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An electric rocket engine (ERE) is a rocket engine whose operating principle is based on the conversion of electrical energy into directed kinetic energy of particles. There are also names that include the words reactive and propulsion

A complex consisting of a set of electric propulsion systems, a system for storing and supplying the working fluid (SHiP), an automatic control system (ACS), and a power supply system (SPS) is called an electric propulsion system (EPS).

Introduction
The idea of using electrical energy in jet engines for acceleration arose almost at the beginning of the development of rocket technology. It is known that this idea was expressed by K. E. Tsiolkovsky. In 1916-1917, R. Goddard conducted the first experiments, and in the 30s of the 20th century in the USSR, under the leadership of V. P. Glushko, one of the first operating electric propulsion engines was created.

From the very beginning, it was assumed that the separation of the energy source and the accelerated substance would provide a high speed of exhaust of the working fluid (PM), as well as a lower mass of the spacecraft (SC) due to a decrease in the mass of the stored working fluid. Indeed, in comparison with other rocket engines, electric propulsion engines make it possible to significantly increase the active lifetime (AS) of a spacecraft, while significantly reducing the mass of the propulsion system (PS), which, accordingly, makes it possible to increase the payload or improve the weight-dimensional characteristics of the spacecraft itself.

Calculations show that the use of electric propulsion will reduce the duration of flights to distant planets (in some cases even make such flights possible) or, with the same flight duration, increase the payload.

Starting from the mid-1960s, full-scale tests of electric propulsion engines began in the USSR and the USA, and in the early 1970s, electric propulsion engines began to be used as standard propulsion systems.

Currently, electric propulsion systems are widely used both in the propulsion systems of Earth satellites and in the propulsion systems of interplanetary spacecraft.

Classification of electric propulsion
The classification of electric propulsion has not been established, however, in the Russian-language literature it is usually customary to classify electric propulsion according to the predominant mechanism of particle acceleration. The following types of engines are distinguished:

electrothermal rocket engines (ETR);

electrostatic motors (ID, SPD);

high-current (electromagnetic, magnetodynamic) motors;

impulse motors. ETDs, in turn, are divided into electric heating (END) and electric arc (EDA) engines.

Electrostatic engines are divided into ion (including colloidal) engines (ID, CD) - particle accelerators in a unipolar beam, and particle accelerators in a quasineutral plasma. The latter include accelerators with closed electron drift and an extended (UZDP) or shortened (UZDU) acceleration zone. The first ones are usually called stationary plasma engines (SPD), and the name is also found (increasingly less often) - linear Hall engine (LHD), in Western literature it is called a Hall engine. Ultrasonic motors are usually called anode-accelerated motors (LAMs).

High-current (magnetoplasma, magnetodynamic) motors include motors with their own magnetic field and motors with an external magnetic field (for example, an end-mounted Hall motor - THD).

Pulse engines use the kinetic energy of gases produced by the evaporation of a solid in an electrical discharge.

Any liquids and gases, as well as their mixtures, can be used as a working fluid in electric propulsion engines. However, for each type of engine there are working fluids, the use of which allows you to achieve the best results. Ammonia is traditionally used for ETDs, xenon is used for electrostatic ones, lithium is used for high-current ones, and fluoroplastic is used for pulsed ones.

The disadvantage of xenon is its cost, due to its small annual production (less than 10 tons per year worldwide), which forces researchers to look for other RTs with similar characteristics, but less expensive. Argon is considered as the main candidate for replacement. It is also an inert gas, but, unlike xenon, it has greater ionization energy at a lower atomic mass (the energy spent on ionization per unit of accelerated mass is one of the sources of efficiency losses).

Brief technical specifications
Electric propulsion engines are characterized by a low RT mass flow rate and a high outflow velocity of an accelerated particle flow. The lower limit of the exhaust velocity approximately coincides with the upper limit of the exhaust velocity of a chemical engine jet and is about 3000 m/s. The upper limit is theoretically unlimited (within the speed of light), however, for promising engine models, a speed not exceeding 200,000 m/s is considered. Currently, for various types of engines, the optimal exhaust velocity is considered to be from 16,000 to 60,000 m/s.

Due to the fact that the acceleration process in an electric propulsion engine takes place at low pressure in the accelerating channel (particle concentration does not exceed 1020 particles/m³), the thrust density is quite low, which limits the use of electric propulsion engines: the external pressure should not exceed the pressure in the accelerating channel, and the acceleration KA is very small (tenths or even hundredths of g). An exception to this rule may be EDD on small spacecraft.

The electric power of electric propulsion engines ranges from hundreds of watts to megawatts.

Electric propulsion engines are characterized by efficiency ranging from 30 to 80%.

Story
In 1964, in the attitude control system of the Soviet Zond-2 spacecraft, 6 erosive pulsed thrusters operating on fluoroplastic operated for 70 minutes; the resulting plasma bunches had a temperature of ~30,000 K and flowed out at a speed of up to 16 km/s (the capacitor bank had a capacity of 100 μF, the operating voltage was ~1 kV).

On October 1, 1966, the Yantar-1 automatic ionospheric laboratory was launched to an altitude of 400 km by a three-stage geophysical rocket 1YA2TA to study the interaction of the jet stream of an electric rocket engine (ERE), running on argon, with ionospheric plasma. The experimental plasma-ion electric propulsion engine was first turned on at an altitude of 160 km, and during the subsequent flight 11 cycles of its operation were carried out. A jet exhaust velocity of about 40 km/s was achieved. The Yantar laboratory reached a specified flight altitude of 400 km, the flight lasted 10 minutes, the electric propulsion engine operated steadily and developed a design thrust of five grams of force. The scientific community learned about the achievement of Soviet science from a TASS report.

In the second series of experiments, nitrogen was used. The exhaust speed was increased to 120 km/s. In 1966-1971, four similar devices were launched (according to other sources, six devices were launched before 1970).

In the fall of 1970, a ramjet electric propulsion system successfully passed tests in real flight. In October 1970, at the XXI Congress of the International Astronomical Federation, Soviet scientists - Professor G. Grodzovsky, Candidates of Technical Sciences Yu. Danilov and N. Kravtsov, Candidates of Physical and Mathematical Sciences M. Marov and V. Nikitin, Doctor of Technical Sciences V. Utkin - reported on testing of an air propulsion system. The recorded jet speed reached 140 km/s.

teorological satellite “Meteor” operated two stationary plasma engines developed by the Institute of Atomic Energy named after. I.V. Kurchatov and OKB Fakel, each of which, with a power supply of ~0.4 kW, developed a thrust of 18-23 mN and an exhaust velocity of over 8 km/s. The RDs had dimensions of 108 × 114 × 190 mm, a mass of 32.5 kg and a PT (compressed xenon) reserve of 2.4 kg. During one of the starts, one of the engines worked continuously for 140 hours. This electric propulsion system is shown in the figure.

Electric rocket engines are also used in the Dawn mission and in the BepiColombo project.

Prospects
Although electric rocket engines have low thrust compared to liquid-fuel rockets, they are capable of operating for long periods of time and performing slow flights over long distances. Today's most advanced electric rocket engines have a characteristic speed ΔV of about 100 km/s and, when using nuclear power sources, are suitable for flights to the outer planets of the solar system in a "reasonable time" as Edgar Choueiri puts it, but are too slow for travel. to distant stars, also according to Michio Kaku, ion and plasma engines are too low-power for human flight to the stars.

If we talk about interstellar flight, then an electric rocket engine with a nuclear power unit was considered for the Daedalus project, but was rejected due to low thrust, the large weight of the nuclear power unit and, as a consequence, low acceleration, due to which it would take centuries to achieve the required speed [source not specified 171 days]. However, Geoffrey Landis (English) considered the use of ion propulsion for interstellar flights with an external power supply via a laser to the solar panels of the spacecraft.

Currently, many countries are exploring the creation of manned interplanetary spacecraft with electric propulsion systems. Existing electric propulsion engines are not optimal for use as propulsion engines for such ships, and therefore in the near future we should expect renewed interest in the development of high-current electric propulsion engines based on liquid metal RT (bismuth, lithium, potassium, cesium) with an electrical power of up to 1 MW, capable of work for a long time at currents up to 5-10 kA. These RDs must develop a thrust of up to 20-30 N and an exhaust velocity of 20-30 km/s with an efficiency of 30% or more (in 1975, a similar RD was tested in the USSR on the Kosmos-728 satellite - a RD with an electrical power of 3 kW, operating on potassium, developed an exhaust velocity of ~ 30 km/s).

In addition to Russia and the USA, research and development of electric propulsion systems is also carried out in the UK, Germany, France, Japan, and Italy. The main areas of activity of these countries: ID (the most successful developments are from Great Britain and Germany, especially joint ones); SPD and DAS (Japan, France); ETD (France). These engines are mainly intended for satellites.

Literature

 * М.В.Ковальчук, В.И.Ильгисонис, В.М.Кулыгин. Плазменные двигатели и будущее космонавтики // Природа : журнал. — 2017. — № 12 (1228). — С. 33—44.
 * Эдгар Чуэйри. Новый рассвет электрических ракет // «В мире науки» № 5, 2009, стр. 34-42.
 * Архивная копия от 20 февраля 2015 на Wayback Machine
 * Электрический ракетный двигатель — статья из Большой советской энциклопедии.
 * Электрический ракетный двигатель // энциклопедия «Космонавтика», под ред. Глушко В. П., 1985 — достаточно исчерпывающий материал о различных типах ЭРД
 * Журнал «Космические исследования», том XII, в.3, стр. 461
 * Глибицкий М. М. Системы питания и управления электрическими ракетными двигателями. — М., Машиностроение, 1981. — 136 с.
 * Глибицкий М. М. Системы питания и управления электрическими ракетными двигателями. — М., Машиностроение, 1981. — 136 с.