Hall-effect thruster
The Hall-effect thruster is classed as a moderate specific impulse (1,600 s) space propulsion technology and has benefited from considerable theoretical and experimental research since the 1960s.
[3] 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.
[11] A considerable amount of development is being conducted in industry, such as IHI Corporation in Japan, Aerojet and Busek in the US, SNECMA in France, LAJP in Ukraine, SITAEL in Italy, and Satrec Initiative in South Korea.
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 flight of an American Hall thruster on an operational mission, was the Aerojet BPT-4000, which launched August 2010 on the military Advanced Extremely High Frequency GEO communications satellite.
Starlink initially used krypton gas, but with its V2 satellites swapped to argon due to its cheaper price and widespread availability.
The project subsequently developed a technology demonstrator prototype using argon propellant with a specific impulse of 2500s at a thrust of 25 mN.
Alongside it, RF-powered 10 kW plasma engines and krypton based low power electric propulsion were being pursued.
Bellatrix Aerospace had previously developed the first commercially available microwave electrothermal thruster, for which the company received an order from ISRO.
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).
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.
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.
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%.
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.
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.
[22] This means that thrusters utilizing krypton need to expend a slightly higher energy per mole to ionize, which reduces efficiency.
As well as the Soviet SPT and TAL types mentioned above, there are: 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.
The cylindrical Hall thruster can be more readily scaled to smaller sizes due to its nonconventional discharge-chamber geometry and associated magnetic field profile.
[29] Sputtering erosion of discharge channel walls and pole pieces that protect the magnetic circuit causes failure of thruster operation.
Plasma discharge is produced and sustained completely in the open space outside the thruster structure, and thus erosion-free operation is achieved.
[35] Hall thrusters are now routinely flown on commercial LEO and GEO communications satellites, where they are used for orbital insertion and stationkeeping.
The first[failed verification] 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.
[36] The solar electric propulsion system of the European Space Agency's SMART-1 spacecraft used a Snecma PPS-1350-G Hall thruster.
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.
[41] The Jet Propulsion Laboratory (JPL) granted exclusive commercial licensing to Apollo Fusion, led by Mike Cassidy, for its Magnetically Shielded Miniature (MaSMi) Hall thruster technology.
The thruster is approximately 80 cm in diameter and weighs 230 kg, and has demonstrated a thrust of 5.4 N.[47] Other high power thrusters include NASA's 40 kW Advanced Electric Propulsion System (AEPS), meant to propel large-scale science missions and cargo transportation in deep space.
