Shulou(Shulou.com)11/24 Report--

Wouldn't it be a little exciting if humans could sail in space for a long time, as in science fiction movies and novels?

▲ my three-body starship Earth (Source: bilibili- my three-body)

Speaking of which, I'm not sleepy.

The rice seeds and Arabidopsis seeds carried in the experimental module launched by China not long ago have successfully germinated and are growing well at present. The grown-up space rice also has a good-sounding name "Xiaowei".

▲ well-growing space rice and Arabidopsis seedlings (source: bilibili- our space)

In addition, the experimental module is equipped with a living ecological experimental cabinet, in which algae, tanks and zebrafish form a tiny ecosystem. By observing the life parameters of micro-ecosystems, we can lay a good foundation for the establishment of large-scale ecosystems in space in the future.

The ▲ test module was successfully launched (source: CCTV)

So, what do you need to pay attention to living in space?

Part I: microgravity environment. First of all, we can't feel gravity in space. You can fly as much as you like.

This is because when we are on a spaceship, a space station or the moon, because they all rotate around the earth with a centripetal acceleration, they can be used as a non-inertial reference frame. We will be subjected to the inertia force, which can also be called the inertia centrifugal force. The magnitude of the force is the same as the earth's gravity, and its direction is opposite to the earth's gravity, so we can't feel the earth's gravity.

(Tips: a non-inertial reference frame is a reference frame with acceleration. When analyzing the motion of an object in a non-inertial reference frame, an inertia force is added. The magnitude of the inertia force is the mass of the object multiplied by the acceleration of the reference frame, and the direction is opposite to the acceleration of the reference frame. )

In the movie interstellar travel, the main horns simulate gravity by rotating the station after entering the space station, which is actually another inertial centrifugal force caused by the rotation of the space station.

A rotating space station in ▲ interstellar travel (source: movie interstellar)

Assuming that the size of the space station is 100m, it can be known through simple calculation that in order to achieve the same gravity as on Earth, the speed of the space station is equivalent to 6000 times the rotation speed of the earth.

Similarly, to change gravity, you only need to design a device that can provide different rotational speeds. In the experimental module, a centrifuge with the size of 900mm is designed, and the fine adjustment of gravity can be realized by controlling the rotational speed.

Seeing here, we can't help but ask, is there any way to achieve weightlessness on earth?

As we all know, free fall is a process of weightlessness. According to this principle, people developed a kind of microgravity laboratory: weightlessness aircraft.

The weightlessness flight of one sortie consists of several weightlessness parabolas, and each weightlessness parabola consists of four stages: rapid jump, weightlessness, descent and peaceful flight. Each flight can achieve 15 to 20 weightlessness times, and each weightlessness can last 25 to 28 seconds. The level of weightlessness can reach 0.01 g.

Schematic diagram of parabolic flight curve of ▲ weightlessness aircraft (source: reference [3])

In addition, the high-altitude balloon can be released from the cabin at a predetermined altitude to achieve weightlessness. This is also a free fall process, the weightlessness time is 30 seconds, and the weightlessness level can reach 10-4 g [4]. Because of the short time of weightlessness, these microgravity laboratories can only complete some simple experiments, which can lay a good foundation for going into space later.

A real weightlessness environment can be simulated by free fall.

In addition, think about it again: if you applied an upward force equal to mg to counteract gravity, wouldn't it also achieve the effect of weightlessness?

Therefore, people have developed the weightlessness experiment of neutral buoyancy flume, in which the human body can achieve equivalent weightlessness by increasing or decreasing the floater in the water, so that the buoyancy and gravity are equal.

▲ astronauts undergo underwater training (source: CCTV News)

However, it is noted that in this case, only the whole human body has achieved the effect of weightlessness, and human tissues and organs are also affected by gravity. Through this method, we can simulate spacewalk, weightlessness engineering control and other training.

Part II: how to block the strong radiation environment? Strong radiation in the universe is generally high-energy particles. On the one hand, there are always high-energy protons, ions, or mesons and other charged particles from the depths of the universe; on the other hand, accidental solar proton events occur. The energy of the highest-energy particles in cosmic rays can even reach tens of millions of times the maximum energy provided by accelerators on Earth.

When the high-energy particles irradiate the surface of the object, they will interact with the atoms and molecules on the surface. For the human body, strong radiation can damage the skin and induce cell carcinogenesis.

Atoms in matter are usually held together by covalent bonds, ionic bonds, metal bonds, or by van der Waals forces between molecules.

These binding modes are essentially achieved through the outer electrons of the atom.

Therefore, if the outer electrons in the atom get energy from the high-energy particles, they will break away from the atom, thus breaking these chemical bonds, causing the atoms to bind unsteadily, thus damaging the object.

In addition, high-energy particles may interact with electrons in the inner layer of atoms to produce a large number of harmful rays.

First, the electrons get very high energy directly from the solid, and secondly, when the electrons in the inner layer at the low energy level are removed from the solid, the electrons in the outer layer at the high energy level jump to the low energy level to radiate photons, which are also called x-rays, and then the radiated x-rays further excite the inner electrons and radiate secondary electrons.

Interaction of ▲ high energy rays with electrons in atoms

Higher-energy particles can even interact with nuclei, breaking the shackles of nuclear force and radiating protons and neutrons.

So how to stop these high-energy particles?

A direct idea is to use thick materials as barriers. But this method requires a lot of material, and even if a space the size of a spaceship is shielded, the anti-radiation material needed needs to be in tons [6]. At the same time, the secondary radiation caused by the interaction between high-energy particles and materials, such as electrons, neutrons and x-rays, will also produce new problems.

Another consideration is: since these high-energy radiation are charged particles, is it possible to constrain or change the trajectory of these particles by using an electric or magnetic field?

This is how the geomagnetic field protects life on Earth from the high-energy rays of the universe.

When a charged particle moves in a magnetic field, it will be affected by Lorentz force, thus changing the trajectory of motion. The electric field also exerts an electric field force on the charged particles, thus changing the magnitude and direction of the particle velocity.

Through the reasonable design of the electromagnetic field distribution in the outer space, we can deflect or slow down the high-energy rays from the universe, so as to protect our space station.

It is worth mentioning that the trajectory of charged particles in the electromagnetic field, such as the following picture, is a common problem in the college entrance examination.

The motion of ▲ electron in electromagnetic field is affected by electric field force and Lorentz force.

So little friends, I have a set of May 3rd secret books here, and it is up to you to lead mankind to fly to the universe.

We can apply electric current to the surface of the spacecraft to generate a magnetic field and simulate the distribution of the geomagnetic field.

Or the use of low-intensity magnetic field to make the hot electrons in the surrounding space gather around the spacecraft to form electron clouds, resulting in a strong electric field, thus blocking charged particles.

Four metal balls can also be connected to the main cabin of the spacecraft, which are negatively charged respectively, thus forming an asymmetric electrostatic field distribution that directly offsets the trajectory of the surrounding charged particles. [6]

Structure diagram of protective device with four metal balls in the main cabin of ▲ space station (source: meal reference 6)

Of course, in the actual operation, radiation protection materials and electromagnetic field methods certainly need to be used together.

Part III: necessities of life: oxygen and water are limited if they want to survive in space for a long time, so what are the convenient and quick ways to produce oxygen and water?

Electrolysis of water is a simple method. By constructing an electrolytic cell, the water molecules at the anode are oxidized and lose electrons to form oxygen and hydrogen ions, which are discharged with the flow of water, and the hydrogen ions combine with the water molecules in the solid polymer film and migrate to the cathode under the action of an electric field. The hydrogen ion at the cathode gets the electrons of the outer circuit and is reduced to hydrogen.

Schematic diagram of ▲ solid polymer water electrolysis cell (picture reference from literature [8])

In addition to getting the oxygen we want, the hydrogen produced by electrolysis of water will also be of great use.

People absorb oxygen and exhale carbon dioxide, and notice that there are oxygen atoms in carbon dioxide, so it can be used to react with hydrogen to produce water.

However, because the properties of hydrogen and carbon dioxide are relatively stable, it is necessary to use catalysts (iron, cobalt, nickel, ruthenium) to react under high temperature and high pressure. Due to the different mixing ratio of carbon dioxide and hydrogen will produce additional carbon monoxide, carbon elemental, methane, methanol and other substances, so in the actual operation, it is necessary to carefully control the proportion of the two involved in the reaction to prevent the production of adverse substances.

In addition, oxygen can also be generated by the reaction between sodium peroxide and carbon dioxide.

▲ reaction equation for the preparation of Water and oxygen from carbon dioxide

In addition to chemical reactions, we can also recycle daily water and urine. The purified water is prepared again by distillation-cooling.

Water behaves differently in space than on the ground, and there is no pressure inside the water without gravity. But because of the attraction of water molecules to each other, water still has surface tension.

The most natural way for a mass of water to exist in space is to form a sphere. This is because the surface area of a spherical object is the smallest at the same volume, and the surface energy of the liquid is equal to the surface tension multiplied by the surface area, so keeping the sphere in space can make the surface energy of water the lowest, that is, the most stable state.

In the previous space lecture, there was a phenomenon that water stably existed in the cup, just like the water in the cup on earth, and the majority of netizens also had a discussion about it. What's going on?

The water in the cup is no different from that on the ground in the ▲ space class.

This is due to infiltration of water and the surface of the glass.

There will be an adhesion layer on the surface where the solid is in contact with the liquid. The attraction of the liquid molecules to the molecules in the attachment layer is cohesion and the direction points to the inside of the liquid; the attraction of the solid molecules to the molecules in the attachment layer is adhesion and the direction points to the interior of the solid.

If the adhesion is greater than the cohesion, the resultant force on the molecules of the adhesion layer points to the inside of the solid, so the liquid molecules will move to the adhesion layer, but this increases the contact area between the liquid and the solid, thus increasing the surface energy. so the phenomenon of infiltration equilibrium as shown in the following figure will eventually be formed. [9]

▲ liquid infiltration phenomenon (Source: Qin Yunhao "Thermodynamics")

Ps: this glass of water is squeezed into the cup by the astronaut sister drop by drop (it is a very hard process). As long as there is no external force on it, the glass of water will remain that way.

So what kind of phenomenon does gas show in space?

The distance between gas molecules is much larger than that of liquids, so there is no intermolecular attraction. The pressure of the gas comes from the thermal motion of the gas molecules, so oxygen is naturally dispersed in space, as it is on the ground.

Part IV: if we can plant plants on a large scale and build ecosystems in space, and plants can absorb carbon dioxide to produce oxygen through photosynthesis, then we can solve not only the problems of water and oxygen, but also the problem of food.

As mentioned earlier, most of the time in space is in microgravity. For plants, without the constraints of gravity, there may be no need for soil support. The cells are no longer squeezed by gravity, the distance between them will not be too tight, and the cells may grow indiscriminately in all directions, so the plants may be larger than on earth.

However, microgravity may also affect the cytoskeleton, lead to abnormal cell growth, or affect the properties of the cell membrane, thus affecting the communication of substances between cells. at the same time, microgravity will also affect the cell division cycle [10].

In a word, the effect of microgravity on plant growth is still the focus of space microgravity science research. The experimental module launched in China also carries an experimental module to study the growth of plants and cells under microgravity.

In most cases, there is a lack of soil in space, so hydroponic cultivation can be used to grow plants. Hydroponic cultivation, also known as soilless cultivation, is usually used to overcome the difficulties encountered in soil cultivation, such as salinization, diseases and insect pests, acid-base imbalance and so on [11]. Hydroponic cultivation enables plants to survive through the allocation of appropriate nutrients.

In general, 75% to 95% of fresh plants are water, and the remaining dry matter includes basic elements such as C, H, O, N, P, K, Ca, Mg, S and trace elements such as Fe, Mn, Zn, Cu, Mo, B, Cl, Ni and other trace elements. Trace elements can regulate plant metabolism, participate in material transformation and transport, signal transmission and osmotic regulation and other functions [12].

In order to provide enough basic elements and trace elements for plants, we can dissolve and mix the compounds containing various elements with distilled water to form a nutrient solution, and we need to set a certain PH value of the solution.

The cultivation process is to first select full and disease-free seeds, and then disinfect them so that they will not be infected by bacteria in the culture process.

Then soak the seeds with water to make the seeds absorb enough water and expand the seed coat, so that the seeds can absorb oxygen and strengthen the life processes such as seed metabolism and enzymatic reaction.

Then wait for it to germinate and transplant to the nutrient solution, and finally change the nutrient solution regularly and replenish the consumed oxygen in time [12].

▲ takes rice hydroponic cultivation as an example, from left to right, for rice seeds to absorb water for whitening, germination and transplanting. (source: reference [12])

Soil planting may also be a way to grow plants in space. For example, in the movie Mars Rescue, the protagonist makes a living by growing potatoes using feces.

▲ Mark grows potatoes on Mars (source: movie Martian)

However, in order to plant soil in a large area, we still need to study the physical and chemical properties of alien soil in more detail, and then transform the soil so that the soil can store water and minerals. At the same time, there must be a biological community composed of bacteria and fungi in the soil to ensure the existence of plant rhizosphere, because microbial nitrogen metabolism, fermentation and respiration play an important role in plant root growth. there is a symbiotic, antagonistic and parasitic relationship between microorganisms and plants [13].

In short, soil planting in space is still in an imaginative stage, so let's settle down and study the lunar soil that has just been brought back from the moon. Ugh! Hey!

▲ can't grow vegetables in the moon soil where he lost his dream (source: bilibili- Guangming Daily)

Part V: through the above analysis process, you want to survive in space, whether it's producing oxygen and water, or growing plants, not to mention the operation of space stations and instruments, which require a lot of energy or electricity. So how do you generate electricity in space?

One way that can be thought of directly is, of course, to use solar energy to generate electricity, that is, to use the photoelectric effect to convert light energy into electricity.

For an atom, electrons are distributed over the energy levels outside the nucleus, and when two atoms are close to each other, these energy levels split. For solids, there are a large number of atoms close to each other, and because the arrangement of atoms is periodic, it will cause the electron orbitals in atoms to cross each other and form energy bands with continuous distribution of energy. The part that can hold electrons is called permissible band, and the part that cannot hold electrons is called forbidden band. The size of the forbidden band is called the energy gap.

The permissible band is divided into conduction band and valence band. For a semiconductor, in the absence of external interference, most of the electrons are in the valence band and do not participate in conduction. Only a small number of electrons will jump to the conduction band to conduct electricity under the influence of temperature. the higher the temperature is, the more electrons will jump into the conduction band, which is the reason why the conductivity of semiconductors becomes better with the increase of temperature. These hot electrons are equilibrium carriers.

Formation process of Energy Band in ▲ solid and Electron Distribution of Semiconductors

Different doping of semiconductors will become n-type semiconductors and p-type semiconductors. For example, for silicon, it is itself an intrinsic semiconductor, that is, the electrons excited to the conduction band are as many as the holes in the valence band.

If the phosphorus atom is doped, an additional electron will be introduced, resulting in more electrons than holes, which mainly rely on electrons to conduct electricity, thus becoming an n-type semiconductor. If boron atoms are added, an extra hole will be introduced, resulting in more holes than electrons, which mainly rely on holes to conduct electricity, that is, to become p-type semiconductors.

P-type semiconductors and n-type semiconductors are combined to form pn junctions.

Because of the higher concentration of electrons in n-type semiconductors, electrons will be spatially diffused from n-type semiconductors to p-type semiconductors. When electrons leave the original region of n-type semiconductors, they will leave immovable positive ions and form a positive charge space region; electrons enter p-type semiconductors to fill the holes in the original region and form a negative charge space region of negative ions. The spatial diffusion of electrons leads to the appearance of a space charge region between the two which are originally neutral, thus forming an electric field inside [11].

When light shines on a semiconductor, if the energy of the photon is greater than the bandgap width of the semiconductor, a large number of electrons will absorb the energy of the photon and transition to the conduction band called non-equilibrium carriers. For pn junctions, these non-equilibrium carriers migrate through the internal spontaneous electric field to form currents. Solar cells rely on this basic principle to convert light energy into electricity.

Schematic diagram of photogenerated current in ▲ pn junction

In addition, nuclear reactions can also be used to generate electricity. At present, the main way of nuclear power generation is nuclear fission, and it is expected to achieve controllable nuclear fusion in the future.

Whether nuclear fusion or nuclear fission, the basic principle is that the nucleus loses protons or neutrons at extremely high temperatures, and protons and neutrons re-form new nuclei. In the process of the formation of a new nucleus, the total mass of the old nucleus and proton neutrons involved in the reaction is larger than that of the new nucleus, because the protons and neutrons in the nucleus are combined by the attraction of the nuclear force, so the binding energy is negative. So in the latter part of this process, there will be a mass loss, and according to Einstein's mass-energy equation, the lost mass will be converted into huge energy.

For example, a typical light nuclear fusion process is the deuteron (one proton plus one neutron) reaction to produce helium nuclei (two protons plus two neutrons), protons and neutrons. The intermediate is accompanied by the production of tritium nuclei (one proton plus two neutrons) and helium 3 (two protons plus one neutron) [15]:

So how to convert nuclear energy into electricity?

In fact, the method is very simple, is to boil water. Nuclear water heating turns it into water vapor with high kinetic energy, which blows the mechanical blade to produce alternating current through electromagnetic inductive effect.

Schematic diagram of ▲ alternator (source: Baidu encyclopedia)

Can other ways of generating electricity be developed in the future?

The answer is yes, such as thermoelectric materials for thermoelectric power generation.

For a thermoelectric material, if there are different temperatures at both ends, an electromotive force will be generated, and a short circuit connected to the wire will generate an electric current.

Schematic diagram of ▲ thermoelectric effect (source: reference [16])

Thermoelectric effect was first discovered by German scientist Seebeck in 1821. The basic principle is that for semiconductors, the carriers at the hot end will have more kinetic energy than the cold end; at the same time, as we mentioned earlier, the thermal excitation will also make the carriers transition from the valence band to the conduction band, so there are more carriers at the hot end to the conduction band. The combined effect of the two makes the carriers spread to the cold end, resulting in the accumulation of charge at both ends of the semiconductor.

For example, for n-type semiconductors, electrons migrate from the hot end to the cold end, thus accumulating negative charge at the cold end and forming a positive charge region at the hot end, so the potential difference between the two ends of the semiconductor will be formed. [16]

At present, thermoelectric materials are still in the stage of development, but they also have broad application prospects.

Conclusion, you have mastered the basic knowledge you need to survive in space. are you ready to settle down and take risks in space?

Although, human beings still have a long way to go to fly to the universe, and we need to rely on the joint efforts of everyone in various industries.

In short, let's move forward to the distant stars and the abyss of the universe!

References:

[1] the four major scientific experiment cabinets of "ask the Heaven" have come for detailed explanation! China Science Journal / 2022 / July / 25 / Page 001.

Microgravity science experiment system based on weightlessness aircraft, Lu Congmin, Xi long, Zhao Guangheng, Zhang Yuhan, Journal of Tsinghua University (Natural Science Edition), Volume 43, No. 8, 2003.

[3] miraculous weightlessness plane, Tang Chengge, Science and Technology Vision 2006.1.

[4] microgravity environment simulation experiment system realized by high-altitude balloon, Wang Jianyi, Aerospace Control, No. 3, 1990.

[5] Research progress of simulated weightlessness test technology for man-machine integrated extravehicular activities, Zhou Qianxiang.

Analysis and Research on active Space radiation Protection methods, Chen Shishi, Zhang Ningbo, Xiong Fenfen, Proceedings of the 9th Annual meeting of the Professional Committee of Deep Space Exploration Technology of Chinese Astronautical Society.

[7] solid State Physics course, Wang Bifeng, Shandong University Press.

[8] study on influencing factors of hydrogen production from electrolytic water, Li Jing, Master thesis of Beijing Architectural University, June 2020.

[9] Thermology, Qin Yunhao, higher Education Press.

Research Progress of cytoskeleton in Space Life Science, Wang Chi, Zhuang Fengyuan, Wang Wen, Medical Biomechanics 2007, Volume 22, No. 2.

[11] Design and control performance analysis of nutrient liquid circulation control system for hydroponic cultivation, Fang Hui, Yang Qichang, Wei Lingling, Wu Guodong, Wei Qiang, Agricultural Mechanization Research, March 2009, No. 3.

Discussion on improving soilless cultivation methods of rice seedlings, Huang Qiu-Chan, Tang Ming, Li Yi, Chemical Engineering and Ecological Environment Research, 2013, vol. 30, no. 3.

[13] screening of hyperaccumulators and phytoremediation of contaminated soil, Wei Shuhe, Ph. D. thesis, Graduate School, Chinese Academy of Sciences, May 2004.

Semiconductor Physics, Liu Enke, Electronic Industry Press.

[15] Atomic Physics, Yang Fujia, higher Education Press.

[16] basic principles, key issues and research progress of thermoelectric materials, Guo Kai, Luo Jun, Zhao Jingtai, Journal of Nature, 2015, vol. 37, no. 3.

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: Xiaoming Editor: Garrett, who doesn't like physics.

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