Craving for the stars

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Craving for the stars
Craving for the stars

Space engines today and tomorrow: real jet monsters and promising technologies of the future.

Space engine of the future

Unlike the usual internal combustion engines, jet engines have neither cylinders nor pistons that create rotational motion. Their action is based on the law of conservation of momentum, which follows from Newton's Third Law: "The force of action is equal to the force of reaction." The thrust is created by a powerful stream of particles emitted during fuel combustion. Flying in one direction, these particles give the rocket or spacecraft an acceleration directed in the opposite direction. The greater the mass and acceleration of the particle flux, the greater the jet thrust created by them.

In a traditional jet engine, the first of which was developed before the Second World War, the particle stream is an incandescent gas, a reaction product of a fuel and an oxidizer. This plasma, escaping from the nozzles of a jet engine, can be formed from solid or liquid fuels - respectively, chemical engines distinguish between solid and liquid ones.

In the beginning there was solid fuel

Historically, the first type of jet engine was solid fuel. The first of them appeared in ancient China, where they were used to launch fireworks, and since the Middle Ages they are found in Europe, where they were used to deliver charges to bomb enemy fortresses. The main trick in this case was to maintain combustion, not turning into an explosion, which would instantly release the energy of the fuel and destroy the rocket. Therefore, for the charge was used "modified" gunpowder with a reduced content of nitrate and sulfur, but an increased amount of coal. This mixture burns very powerfully and quickly, but - with due care - does not explode.


In modern solid fuel engines, of course, mixtures are used much more efficient - for example, this: ammonium perchlorate (oxidizer, about 70% by weight), aluminum (main fuel, 16%), iron oxide (catalyst, 0.4%), polymers and epoxies (provide contact between fuel and oxidizer and uniform combustion, about 14%). A complex configuration of the arrangement of solid components, in the form of a multi-pointed star, is also used, at which a large surface area of ​​the contact between the fuel and the oxidizer and, consequently, a high combustion rate is achieved.

Solid fuel engines are cheap, simple and safe, but once started, the combustion process can no longer be stopped or controlled. Therefore, today they are more often used not for space, but, say, for intercontinental ballistic missiles (ICBMs) operating on the “fire and forget” principle. In space carriers, liquid engines are usually installed.

Liquid fuel: the start of the space age

The first liquid-propellant jet engines (LRE) began to appear in the 1920s, thanks to the work of the famous physicist Robert Goddard, after whom one of the largest research centers of NASA is named today. Goddard managed to solve a number of problems associated with the design and use of such engines, including pumping fuel and cooling, and most importantly, creating a schematic diagram of such an engine.


The scheme is simple to the point of genius: liquid fuel (Goddard used gasoline) and liquid oxidizer (oxygen) are placed in separate tanks, from where they are fed into the combustion chamber with the help of special pumps through separate channels. Here a reaction takes place, the hot products of which fly out of the nozzle at high speed, creating thrust.

Of course, in reality, a modern liquid-propellant engine is a much more complex system than this concept of Goddard.Suffice it to say that liquefied gases are used as fuel and oxidizer, which must be kept at a low temperature and immediately heated before being fed into the combustion chamber. For this, very sophisticated technical solutions have been found - for example, channels are drilled in the nozzles of some engines through which the fuel flows, heating up from a hot nozzle. This technology is so complex that neither American nor Chinese engine builders have yet mastered it.


Shuttle math

The US Space Shuttle spacecraft themselves, recently "decommissioned", weighed about 75 tons. An external fuel tank for each of them (empty) added another 35 tons. Let's add a couple more solid-fuel boosters, 83 tons each. This is only net weight - now we need fuel: about 100 tons of liquid hydrogen and 616 tons of an oxidizing agent - liquid oxygen. In total, we will receive about 2000 tons of weight - all in order to launch a 75-ton ship into orbit, or rather, a payload, the mass of which can reach about 25 tons. At the same time, the entire colossal mass of fuel burns up in a matter of minutes: when starting, the solid-propellant engines work for about 2 minutes, and then the three main engines of the ship turn on for another 8 minutes. It doesn't look very effective.

Many are good at chemical jet engines: their thrust remains unsurpassed and has already allowed humanity to land their representatives on the moon, as well as send spacecraft to the far reaches of the solar system. However, they have one significant limitation. Let's recall Newton's Second Law - in order to create sufficient acceleration, it is required either to increase the speed of the jet stream, which is limited by the energy of the oxidation reaction, or to increase the mass of the fuel burned.

Of course, chemists are constantly struggling to create more efficiently combustible fuels and more and more aggressive oxidants, but the process is complex and has almost reached the ceiling of its capabilities. It is even more difficult to increase the mass: to accelerate the additional fuel, even more fuel is required - its amount grows logarithmically. Free space flight requires new solutions.


Chemical engines are not powerful and efficient enough to fully explore the limits of the solar system. However, it is not just oxidation that can heat and accelerate the jet gas. The same role can be played by a much more economical reaction - a nuclear one. The fuel required for such an engine will no longer be measured in hundreds of tons, but in hundreds of kilograms. The energy released during the radioactive decay of heavy nuclei will heat the working fluid - and then the already familiar scheme of jet propulsion works. Moreover, pure hydrogen, the lowest molecular weight gas capable of providing maximum specific thrust, can serve as the working fluid.


The first nuclear engines appeared in space a long time ago - in the form of RTGs, radioisotope thermoelectric generators. The essence of their work is simple: the decay of radioactive fuel is converted into thermal and / or electrical energy. Plutonium RTGs power many spacecraft - long-range probes that do not require huge thrust and take years to reach their target. Such a power plant is used by the engines of the Voyager, Cassini, and New Horizons probes. The RTG complements solar panels for the Curiosity rover. Thrust The "force" of a jet engine with which it pushes the craft through space is called its thrust and is measured in Newtons. The point of application of the jet thrust is the center of the outflow of combustion products - the center of the cutoff of the engine nozzle, and the direction is opposite to the velocity vector of this outflow. The thrust is determined by the rate of outflow of combustion products, and it is determined by the physicochemical properties of the fuel components and the design features of the engine.

However, RTGs are incapable of providing high thrust, and speaking of the development of nuclear rocket engines seriously, we will have to approach the problem from a completely different angle - to launch full-fledged nuclear reactors into space. Despite the fact that the first such apparatus, SNAP, was American, our country still retains its technological leadership in this area. Sergei Korolev was also involved in the development of space engines, the energy of which would be supplied by controlled nuclear decay in a reactor. In the 1960s, a similar power plant "Romashka" was tested in the USSR; in the 1970s, top-secret vehicles with a nuclear plant "Buk" were tested in space. In the late 1980s, the Topaz uranium reactor operated safely in orbit for about a year.

Work on the creation of space engines with a nuclear power plant continues today both in Russia and in the United States. The simplest calculations show that only they will make the nearest planets and bodies of the solar system truly accessible. And when humanity finally harnesses thermonuclear energy, reactors will become several times more efficient.


However, the spectrum of possible solutions is not limited to this either. It is possible to create jet thrust using, in fact, any source of energy - an RTG, a solar battery, or just a battery. The electrostatic field created by it ionizes the gas, accelerating the resulting ions to very high speeds inaccessible to classical jet engines. The magnetic field forms a directed flow from them, pushing the apparatus further and further forward. The cold plasma flowing from the nozzle of an ion engine is not at all like the hellish furnaces of chemical reactions, but its efficiency is simply amazing.


The working fluid of such an electric motor can be hydrogen or a light inert gas, usually xenon or argon - Robert Goddard experimented with such solutions. And although they are not enough to create a serious thrust, they can work literally for years, consuming fuel in a few grams, and for long periods of time they accelerate not too large devices to very decent speeds.

For example, the ion engine is used as the main one on the distant probe Dawn, which is conducting research on the main asteroid belt, and on the Japanese spacecraft Hayabusa, which delivered samples of matter from the asteroid Itokawa to Earth. However, as a rule, they are used as correction and orientation engines to maintain the orbit of satellites - and soon the VASIMR ion engine can work on the ISS.

Antimatter superpower

Both theoretical calculations and practical experiments show that antiparticles, meeting with particles of ordinary matter, annihilate, releasing unheard of energy. A kilogram of antimatter and a kilogram of matter will release 43 megatons of energy in TNT equivalent - almost the same as in the explosion of the legendary 26-ton Tsar Bomb. The transformation of mass into energy occurs almost one hundred percent, 1000 times more efficient than a nuclear reaction and 300 times more efficient than a thermonuclear reaction.


This promises huge prospects - calculations show that a flight to Mars thanks to such engines may take not a year, but only a month - so scientists are seriously considering the possibilities of using them in the future, when they will allow us to move not only within the solar system, but and get to nearby stars.


Bassard's interstellar ramjet engine is a rocket engine concept for interstellar travel, proposed in 1960 by physicist Robert Bussard. The concept is based on the capture of the substance of the interstellar medium (hydrogen and dust) by a spacecraft traveling at high speed and the use of this substance as a working fluid (or directly as fuel) in the spacecraft's thermonuclear rocket engine.

It would seem that you can start developing? Unfortunately, first we will have to solve a number of technological problems, which so far seem completely overwhelming. The first is the tiny amounts of antimatter available to us. So far, it is obtained with only a few antiparticles and at enormous costs. Antimatter is the most expensive substance in the world - in 1999 prices, the production of one gram of antihydrogen will cost more than $ 60 trillion. And for interstellar travel, you will need to receive it in tons.


Fortunately, the prospects in this area are quite bright: according to some experts, literally decades separate us from the creation of a real engine based on antimatter. In 2000, NASA announced a project to develop a still small engine, which requires a very tiny amount of antiparticles to operate - 10 grams of antiprotons will be enough for a flight to Mars.

The projected antimatter engine will include three key components. An electromagnetic toroidal chamber will allow fuel storage. The feed system will push particles against antiparticles. The electromagnetic nozzle will release the energy in the desired direction, creating thrust for the spacecraft.

Crumpling space-time

The only known engine of this type is installed on the cruiser USS Enterprise from the cult series "Star Trek": so far, this technology belongs only to the genre of science fiction. However, theoretically, only such an approach is capable of providing mankind with superluminal speed, and with it - genuine freedom of movement across all the vast expanses of the Universe.


For example, the calculations of Einstein's theories will not be violated: the movement will remain subluminal, only movement will become instantaneous. Immediately - from one point in space - to another. Anywhere. Moreover, it is from the General Theory of Relativity that the very principle of the "space-time engine" (STE) follows.

Recall that, according to general relativity, gravity is a geometric aspect of space-time: the greater the mass of an object, the more distorted its rectilinear continuum in its vicinity. It is this aspect of gravity that allows (in theory) manipulation of space-time. A spaceship, in which there is a fantastic device capable of creating a directed gravitational field of sufficient power, will be able to "crumple" the space in front of it, jumping to the desired point.


NASA physicist Harold White is busy with the future: he is working on a futuristic spacecraft with a warp drive that can wrinkle space-time. Until the future came, White and modeling artist Mike Okuda created models of what these fantastic cruisers would look like.

Unfortunately, calculations show that an incredibly large amount of energy is required for such manipulations. Even the fusion of matter and antimatter will not give the required amount - more precisely, for this it will take so much that we will hardly be able to load such “fuel” even into the USS Enterprise. Perhaps, in the future, this energy will somehow be obtained from the most powerful objects known to us - supermassive black holes. Or, perhaps, they themselves will serve as "wormholes", diving into which the spacecraft will be able to emerge somewhere in a completely different part of the Universe. But that's a completely different story.

As for EmDrive, a whole article is devoted to this topic in the latest issue of Naked Science magazine. The issue will be released in a week.

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