![Xenon hall thruster](https://upload.wikimedia.org/wikipedia/commons/8/85/Xenon_hall_thruster.jpg)
In
spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric e ...
, a Hall-effect thruster (HET) is a type of
ion thruster
An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity.
An ion thruster ionizes a neutral gas by extracting some electrons out of a ...
in which the
propellant
A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
is accelerated by an
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
. Hall-effect thrusters (based on the discovery by
Edwin Hall
Edwin Herbert Hall (November 7, 1855 – November 20, 1938) was an American physicist, who discovered the eponymous Hall effect. Hall conducted thermoelectric research and also wrote numerous physics textbooks and laboratory manuals.
Biograp ...
) are sometimes referred to as Hall thrusters or Hall-current thrusters.
Hall-effect
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discove ...
thrusters use a
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
to limit the electrons' axial motion and then use them to ionize propellant, efficiently accelerate the
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s to produce
thrust
Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...
, and neutralize the ions in the plume. The Hall-effect thruster is classed as a moderate
specific impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
(1,600s) space propulsion technology and has benefited from considerable theoretical and experimental research since the 1960s.
Hall thrusters operate on a variety of propellants, the most common being
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
and
krypton
Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...
. Other propellants of interest include
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
,
bismuth
Bismuth is a chemical element with the Symbol (chemistry), symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental ...
,
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and
adamantane
Adamantane is an organic compound with a formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the ...
.
Hall thrusters are able to accelerate their exhaust to
speeds between 10 and 80 km/s (1,000–8,000 s specific impulse), with most models operating between 15 and 30 km/s. The thrust produced depends on the power level. Devices operating at 1.35 kW produce about 83 mN of thrust. High-power models have demonstrated up to 5.4 N in the laboratory. Power levels up to 100 kW have been demonstrated for xenon Hall thrusters.
, Hall-effect thrusters ranged in input power levels from 1.35 to 10 kilowatts and had
exhaust velocities of 10–50 kilometers per second, with thrust of 40–600
millinewton
The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in r ...
s and efficiency in the range of 45–60 percent.
The applications of Hall-effect thrusters include control of the orientation and position of orbiting
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
s and use as a main propulsion engine for medium-size robotic space vehicles.
History
Hall thrusters were studied independently in the United States and the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
. They were first described publicly in the US in the early 1960s.
However, the Hall thruster was first developed into an efficient propulsion device in the Soviet Union. In the US, scientists focused on developing
gridded ion thruster
The gridded ion thruster is a common design for ion thrusters, a highly efficient low-thrust spacecraft propulsion method running on electrical power by using high-voltage grid electrodes to accelerate ions with electrostatic forces.
History
The ...
s.
Two types of Hall thrusters were developed in the Soviet Union:
*thrusters with wide acceleration zone, SPT (russian: СПД, стационарный плазменный двигатель; en, SPT, Stationary Plasma Thruster) at
Design Bureau Fakel
*thrusters with narrow acceleration zone, DAS (russian: ДАС, двигатель с анодным слоем; en, TAL, Thruster with Anode Layer), at the
Central Research Institute for Machine Building (TsNIIMASH).
![Russian stationary plasma thrusters](https://upload.wikimedia.org/wikipedia/commons/6/6b/Russian_stationary_plasma_thrusters.jpg)
The SPT design was largely the work of A. I. Morozov.
The first SPT to operate in space, an SPT-50 aboard a Soviet
Meteor spacecraft, was launched December 1971. They were mainly used for satellite stabilization in north–south and in east–west directions. Since then until the late 1990s 118 SPT engines completed their mission and some 50 continued to be operated. Thrust of the first generation of SPT engines, SPT-50 and SPT-60 was 20 and 30 mN respectively. In 1982, the SPT-70 and
SPT-100
SPT-100 is a Hall-effect ion thruster, part of the SPT-family of thrusters. SPT stands for ''Stationary Plasma Thruster''. It creates a stream of electrically charged xenon ions accelerated by an electric field and confined by a magnetic field.
T ...
were introduced, their thrusts being 40 and 83 mN, respectively. In the post-Soviet
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
high-power (a few
kilowatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s) SPT-140, SPT-160, SPT-200, T-160 and low-power (less than 500 W) SPT-35 were introduced.
Soviet and Russian TAL-type thrusters include the D-38, D-55, D-80, and D-100.
Soviet-built thrusters were introduced to the West in 1992 after a team of electric propulsion specialists from NASA's
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
,
Glenn Research Center
NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a subsidiary facilit ...
, and the
Air Force Research Laboratory
The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of aerospace warfighting technologies, pl ...
, under the support of the
Ballistic Missile Defense Organization
The Ballistic Missile Defense Organization (BMDO) was an agency of the United States Department of Defense that began on 20 May 1974 with the responsibility for all U.S. ballistic missile defense efforts. It was renamed the Missile Defense Agenc ...
, visited Russian laboratories and experimentally evaluated the SPT-100 (i.e., a 100 mm diameter SPT thruster). Over 200 Hall thrusters have been flown on Soviet/Russian satellites in the past thirty years. No failures have ever occurred on orbit. Hall thrusters continue to be used on Russian spacecraft and have also flown on European and American spacecraft.
Space Systems/Loral
SSL, formerly Space Systems/Loral, LLC (SS/L), of Palo Alto, California, is a wholly owned manufacturing subsidiary of Maxar Technologies.
SSL designs and builds satellites and space systems for a wide variety of government and commercial cust ...
, an American commercial satellite manufacturer, now flies Fakel SPT-100's on their GEO communications spacecraft.
Since their introduction to the West in the early 1990s, Hall thrusters have been the subject of a large number of research efforts throughout the United States, France, Italy, Japan, and Russia (with many smaller efforts scattered in various countries across the globe). Hall thruster research in the US is conducted at several government laboratories, universities and private companies. Government and government funded centers include NASA's
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
, NASA's
Glenn Research Center
NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a subsidiary facilit ...
, the
Air Force Research Laboratory
The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of aerospace warfighting technologies, pl ...
(Edwards AFB, California), and
The Aerospace Corporation
The Aerospace Corporation is an American nonprofit corporation that operates a federally funded research and development center (FFRDC) in El Segundo, California. The corporation provides technical guidance and advice on all aspects of space mi ...
. Universities include the
US Air Force Institute of Technology
The Air Force Institute of Technology (AFIT) is a graduate school and provider of professional and continuing education for the United States Armed Forces and is part of the United States Air Force. It is in Ohio at Wright-Patterson Air Forc ...
,
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
,
Stanford University
Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...
,
The Massachusetts Institute of Technology
''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...
,
Princeton University
Princeton University is a private university, private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial Colleges, fourth-oldest ins ...
,
Michigan Technological University, and
Georgia Tech
The Georgia Institute of Technology, commonly referred to as Georgia Tech or, in the state of Georgia, as Tech or The Institute, is a public research university and institute of technology in Atlanta, Georgia. Established in 1885, it is part of ...
. A considerable amount of development is being conducted in industry, such as
IHI Corporation
, formerly known as , is a Japanese engineering corporation headquartered in Tokyo, Japan that produces and offers ships, space launch vehicles, aircraft engines, marine diesel engines, gas turbines, gas engines, railway systems, turbochargers f ...
in Japan,
Aerojet
Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp. ...
and
Busek
Busek Co. Inc. is an American spacecraft propulsion company that provides thrusters, electronics, and complete systems for spacecraft.
History
Busek was founded in 1985 by Vlad Hruby and incorporated in Natick, Massachusetts. It started as a l ...
in the US,
SNECMA
Safran Aircraft Engines, previously Snecma (''Société nationale d'études et de construction de moteurs d'aviation'') or Snecma Moteurs, is a French aerospace engine manufacturer headquartered in Courcouronnes and a subsidiary of Safran. It ...
in France,
LAJP in Ukraine,
SITAEL in Italy, and
Satrec Initiative
Satrec Initiative Co., Ltd. (Korean: 쎄트렉아이) or Satrec i or SI is a South Korean satellite manufacturing company headquartered in Daejeon, South Korea The company was founded in 1999 by the engineers who developed the first Korean satel ...
in South Korea.
The first use of Hall thrusters on lunar orbit was the European Space Agency (ESA) lunar mission
SMART-1 in 2003.
Hall thrusters were first demonstrated on a western satellite on the Naval Research Laboratory (NRL) STEX spacecraft, which flew the Russian D-55. The first American Hall thruster to fly in space was the
Busek
Busek Co. Inc. is an American spacecraft propulsion company that provides thrusters, electronics, and complete systems for spacecraft.
History
Busek was founded in 1985 by Vlad Hruby and incorporated in Natick, Massachusetts. It started as a l ...
BHT-200 on
TacSat-2
TacSat-2 is the first in a series of U.S. military experimental technology and communication satellites.TacSat-2 (also known as JWS-D1 ((Joint Warfighting Space-Demonstrator 1) or RoadRunner) was an experimental satellite built by the USAF's A ...
technology demonstration spacecraft. The first flight of an American Hall thruster on an operational mission, was the
Aerojet
Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp. ...
BPT-4000, which launched August 2010 on the military
Advanced Extremely High Frequency
Advanced Extremely High Frequency (AEHF) is a constellation of communications satellites operated by the United States Space Force. They are used to relay secure communications for the United States Armed Forces, the British Armed Forces, the C ...
GEO communications satellite. At 4.5 kW, the BPT-4000 is also the highest power Hall thruster ever flown in space. Besides the usual stationkeeping tasks, the BPT-4000 is also providing orbit-raising capability to the spacecraft. The
X-37B has been used as a testbed for the Hall thruster for the AEHF satellite series.
Several countries worldwide continue efforts to qualify Hall thruster technology for commercial uses. The
SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
Starlink
Starlink is a satellite internet constellation operated by SpaceX, providing satellite Internet access coverage to 45 countries. It also aims for global mobile phone service after 2023. SpaceX started launching Starlink satellites in 2019. As ...
constellation, the largest satellite constellation in the world, uses Hall thrusters. They are also included in the design of the
Psyche spacecraft for asteroid exploration.
Principle of operation
The essential working principle of the Hall thruster is that it uses an
electrostatic potential
Electrostatics is a branch of physics that studies electric charges at rest ( static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ambe ...
to accelerate ions up to high speeds. In a Hall thruster, the attractive negative charge is provided by an electron plasma at the open end of the thruster instead of a grid. A radial magnetic field of about is used to confine the electrons, where the combination of the radial magnetic field and axial electric field cause the electrons to drift in azimuth thus forming the Hall current from which the device gets its name.
![Wfm hall thruster](https://upload.wikimedia.org/wikipedia/commons/2/2d/Wfm_hall_thruster.svg)
A schematic of a Hall thruster is shown in the adjacent image. An
electric potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
of between 150 and 800 volts is applied between the
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
and
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
.
The central spike forms one pole of an
electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...
and is surrounded by an annular space, and around that is the other pole of the electromagnet, with a radial magnetic field in between.
The propellant, such as
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
gas, is fed through the anode, which has numerous small holes in it to act as a gas distributor. As the neutral xenon atoms diffuse into the channel of the thruster, they are ionized by collisions with circulating high-energy electrons (typically 10–40 eV, or about 10% of the discharge voltage). Most of the xenon atoms are ionized to a net charge of +1, but a noticeable fraction (c. 20%) have +2 net charge.
The xenon ions are then accelerated by the
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
between the anode and the cathode. For discharge voltages of 300 V, the ions reach speeds of around for a specific impulse of 1,500 s (15 kN·s/kg). Upon exiting, however, the ions pull an equal number of electrons with them, creating a
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
plume with no net charge.
The radial magnetic field is designed to be strong enough to substantially deflect the low-mass electrons, but not the high-mass ions, which have a much larger
gyroradius The gyroradius (also known as radius of gyration, Larmor radius or cyclotron radius) is the radius of the circular motion of a charged particle in the presence of a uniform magnetic field. In SI units, the non-relativistic gyroradius is given by
:r_ ...
and are hardly impeded. The majority of electrons are thus stuck orbiting in the region of high radial magnetic field near the thruster exit plane, trapped in ''E''×''B'' (axial electric field and radial magnetic field). This orbital rotation of the electrons is a circulating
Hall current
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discove ...
, and it is from this that the Hall thruster gets its name. Collisions with other particles and walls, as well as plasma instabilities, allow some of the electrons to be freed from the magnetic field, and they drift towards the anode.
About 20–30% of the discharge current is an electron current, which does not produce thrust, thus limiting the energetic efficiency of the thruster; the other 70–80% of the current is in the ions. Because the majority of electrons are trapped in the Hall current, they have a long residence time inside the thruster and are able to ionize almost all of the xenon propellant, allowing mass use of 90–99%. The mass use efficiency of the thruster is thus around 90%, while the discharge current efficiency is around 70%, for a combined thruster efficiency of around 63% (= 90% × 70%). Modern Hall thrusters have achieved efficiencies as high as 75% through advanced designs.
Compared to chemical rockets, the thrust is very small, on the order of 83 mN for a typical thruster operating at 300 V and 1.5 kW. For comparison, the weight of a coin like the
U.S. quarter or a 20-cent
euro coin
There are eight euro coin denominations, ranging from one cent to two euros (the euro is divided into a hundred cents). The coins first came into use in 2002. They have a common Obverse and reverse, reverse, portraying a map of Europe, but each cou ...
is approximately 60 mN. As with all forms of
electrically powered spacecraft propulsion
Spacecraft electric propulsion (or just electric propulsion) is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed and thus generate thrust to modify the velocity of a s ...
, thrust is limited by available power, efficiency, and
specific impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
.
However, Hall thrusters operate at the high
specific impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
s that are typical for electric propulsion. One particular advantage of Hall thrusters, as compared to a
gridded ion thruster
The gridded ion thruster is a common design for ion thrusters, a highly efficient low-thrust spacecraft propulsion method running on electrical power by using high-voltage grid electrodes to accelerate ions with electrostatic forces.
History
The ...
, is that the generation and acceleration of the ions takes place in a quasi-neutral plasma, so there is no
Child-Langmuir charge (space charge)
saturated current limitation on the thrust density. This allows much smaller thrusters compared to gridded ion thrusters.
Another advantage is that these thrusters can use a wider variety of propellants supplied to the anode, even oxygen, although something easily ionized is needed at the cathode.
Propellants
Xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
has been the typical choice of propellant for many electric propulsion systems, including Hall thrusters. Xenon propellant is used because of its high
atomic weight
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
and low
ionization potential
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
. Xenon is relatively easy to store, and as a gas at spacecraft operating temperatures does not need to be vaporized before usage, unlike metallic propellants such as bismuth. Xenon's high atomic weight means that the ratio of energy expended for ionization per mass unit is low, leading to a more efficient thruster.
Krypton
Krypton is another choice of propellant for Hall thrusters. Xenon has an ionization potential of 12.1298 eV, while krypton has an ionization potential of 13.996 eV. This means that thrusters utilizing krypton need to expend a slightly higher energy per mole to ionize, which reduces efficiency. Additionally, krypton is a lighter ion, so the unit mass per ionization energy is further reduced compared to xenon. However, xenon can be more than ten times as expensive as krypton per
kilogram
The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially ...
, making krypton a more economical choice for building out
satellite constellations
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisoto ...
like that of
SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
's
Starlink
Starlink is a satellite internet constellation operated by SpaceX, providing satellite Internet access coverage to 45 countries. It also aims for global mobile phone service after 2023. SpaceX started launching Starlink satellites in 2019. As ...
, whose Hall thrusters are fueled with krypton.
Variants
Cylindrical Hall thrusters
![Hall Effect Thruster in a vacuum chamber](https://upload.wikimedia.org/wikipedia/commons/c/c3/Hall_Effect_Thruster_in_a_vacuum_chamber.jpg)
Although conventional (annular) Hall thrusters are efficient in the
kilowatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
power regime, they become inefficient when scaled to small sizes. This is due to the difficulties associated with holding the performance scaling parameters constant while decreasing the channel size and increasing the applied
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
strength. This led to the design of the cylindrical Hall thruster. The cylindrical Hall thruster can be more readily scaled to smaller sizes due to its nonconventional discharge-chamber geometry and associated
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
profile.
The cylindrical Hall thruster more readily lends itself to miniaturization and low-power operation than a conventional (annular) Hall thruster. The primary reason for cylindrical Hall thrusters is that it is difficult to achieve a regular Hall thruster that operates over a broad envelope from c.1 kW down to c. 100 W while maintaining an efficiency of 45–55%.
External discharge Hall thruster
Sputtering erosion of discharge channel walls and pole pieces that protect the magnetic circuit causes failure of thruster operation. Therefore, annular and cylindrical Hall thrusters have limited lifetime. Although magnetic shielding has been shown to dramatically reduce discharge channel wall erosion, pole piece erosion is still a concern. As an alternative, an unconventional Hall thruster design called external discharge Hall thruster or external discharge plasma thruster (XPT) has been introduced. The external discharge Hall thruster does not possess any discharge channel walls or pole pieces. Plasma discharge is produced and sustained completely in the open space outside the thruster structure, and thus erosion-free operation is achieved.
Applications
![GATEWAY (Moon Space Station)](https://upload.wikimedia.org/wikipedia/commons/6/61/GATEWAY_%28Moon_Space_Station%29.png)
Hall thrusters have been flying in space since December 1971, when the Soviet Union launched an SPT-50 on a Meteor satellite. Over 240 thrusters have flown in space since that time, with a 100% success rate.
Hall thrusters are now routinely flown on commercial LEO and GEO communications satellites, where they are used for orbital insertion and
stationkeeping.
The first Hall thruster to fly on a western satellite was a Russian D-55 built by TsNIIMASH, on the NRO's
STEX spacecraft, launched on October 3, 1998.
The
solar electric propulsion
Solar electric propulsion (SEP) refers to the combination of solar cells and electric thrusters to propel a spacecraft through outer space. This technology has been exploited in a variety of spacecraft by the European Space Agency (ESA), th ...
system of the
European Space Agency
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1205 ...
's
SMART-1 spacecraft used a Snecma
PPS-1350
PPS-1350 is a Hall-effect thruster, a kind of ion propulsion system for spacecraft. It was used in the SMART-1 mission to the moon and one geostationary satellites: Inmarsat-4A F4.
It creates a stream of electrically charged xenon ions acceler ...
-G Hall thruster.
SMART-1 was a technology demonstration mission that orbited the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. This use of the PPS-1350-G, starting on September 28, 2003, was the first use of a Hall thruster outside
geosynchronous earth orbit (GEO). Like most Hall thruster propulsion systems used in commercial applications, the Hall thruster on SMART-1 could be throttled over a range of power, specific impulse, and thrust. It has a discharge power range of 0.46–1.19 kW, a
specific impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
of 1,100–1,600 s and thrust of 30–70 mN.
Many small satellites of the
SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
Starlink
Starlink is a satellite internet constellation operated by SpaceX, providing satellite Internet access coverage to 45 countries. It also aims for global mobile phone service after 2023. SpaceX started launching Starlink satellites in 2019. As ...
cluster use krypton-fueled Hall thrusters for position-keeping and deorbiting.
Tiangong space station is fitted with Hall-effect thrusters.
Tianhe core module
''Tianhe'' (), officially the ''Tianhe'' core module (), is the first module to launch of the Tiangong space station. It was launched into orbit on 29 April 2021, as the first launch of the final phase of Tiangong program, part of the Ch ...
is propelled by both chemical thrusters and four
ion thruster
An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity.
An ion thruster ionizes a neutral gas by extracting some electrons out of a ...
s, which are used to adjust and maintain the station's orbit. The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention". Hall-effect thrusters are created with crewed mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles. A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters. According to the
Chinese Academy of Sciences
The Chinese Academy of Sciences (CAS); ), known by Academia Sinica in English until the 1980s, is the national academy of the People's Republic of China for natural sciences. It has historical origins in the Academia Sinica during the Republ ...
, the ion drive used on Tiangong has burned continuously for 8,240 hours without a glitch, indicating their suitability for the Chinese space station's designated 15-year lifespan. This is the world's first Hall thruster on a human-rated mission.
The
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
(JPL) granted exclusive commercial licensing to Apollo Fusion, led by
Mike Cassidy, for its Magnetically Shielded Miniature (MaSMi) Hall thruster technology. In January 2021, Apollo Fusion announced they had secured a contract with York Space Systems for an order of its latest iteration named the "Apollo Constellation Engine".
The
NASA mission to the asteroid Psyche will utilize xenon gas Hall thrusters. The electricity will come from the craft's 75 square meter solar panels.
NASA's first Hall thrusters on a human-rated mission will be a combination of 6 kW Hall thrusters provided by
Busek
Busek Co. Inc. is an American spacecraft propulsion company that provides thrusters, electronics, and complete systems for spacecraft.
History
Busek was founded in 1985 by Vlad Hruby and incorporated in Natick, Massachusetts. It started as a l ...
and NASA
Advanced Electric Propulsion System
Advanced Electric Propulsion System (AEPS) is a solar electric propulsion system for spacecraft that is being designed, developed and tested by NASA and Aerojet Rocketdyne for large-scale science missions and cargo transportation.[Power and Propulsion Element
The Power and Propulsion Element (PPE), previously known as the Asteroid Redirect Vehicle propulsion system, is a planned solar electric ion propulsion module being developed by Maxar Technologies for NASA. It is one of the major components of ...]
(PPE) for the
Lunar Gateway
The Lunar Gateway, or simply Gateway, is the first planned extraterrestrial space station in lunar orbit intended to serve as a solar-powered communication hub, science laboratory, and short-term habitation module for government-agency astr ...
under NASA's
Artemis program
The Artemis program is a robotic and human Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA) along with three partner agencies: European Space Agency (ESA), Japan Aerospace Exploration ...
. The high specific impulse of Hall thrusters will allow for efficient orbit raising and station keep for the Lunar Gateway's polar
near-rectilinear halo orbit
A near-rectilinear halo orbit (NRHO) is a halo orbit with slightly curved – or nearly straight – sides between close passes with an orbiting body. The 2022 CAPSTONE mission is the first such orbit in cislunar space, and this Moon-centric o ...
.
In development
The highest power Hall-effect thruster in development (as of 2021) is the
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
's 100 kW X3 Nested Channel Hall Thruster. The thruster is approximately 80 cm in diameter and weighs 230 kg, and has demonstrated a thrust of 5.4 N.
Other high power thrusters include NASA's 40 kW
Advanced Electric Propulsion System
Advanced Electric Propulsion System (AEPS) is a solar electric propulsion system for spacecraft that is being designed, developed and tested by NASA and Aerojet Rocketdyne for large-scale science missions and cargo transportation.