In spacecraft propulsion, a
Hall-effect thruster (HET) is a type of
ion thruster in which the propellant is accelerated by an electric
field. Hall-effect thrusters trap electrons in a magnetic field and
then use the electrons to ionize propellant, efficiently accelerate
the ions to produce thrust, and neutralize the ions in the plume.
Hall-effect thrusters (based on the discovery by Edwin Hall) are
sometimes referred to as Hall thrusters or Hall-current thrusters.
Hall thrusters are often regarded as a moderate specific impulse
(1,600 s) space propulsion technology. The Hall-effect thruster
has benefited from considerable theoretical and experimental research
since the 1960s.
6-kW Hall thruster in operation at the
NASA Jet Propulsion Laboratory.
Hall thrusters operate on a variety of propellants, the most common
being xenon. Other propellants of interest include krypton, argon,
bismuth, iodine, magnesium, and zinc.
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 (1,500–3,000 s
The thrust produced by a Hall thruster varies depending 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
by xenon Hall thrusters.
As of 2009[update], 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 millinewtons and
efficiency in the range of 45–60 percent.
The applications of Hall-effect thrusters include control of the
orientation and position of orbiting satellites and use as a main
propulsion engine for medium-size robotic space vehicles.
3 Cylindrical Hall thrusters
4 External discharge Hall thruster
7 External links
Hall thrusters were studied independently in the United States and the
Soviet Union. 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 instead on developing gridded ion thrusters.
Two types of Hall thrusters were developed in the Soviet Union:
thrusters with wide acceleration zone, SPT (Russian: СПД,
стационарный плазменный двигатель;
English: SPT, Stationary Plasma Thruster) at Design Bureau Fakel
thrusters with narrow acceleration zone, DAS (Russian: ДАС,
двигатель с анодным слоем; English: SPT,
Anode Layer), at the Central Research Institute for
Machine Building (TsNIIMASH).
Soviet and Russian SPT thrusters
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, SPT-70 and
SPT-100 were introduced, their thrusts being 40 and
83 mN, respectively. In the post-Soviet
Russia high-power (a few
kilowatts) 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,
Soviet-built thrusters were introduced to the West in 1992 after a
team of electric propulsion specialists from NASA's Jet Propulsion
Laboratory, Glenn Research Center, and the Air Force Research
Laboratory, under the support of the Ballistic Missile Defense
Organization, visited Russian laboratories and experimentally
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, 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
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,
NASA's Glenn Research Center, the Air Force Research Laboratory
(Edwards AFB, CA), and The Aerospace Corporation. Universities include
the US Air Force Institute of Technology, University of Michigan,
Stanford University, The Massachusetts Institute of Technology,
Princeton University, Michigan Technological University, and Georgia
Tech. A considerable amount of development is being conducted in
industry, such as IHI in Japan,
Busek in the USA, SNECMA
in France, LAJP in Ukraine, and SITAEL in Italy.
The first use of Hall thrusters on lunar orbit was the European Space
Agency (ESA) lunar mission
SMART-1 in 2003.
On a western satellite Hall thrusters were first demonstrated 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 BHT-200 on
TacSat-2 technology demonstration spacecraft. The
first flight of an American Hall thruster on an operational mission,
Aerojet BPT-4000, which launched August 2010 on the military
Advanced Extremely High Frequency
Advanced Extremely High Frequency 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. Several
countries worldwide continue efforts to qualify Hall thruster
technology for commercial uses.
The essential working principle of the Hall thruster is that it uses
an electrostatic potential 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 100–300 G (0.01–0.03 T)
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
Hall thruster. Hall thrusters are largely axially symmetric. This is a
cross-section containing that axis.
A schematic of a Hall thruster is shown in the adjacent image. An
electric potential between 150 and 800 volts is applied between the
anode and cathode.
The central spike forms one pole of an electromagnet 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 gas, is fed through the anode, which has
numerous small holes in it to act as a gas distributor. Xenon
propellant is used because of its high atomic weight and low
ionization potential. 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). Once ionized, the xenon ions typically
have a charge of +1, though a small fraction (~20%) have +2.
The xenon ions are then accelerated by the electric field between the
anode and the cathode. For discharge voltages of 300 V, the ions
reach speeds of around 15 km/s (9.3 mps) for a specific impulse
of 1,500 seconds (15 kN·s/kg). Upon exiting, however, the ions
pull an equal number of electrons with them, creating a plasma 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 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, 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 utilizations of 90–99%.
The mass utilization 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
Compared to chemical rockets, the thrust is very small, on the order
of 83 mN for a typical thruster operating at 300 V,
1.5 kW. For comparison, the weight of a coin like the U.S.
quarter or a 20-cent
Euro coin is approximately 60 mN. As with
all forms of electrically powered spacecraft propulsion, thrust is
limited by available power, efficiency, and specific impulse.
However, Hall thrusters operate at the high specific impulses that is
typical for electric propulsion. One particular advantage of Hall
thrusters, as compared to a gridded ion thruster, 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.
Cylindrical Hall thrusters
Although conventional (annular) Hall thrusters are efficient in the
kilowatt 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 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 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
~1 kW down to ~100 W while maintaining an efficiency of
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. External
discharge Hall thruster does not possess any discharge channel walls
or pole pieces. Plasma discharge is produced and sustained completely
in open space outside the thruster structure, and thus erosion free
operation is achieved.
Hall thrusters have been flying in space since December 1971 when the
Soviets 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 GEO
communications satellites where they are used for orbital insertion
The first[not in citation given] 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 system of the European Space Agency's
SMART-1 spacecraft used a Snecma PPS-1350-G Hall thruster. SMART-1
was a technology demonstration mission that orbited the Moon. 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). Unlike
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.
Discharge power: 0.46–1.19 kW
Specific impulse: 1,100–1,600 s
Thrust: 30–70 mN
^ Hofer, Richard R. "Development and Characterization of
High-Efficiency, High-Specific Impulse
Xenon Hall Thrusters".
NASA STI Program. Retrieved 17 October
^ a b Choueiri, Edgar Y. (2009). "New Dawn for Electric Rockets".
Scientific American. 300: 58–65. Bibcode:2009SciAm.300b..58C.
^ Janes, G.; Dotson, J.; Wilson, T. (1962). Momentum transfer through
magnetic fields. Proceedings of third symposium on advanced propulsion
concepts. 2. Cincinnati, OH, USA. pp. 153–175.
^ Meyerand, RG. (1962). Momentum Transfer Through the Electric Fields.
Proceedings of Third Symposium on Advanced Propulsion Concepts. 1.
Cincinnati, OH, USA. pp. 177–190.
^ Seikel, GR. (1962). Generation of
Thrust – Electromagnetic
Thrusters. Proceedings of the NASA-University Conference on the
Science and Technology of Space Exploration. 2. Chicago, IL, USA.
^ "Hall thrusters". 2004-01-14. Archived from the original on February
^ Morozov, A.I. (March 2003). "The conceptual development of
stationary plasma thrusters". Plasma Physics Reports.
Nauka/Interperiodica. 29 (3): 235–250. Bibcode:2003PlPhR..29..235M.
^ a b "Native Electric Propulsion Engines Today" (in Russian). Novosti
Kosmonavtiki. 1999. Archived from the original on 6 June 2011.
^ "Hall-Effect Stationary Plasma thrusters". Electric Propulsion for
Inter-Orbital Vehicles. Retrieved 2014-06-16. 
^ Y. Raitses; N. J. Fisch. "Parametric Investigations of a
Nonconventional Hall Thruster" (PDF). Physics of Plasmas, 8, 2579
^ A. Smirnov; Y. Raitses; N.J. Fisch. "Experimental and theoretical
studies of cylindrical Hall thrusters" (PDF). Physics of Plasmas 14,
^ Polzin, K. A.; Raitses, Y.; Gayoso, J. C.; Fisch, N. J. "Comparisons
in Performance of
Electromagnet and Permanent-Magnet Cylindrical
NASA Technical Reports Server. Marchall Space
Flight Center. Retrieved 17 October 2011.
^ Polzin, K. A.; Raitses, Y.; Merino, E.; Fisch, N. J. "Preliminary
Results of Performance Measurements on a Cylindrical Hall-Effect
Thruster with Magnetic Field Generated by Permanent Magnets". NASA
Technical Reports Server. Princeton Plasma Physics Laboratory.
Retrieved 17 October 2011.
^ "Pole-piece Interactions with the Plasma in a Magnetically Shielded
^ "Preliminary Investigation of an External Discharge Plasma
^ "Numerical Investigation of an External Discharge Hall Thruster
Design Utilizing Plasma-lens Magnetic Field" (PDF).
^ "Low–voltage External Discharge Plasma Thruster and Hollow
Cathodes Plasma Plume Diagnostics Utilising Electrostatic Probes and
Retarding Potential Analyser".
^ Turner, Martin J. L. (5 November 2008). Rocket and Spacecraft
Propulsion: Principles, Practice and New Developments, page 197.
Springer Science & Business Media. Retrieved 28 October
^ This article incorporates public domain material from the
National Aeronautics and Space Administration document ""In-space
propulsion systems roadmap." (April 2012)." by Meyer, Mike, et al.
^ "National Reconnaissance Office
Satellite Successfully Launched"
(PDF). Naval Research Laboratory (Press Release). October 3,
^ Cornu, Nicolas; Marchandise, Frédéric; Darnon, Franck; Estublier,
Denis (2007). PPS®1350 Qualification Demonstration: 10500 hrs on the
Ground and 5000 hrs in Flight. 43rd AIAA/ASME/SAE/ASEE Joint
Propulsion Conference & Exhibit. Cincinnati, OH, USA.
Ion engine gets
SMART-1 to the Moon: Electric Propulsion
Subsystem". ESA. August 31, 2006. Retrieved 2011-07-25.
Edgar Y. (2009). New dawn of electric rocket. The Hall thruster
NASA Jet Propulsion Laboratory
SITAEL S.p.A. (Italy) – Page presenting
Hall effect thruster
products & data sheets.
Aerojet (Redmond, WA USA) – Hall-thruster vendor
Busek (Natick, MA USA) – Hall-thruster vendor
Experimental Design Bureau Fakel (Kaliningrad, Russia) –
MIT Space Propulsion Laboratory
Michigan Tech. Univ.
Ion Space Propulsion Laboratory
Georgia Institute of Technology High-Power Electric Propulsion
Colorado State University Electric Propulsion & Plasma Engineering
University of Michigan
University of Michigan Plasmadynamics and Electric Propulsion
Glenn Research Center
Glenn Research Center Hall Thruster Program
Princeton Plasma Physics Laboratory
Princeton Plasma Physics Laboratory page on Hall Thrusters
Snecma SA (France) page on
PPS-1350 Hall thruster
ESA page on Hall thrusters
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