts will become extremely difficult, which brings difficulties to many space scientific research projects.

In order to enable astronauts to carry out scientific experiments in the space environment more conveniently, quickly and for a longer period of time, people also designed the space station, which is a large manned spacecraft that provides astronauts with work, research and life. The space station adopts a closed design to ensure the stability of the internal environment of the space station, and has a powerful water-gas circulation system, temperature control system and oxygen supply system.

It is worth noting that in the cold environment of about 270 degrees below zero in space, the space station not only has no worries about low temperature, but also needs to continue to "dissipate heat", which is really incredible. What's going on here?

First of all, to understand the concepts of cold and heat, we must first know what is the most essential molecular thermal motion of temperature.

You know, objects are actually made up of molecules, atoms and ions. In the microscopic world, these molecules have actually been moving and spreading irregularly. For example, a gold nugget and a lead nugget stick together, and after five years, it will be found that the gold nugget and the lead nugget penetrate each other by one millimeter.

Molecular thermal motion is based on molecular diffusion phenomenon, and the temperature is also inseparable from molecular thermal motion. The higher the temperature, the stronger the molecular motion, while the lower the temperature, the weaker the molecular motion.

Molecular thermal motion can be carried out arbitrarily between solid, liquid and gas. From the point of view of molecular gap, gas and liquid are solids. Therefore, gas is more likely to generate molecular thermal motion than solid, and the higher the temperature.

The three forms of water are also notable examples of molecular thermal motion. The temperature of water vapor is the highest, followed by liquid, and solid water is ice, which is the coldest intuitively. Therefore, temperature also reflects the kinetic energy between molecules of an object, so temperature cannot be separated from the propagation of matter. Without matter, there would be no temperature.

You know, the temperature of the earth comes from the burning furnace of the sun. The earth itself is a big piece of matter. Based on this, under the influence of solar radiation, heat conduction and thermal convection, various molecular movements are taking place all the time on the earth, so various temperatures will also be produced.

At the same time, with its heavy atmospheric protection and high-speed wind, the earth filters and diffuses redundant thermal radiation and cosmic rays, forming a temperature environment suitable for our human life and survival.

In other planets in the solar system, not every planet can have the protection of the atmosphere and the medium of air to transfer heat.

For example, the blue planet Mercury has neither air nor atmosphere, so the temperature difference between day and night can be as high as 600 degrees Celsius. On Venus, the atmosphere is too dense and the greenhouse effect is serious. The tiny temperature difference also causes Venus to be always in an extremely high temperature environment as high as several hundred degrees Celsius, just like the planet of purgatory.

However, in the "empty" space environment, because it is too vast and empty, its spatial density is extremely thin, with an average of only one atom in a cubic meter of space.

The distance between molecules is separated by the distance of Qian Shan, so it is impossible to form so-called medium and substance, so it is almost impossible to produce molecular friction and energy transfer, and there will be no temperature. In short, heat cannot be transferred in a vacuum.

That's why the temperature in space is so cold. For example, the thermos cup can insulate heat because the outer interlayer of the thermos cup is vacuumized, which effectively blocks the emission and diffusion of heat, so the heat is not easy to be lost, and it is always close to the legendary "absolute zero" category.

Absolute zero, namely -273. 15 degrees Celsius, is considered as the current low temperature limit. At this temperature, all molecular thermal motion will stop, which is the lowest temperature that can only be infinitely approached but can't really be reached. The space we are talking about is infinitely close to this absolute zero, which has reached about -270. 15 degrees Celsius, only three degrees higher than absolute zero, which is the lowest temperature in the known range of the universe.

According to the research of scientists, this temperature may be the residual temperature of thermal radiation left by BIGBANG in space hundreds of millions of years ago. At present, in the solar system, only Uranus, Pluto and Titan can reach the degree of "frozen planet" of MINUS 200 degrees Celsius.

In the extremely low temperature world, air will turn into light blue liquid at minus 190 degrees Celsius, eggs will turn into beating fluorescent blue balls, and flower goldfish will turn into fragile glass texture. We don't know what the world of absolute zero will become.

But in theory, at absolute zero, the movement of molecules completely approaches to a stop, which means that all the movements in the universe stop, time is squeezed, and the whole world becomes cold and static. Then, when humans build a space station in space with a temperature close to absolute zero, shouldn't the focus be on how to keep warm and cold? Why does it keep radiating outward?

Obviously, the space station itself is made of matter, and matter is made of molecules, so according to the principle of molecular thermodynamic dynamics, the heat of the sun will be transferred to the space station itself.

Because there is no atmospheric protection space station in the universe, the side of the space station irradiated by the sun will heat up sharply, even reaching the high temperature of 120 degrees Celsius. The side that is not irradiated by the sun will drop to a low temperature of about MINUS 140 degrees Celsius, and the temperature difference between the two sides is as high as more than 200 degrees. In addition, the space station experiences 16 sunrises and sunsets every day, and the temperature changes like riding a roller coaster.

At the same time, because there is no medium that can be used for heat transfer in space, the temperature received by the space station cannot dissipate heat through heat transfer.

Natural heat dissipation can only be achieved by thermal radiation, but the rate of thermal radiation is very slow, and the heat consumed is not as good as the heat supplemented by the space station itself.

Therefore, the space station is attacked by extreme ice and fire at any time, so it is very important for the space station to maintain a constant temperature and adjust the temperature, and "heat dissipation" is naturally a crucial part in this temperature adjustment. Only timely heat dissipation can deal with the invasion and damage of the high temperature part to the space station, ensure the personal safety of Chinese astronauts on the space station and ensure the smooth development of space science research.

Taking the historic International Space Station as an example, the International Space Station is equipped with an active thermal control system, which transports the cooling liquid through the liquid ammonia cooling liquid circuit on the main truss structure to cool the solar panels. After the cooling liquid liquid ammonia absorbs heat, it circulates from the external pipeline, and brings the absorbed heat to the photovoltaic heat dissipation plate for heat dissipation, thus maintaining the normal temperature of the solar panel and preventing the solar panel from overheating or supercooling.

The reason why liquid ammonia is used to help cool down is because the freezing temperature of liquid ammonia is about MINUS 77 degrees Celsius, which is not easy to solidify and can achieve better constant temperature heat dissipation effect.

At the same time, the whole space station is covered with multi-layer heat insulation materials with high reflectivity to reduce the surface temperature difference, so that the irradiation surface of the sun can be fully radiated, the shady surface of the sun can be insulated, and the internal instruments can work normally under the appropriate temperature guarantee.

The design of cooling system is equally important in the spacesuit that astronauts wear at any time. In the design of EMU series spacesuits, a water evaporation system is usually designed on the next floor. It absorbs sweat to keep the body dry and maintain the normal body temperature of astronauts.

The whole circulation system firstly outputs the absorbed heat to the heat exchanger. In the exchanger, the water stored in the water circulation system of clothes is output to a nickel plate with micropores. A thin layer of ice will quickly form on the surface of nickel plate, but at the same time, due to the influence of low-pressure environment in space, the ice will be transformed into water vapor after heating and leave the spacesuit.

In the process of water evaporation, it will take away excess heat, achieve the effect of cold and warmth, and protect astronauts from working normally in the special environment of space.

Therefore, it is unthinkable for human beings living on the earth to live in such an environment where extreme low temperature and extreme high temperature intersect.

Although we humans have thought enough ways to deal with this extreme temperature condition in space construction, extreme temperature and harsh environment will inevitably hinder our human exploration of space.

However, exploring the future prospects of space is of great significance. I hope that with the continuous progress and development of people's science and technology, we can gradually solve various problems in the aerospace process. And while understanding the truth of the universe, we should rationally develop and utilize the resources of the universe. By then, interstellar migration may also become a reality, and human civilization and wisdom will reach a new height through the universe.