Modern rocket engines do a good job of putting technology into orbit, but they are completely unsuitable for long space travel. Therefore, for more than a dozen years, scientists have been working on the creation of alternative space engines that could accelerate ships to record speeds. Let's take a look at seven key ideas from this area.
EmDrive
To move, you need to push off from something - this rule is considered one of the unshakable pillars of physics and astronautics. What exactly to start from - from earth, water, air or a jet of gas, as in the case of rocket engines - is not so important.
A well-known thought experiment: imagine that an astronaut went into outer space, but the cable connecting him to the spacecraft suddenly broke and the person begins to slowly fly away. All he has is a toolbox. What are his actions? Correct answer: he needs to throw tools away from the ship. According to the law of conservation of momentum, the person will be thrown away from the instrument with exactly the same force as the instrument from the person, so he will gradually move towards the ship. This is jet thrust - the only possible way to move in empty space. True, EmDrive, as experiments show, has some chances to refute this unshakable statement.
The creator of this engine is British engineer Roger Shaer, who founded his own company Satellite Propulsion Research in 2001. The design of the EmDrive is quite extravagant and is a metal bucket in shape, sealed at both ends. Inside this bucket is a magnetron that emits electromagnetic waves - the same as in a conventional microwave. And it turns out to be enough to create a very small, but quite noticeable thrust.
The author himself explains the operation of his engine through the pressure difference of electromagnetic radiation at different ends of the "bucket" - at the narrow end it is less than at the wide one. This creates a thrust directed towards the narrow end. The possibility of such an engine operation has been challenged more than once, but in all experiments, the Shaer installation shows the presence of thrust in the intended direction.
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Experimenters who have tested Shaer's bucket include organizations such as NASA, the Technical University of Dresden and the Chinese Academy of Sciences. The invention was tested in a variety of conditions, including in a vacuum, where it showed the presence of a thrust of 20 micronewtons.
This is very little relative to chemical jet engines. But, given that the Shaer engine can work as long as you want, since it does not need a supply of fuel (solar batteries can provide the magnetron to work), it is potentially capable of accelerating spacecraft to tremendous speeds, measured as a percentage of the speed of light.
To fully prove the motor's performance, it is necessary to carry out many more measurements and get rid of side effects that can be generated, for example, by external magnetic fields. However, alternative possible explanations for the abnormal thrust of the Shaer engine are already being put forward, which, in general, violates the usual laws of physics.
For example, versions are being put forward that the engine can create thrust due to its interaction with a physical vacuum, which at the quantum level has nonzero energy and is filled with constantly emerging and disappearing virtual elementary particles. Who will be right in the end - the authors of this theory, Shaer himself or other skeptics, we will find out in the near future.
Solar sail
As mentioned above, electromagnetic radiation exerts pressure. This means that in theory it can be converted into movement - for example, with the help of a sail. Just as the ships of the past centuries caught the wind in their sails, the spaceship of the future would catch the sun or any other starlight in its sails.
The problem, however, is that the light pressure is extremely small and decreases with increasing distance from the source. Therefore, to be effective, such a sail must be very lightweight and very large. And this increases the risk of destruction of the entire structure when it encounters an asteroid or other object.
Attempts to build and launch solar sailing ships into space have already taken place - in 1993, Russia tested the solar sail on the Progress spacecraft, and in 2010, Japan carried out successful tests on its way to Venus. But not a single ship has ever used the sail as its primary source of acceleration. Another project, an electric sail, looks somewhat more promising in this respect.
Electric sail
The sun emits not only photons, but also electrically charged particles of matter: electrons, protons and ions. All of them form the so-called solar wind, which carries away from the surface of the sun about one million tons of matter every second.
The solar wind spreads over billions of kilometers and is responsible for some of the natural phenomena on our planet: geomagnetic storms and the northern lights. The earth is protected from the solar wind by its own magnetic field.
The solar wind, like the air wind, is quite suitable for travel, you just need to make it blow in the sails. The project of the electric sail, created in 2006 by the Finnish scientist Pekka Janhunen, outwardly has little in common with the solar one. This engine consists of several long, thin cables, similar to the spokes of a wheel without a rim.
Thanks to the electron gun emitting against the direction of travel, these cables acquire a positive charged potential. Since the mass of an electron is about 1800 times less than the mass of a proton, the thrust created by electrons will not play a fundamental role. The electrons of the solar wind are not important for such a sail. But positively charged particles - protons and alpha radiation - will be repelled from the ropes, thereby creating jet thrust.
Although this thrust will be about 200 times less than that of a solar sail, the European Space Agency is interested in the project. The fact is that an electric sail is much easier to design, manufacture, deploy and operate in space. In addition, using gravity, the sail also allows you to travel to the source of the stellar wind, and not just away from it. And since the surface area of such a sail is much less than that of a solar sail, it is much less vulnerable to asteroids and space debris. Perhaps we will see the first experimental ships on an electric sail in the next few years.
Ion engine
The flow of charged particles of matter, that is, ions, is emitted not only by stars. Ionized gas can also be created artificially. Normally, gas particles are electrically neutral, but when its atoms or molecules lose electrons, they turn into ions. In its total mass, such a gas still does not have an electric charge, but its individual particles become charged, which means they can move in a magnetic field.
In an ion engine, an inert gas (usually xenon) is ionized by a stream of high-energy electrons. They knock electrons out of atoms, and they acquire a positive charge. Further, the resulting ions are accelerated in an electrostatic field to speeds of the order of 200 km / s, which is 50 times greater than the rate of gas outflow from chemical jet engines. Nevertheless, modern ion thrusters have a very small thrust - about 50-100 millinewtons. Such an engine would not even be able to move off the table. But he has a serious plus.
A large specific impulse can significantly reduce fuel consumption in the engine. Energy obtained from solar batteries is used to ionize gas, so the ion engine is able to work for a very long time - up to three years without interruption. For such a period, he will have time to accelerate the spacecraft to speeds that chemical engines never dreamed of.
Ion engines have repeatedly plowed the vastness of the solar system as part of various missions, but usually as auxiliary, and not main ones. Today, as a possible alternative to ion thrusters, they are increasingly talking about plasma thrusters.
Plasma engine
If the degree of ionization of atoms becomes high (about 99%), then such an aggregate state of matter is called plasma. Plasma state can be reached only at high temperatures, therefore, ionized gas is heated up to several million degrees in plasma engines. Heating is carried out using an external energy source - solar panels or, more realistically, a small nuclear reactor.
The hot plasma is then ejected through the rocket nozzle, creating thrust tens of times greater than that of an ion thruster. One example of a plasma engine is the VASIMR project, which has been developing since the 70s of the last century. Unlike ion thrusters, plasma thrusters have not yet been tested in space, but great hopes are pinned on them. It is the VASIMR plasma engine that is one of the main candidates for manned flights to Mars.
Fusion engine
People have been trying to tame the energy of thermonuclear fusion since the middle of the twentieth century, but so far they have not been able to do this. Nevertheless, controlled thermonuclear fusion is still very attractive, because it is a source of enormous energy obtained from very cheap fuel - isotopes of helium and hydrogen.
At the moment, there are several projects for the design of a jet engine on the energy of thermonuclear fusion. The most promising of them is considered to be a model based on a reactor with magnetic plasma confinement. A thermonuclear reactor in such an engine will be an unpressurized cylindrical chamber 100-300 meters long and 1-3 meters in diameter. The chamber should be supplied with fuel in the form of high-temperature plasma, which, at sufficient pressure, enters into a nuclear fusion reaction. The coils of the magnetic system located around the chamber should keep this plasma from contacting the equipment.
The thermonuclear reaction zone is located along the axis of such a cylinder. With the help of magnetic fields, extremely hot plasma flows through the reactor nozzle, creating a tremendous thrust, many times greater than that of chemical engines.
Antimatter engine
All the matter around us consists of fermions - elementary particles with half-integer spin. These are, for example, quarks that make up protons and neutrons in atomic nuclei, as well as electrons. Moreover, each fermion has its own antiparticle. For an electron, this is a positron, for a quark - an antiquark.
Antiparticles have the same mass and the same spin as their usual "comrades", differing in the sign of all other quantum parameters. In theory, antiparticles are capable of making up antimatter, but so far nowhere in the Universe has antimatter been registered. For basic science, the big question is why it does not exist.
But under laboratory conditions, you can get some antimatter. For example, an experiment was recently conducted comparing the properties of protons and antiprotons that were stored in a magnetic trap.
When antimatter and ordinary matter meet, a process of mutual annihilation occurs, accompanied by a burst of colossal energy. So, if you take a kilogram of matter and antimatter, the amount of energy released when they meet will be comparable to the explosion of the "Tsar Bomb" - the most powerful hydrogen bomb in the history of mankind.
Moreover, a significant part of the energy will be released in the form of photons of electromagnetic radiation. Accordingly, there is a desire to use this energy for space travel by creating a photon engine, similar to a solar sail, only in this case the light will be generated by an internal source.
But in order to effectively use the radiation in a jet engine, it is necessary to solve the problem of creating a "mirror" that would be able to reflect these photons. After all, the ship must somehow push off in order to create thrust.
No modern material simply cannot withstand the radiation born in the event of such an explosion and will instantly evaporate. In their science fiction novels, the Strugatsky brothers solved this problem by creating an "absolute reflector". In real life, nothing like this has yet been done. This task, like the issues of creating a large amount of antimatter and its long-term storage, is a matter for the physics of the future.