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

At 23:08 this evening, the Shenzhou 15 manned spacecraft will be launched from the Jiuquan Satellite launch Center with a long March 2 F remote 15 rocket. This launch will send three more astronauts into the Tiangong space station, namely, Fei Junlong, Deng Qingming and Zhang Lu. At that time, the Tiangong space station will welcome an unprecedented six astronauts on duty at the same time! This is also the first time that our space station has been rotated in orbit, and six astronauts will live together on the space station for a period of time. It is worth mentioning that Deng Qingming is China's first batch of astronauts, and Yang Liwei in the same group, stick to it to this day, and finally realize the dream of flying. This launch is the last manned space mission during the construction phase of the space station. Let us wish the launch a complete success.

This launch still uses our Chinese "Shenjian" long March II F rocket, and Chang-2 F has carried out China's manned space missions many times, all of which have been a complete success. I believe that this time they will live up to everyone's expectations. This launch is scheduled at the Jiuquan Satellite launch Center. Everyone should know more about Jiuquan. If you do not understand, the editor will find an opportunity to take you to understand.

Long March II F uses nitrogen tetroxide and unsymmetrical dimethylhydrazine propellant, which is a typical liquid rocket. What on earth is the liquid propellant rocket engine? When it comes to liquid rocket motors, you may think that this is already backward technology, and solid rocket motors are the future. But in fact, liquid rocket engine is still a well-deserved main force in the world today.

When we talk about the origin of rockets in the history of rockets, we should start from the period of the three Kingdoms. In other words, during the years of the Han and three Kingdoms, we had rockets. That's the word.

. Of course, the rockets here are not the same thing as the rockets we are talking about now, not even distant relatives.

After gunpowder was invented, people thought about using the reaction force to go to heaven. Wanhu, the Chinese people of the Ming Dynasty, were the first to practice this method. He tied firecrackers to a chair, hoping to fly with the help of its thrust and the lift of kites. In the end, of course, it failed, but this spirit deserves our respect.

Modern rockets began in 1903. In 1903, Konstantin Edualdovich Tsiolkovsky published a paper entitled "exploring Space with reaction facilities", which theoretically demonstrated the model of spacecraft propelled by rockets. In this article, he proposes that liquid hydrogen / liquid oxygen can be used as a propellant to develop rockets. This is also one of the propellant combinations that we often use now. In this article, Tsiolkovsky also proposed the famous homogeneous equation:

Δ v is the velocity increment of the spacecraft, ω is the jet velocity, and m "and m" are the mass of the spacecraft before and after acceleration, respectively.

Among them, the jet speed and the mass ratio before and after reflect the two important indexes of the spacecraft engine, the specific impulse and the dry-mass ratio.

Tsiolkovsky | the picture is from wiki about specific impulse. We have already answered the question and answer for you in Chang'e. If you are interested, you can go back and look it up. Here is a brief introduction to the dry-mass ratio, that is, the mass ratio, which is actually the mass ratio in the homogeneous equation. in space flight, we generally pay attention to the mass ratio of the rocket before launch and after it is completely flameout. it has something to do with the structure of the rocket itself and the load mass carried. It is not difficult to see from this equation that the greater the dry-mass ratio, the greater the speed increment, but in fact, the dry-mass ratio of the carrier rocket is very difficult to achieve. At present, no single rocket dry-mass ratio can reach to send the spacecraft into space. Therefore, Tsiolkovsky put forward the idea of a multi-stage rocket, which ignites the load into space through multiple rockets in turn. Current rocket thrusters require at least 1.5-stage rockets to complete the launch mission.

In fact, the first rocket was a liquid rocket, which was built even before the homogeneous equation.

As early as 1926, R.H. Goddard successfully launched the first liquid fuel rocket in Auburn, Massachusetts, using gasoline / liquid oxygen as propellant. the rocket flew only 12.5 meters high and 57 meters away. To be honest, it was not as good as a firecracker.

But this is indeed the first human rocket, and Goddard is also known as the father of American rockets.

Goddard and his rocket | the picture is from Resources. The really practical liquid rocket should be the German V2 rocket. In 1944, Germany successfully developed the V2 rocket, which uses liquid oxygen / alcohol as propellant and has a range of 300km, which actually created the development process of modern liquid rocket. But Nazi Germany developed the rocket for war, and in 1944, Nazi Germany attacked London with it.

After that, the United States and the Soviet Union carried out the research and development of liquid rockets on the basis of this rocket.

The structure of rocket engine there are three main structures of liquid rocket engine: thrust chamber, propellant supply system and engine control system. It can be said to be three big pieces.

Thrust chamber is a device for rocket engine to complete energy conversion and generate thrust, which is composed of injector, combustion chamber and nozzle. The propellant is injected into the combustion chamber through the injector, and a violent redox reaction occurs after atomization, evaporation and mixing, resulting in a high-speed air flow ejected from the nozzle. The air velocity is 2500-5000m / s, the pressure in the combustion chamber is about 20MPa, and the temperature is about 3000-4000 ℃. Therefore, the cooling of combustion chamber is also an important subject of rocket engine.

The propellant supply system is a system that transports the propellant in the tank to the thrust chamber at a specified mixing ratio and flow rate under the required pressure. According to the transportation mode, it can be divided into two types: extrusion type (pneumatic type) and pumping type. The former is generally used in small thrust engines, while the latter is mostly used in high thrust engines.

As for the engine control system, there is no need to mention it, its function is to adjust and control the working procedures and parameters of the engine.

In addition to these three pieces, the rocket engine may also have pre-cooling system, thrust vector control system and other components.

The working process of the rocket engine is relatively clear. under the control of the propellant supply system, the propellant is sent into the thrust chamber with a specified mixing ratio and flow rate, and the thrust chamber is injected into the combustion chamber through the injector. during combustion, high temperature gas is generated by full combustion, which is ejected from the nozzle at high speed to obtain huge thrust.

As for the specific way of working, if you have the opportunity, you can find the opportunity to talk again.

Propellant in liquid rocket engine, the most important thing is propellant. In the course of the development of liquid rocket engine, our research on propellant has been on the way.

The thruster of liquid rocket engine can be divided into single-component and two-component, and the two-component is easy to understand. An oxidizer and a reductant, both of which have a violent redox reaction, produce gas to propel the rocket into space. However, unipropellant propellants may be relatively unfamiliar to us.

The so-called single-component propellant, as the name implies, there is only one component, the thrust of this propellant comes from its own catalytic decomposition, single-component propellant is generally used to provide control of the engine, the most commonly used is hydrazine.

Hydrazine, also known as hydrazine | the figure comes from references. Hydrazine is a unit propellant that can be stored on the ground. It has a high freezing point and is liquid at room temperature. It is good for storage, but it has poor thermal stability and can be decomposed into ammonia and nitrogen and produce heat under the catalysis of the catalyst. However, although it is a single-component propellant, it is generally not only hydrazine. It is generally made with MMH (methylhydrazine or monomethylhydrazine, mentioned later) to form a single-component propellant composed of hydrazine, hydrazine nitrate and water, which is generally used in spacecraft attitude control, orbit adjustment and final booster control. Some 10N or so micro engines usually choose to use hydrazine. Hydrazine has excellent pulse specific impulse, sensitive response, high reliability and, most importantly, easy storage and low cost. Of course, another obvious disadvantage is that it is highly toxic.

Two-component propellants can be divided into two categories: cryogenic propellants and storable propellants. The commonly used cryogenic propellants are liquid oxygen / liquid hydrogen and liquid oxygen / RP-1; storable propellants such as N'O'/ mixed hydrazine, N'O'/ UDMH, N'O'/ MMH, nitric acid / UDMH, nitric acid / hydrazine and so on.

The first is the storable propellant, which is liquid at room temperature, so it can be stored more easily. The main members of storable propellants are hydrazine.

First of all, UDMH may seem strange to you at first, but when it comes to its Chinese name, you should be more familiar with it. This is unsymmetrical dimethylhydrazine. This is a kind of fuel with the best thermal stability among the hydrazine series fuels, which can be used alone or mixed with hydrazine or kerosene. But in fact, the specific impulse of unsymmetrical dimethylhydrazine is general, even for RD-253, the vacuum specific impulse is only 310s.

Hydrazine is often mixed with other fuels.

For example, the fuel composed of 50% unsymmetrical dimethylhydrazine and 50% hydrazine is mixed hydrazine 50, which is more stable, higher density and boiling point and safer. Like the American Hercules rocket L87 and the Russian SL-13 both use mixed hydrazine 50.

Take another example: amine hydrazine. Aminohydrazine is a fuel formed by the mixture of hydrazine and diethylenetriamine. The cooling performance of amine hydrazine is good, and the specific impulse is higher than that of hydrazine.

Then there is still the hydrazine fuel-MMH, that is, methylhydrazine or monomethylhydrazine. As a member of the hydrazine family, MMH is also a liquid propellant that can be stored around the clock, with a low freezing point and can be used alone or mixed with hydrazine or UDMH or with hydrazine and hydrazine nitrate. The MMH energy is between hydrazine and unsymmetrical dimethylhydrazine. It has a wide liquid temperature range, high temperature and high altitude performance better than mixed hydrazine 50. However, the production of MMH is complex, the price is high, and it is the most toxic of the three hydrazine, even the thrust is lower than hydrazine. But MMH has a good ability to start multiple times. With high precision, it can be used as a propellant for attitude control, speed control and reaction control of the upper stage rocket.

In the two-component propellant, hydrazine fuel is usually used as reducing agent, and the oxidizer is usually N-O-O. N "O" has a remarkable feature, its color is the same as nitrogen dioxide, is reddish brown, so when launching, there is a rise in red smoke is generally N2O4 as an oxidant. The long March II F rocket used in this launch uses unsymmetrical dimethylhydrazine and nitrogen tetroxide as propellant. You can pay attention to the grand occasion of the ignition.

Red tail flame | the picture is from Resources. In addition to N "O", hydrazine also has the use of nitrooxidants. The advantage of this combination is that the ignition delay period is shorter. Ignition with shorter delay is more reliable and starts faster. The ignition delay period of using nitric acid as oxidant and mixed hydrazine is 25ms, with UDMH is 4ms, and with anhydrous hydrazine is only 2ms.

Next, let's introduce cryogenic propellants.

The so-called cryogenic propellant refers to the propellant which is gaseous at room temperature and liquid only at low temperature. this propellant is not easy to store, of course, it also has some other advantages, such as cheap or high specific impulse.

The first is RP-1, don't be fooled by the name, this thing is actually kerosene, a highly refined aviation kerosene. Its oxidant is generally liquid oxygen.

It was mentioned at the beginning that the fuel used in the early rockets was alcohol, but later it was found that fossil fuels were better, because hydrocarbon fuels were more efficient and denser. So people set their sights on kerosene, which is very cheap, more stable and safer at room temperature, non-toxic and environmentally friendly. But kerosene brings another problem. Kerosene will decompose and polymerize at high temperatures, and heavy components will produce deposits that deposit on the engine and block the cooling channel. So RP-1 was born.

RP-1 strictly controls the content of sulfur, which not only corrodes metals at high temperatures, but also aggravates the polymerization of hydrocarbon fuels. At the same time, by reducing the content of unsaturated olefins and aromatic hydrocarbons, these compounds are easy to polymerize, and isomers are used instead of linear alkanes to enhance the ability of thermal decomposition resistance.

There are still many rockets that use kerosene. The Saturn-1 engine F1 for the American lunar landing is a liquid oxygen / kerosene engine. China's YF100 also uses kerosene. Today's space X also uses this scheme.

This is F1. What will happen if F1 is on the F1 track? | the picture is derived from references, followed by liquid hydrogen / liquid oxygen.

This is very simple and rough, it is the highest specific impulse propellant combination (practical) today, and it is environmentally friendly and pollution-free.

Both liquid oxygen and liquid hydrogen need to be kept liquid at low temperatures, so the long March 5, which uses this combination, is affectionately known as the "ice arrow". The density of liquid hydrogen is very small, so its volume is very large, so we have a concept of density specific impulse, that is, the specific impulse of propellant per unit volume, and the density specific impulse of liquid oxygen / liquid hydrogen is not as good as kerosene / liquid oxygen. In addition, liquid oxygen liquid hydrogen storage is difficult and easy to volatilize.

Vacuum theoretical specific impulse of some propellant combinations (s)

Finally, some other propellant combinations are briefly introduced.

The first is liquid fluorine. Everyone should know that when it comes to oxidation, fluorine is the real big brother, so in theory, liquid fluorine and liquid hydrogen are the strongest specific impulse. However, because fluoride and fluoride are highly toxic, the propellant has not yet entered the practical stage.

The second is methane, which is also a fossil fuel, but its limit temperature of coking is much higher than that of kerosene, there is no carbon deposition in different mixing ratio with liquid oxygen, and the corrosion of the material is much less. However, it is less safe than kerosene and more expensive than kerosene.

Reference:

[1] Charlie. Liquid rocket engine technology [J]. Defense Science and Technology, 2004 (08): 25-30.

[2] the whole army. Present situation and future development trend of liquid propellant [J]. Rocket Propulsion, 2004 (01): 1-6.

[3] Zhang Yuan. Development and present situation of foreign liquid propellants [J]. Foreign Missile and Aerospace, 1980 (09): 7-15.

[4] Sun Hongming. Review of liquid oxygen / methane engine [J]. Rocket Propulsion, 2006 (02): 23-31.

[5] the list of Shenzhou 15 crew was announced: Fei Junlong, Deng Qingming, Zhang Lu

[6] the transfer of the Shenzhou 15 ship and arrow assembly to the launch area is planned to be launched in the near future.

[7] about rocket fuel-the development and classification of liquid propellants

[8] brief introduction of aerospace kerosene RP-1

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: mu Zi

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