The main problem in the exploration of outer space is extremely low speeds in man-made aircraft. Modern developments also have huge expense fuel. Thus, if you build a rocket and launch it, for example, to Mars and back, then the ship will be just huge. And most of it will be occupied by fuel. Approximately more than a billion tons of high-quality rocket fuel is needed to land on Mars. Fortunately, such a modern development of scientists as an ion engine will be able to solve this problem in the near future. Theoretically, with its help, you can accelerate to two hundred kilometers per second. The main advantages can be called precisely the huge developed speeds and a small supply of fuel. For the operation of such a unit as an ion engine, only electricity and an inert gas are needed. However, it also has some disadvantages, for example, a weak acceleration speed. This makes us think about many problems of using the engine in the presence of gravitational fields.
Ion engine: principle of operation
Due to the high voltage, the gas is ionized in a special chamber. As a result, gas ions begin to be thrown away from the chamber and create thrust. However, since this is a chain reaction, and the thrust increases very slowly and gradually, it will take about half a year to accelerate to two hundred kilometers per second. Approximately the same amount of time will be spent on braking. On the other hand, objectively these figures are very small in comparison with the indicators of modern space engines who would need to spend twenty times as much time to achieve results of similar quality. Moreover, inert gas takes up hundreds of times less space than rocket fuel. The only problem that is difficult to solve is the availability of electricity. Solar panels simply won't be enough to power things like ion thrusters, so a nuclear reactor is likely.
Another disadvantage can be considered low maneuverability. Also the main issue is the problem with gravity. Being within the field of the Earth, the engine simply will not work. On the other hand, in open space there are no analogues of such a device as an ion engine.
A bit of history and perspective
In fantasy literature, such devices are quite common. However, it was only in 1960 that an ion engine was created by one's own hands (or rather, by the hands of NASA scientists). It was called a wide-beam electrostatic device. Already in the early seventies, mercury electrostatic engines were tested in outer space.
By the end of the seventies, Hall effect generators were being used in the Soviet Union. As the main engine, the ion was used on the American spacecraft in 1998. It was followed by a European probe, a Japanese spaceship in 2003. To date, NASA is developing a famous project called Prometheus. A super-powerful ion engine is being designed for it, which is powered by a nuclear reactor.
The problem of movement in space has been facing mankind since the beginning of orbital flights. A rocket taking off from the ground consumes almost all of its fuel, plus the charges of boosters and stages. And if the rocket can still be torn off the ground, filling it with a huge amount of fuel, at the cosmodrome, then in outer space there is simply nowhere and nothing to refuel. But after entering orbit, you need to move on. And there is no fuel.
And this is the main problem of modern astronautics. It is still possible to throw a ship into orbit with a supply of fuel to the moon, under this theory plans are being made to create a refueling base on the moon for "long-range" spacecraft flying, for example, to Mars. But it's all too complicated.
And the solution to the problem was created a long time ago, back in 1955, when Aleksey Ivanovich Morozov published an article "On plasma acceleration by a magnetic field." In it, he described the concept of a fundamentally new space engine.
Ion plasma engine device
Operating principle plasma engine is that the working fluid is not burning fuel, as in jet engines, but a stream of ions accelerated by a magnetic field to insane speeds.
The source of ions is gas, usually argon or hydrogen, the gas tank is at the very beginning of the engine, from there the gas is supplied to the ionization compartment, cold plasma is obtained, which is heated in the next compartment by means of ion cyclotron resonant heating. After heating, the high-energy plasma is fed into the magnetic nozzle, where it is shaped into a stream by magnetic field, accelerates and is ejected into environment. This is how traction is achieved.
Since then, plasma engines have come a long way and have been divided into several main types, these are electrothermal engines, electrostatic engines, high-current or magnetodynamic engines, and impulse engines.
In turn, electrostatic engines are divided into ion and plasma (particle accelerators on a quasi-neutral plasma).
In this article we will write about modern ion engines and them promising developments, since in our opinion the future of the space fleet is behind them.
The ion engine uses either xenon or mercury as fuel. The first ion thruster was called the gridded electrostatic ion thruster.
The principle of its operation is as follows:
The ionizer is fedxenon, which is neutral in itself, but ionizes when bombarded by high-energy electrons. Thus, a mixture of positive ions and negative electrons is formed in the chamber. To “filter out” the electrons, a tube with cathode grids is brought into the chamber, which attracts electrons to itself.
Positive ions are attracted to the extraction system, which consists of 2 or 3 grids. Between Grids Supported a big difference electrostatic potentials (+1090 volts on the inside against - 225 on the outside). As a result of ions falling between the grids, they are accelerated and thrown into space, accelerating the ship, according to Newton's third law.
Russian ion engines. The cathode tubes directed towards the nozzle are clearly visible on all
The electrons trapped in the cathode tube are ejected from the engine at a slight angle to the nozzle and ion flow. This is done for two reasons:
Firstly, so that the hull of the ship remains neutrally charged, and secondly, so that the ions "neutralized" in this way are not attracted back to the ship.
For the ion engine to work, only two things are needed - gas and electricity. With the first, everything is just fine, the engine of the American interplanetary apparatus Dawn, which was launched in the fall of 2007, will need only 425 kilograms of xenon to fly for almost 6 years. For comparison, 7.5 tons of fuel is spent every year to correct the ISS orbit using conventional rocket engines.
One bad thing - ion engines have very little thrust, on the order of 50-100 millinewtons, which is absolutely insufficient when moving in the Earth's atmosphere. But in space, where there is practically no resistance, the ion engine can reach significant speeds during long acceleration. The total speed increase over the entire duration of the Dawn mission will be on the order of 10 kilometers per second.
Ion thruster test for Deep Space ship
Recent tests conducted by the American company Ad Astra Rocket, carried out in a vacuum chamber, showed that their new Variable Specific Impulse Magnetoplasma Rocket VASIMR VX-200 can produce thrust as early as 5 Newtons.
The second issue is electricity. The same VX-200 consumes 201 kW of energy. Solar panels are simply not enough for such an engine. Therefore, it is necessary to invent new ways of obtaining energy in space. There are two ways here - refueling batteries, for example, tritium, launched into orbit along with the ship, or an autonomous nuclear reactor, which will power the ship throughout the flight.
Back in 2006, the European Space Agency and the Australian National University (Australian National University) successfully tested a new generation of space ion thrusters, reaching record levels.
Engines in which charged particles are accelerated in an electric field have long been known. They are used for orientation, orbit correction on some satellites and interplanetary vehicles, and in a number of space projects (both already implemented and just conceived - read, and) - even as marching ones.
With them, experts associate the further development of the solar system. And although all varieties of so-called electric rocket engines are much inferior to chemical ones in maximum thrust (grams versus kilograms and tons), they are radically superior in efficiency (fuel consumption per gram of thrust per second). And this economy (specific impulse) is directly proportional to the speed of the ejected jet.
So, in an experimental engine called "Dual-Stage 4-Grid - DS4G", built under an ESA contract in Australia, this speed reached a record 210 kilometers per second.
This, for example, is 60 times higher than the exhaust velocity of good chemical engines, and 4-10 times higher than that of the old "ion engines".
As it is clear from the name of the development, this speed was achieved by a two-stage ion acceleration process using four successive gratings (instead of the traditional one stage and three gratings), as well as high voltage- 30 kilovolts. In addition, the divergence of the output jet beam was only 3 degrees, compared to about 15 degrees for previous systems.
And here is the information of the last days.
The ion engine (ID) works simply: the gas from the tank (xenon, argon, etc.) is ionized and accelerated by an electrostatic field. Since the mass of the ion is small, and it can receive a significant charge, the ions fly out of the engine at speeds up to 210 km/s. Chemical engines can achieve ... no, not anything like that, but only twenty times less exhaust velocity of combustion products only in exceptional cases. Accordingly, the consumption of gas in comparison with the consumption of chemical fuel is extremely small.
That is why such “long-range” probes as Hayabusa, Deep Space One and Dawn have been fully or partially working on ID. And if you are going not just to fly by inertia to distant celestial bodies, but also to actively maneuver near them, then you cannot do without such engines.
In 2014, ion thrusters celebrate their 50th anniversary in space. All this time, the problem of erosion could not be solved even in the first approximation. (Here and below ill. NASA, Wikimedia Commons.)
Like all good things, the ID likes to be fed: up to 25 kW of energy is needed for one newton of thrust. Let's imagine that we were assigned to launch a 100-ton spacecraft to Pluto (forgive us for dreaminess!). Ideally, even for Jupiter, we need 1,000 newtons of thrust and 10 months, and to Neptune at the same thrust - a year and a half. In general, let's not talk about Pluto, otherwise it's somehow sad ...
Well, to get these so far speculative 1,000 newtons, we need 25 megawatts. In principle, nothing technically impossible - a 100-ton ship could take a nuclear reactor. Incidentally, NASA and the US Department of Energy are currently working on the Fission Surface Power project. True, we are talking about bases on the Moon and Mars, and not about ships. But the mass of the reactor is not so high - only five tons, with dimensions of 3 × 3 × 7 m ...
Well, okay, dreamed and that's enough, you say, and immediately remember the ditty, allegedly invented by Leo Tolstoy during the Crimean War. After all, such a large flow of ions passing through the engine (and this is a key obstacle) will cause it to erode, and much faster than in ten months or a year and a half. Moreover, this is not a problem of choosing a structural material - both titanium and diamond will be destroyed under such conditions - but an integral part of the design of an ion engine per se.
Adapted from Gizmag. and http://lab-37.com
Do you know that Russia is activeworking on a nuclear engine for rocketsor, for example,
what might be coming soon
The purpose of the work: to study the history of the ion engine, consider the prospects for its use in the near future and carry out calculations related to its use.
During the work, the following tasks were set:
find, study and analyze literature on the ionic form of engines
compose a short introductory course on the history of creation, application, as well as the principle of operation of ion engines
after analyzing the results of the space flights carried out, carry out my own calculations in order to obtain the necessary information about the flight I am simulating
draw conclusions
A hypothesis was put forward: the ion engine has some notable advantages over conventional rocket engines, making its use promising.
The following research methods were used in the work:
analysis
synthesis
modeling
measurement
Object of study: Ion engine
Relevance of the topic:
A person tries to see and get into more and more distant from himspace places. And for the successful development of mankind in this industry,it is necessary to constantly improve spacecraft, using in themnew technologies that optimize fuel consumption, increasecapacity and so on. The ion engine is quite advantageous in view oflow fuel consumption, which means that it can replaceconventional engines and help man in further space exploration.
Hypothesis: The ion thruster has some notable advantages overconventional rocket engines, making its usepromising.
Definition
Ion thruster – type of electric rocket motor, principlework, which is based on the creation of reactive thrust based onionized gas accelerated to high speeds in electricalfield.
Principle of operation
The principle of operation of the engine is to ionize the gas and accelerate itelectrostatic field. However, due to the high charge ratioto mass, it becomes possible to accelerate the ions to very high speeds. Thus, it is possible to achieve a very high specific impulse in an ion thruster, which makes it possible to significantly reduce the consumption of the reactive mass of ionized gas, but requires large amounts of energy.Xenon is supplied to the ionizer, which is neutral in itself, but whenbombarded by high-energy electrons, it ionizes. SoThus, a mixture of positive ions and negative ions is formed in the chamber.electrons. A tube is inserted into the chamber to "filter" the electrons.with cathode grids, which attracts electrons to itself.Positive ions are attracted to the extraction system, which consists of2 or 3 grids. Large difference supported between gridselectrostatic potentials (+1090 volts on the internal versus - 225 onexternal). As a result of ions entering between the grids, they are accelerated andare thrown into space, accelerating the ship, according to the third lawNewton.The electrons trapped in the cathode tube are ejected from the engine undersmall angle to the nozzle and ion flow. This is done so that the ions"neutralized" thus were not attracted back to the ship.
Story
The principle of the ion engine has been known for a long time and is widely represented in science fiction literature, computer games and cinema, but for astronautics it has become available only recently. In 1960, the first functioning wide-beam ion electrostatic thruster was built (created in the USA at NASA Lewis Research Center). In 1964, the first successful suborbital ion thruster demonstration (SERT I), a test of the feasibility of ion beam neutralization in space. In 1970 - a test for long work mercury ion electrostatic thrusters in space (SERT II). Since the 1970s, Hall-effect ion thrusters have been used in the USSR as navigational thrusters (SPT-60 thrusters were used in the 1970s on the Meteors, SPT-70 on the Kosmos and Luch satellites in the 1980s, SPT-100 on a number of satellites in the 1990s). As the main (propulsion) engine, the ion engine was first used on the Deep Space 1 spacecraft (the engine was first launched on November 10, 1998). The European lunar probe Smart-1, launched on September 28, 2003, and the Japanese Hayabusa probe, launched to the asteroid in May 2003, were the next vehicles. September 27, 2007. Dawn is intended to explore Vesta and Ceres and carries three NSTAR thrusters successfully tested on Deep Space 1. The European Space Agency has installed an ion thruster aboard the GOCE satellite, which was launched on March 17, 2009 into an ultra-low Earth orbit only about 260 km high. The ion engine creates a constant pulse that compensates for atmospheric friction and other non-gravitational effects on the satellite.
Upcoming space programs
In the near future, ESA (European Space Agency), together with JAXA (Japanese Space Agency) and Roscosmos, plans to use an ion thruster in the BepiColombo Mercury mission (April 2018). Two orbital stations will go to the planet on one Mercury Transfer Module (MTM). BepiColombo will use the ion thrusters tested on the Smart-1 module.
NASA is leading the Prometheus project, for which a powerful ion engine is being developed, powered by electricity from an onboard nuclear reactor. It is assumed that such engines in the amount of eight pieces will be able to accelerate the device to 90 km / s. The first device of this project Jupiter Icy Moons Explorer was planned to be sent to Jupiter in 2017, but the development of this device was suspended in 2005 due to technical difficulties. Currently searching for more simple project AMS for the first test under the Prometheus program.
Ability to deliver goods
Due to the small acceleration, it is more reasonable to use devices with an ion engine for interplanetary (or other, on long distances) flights (for which it has already been used more than once).
And if we compare the characteristics of conventional and ion engines, in this interval, then the profitability of using the second one will be clearly visible. With less fuel will increase payload, cash costs for fuel will decrease, and the device itself will reach the target faster, developing speed much more than vehicles with other types of engines.
I carried out my calculations in order to find out for how long the device with the mass and other technical specifications will be able to get to Mars using the ion drive as the main one. As a basis, I took the data of the Dawn apparatus already called by me and some data of its flight.
I used the Dawn Xenon Ion Thruster, which was developed on the basis of the sample tested on the Deep Space 1 probe with a thrust of 30 mN and a specific impulse of 3100 s, as the engine in the calculations.
Using an approximate flight and maneuver scheme, I calculated that total length trajectory is ~1 billion km.
Using the flight data, I found out that ~275 kg of xenon was consumed by one engine for the flight from Earth to Vesta, then by comparing the lengths of the flight trajectories to Mars and Vesta, I calculated that only 100 kg of xenon would be needed for one engine.
I decided to install 3 engines with these characteristics on the proposed vehicle, as a result of which the mass of fuel with a small margin should be ~ 325 kgAs the purpose of this apparatus, I chose the one-way transportation of goods from Earth to Mars. Under such conditions, the mass of the truck will consist of: 325 kg of fuel, 250 kg of software, and some mass of the transported cargo. For example, I took 600 kg, 1 t and 5 t.According to the formulas of uniformly accelerated motion, I found that the device will reach the target only after 3.5 years, 4.5 years and about 10 years at a final speed of 17, 13 and 6 km / s, which will need to be reduced when approaching Mars. As a result, I got a rather weak disadvantageous result, however, for 3 engines with such little thrust, this result is not bad. In the future, I will take data from more powerful, modern and advanced ion engines as a basis, or create and calculate the characteristics of my own model.
- The work of linear accelerators of elementary particles requires a lot of energy. The only technology currently available that allows required amount energy for the required time is a nuclear reactor on board the ship. However, in this case, the device ceases to be completely safe.The ion thruster accelerates slowly, so it cannot be used to propel a spacecraft into Earth's orbit. It is only functional for a ship already in space.
Summarizing
I believe that at present, the ion engine is one of the really most promising devices for movement in space, which has a number of advantages over other types of engines.
Scientists are already supplying satellites and small space stations exploring other planets with ion engines both to stabilize the devices in space and as the main engine.
Due to its specific advantages, perhaps in the future, it is the ion drive that will move huge interplanetary and intergalactic starships with many people on board.
Conclusion
The goals and objectives set in the project have been fulfilled. I studied the principle of the ion thruster, considered the pros and cons of its use, and learned about the main space programs involving this type of thruster. In the future, the work can be improved by making more accurate calculations in other possible areas of use of the ion engine, based on other official data, as well as by assembling a working model of the ion engine.
NASA has completed testing of an ionized gas propulsion system that began in June 2005. Now it can be equipped with spacecraft, accelerating them to previously unseen speeds.
A new generation xenon engine is being tested. (Photo by NASA.)
Often featured in science fiction, ion thrusters have been used in practice since the 70s. The thrust in them is created due to the acceleration of ionized gas in an electrostatic field.
The advantage of such propulsion systems compared to traditional chemical solutions is high efficiency, namely, the ability to accelerate the device to tens of kilometers per second with low fuel consumption. True, this happens already in outer space during a long operation of the ion engine: its starting thrust is small. Therefore, as the main system that sets the spacecraft in motion, this scheme began to be used quite recently.
The American spacecraft Deep Space 1, launched in 1998, became the pioneer of ion propulsion. It was followed by the European and Japanese probes, and the last major project today became the automatic interplanetary station Dawn, sent by NASA to study the asteroid Vesta and the dwarf planet Ceres.
The Dawn ion engine became the model for creating NASA's Evolutionary Xenon Thruster (NEXT) xenon system. Developers from the Glenn Research Center and Aerojet have modeled a wide variety of missions in which such a remote control can be involved.
Since 2005, NEXT has worked 35.5 thousand hours, which is 5 thousand more than the previous record. The experiments took 600 kg of xenon. Based on test models, engineers have designed a propulsion system of several ion thrusters, the service life of which will exceed 6 years, and now NASA only has to choose which missions will be more convenient to operate the development. Perhaps the space program proposed by the US National Academy of Sciences for the next decade will come in handy here?
Source: Computerra-Online
ion engine
Ion thruster is a type of electric rocket motor. Its working fluid is an ionized gas (argon, xenon, cesium...).
Operating principle
The principle of operation of the engine is to ionize the gas and accelerate it with an electrostatic field. At the same time, due to the high charge-to-mass ratio, it becomes possible to accelerate ions to very high velocities (up to 210 km/s compared to 3-4.5 km/s for chemical rocket engines). Thus, a very high specific impulse can be achieved in an ion thruster. This makes it possible to significantly reduce the consumption of the reactive mass of ionized gas in comparison with the consumption of the reactive mass in chemical rockets, but requires a large amount of energy. The disadvantage of the engine in its current implementations is very weak thrust (on the order of tenths of a Newton). Thus, it is not possible to use an ion engine to launch from a planet, but, on the other hand, in outer space, with a sufficiently long operation of the engine, it is possible to accelerate the spacecraft to speeds that are currently inaccessible to any other existing species engines.
Existing implementations use solar panels to support engine operation. But for work in deep space, this method is unacceptable. Therefore, even now nuclear installations are sometimes used for these purposes.
The principle of an ion engine has been known for a long time and is widely represented in science fiction literature, computer games and cinema, but it has become available for astronautics only recently.
In 1960, the first functioning broad-beam (broad-beam) ion electrostatic thruster was built (created in the USA at NASA Lewis Research Center). In 1964, the first successful suborbital demonstration of an ion thruster (SERT I) was a test of the feasibility of ion beam neutralization in space.
In 1970, the test for long-term operation of mercury ion electrostatic thrusters in space (SERT II). Since the 1970s, Hall-effect ion thrusters have been used in the USSR as navigational thrusters (SPT-60 thrusters were used in the 1970s on the Meteors, SPT-70 on the Kosmos and Luch satellites in the 1980s, SPT-100 on a number of satellites in the 1990s).
As the main (propulsion) engine, the ion engine was first used on the Deep Space 1 spacecraft (the engine was first launched on November 10, 1998). The European lunar probe Smart-1, launched on September 28, 2003, and the Japanese Hayabusa probe, launched to the asteroid in May 2003, were the next vehicles.
The next NASA spacecraft with sustainer ion engines was (after a series of freezes and resumption of work) the AMS Dawn, which launched on September 27, 2007. Dawn is intended to study Vesta and Ceres, and carries three NSTAR engines successfully tested on Deep Space 1.
The European Space Agency has installed an ion thruster on board the GOCE satellite, which was launched on March 17, 2009 into an ultra-low Earth orbit only about 260 km high. The ion engine creates a constant pulse that compensates for atmospheric friction and other non-gravitational effects on the satellite.
prospects
ESA plans to use an ion thruster in the BepiColombo Mercury mission. It will be based on an engine based on the Smart-1, but will be more powerful (launch is scheduled for 2011-2012).
NASA is leading the Prometheus project, for which a powerful ion engine is being developed, powered by electricity from an onboard nuclear reactor. It is assumed that such engines in the amount of eight pieces will be able to accelerate the device to 90 km / s. The first device of this project Jupiter Icy Moons Explorer was planned to be sent to Jupiter in 2017, but the development of this device was suspended in 2005 due to technical difficulties. Currently, a search is underway for a simpler AMC project for the first test under the Prometheus program.
Article in Computerra
On the use of nuclear reactors for ion engines (Membrana.ru)
BepiColombo on the ESA website
Project Prometheus on the NASA website
The ion-powered AMS Dawn launched on September 25, 2007.
Photonic and ion thrusters
From fantasy to reality
PHOTON ENGINE - jet engine, the thrust of which is created due to the outflow of quanta of electromagnetic radiation or photons. The main advantage of such an engine is the maximum possible exhaust velocity within the framework of relativistic mechanics, equal to speed light in a vacuum. For a rocket apparatus, this is the only widely known way to achieve any significant fraction of the speed of light at reasonable values of the Tsiolkovsky number, which characterizes the ratio of the masses of a fueled and empty rocket. It should be noted, however, that in this case we are talking about the number Z of the order of several tens - hundreds, with technically realized values of the order of 10 for multistage rockets. The main drawback of the photon engine is the low efficiency of the energy conversion chain from the primary source to the photon jet. The use of the annihilation reaction for the direct production of optical and gamma quanta does not greatly reduce the severity of the problem, since it is necessary to take into account the losses for the storage of antimatter (not to mention its production) and the difficulty of focusing the resulting radiation. In addition, as more realistic, the use of thermonuclear plasma as a source of photons (including for generating laser radiation) and the use of electromagnetic quanta of a longer wavelength range (“radio engine”) were considered. In the first case, the problems of generation and maintenance of plasma with necessary parameters. The "radio engine" greatly simplifies the task of focusing the "reactive jet", but sharply reduces the efficiency of the propulsion complex.
Photon engine: space breakthrough
The effect of dust emission under the influence of light radiation will make it possible to create an interesting and promising type of space propulsion for flights to other planets of the solar system. Under the influence of light and heat, dust particles defy gravity and rush upwards. This effect, which played an important role in the formation of planets and asteroids, can also find practical application in dust removal devices, as well as in the engines of Martian probes and in the creation of a new type of space sail.
When a layer of dust is exposed to red laser radiation, a spouting emission of particles is observed, reminiscent of the eruption of a tiny volcano. Comprehensively studying this phenomenon, scientists Gerhard Wurm (Gerhard Wurm) and Oliver Krauss (Oliver Krauss) from the University of Muenster came to the conclusion that its occurrence is associated with photophoresis and "greenhouse effect" in the solid state, according to PhysOrg.
Photophoresis - or the movement of particles under the influence of light - is based on a long-known effect called thermophoresis, that is, the movement of particles under the influence of heat. In environments with temperature gradients, particles will move from a hotter region to a less hot one. When the heat source is the energy of absorbed light, this process is called photophoresis.
Photon engine - an engine whose thrust is created due to the expiration of e / magnetic radiation quanta or photons. Emission of particles of graphite powder (inset - "eruption" of glassy carbon particles).
Photon engine - is it a reality?
In addition to the surface temperature gradient, the "greenhouse effect" of solids also plays a role in dust eruptions. The greenhouse effect occurs due to the fact that the laser beam most strongly heats dust particles that are slightly deeper than the surface layers (at least at a depth of 100 microns, which is several tens of particle layers).
Scientists have calculated that a force of approximately 10-7 N is required to release a single 1 µm spherical particle. , but this is still not the limit. The limit probably depends on the distribution and size of the particles, the strength of their mutual adhesion and the power of the laser beam."
At a power of 50 mW, the radiation penetrates the dust layer to a depth of several millimeters. The temperature tends to decrease with increasing depth, but in fact it reaches its maximum not at the surface, but at a depth of 100 µm. Thus, a reverse temperature gradient is created near the surface, which causes the dust particles to erupt. During the experiments, it was also found that within a few tens of seconds after the laser is turned off, the point of the maximum temperature gradient will move deeper due to the rapid cooling of the surface, which further increases the photophoresis power.
Photophoresis is best observed at low pressure. The experiments were carried out at a pressure of 10 millibars, which is approximately 0.01 of the normal atmospheric pressure of the Earth, so the effect of photophoresis on terrestrial dust is insignificant. However, in the early stages of the formation of planets and stars, photophoresis at low pressures probably played a significant role in the formation of gas and dust disks, which in turn led to the formation of asteroids and other Kuiper belt space objects.
Scientists believe that in the future, photophoresis may find practical application in the rarefied atmosphere of Mars. For example, this technology can be used in automated research stations to remove dust from solar cell blocks and lenses of optical instruments. In addition, scientists plan to create a solar sail that would use the power of photophoresis instead of radiation pressure. Such a sail, resembling a fishing net and working on the basis of negative photophoresis, according to physicists, can set small probes in motion. A sail measuring 10x10 m is capable of carrying a payload weighing several tens of kilograms only due to the "passive" radiation of the Sun.
Ion Drive: Space Breakthrough
ION ENGINE - on Saturday 09/30/2003, the research station of the European Space Agency SMART 1 was successfully launched from the Kourou cosmodrome by the Ariane 5 launch vehicle. participation of almost 30 subcontractors out of 11 European countries and USA. The total cost of the project was 110 million euros.
SMART 1 is ESA's first automatic station for lunar exploration. At the same time, it is a unique research station of a new type, the first in a new ESA program called Small Missions for Advanced Research in Technology. During the implementation of the program, it is planned to test a number of new technologies, for example, communications in the Ka-band and laser communications, autonomous navigation, and much more.
When enough in large numbers equipment, SMART 1 is lightweight (370 kg, including scientific equipment - 19 kg) and compact. With folded solar panels it is a rectangle the size of a meter. The cost of SMART 1 is about five times less than a typical ESA interplanetary station. But the most main feature new spacecraft is that for the first time in the history of astronautics, the ion engine will be used as the main one. ESA plans to include two more vehicles equipped with an ion propulsion system. These are BepiColombo for the study of Mercury and Solar Orbiter for the study of the Sun.
The ion engine installed in the SMART 1 consumes 1350 watts of electricity generated by solar panels and develops a thrust of 0.07 Newton, which is about the weight of a postcard. The working substance is xenon (fuel supply 82 kg). At the same time, it took the station 16 months to enter an elliptical polar orbit around the Moon. Launching SMART 1 into the calculated orbit was a complex multi-stage process consisting of stages.
Strictly speaking, ion thrusters have already been installed on spacecraft - in recent years, in particular, at NASA's Deep Space 1 (DS 1) research station and on the ESA Artemis experimental geostationary communications satellite. In the latter case, thanks to the presence of ion engines on board, it was possible to save a satellite that seemed completely lost at the cost of millions of dollars.
Abnormal operation of the upper stage of the Ariane 5 launch vehicle, which launched the Artemis satellite into orbit, led to the Artemis orbit being significantly lower than the calculated one. This usually results in the loss of a satellite. If it carries a threat to other spacecraft, it is drowned (heavy vehicles) or "burned" in the atmosphere. But Artemis escaped this sad fate.
Thanks to urgent measures taken and at the cost of spending almost the entire supply of chemical fuel on board, the satellite was transferred to a circular orbit with a height of 31 thousand km. But after that, it was necessary to transfer Artemis to the estimated geostationary (with a height of about 36 thousand km). Then it was decided to use four ion engines installed on board in pairs. They were originally intended to control the orientation (tilt) of the satellite. To make the transition, the thrust vector of the engines was directed perpendicular to the plane of the orbit. But in order to save the apparatus, it had to be given an impulse in the plane of the orbit, and thus transferred to a higher geostationary orbit. Artemis needed to be rotated 90 degrees from its normal orientation.
The most difficult rescue operation, required the development of "on the go" new strategy actions, new modes of satellite control and operation of onboard equipment. It took 20% of all onboard software to be modified. And yet the operation was very successful. Its complexity is evidenced by the fact that only for reprogramming onboard system management needed to download modified software blocks from the Earth with a total volume of 15 thousand words. It was the largest operation to reprogram a telecommunications satellite from Earth.
Despite the modest thrust (only 15 millinewtons), Artemis began to “climb” into the calculated orbit, climbing 15 km per day. The entire rescue operation took 18 months. January 31, 2003 Artemis was exactly where he should have been a year and a half ago. The world's first rescue operation, the outcome of which depended entirely on the reliability of ion engines and the coordinated actions of people on Earth, was a success. The satellite, thought to be hopelessly lost, returned to normal operation.
The design of the SMART 1 main engine differs significantly from the engines installed on the DS 1 and Artemis. In the case of the last two devices, a grating with a potential applied to it (the so-called gridded ion engine) was used to accelerate the ions. In contrast, SMART 1 is equipped with a Hall ion engine, which is significantly different in its design. An important advantage Hall-effect engines is the absence of a lattice subjected to constant bombardment by high-energy ions, as a result of which its rapid degradation occurs. As for other characteristics of ion thrusters of various designs, the situation is not so obvious. In general, grating engines allow you to get a greater specific impulse and consume about twice less fuel(working fluid) than Hall engines. However, at the same time, Hall engines make it possible to develop a large specific thrust with the same power consumption. Both designs have their advantages and disadvantages, and the choice of the preferred option depends in each case on the nature of the tasks facing the apparatus and on its energy capabilities.
The European Space Agency has tested a ramjet ion thruster using air from the surrounding atmosphere as a working fluid. It is assumed that small satellites with such an engine will be able to be in orbits with an altitude of 200 kilometers or less almost indefinitely, according to a press release from the agency.
The principle of operation of ion engines is based on the ionization of gas particles and their acceleration using an electrostatic field. Gas particles in such engines are accelerated to significantly high speeds, than in chemical engines, which is why ion engines have a much higher specific impulse and consume less fuel. But the ion engine has and important disadvantage- extremely low thrust compared to chemical engines. Because of this, they are rarely used in practice, mainly on small devices. For example, such engines are used on the Dawn probe, currently orbiting the dwarf planet Ceres, and will be used in the BepiColombo mission, which is due to go to Mercury at the end of 2018.
Like chemical propulsion, the ion propulsion systems currently in use use a fuel supply, typically xenon. But there is also the concept of direct-flow ion engines, which, however, has not yet been used on vehicles flying into space. Its difference lies in the fact that it is proposed to use as a working fluid not the final supply of gas loaded into the tank before launch, but air from the Earth's atmosphere or another atmospheric body.
Engine operation scheme
ESA-A. Di Giacomo
It is assumed that a relatively small apparatus with such an engine will be able to be practically unlimited in low orbits with an altitude of about 150 kilometers, compensating for atmospheric braking by the thrust of the engine operating on air entering it from the atmosphere. In 2009, ESA launched the GOCE satellite, which was able to stay in a 255-kilometer orbit for almost five years due to a constantly on ion engine with a supply of xenon. Since then, the agency has been developing a ramjet ion thruster for similar low-orbit satellites, and has now conducted the first tests of such a thruster.
The tests took place in a vacuum chamber in which the engine was located. Initially, accelerated xenon was fed into it. After that, a mixture of oxygen and nitrogen was added to the gas intake device, simulating the atmosphere at an altitude of 200 kilometers. At the end of the tests, the engineers conducted tests with exclusively air mixture to check the performance in the main mode.
Engine tests with air as fuel
Direct-flow ion engine
