The primary function of the space propulsion system is to provide thrust, which helps in the functioning of the launch vehicle or satellite. In propulsion systems, the fluid (either solid, liquid, or electric) reacts to initiate acceleration and provide force in the system.
The use of electric propulsion (EP) for space applications is currently undergoing rapid expansion. There are hundreds of operational spacecraft employing EP technologies with industry projections showing that nearly half of all commercial launches in the next decade will have a form of electric propulsion.
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. As the ionised particles escape from the aircraft, they generate a force moving in the other direction. Power supplies for ion thrusters are usually electric solar panels, but at sufficiently large distances from the sun, nuclear power is used.
Current ion engines are powered by solar cells, effectively making them solar-powered, and requiring very little propellant. They have been used on Esa’s SMART-1 mission to the Moon and Bepi-Colombo mission en-route to Mercury. Nasa are currently developing a high power electric propulsion system for the Lunar Gateway, an outpost which will orbit the Moon.
Ion drives are commonly used for attitude control (changing which direction a spacecraft is facing) and have been considered for deorbiting old satellites.
Ion thrusters are being designed for a wide variety of missions—from keeping communications satellites in the proper position (station-keeping) to propelling spacecraft throughout our solar system. “Ion propulsion is even considered to be mission-enabling for some cases where sufficient chemical propellant cannot be carried on the spacecraft to accomplish the desired mission,” says NASA. The technology could be used to power a return trip to Mars without refueling, and use recycled space junk for the fuel.
Ion thrusters are used in the European Space Agency’s (ESA) mission to Mercury. BepiColombo is Europe’s first mission to Mercury. Launched on 20 October 2018, it is on a seven year journey to the smallest and least explored terrestrial planet in our Solar System. When it arrives at Mercury in late 2025, it will endure temperatures in excess of 350 °C and gather data during its one-year nominal mission, with a possible one-year extension.
EPS is expected to drive half of all new spacecraft by 2020. For Space-dependent sectors across the globe, the economic benefits of EP systems are said to be immense. Currently government-owned and private space players agencies are said to be scrambling to make space missions 30 per cent cheaper than now – by lowering the per-kg cost of lifting payloads to specific distances.
Ion Propulsion Vs Chemical propulsion
As NASA explain: “An ion thruster ionizes propellant by adding or removing electrons to produce ions. Most thrusters ionize propellant by electron bombardment: a high-energy electron (negative charge) collides with a propellant atom (neutral charge), releasing electrons from the propellant atom and resulting in a positively charged ion. ” The gas produced consists of positive ions and negative electrons in proportions that result in no over-all electric charge. This is called a plasma. Plasma has some of the properties of a gas, but it is affected by electric and magnetic fields. Common examples are lightning and the substance inside fluorescent light bulbs. Ion thrusters have an input power need of 1–7 kW, exhaust velocity 20–50 km/s, thrust 25–250 millinewtons and efficiency 65–80%.
These thrusters have high specific impulses—ratio of thrust to the rate of propellant consumption, so they require significantly less propellant for a given mission than would be needed with chemical propulsion,” says NASA. These can be more than 10 times as fuel efficient as other rocket engines. Another attraction of using this kind of thruster is that it does not need the kind of high temperatures required by forms of chemical propulsion. This kind of electric propulsion system is also lighter in weight, meaning that future space trips could be more feasible. A xenon based EPS can be five to six times more efficient than chemical-based propulsion on spacecraft and has many uses, according to Dr Annadurai, whose centre assembles all Indian spacecraft. A 3,500-kg EPS-based satellite, for example, can do the work of a conventional spacecraft weighing 5,000 kg, but cost far less.
The advantages include : Highest specific impulse offers substantial mass saving (>3000s); High performance at low complexity; Reduced power processing unit mass; Narrow beam divergence; Robust design concept with a large domain of operational stability; Large throttle range and adaptable to available electric power; Excellent thrust stability and fast thrust response and Highest growth potential with increasing electric power in near and medium-term future
However Ion thrust engines create small thrust levels (the thrust of Deep Space 1 is approximately equal to the weight of one sheet of paper ) compared to conventional chemical rockets. They are practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Besides, the engine’s minuscule thrust would not matter when air resistance comes into play.
Michael Patterson, senior technologist for NASA’s In-Space Propulsion Technologies Program compared ion and chemical propulsion with “Tortoise and the Hare”. “The hare is a chemical propulsion system and a mission where you might fire the main engine for 30 minutes or an hour and then for most of the mission you coast.” “With electric propulsion, it’s like the tortoise, in that you go very slow in the initial spacecraft velocity but you continuously thrust over a very long duration — many thousands of hours — and then the spacecraft ends up picking up a very large delta to velocity.”
Ion Thruster technology
As NASA explain: “An ion thruster ionizes propellant by adding or removing electrons to produce ions. Most thrusters ionize propellant by electron bombardment: a high-energy electron (negative charge) collides with a propellant atom (neutral charge), releasing electrons from the propellant atom and resulting in a positively charged ion. ” The gas produced consists of positive ions and negative electrons in proportions that result in no over-all electric charge. This is called a plasma. Plasma has some of the properties of a gas, but it is affected by electric and magnetic fields. Common examples are lightning and the substance inside fluorescent light bulbs. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic thrusters use the Lorentz force.
The most common propellant used in ion propulsion is xenon, which is easily ionized and has a high atomic mass, thus generating a desirable level of thrust when ions are accelerated. It also is inert and has a high storage density; therefore, it is well suited for storing on spacecraft. In most ion thrusters, electrons are generated with the discharge hollow cathode by a process called thermionic emission.
Electrons produced by the discharge cathode are attracted to the discharge chamber walls, which are charged to a high positive potential by the voltage applied by the thruster’s discharge power supply. Neutral propellant is injected into the discharge chamber, where the electrons bombard the propellant to produce positively charged ions and release more electrons. High-strength magnets prevent electrons from freely reaching the discharge channel walls. This lengthens the time that electrons reside in the discharge chamber and increases the probability of an ionizing event. The positively charged ions migrate toward grids that contain thousands of very precisely aligned holes (apertures) at the aft end of the ion thruster. The first grid is the positively charged electrode (screen grid). A very high positive voltage is applied to the screen grid, but it is configured to force the discharge plasma to reside at a high voltage. As ions pass between the grids, they are accelerated toward a negatively charged electrode (the accelerator grid) to very high speeds (up to 90,000 mph).
“The positively charged ions are accelerated out of the thruster as an ion beam, which produces thrust. The neutralizer, another hollow cathode, expels an equal amount of electrons to make the total charge of the exhaust beam neutral. Without a neutralizer, the spacecraft would build up a negative charge and eventually ions would be drawn back to the spacecraft, reducing thrust and causing spacecraft erosion.”
The primary parts of an ion propulsion system are the ion thruster, power processing unit (PPU),propellant management system (PMS), and digital control and interface unit (DCIU). The PPU converts the electrical power from a power source—usually solar cells or a nuclear heat source—into the voltages needed for the hollow cathodes to operate, to bias the grids,and to provide the currents needed to produce the ion beam. The PMS may be divided into a high-pressure assembly (HPA) that reduces the xenon pressure from the higher storage pressures in the tank to a level that is then metered with accuracy for the ion thruster components by a low-pressure assembly (LPA). The DCIU controls and monitors system performance,and performs communication functions with the spacecraft computer.
Generally, an ion thruster has a few advantages over a chemical-powered rocket. Ion thruster can drive a spacecraft to speeds of up to 40 kilometers per second; its chemical counterpart can only manage 5 kilometers per second. Secondly, an ion thruster has ten times more fuel efficiency which is ideal for space travel. Chemical rockets need to bring their fuel supply for the whole journey and that load means more mass and additional fuel requirement for take-off.
Race to develop Ion Thrusters
Many countries led by US are developing Ion thrusters. University of Michigan researchers have developed an ion thruster that has the potential to power manned missions to Mars. Dubbed the X3, the ion thruster has already surpassed current thrusters in its category in terms of power output, thrust and operating current. China has finished building the world’s most powerful ion thruster and will soon use it to improve the mobility and lifespan of its space assets, according to a state media report. India has launched a 2,195-kg, GSAT-9 or the South Asia Satellite om May 5 carrying an electric propulsion or EP system, the first on an Indian spacecraft. The European Space Agency (ESA) has successfully tested a prototype ion engine powered by air that could provide propulsion for orbiting satellites almost indefinitely, and could even help power future missions to Mars.
Dr Paddy Neumann of Neumann Space and two professors have developed an ion thruster that is heading to the International Space Station (ISS) for a year-long experiment that ultimately could revolutionise space travel. University of Sydney doctoral candidate in Physics, Paddy Neumann, has developed a “new kind of ion space drive” that outperforms NASA’s in fuel efficiency and that can use a variety of metals, even those found in space junk, according to student newspaper Honi Soit.
NASA to fly ion thrusters
NASA Engineers want to add ion engines to the orbiter and fly the efficient electrically-powered thruster system to Mars for the first time, “The Mars mission model based on the asteroid retrieval mission would have enough power from its ion engines to launch to the red planet and return to Earth, and still fit in the envelope of a Falcon 9 or low-end Atlas 5 rocket, according to NASA official.
A Mars orbiter launching in 2022 is a prime candidate to test out new technologies — like ion drive engines, better solar arrays, and lightning-fast broadband communications between Earth and Mars — to help scientists return samples from the Martian surface, and eventually send humans there, according to Charles Whetsel, who oversees formulation of future Mars missions at NASA’s Jet Propulsion Laboratory in Pasadena, California.
In August 2022, a NASA probe called Psyche will set out to explore a giant metallic asteroid called Psyche 16, to help scientists learn more about how planets form. Building on technology used in previous missions, including Dawn and Deep Space 1, solar power will help propel Psyche into deep space. Psyche will use two giant solar arrays to convert solar energy into electricity that will power four ion thrusters.
Paulo Lozano, director of MIT’s space propulsion laboratory, says Psyche could lay the groundwork for more solar-powered space exploration. Eventually, the technology could help us investigate multiple celestial objects for longer periods and potentially make human-crewed missions outside of Earth’s orbit more affordable and feasible.
Psyche’s thrusters will be able to generate three times as much thrust as its predecessors, and about a year after launch, it will get some help from Mars’s gravitational pull to change its trajectory before eventually reaching its target in 2026.
In 2016, International Space Station trialed Aussie-designed thrusters that could power journey to Mars
Dr Paddy Neumann of Neumann Space and two professors have developed an ion thruster that is heading to the International Space Station (ISS) for a year-long experiment that ultimately could revolutionise space travel. Professor Marcela Bilek, one of the co-inventors, said they built a system in the early 2000s that was a “cathodic arc pulsed with a centre trigger and high ionisation flux”. Professor Bilek explained a cathodic arc was a system that used solid fuels — metals — and worked similar to a welding arc. “Where you’re ablating the material from the solid and turning it into what’s called a plasma — the sort of stuff you see in the sun,” she said. Professor Bilek said magnesium came out on top in their tests as the fuel with the highest specific impulse, and so the most fuel efficient. “Magnesium happens to be a light metal, which is very abundant in aerospace materials,” she said.
China’s New Space Station Will Be Powered by Ion Propulsion System, reported in 2021
China’s upcoming Tiangong space station’s first module will be equipped with an ion propulsion system which will greatly improve energy efficiency and could slash journey times to Mars, the South China Morning Post (SCMP) reports. The space station’s core Tianhe module, is propelled by four ion thrusters. According to the Chinese Academy of Sciences, the ISS’s thrusters require four tons of rocket fuel to keep it afloat for a year, whereas ion thrusters would require only 882 pounds (400kg) to do the same.
These charged particles can degrade engine components, reducing satellite longevity and possibly putting astronauts at risk. Moreover, the thrust is usually fairly low. However, the Chinese Academy of Sciences says they found a way to make it work. The Chinese scientists put the thrusters through rigorous testing to make sure the engines could resist the damage caused by the particles. By putting a magnetic field over the engine’s inner wall to repel damaging particles, they were able to protect the engine from erosion. They also developed a unique ceramic material designed to withstand severe heat or radiation for an extended period of time.m adoption has been hampered by the fact that the thrust produced isn’t very significant. Their ion thruster has reportedly run non-stop for more than 11 months without a hitch.
Ion propulsion for New space satellites
Until recently, the exploration of space had been subjected to strong political and economic constraints due to the immense costs involved. As a result, space was only accessible to countries that had the necessary financial and technological resources. The organization of space missions was the responsibility of potent space agencies such as ESA, NASA, JAXA, CNSA, ISRO, or ROSCOSMOS. The fields of activity of these agencies were manifold. As governmental institutions, they also fulfilled societal functions such as in education, as knowledge carriers, and in transferring and promoting technology. Furthermore, they developed into a large scientific, technical, and administrative apparatus.
Since the beginning of the new millennium, however, a paradigm shift, which is often referred to as “new space,” has taken place. A number of companies have emerged with the aim of carrying out space missions at a fraction of the cost spent before and accepting the risk of failure in space due to shorter development times and cheaper production. This group of companies includes Blue Origin, Rocketplane Kistler, or SpaceX, to name a few.
There are also a number of new companies in the EP sector—similar to the case of the big launchers—which are offering low-cost EP systems for satellites and competing with the incumbent companies. Many of these propulsion systems focus on smaller satellites, which are currently gaining importance, principally due to the low cost of a rocket launch facilitated by new space, e.g., in the context of mega constellations.
A test firing of Europe’s Helicon Plasma Thruster, developed with ESA by SENER in Spain. This compact, electrodeless and low voltage design is ideal for the propulsion of small satellites, including maintaining the formation of large orbital constellations. The technology has since been selected for a grant by the European Commission’s Strategic Research Cluster on Electric Propulsion, aimed at the development and verification of the HPT technology for non-geostationary satellite constellations and other small spacecraft. The result has been the new Helicon Plasma Thruster for In-Space Applications, HIPATIA, project.
NexGen Ion Propulsion System in the Works by ArianeGroup and Boeing
Boeing has signed an agreement with the Orbital Propulsion unit of Ariane Group (based in Lampoldshausen, Germany) regarding joint development of a new generation of ion propulsion systems for satellites. The system will be based on Ariane Group’s dual mode Radio frequency Ion Thruster (RIT) technology, which offers a high-thrust mode for orbital transfer manœuvres.
Thanks to its high-thrust mode for orbit-raising operations, the RIT thruster system will enable Boeing to increase payload mass while reducing time-to-orbit on its satellites. Boeing is using its experience in on-orbit electric propulsion operations to update its satellite architectures for integration of the advanced RIT propulsion system. The RIT 2X subsystem comprises the thruster itself, a high-power processing unit and a radio frequency generator. The subsystem successfully passed its preliminary design review milestone in mid-2016 and is moving towards a critical design review.
Boeing announced its investment in Accion Systems Inc., a Boston, Mass.,-based startup pioneering scalable electric propulsion technology to transform satellite capabilities in and beyond Earth’s orbit. Accion’s new Tiled Ionic Liquid Electrospray (TILE) in-space propulsion system aims to increase the lifespan and maneuverability of satellites and other vehicles in space. Leveraging a non-toxic, ionic liquid propellant and postage stamp-size thrusters, the TILE system is smaller, lighter and more cost-effective than traditional ion engines.
ISRO first Electric Propulsion Satellite
Indian Space Research Organisation (ISRO) is working to power its rockets and satellites using non-hazardous and environment-friendly fuels. In addition, the Indian space agency is also aiming to use electric propulsion for its satellites, as has been confirmed by the ISRO Chairman.
The Indian Space Research Organisation (ISRO) has started work on developing an electric propulsion system (EPS) with a higher thrust level, which can reduce the dependence on chemical propellant, the Indian government said. Unlike chemical propulsion, electric propulsion is not limited in energy and can send a spacecraft further out at a low-level thrust with very little mass.
“The EPS system was the first (trial) drone South Asia Satellite (SAS) – GSAT-9 launched in the year 2017 and is working satisfactory,” Singh added India launched a 2,195-kg, GSAT-9 or the South Asia Satellite on May 5 2017 carrying an electric propulsion or EP system, the first on an Indian spacecraft. GSAT-9’s EPS would be used to keep its functions going when it reaches its final slot – which is roughly about two weeks after launch – and throughout its lifetime. The new feature that will eventually make advanced Indian spacecraft far lighter. It will even lower the cost of launches tangibly in the near future.
M.Annadurai, Director of the ISRO Satellite Centre, Bengaluru, explained its immediate and potential benefits: the satellite will be flying with around 80 kg of chemical fuel – or just about 25% of what it would have otherwise carried. Managing it for more than a decade in orbit will become cost efficient. Dr. Annadurai said, “In this mission, we are trying EPS in a small way as a technology demonstrator. Now we have put a xenon-based EP primarily for in-orbit functions of the spacecraft. In the long run, it will be very efficient in correcting the [initial] transfer orbit after launch.”
“Using electric propulsion, we can send a four-tonne satellite, which is equivalent to a six-tonne satellite. Instead of chemical fuel, we save on weight and pack it with more transponders,” said A S Kiran Kumar, chairman of Isro. “With electric propulsion, we can add more transponders into space on our own.” In addition, it will also have a few extra years of life compared to chemical propulsion,” Jitendra Singh, Minister of State for Space, informed India’s parliament. Currently, ISRO is dependent on foreign facilities located in Ariane, French Guiana, to launch heavier satellites.
Sources told Sputnik that ISRO is striving to increase the thrust level of electronic propulsion that presently hovers at below 300 millinewtons. With this low thrust level, any spacecraft will have to wait up to 6 months to slowly reach its destination. Presently, the chemical propulsion used by the ISRO provides 440-Newton thrust, which sends the satellite to the final destination within a few days.
US Glenn Research Center leader in ion propulsion
At a recent demonstration at NASA’s Glenn Research Center in Ohio, the X3 broke several records achieved by any Hall thruster. “We have shown that X3 can operate at over 100 kW of power,” said Alec Gallimore, lead researcher and U-M’s dean of engineering, in an interview with Space.com. “It operated at a huge range of power from 5 kW to 102 kW, with electrical current of up to 260 amperes. It generated 5.4 Newtons of thrust, which is the highest level of thrust achieved by any plasma thruster to date.”
There are several types of ion thrusters and X3 is classified as a Hall thruster. A Hall thruster (also referred to as Hall-effect thruster, after discoverer Edwin Hall) uses an electric field to accelerate the propellant material. The process starts when electrons run through a circular channel and collide with atoms of a propellant (xenon is commonly used). The collisions knock electrons off and turn atoms into positively-charged ions. The process also creates a powerful electric field that pulls the plasma out of an exhaust, which in turn, generates the thrust.
Gallimore’s team though was able to address low thrust limitation with the X3: “We figured out that instead of having one channel of plasma, where the plasma generated is exhausted from the thruster and produces thrust, we would have multiple channels in the same thruster…We call it a nested channel,” Gallimore said.
NASA is involved in work on two different ion thrusters: the NASA Evolutionary Xenon Thruster (NEXT) and the Annular Engine. NEXT, a high-power ion propulsion system designed to reduce mission cost and trip time, operates at 3 times the power level of NSTAR and was tested continuously for 51,000 hours (equivalent to almost 6 years of operation) in ground tests without failure, to demonstrate that the thruster could operate for the required duration of a range of missions. In addition to flying the NEXT system on NASA science missions, NASA plans to take the NEXT technology to higher power and thrust-to-power so that it can be used for a broad range of commercial, NASA, and defense applications.
When NASA announced the Next Space Technologies for Exploration Partnerships (NextSTEP) in 2016, thrusters were one of the projects of the program. NASA Glenn’s patented Annular Engine has the potential to exceed the performance capabilities of the NEXT ion propulsion system and other electric propulsion thruster designs. It uses a new thruster design that yields a total (annular) beam area that is 2 times greater than that of NEXT. Thrusters based on the Annular Engine could achieve very high power and thrust levels, allowing ion thrusters to be used in ways that they have never been used before. The objectives are to reduce system cost, reduce system complexity, and enhance performance (higher thrust-to-power capability).
NASA granted $6.5 million over three years to California-based rocket manufacturer Aerojet Rocketdyne to fabricate two NEXT flight systems known as XR-100 (thrusters and power processors) for use on a future NASA science mission. The X3 thruster is a key component of XR-100 and U-M researchers got $1 million from that grant for their work. Known as the Advanced Electric Propulsion System (AEPS), the company recently completed a successful early systems integration test on this thruster, which will enable deep space exploration missions as well as commercial space endeavor.
The test took place at NASA’s Glenn Research Center and focused on the discharge supply unit (DSU) and the power processing unit (PPU), which were combined with a NASA-development thruster and then tested in a thermal vacuum chamber. The test proved that the system could covert power efficiently, turning solar energy into thrust while producing minimal waste heat.
Much like conventional Hall Effect thrusters, SEP relies on an electrical field to ionize and accelerate a propellant (in most cases, a noble gas like xenon). In the case of SEP, the necessary electricity is generated by photovoltaic cells (aka. solar panels). An immediate benefit of this kind of system is that it can offer thrust comparable to a conventional chemical propulsion system, but using one-tenth the propellant.
Using a 10 kW SEP thruster system and 425 kg (937 lbs) of xenon propellant, the Dawn spacecraft was able to reach a maximum speed of 41,260 km/h (mph). This most recent test involved a 13-kilowatt system, and Aerodyne plans to scale that up in the coming years. For example, a 50-kW SEP thruster system is planned for use on NASA’s proposed Lunar Orbital Platform-Gateway (LOP-G) – formerly known as the Deep Space Gateway.
The NASA Glenn Research Center has been a leader in ion propulsion technology development since the late 1950s, the NASA Solar Technology Application Readiness (NSTAR) ion propulsion system enabled the Deep Space 1 mission, the first spacecraft propelled primarily by ion propulsion, to travel over 163 million miles and make flybys of the asteroid Braille and the comet Borelly.
Russia plan to use a nuclear reactor to power an electric ion propulsion system
To scale up the operation of power-hungry electric thrusters, engineers long considered replacing heavy and bulky solar panels with nuclear power sources which could provide plenty of electricity for years if not decades and would not be dependent on solar radiation in the remote and cold regions of the Solar System, as demonstrated by planetary missions such as Voyager, Cassini and many others.
A series of photos and computer-generated imagery, which surfaced on the Internet in 2020 and originated from KB Arsenal revealed the apparent latest version and the planned operation of a very large space tug propelled by electric engines and powered by a nuclear source. The project officially known as the Transport and Energy Module, TEM, has been well known to the watchers of the Russian space program for more than a decade. Tracing its roots to the dawn of the Space Age, the TEM concept is attempting to marry a nuclear reactor with an electric rocket engine.
The heart of the TEM tug is a nuclear reactor, which generates heat. The heat is then converted into electrical power either through a mechanical turbine or via the so-called thermal emission method, which does not involve any moving parts. Though less effective than a turbine, the simpler, and more familiar to the Russian industry, thermo-emission conversion appeared to be in use aboard the TEM vehicle revealed in 2020. The excessive heat energy inevitably generated in the process of reactor work is released into space with a system of radiators, which can also use a variety of different technologies to operate in weightlessness and beyond the atmosphere.
Hall thrusters were developed by the Soviets in the 1950’s and first deployed in 1971 on a Russian weather satellite. Over 240 have flawlessly flown since, often to boost satellites into orbit and keep them there. The Russian government began the nuclear energy propulsion project back in 2010, providing over $17 million dollars as an initial investment. Anatoli Perminov, the former head of Russian space agency Roscosmos, told Interfax that “while the engine is expected to be fully assembled by 2017 the accompanying craft will not be ready before 2025.”
Nuclear energy can be used in two ways in powering propulsion systems: either its energy can be used to generate heat that is turned into energy or it may provide power directly. Russia is targeting this latter technology for development. They plan to use a nuclear reactor to power an electric ion propulsion system.
If Russia is able to harness nuclear energy to power long-duration space missions by 2025, it would give them a significant lead in the modern space race. “Nuclear energy has significant advantages for deep space missions, in which the ability to carry fuel is a limiting factor in determining a mission’s duration. Solar power can be used for extended missions within the inner Solar System, but outer system missions are too far from the Sun to make this a practical energy source,” writes Ines Hernandez
Europe ion thruster development
European research into radio-frequency Ion propulsion was initially conducted in the 1960’s by the University of Giessen, Germany. Since 1970, the Lampoldshausen team has continued with the research, development and refinement of Radio-Frequency Ion Thruster technologies, associated propulsion systems, analytical tools and techniques, processes and materials technologies. Lampoldshausen’s first Radio-frequency Ion Thruster Assembly (RITA) was successfully demonstrated in space aboard ESA’s European Retrievable Carrier EURECA, launched by the Space Shuttle Atlantis in 1992. At that time, the RIT-10 system aboard EURECA provided a nominal specific impulse of 3,058 seconds.
Scientists at the European Space Agency (ESA), Polish company QuinteScience, and Italian space company SITAEL has successfully tested an ion thruster that utilizes a method known as air-breathing electric propulsion (ABEP), or RAM electrical propulsion. That means it quite literally runs on air. ESA’s prototype works by sucking in air molecules from the top of Earth’s atmosphere. Then, it gives those molecules an electric charge and accelerates them. Finally, it ejects the ionized molecules back out into space. This ejection of ions is what causes thrust.
Besides supporting future long-distance missions, these air-powered thrusters could be superior alternatives to the thrusters that currently help satellites maintain their positioning. Those systems eventually run out of propellant and can no longer function, as was the case with the ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite.
The ESA’s ion thruster could also cut down on the weight of spacecraft, which is a constant limiting factor for launches. The GOCE satellite, for example, carried 40 kilograms (88 pounds) of xenon for propellant. Getting rid of this weight could be a significant benefit to using these thrusters.
QinetiQ has delivered four electric propulsion thrusters to the European Space Agency (ESA),that were used on the BepiColombo mission to Mercury. Reaching Mercury requires an extremely high-velocity change, which can be achieved by ion thrusters with modest propellant quantities, compared to traditional chemical thrusters. The engines are based on the T6 ion thruster model, a development from the smaller T5 used by ESA on the successful GOCE mission. These thrusters are more effective for the BepiColombo mission than the alternative Hall and chemical technologies.
Field-emission electric propulsion (FEEP)
Field-emission electric propulsion (FEEP) is an advanced electrostatic space propulsion concept, a form of ion thruster, that uses liquid metal (usually either caesium, indium or mercury) as a propellant. A FEEP device consists of an emitter and an accelerator electrode. A potential difference of the order of 10 kV is applied between the two, which generates a strong electric field at the tip of the metal surface.
The interplay of electric force and surface tension generates surface instabilities which give rise to Taylor cones on the liquid surface. At sufficiently high values of the applied field, ions are extracted from the cone tip by field evaporation or similar mechanisms, which then are accelerated to high velocities (typically 100 km/s or more).
A separate electron source is required to keep the spacecraft electrically neutral. Due to its very low thrust (in the micronewton to millinewton range), FEEP thrusters are primarily used for microradian, micronewton attitude control on spacecraft, such as in the ESA/NASA LISA Pathfinder scientific spacecraft.
Austrian startup commercializing Field Emission Electric Propulsion, or FEEP,
Enpulsion is commercializing a Field Emission Electric Propulsion, or FEEP, thruster starting with small satellites ranging from 3 to 100 kilograms, Sypniewski said. ESA and industry have studied FEEP systems for well over a decade, but with limited success getting the technology beyond the laboratory. The lure of FEEP thrusters is their ability to enable extremely precise movements or station-keeping while in space. ESA intended to use FEEP thrusters from Austria’s Fotec for the Lisa Pathfinder science mission, but production complications contributed meaningfully to the mission’s delays and ESA ultimately replaced the thrusters with more mature cold gas thrusters.
Enpulsion spun out of Fotec, a research division of the University of Applied Sciences Wiener Neustadt in Austria, to commercialize a breakthrough involving the use of a “porous tungsten crown emitter,” which Sypniewski said “provides a stable and repeatable technology that can be produced on a mass-production scale.” “We have an enormous interest from worldwide small satellite manufacturers in our product,” Alexander Reissner, Enpulsion’s founder and CEO, said in a statement. “The key to this success is the concept of clustering pre-qualified building blocks, which is made possible by our proprietary Indium-FEEP technology. It seems that our offer of providing a custom propulsion solution at a catalog price and with less than two months lead time is really hitting a nerve of the industry.”
Sypniewski said the company plans to produce 100 to 200 thrusters per year, and has 150 pre-orders from customers in Europe and the United States. Among those customers is Iceye, a Finnish synthetic aperture radar startup that is flying a cluster of Enpulsion FEEP thrusters next year.