A pulsed inductive thruster (PIT) is a form 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 ...

, used in spacecraft propulsion. It is a

plasma propulsion engine A plasma propulsion engine is a type of electric propulsion that generates thrust from a quasi-neutral plasma. This is in contrast with ion thruster engines, which generate thrust through extracting an ion current from the plasma source, which ...

using perpendicular

electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

and magnetic fields to accelerate a propellant with no

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

Operation

A nozzle releases a puff of gas which spreads across a flat spiraling induction coil of

wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is c ...

about 1 meter across. A bank of

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

s releases a pulse of

high voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...

electric current of tens of kilovolts lasting 10 microseconds into the coil, generating a radial magnetic field. This

induces Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1831, and James Cler ...

a circular electrical field in the gas,

ionizing 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 i ...

it and causing

charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary pa ...

s (free

electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

and

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 revolve in the opposite direction as the original pulse of current. Because the motion of this induced current flow is perpendicular to the magnetic field, the plasma is accelerated out into space by the Lorentz force at a high exhaust velocity (10 to 100 km/s).

Advantages

Unlike an

electrostatic 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 Th ...

which uses an electric field to accelerate only one

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

(positive ions), a PIT uses the Lorentz body force acting upon all charged particles within a quasi-neutral plasma. Unlike most other ion and plasma thrusters, it also requires no

s (which are susceptible to erosion) and its power can be scaled up simply by increasing the number of pulses per second. A 1-

megawatt 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 ...

system would pulse 200 times per second. Pulsed inductive thrusters can maintain constant

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 is ...

and thrust efficiency over a wide range of input power levels by adjusting the pulse rate to maintain a constant discharge energy per pulse. It has demonstrated efficiency greater than 50%. Pulsed inductive thrusters can use a wide range of gases as a propellant, such as

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

, hydrazine,

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

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 ...

, or

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 ...

, among many others. Due to this ability, it has been suggested to use PITs for

Martian Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. It became the most popular celestial object in fiction in the late 1800s as the Moon was evidently lifeless. At the time, the pr ...

missions: an orbiter could refuel by scooping CO₂ from the

atmosphere of Mars The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

, compressing the gas and liquefying it into storage tanks for the return journey or another

interplanetary mission Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the S ...

, whilst orbiting the planet.

Developments

Early development began with fundamental proof-of-concept studies performed in the mid-1960s. NASA conducts experiments on this device since the early 1980s.

PIT Mk V, VI and VII

NGST ( Northrop Grumman Space Technology), as a contractor for NASA, built several experimental PITs. Research efforts during the first period (1965–1973) were aimed at understanding the structure of an inductive current sheet and evaluating different concepts for propellant injection and preionization. In the second period (1979–1988), the focus shifted more towards developing a true propulsion system and increasing the performance of the base design through incremental design changes, with the build of ''Mk I'' and ''Mk IV'' prototypes. The third period (1991-today) began with the introduction of a new PIT thruster design known as the ''Mk V''. It evolved into the ''Mk VI'', developed to reproduce Mk V single-shot tests, which completely characterize thruster performance. It uses an improved coil of hollow copper tube construction and an improved propellant valve, but is electrically identical to the Mk V, using the same capacitors and switches. The ''Mk VII'' (early 2000s) has the same geometry as Mk VI, but is designed for high pulse frequency and long-duration firing with a liquid-cooled coil, longer-life capacitors, and fast, high-power solid-state switches. The goal for Mk VII is to demonstrate up to 50 pulses per second at the rated efficiency and impulse bit at 200 kW of input power in a single thruster. Mk VII design is the base for the most recent ''NuPIT'' (Nuclear-electric PIT). The PIT has obtained relatively high performance in the laboratory environment, but it still requires additional advancements in switching technology and energy storage before becoming practical for high-power in-space applications, with the need for a nuclear-based onboard power source.

FARAD

''FARAD'', which stands for ''Faraday accelerator with radio-frequency assisted discharge'', is a lower-power alternative to the PIT that has the potential for space operation using current technologies. In the PIT, both propellant ionization and acceleration are performed by the HV pulse of current in the induction coil, while FARAD uses a separate inductive RF discharge to preionize the propellant before it is accelerated by the current pulse. This preionization allows FARAD to operate at much lower discharge energies than the PIT (100 joules per pulse vs 4 kilojoules per pulse) and allows for a reduction in the thruster's size.

References

{{spacecraft propulsion Ion engines Magnetic propulsion devices