A Guide to In-Space Electric Propulsion: Manufacturers and Products

What is Electric Propulsion (and Why Does it Matter)?

For most of space history, getting anywhere meant a violent, controlled explosion. This is the domain of chemical rockets, which burn a fuel and an oxidizer to create a massive, high-pressure plume of hot gas. This method generates enormous thrust, which is the “push” needed to escape Earth’s gravity.

But once a satellite is in space, its needs change. It no longer needs to fight gravity, but it does need to move. It may need to raise its orbit, dodge a piece of debris, or begin a decade-long journey to another planet. For these tasks, chemical rockets are wildly inefficient.

The “Gas Mileage” Problem in Space

Imagine a chemical rocket as a drag racer. It has spectacular acceleration, burning through its entire fuel tank in minutes to achieve incredible speed. This is perfect for a launch.

Electric Propulsion (EP) is the opposite. Think of it as a hyper-efficient sedan or a solar-powered car that gets thousands of miles per gallon. Its acceleration is tiny. The thrust, or “push,” from a typical electric thruster is often described as being equal to the weight of a piece of paper or a single coin resting on your hand.

You can’t use this to launch off the ground. But in the vacuum of space, where there is no friction or air resistance, a tiny, continuous push has an enormous effect. If you gently push a bowling ball in a frictionless hallway for a few seconds, it moves slowly. If you gently push it continuously for the entire length of a mile-long hallway, it will be moving at a very high speed by the end.

This is the principle of electric propulsion. It’s a “low-thrust, high-efficiency” system. The key metric is Specific Impulse Isp, which is the rocket-science equivalent of “miles per gallon.”

• Chemical Rockets: High thrust, low Isp (typically 300-450 seconds). They are propellant-hungry.
• Electric Thrusters: Very low thrust, very high Isp (typically 1,500 to over 10,000 seconds). They are propellant-sippers.

How Electric Propulsion Works (The Simple Version)

All rockets work by throwing mass out the back at high speed. Newton’s Third Law (for every action, there is an equal and opposite reaction) does the rest.

A chemical rocket creates its own mass by burning propellants into a hot gas, which it shoots out a nozzle at high speed.

An electric thruster brings a tank of propellant with it, usually an inert (non-reactive) gas like xenon or krypton. It doesn’t burn it. Instead, it uses electricity, almost always generated by the spacecraft’s solar panels, to accelerate that gas.

The core of the technology involves turning the propellant atoms into “ions.” An ion is just an atom that has had one or more of its electrons knocked off, leaving it with a positive electrical charge. Once the atom is charged, it’s no longer neutral – it can be controlled and “pushed” by electric and magnetic fields.

An electric thruster uses these fields to grab the ions and accelerate them to truly extreme speeds – tens of thousands of miles per hour – before shooting them out the back. Each individual ion has almost no mass, so the push is tiny. But the speed at which they are expelled is so high that the process is incredibly efficient.

The Benefits: More Mission for Less Mass

This efficiency is the whole point. Propellant is mass, and in space, mass is everything. Every kilogram of propellant you need has to be launched on a rocket, which costs millions of dollars. If an electric thruster is 10 times more efficient than a chemical one, the satellite can carry 10 times less propellant to do the same job.

This has several benefits:

1. Cheaper Launches: A satellite with less propellant mass can be launched on a smaller, cheaper rocket.
2. More Payload: For the same launch rocket, a satellite using EP can dedicate its “saved” mass to more valuable things, like more communications transponders, bigger science instruments, or a larger telescope.
3. Longer Life: With the same amount of propellant, the satellite can operate for many more years, performing station-keeping maneuvers (fighting drag) or moving around.
4. New Missions: EP enables missions that are simply impossible with chemical rockets. NASA’s Dawn mission, for example, orbited two separate asteroid belt objects, Vesta and Ceres. A chemical rocket could never have carried enough fuel to blast from one orbit to the next. Dawn‘s ion engines pushed gently for years to make the journey.

This is why the EP market has exploded. The rise of large satellite constellations in low Earth orbit (LEO), like Starlink, would not be economically feasible without cheap, mass-producible electric thrusters to handle orbit-raising, drag compensation, and end-of-life de-orbiting.

The Different Flavors of Electric Propulsion

“Electric Propulsion” is a broad category. The main families are defined by how they use electricity to accelerate the propellant.

Electrothermal Thrusters

This is the simplest form of EP. It uses electricity simply to heat the propellant, which then expands and escapes through a nozzle, just like a tiny, conventional rocket.

• Resistojets: Imagine a tea kettle. Electricity runs through a simple resistive heating element, which gets red hot. Propellant gas (like hydrazine) passes over this element, gets extremely hot, and expands, providing thrust. They are more efficient than a simple cold-gas thruster but are the lowest-performing EP type. They are reliable and often used for small attitude-control maneuvers.
• Arcjets: Imagine a tiny welder. Instead of a heating coil, an arcjet strikes a high-energy electric arc (like a bolt of lightning) directly through the propellant gas. This superheats the gas to a plasma state, creating higher exhaust speeds and better efficiency than a resistojet.

Electrostatic Thrusters (Gridded Ion Engines)

This is the high-efficiency champion. These are the engines used on deep-space science missions like Dawn and BepiColombo. They are complex but achieve the highest “gas mileage” (Isp).

Here’s the process:

1. Ionization: Propellant (usually xenon) is fed into a chamber. Electrons are shot into the chamber, colliding with the xenon atoms and knocking off their electrons. This creates a cloud of positively-charged xenon ions (a plasma).
2. Acceleration: At the end of the chamber are two or three “grids,” which are thin metal screens with thousands of tiny, perfectly-aligned holes. A very high positive voltage is applied to the inner grid, and a high negative voltage is applied to the outer grid.
3. The positive ions are repelled by the positive inner grid and intensely attracted to the negative outer grid. They accelerate rapidly toward the grids, shooting through the aligned holes and exiting the thruster at speeds up to 90,000 mph.
4. Neutralization: A small device called a “neutralizer” or “cathode” sits at the exit and shoots a stream of electrons into the exiting ion beam. This is essential. If the spacecraft only shot out positive ions, the ship itself would build up a negative charge, and eventually, the positive ions would be attracted back to the ship, killing the thrust. The neutralizer makes the exhaust beam electrically neutral.

Electromagnetic Thrusters (Hall Thrusters)

This is the most popular type of thruster used on commercial satellites today. Hall-effect thrusters (HETs) are the perfect “sweet spot”: they offer much better Isp than chemical rockets and much more thrust than a gridded ion engine. This means they can get the job done (like moving a satellite from its launch orbit to its final geostationary orbit) much faster than an ion engine.

A Hall thruster works by creating an “electron trap”:

1. The Chamber: The thruster has a circular, ceramic-lined channel. A large anode is at the back of the channel, and a neutralizer cathode is at the outside opening.
2. The Electron Trap: A powerful magnetic field is applied across the channel. When the thruster fires, the cathode shoots electrons toward the anode at the back. However, the magnetic field is so strong that the electrons can’t fly straight. They are trapped, forced to swirl around the channel in a high-speed, dense cloud.
3. Ionization & Acceleration: Propellant gas (xenon or krypton) is injected from the anode. As the neutral propellant atoms drift into the swirling electron cloud, the electrons slam into them, knocking off their electrons and creating positive ions.
4. These new positive ions are now “born” inside a powerful electric field (between the positive anode at the back and the electron cloud at the front). They are immediately and powerfully accelerated out of the channel at high speed, creating thrust. The trapped electrons, in effect, act as the “grid” that an ion engine needs.

A key innovation for Hall thrusters is “magnetic shielding.” In older designs, high-energy ions would slam into the ceramic channel walls, eroding them over time. Modern thrusters use carefully-shaped magnetic fields to protect the walls, ensuring the ions never touch them. This has extended the operational lifetime of Hall thrusters from thousands of hours to tens of thousands of hours.

Other Emerging Technologies

• Field-Emission Electric Propulsion (FEEP) / Electrospray: These thrusters are designed for tiny satellites, like CubeSats, that need incredibly precise, microscopic adjustments. They work by applying an intense electric field to a liquid propellant, usually an “ionic liquid” (a type of liquid salt). The field is so strong that it literally pulls individual ions or tiny charged droplets directly from the liquid’s surface and accelerates them.
• RF Thrusters: Radio-Frequency (RF) thrusters use radio waves, similar to a microwave, to energize the propellant and create a plasma. They often don’t need the cathode neutralizer, which is a common life-limiting component in other designs. This makes them potentially simpler and more robust.
• Variable Specific Impulse Magnetoplasma Rocket (VASIMR): This is a high-power concept being developed by Ad Astra Rocket Company. It’s a three-stage process: it uses RF waves to create the plasma, more RF waves to heat it to millions of degrees (hotter than the sun’s surface), and then a magnetic “nozzle” to accelerate it. Its unique feature is the ability to act like a “gear shifter” in space – it can be tuned for high thrust (low Isp) to get moving quickly, or for low thrust (high Isp) for efficient cruising. It requires an enormous amount of power, likely from a dedicated in-space nuclear reactor.

The table below provides a simple comparison of these different technologies.

The Major Players: Legacy and Large-Scale Manufacturers

The electric propulsion market is dominated by a few large, established aerospace and defense contractors who have supplied high-power systems for decades. They are known for their extensive flight heritage and ability to deliver complex systems for large government and commercial satellites.

Aerojet Rocketdyne (an L3Harris Technologies company)

A giant in American propulsion, Aerojet Rocketdyne has roots stretching back to the Apollo program. While famous for its chemical engines, it’s also a world leader in electric propulsion.

• Key Technologies: Gridded Ion Engines and high-power Hall thrusters.
• Products & Missions:
  • NSTAR: This is the gridded ion engine that made history. Aerojet Rocketdyne built the NSTAR thruster for NASA’s Jet Propulsion Laboratory, which powered the Deep Space 1 mission (launched in 1998) and the Dawn asteroid orbiter. It was a complete validation of ion propulsion for interplanetary science.
  • NEXT-C: The successor to NSTAR, “NASA’s Evolutionary Xenon Thruster – Commercial.” This is a larger, more powerful, and more efficient gridded ion engine. It was successfully demonstrated on NASA’s DART (Double Asteroid Redirection Test) mission, which famously impacted the asteroid Dimorphos. NEXT-C provided the long, gentle push to get the spacecraft on its intercept course.
  • AEPS (Advanced Electric Propulsion System): This is one of the most powerful Hall thruster systems ever built. Developed with NASA’s Glenn Research Center, the 13-kilowatt AEPS thruster is a cornerstone of NASA’s Artemis program. A cluster of these thrusters will be the primary engines for the Power and Propulsion Element (PPE) of the Gateway, the new lunar space station. They will maneuver the station in lunar orbit and provide power for its systems.
  • XR-5: This is the company’s workhorse Hall thruster for commercial satellites. It’s a 5-kW class engine that has flown on numerous commercial geostationary (GEO) satellites, using EP to raise their orbit and handle station-keeping for 15+ years.

Northrop Grumman

Another American aerospace and defense behemoth, Northrop Grumman (which acquired Orbital ATK) has a long history in spacecraft manufacturing and solid rocket motors. It also produces electric propulsion systems, often for its own line of commercial satellites.

• Key Technologies: Hall thrusters and electrothermal resistojets.
• Products & Missions:
  • GEOStar Satellites: Northrop Grumman is a major builder of commercial communications satellites, such as its GEOStar bus. Many of these satellites use the company’s own Hall thruster systems for orbit-raising and station-keeping.
  • Resistojets: The company has a long heritage of providing smaller, simpler electrothermal resistojets. These are a flight-proven, reliable option for attitude control (making small adjustments to a satellite’s pointing direction) and are used on many different government and commercial spacecraft.
  • Gateway PPE Contribution: Like Aerojet Rocketdyne, Northrop Grumman is a prime contractor for the Gateway’s Power and Propulsion Element (PPE). While Aerojet provides the thrusters, Northrop Grumman is responsible for the spacecraft bus itself, including its structure, propellant tanks, and power distribution.

Safran Spacecraft Propulsion

Based in France, Safran is a global leader in aircraft and rocket engines. Its space propulsion division is arguably the most dominant force in the commercial Hall thruster market.

• Key Technologies: Hall Thrusters (Plasma Propulsion Systems).
• Products & Missions:
  • PPS-1350: This 1.5-kW Hall thruster is one of the most successful and flight-proven electric thrusters in history. It famously powered the European Space Agency (ESA)‘s SMART-1 mission, which spiraled out from Earth to orbit the Moon from 2003 to 2006, proving the viability of EP for lunar missions. It has since been used on dozens of commercial telecommunications satellites.
  • PPS-5000: This is the more-powerful 5-kW version, designed for the “all-electric” satellite revolution. All-electric satellites use EP for 100% of their post-launch propulsion, including the very long (months-long) but very efficient trip from their initial drop-off orbit to their final geostationary orbit. This saves thousands of kilograms of propellant. The PPS-5000 is a flagship product used by major satellite operators worldwide.
  • Starlink: While SpaceX builds many components in-house, its first-generation Starlink satellites were notable for being one of the first megaconstellations to use Hall thrusters. These thrusters use krypton instead of the more expensive xenon, a key cost-saving measure. Safran’s technology and expertise in this area were foundational, and SpaceX’s in-house thrusters were developed from this heritage.

Thales Alenia Space

Thales Alenia Space is a Franco-Italian joint venture and a major satellite manufacturer, competing directly with Northrop Grumman, Airbus, and Maxar Technologies. It often partners with Safran on propulsion but also develops its own technologies.

• Key Technologies: Hall Thrusters.
• Products & Missions:
  • Spacebus NEO Platform: This is Thales’s modern, all-electric satellite platform. It relies entirely on electric propulsion for orbit-raising and station-keeping and is often equipped with either the Safran PPS-5000 or Thales’s own HEMPT thrusters.
  • HEMPT (High-Efficiency Multistage Plasma Thruster): Developed by Thales in Germany, the HEMPT is an alternative Hall thruster design. It uses a unique magnetic field configuration that proponents say offers very high efficiency and an extremely long lifespan by minimizing wall erosion.
  • BepiColombo: Thales was the prime contractor for the ESA, building the BepiColombo spacecraft that is currently on its way to Mercury. The spacecraft’s solar-electric propulsion module uses two powerful T6 gridded ion engines, built by the UK company QinetiQ. This mission is a testament to the power of ion propulsion for the most demanding deep-space journeys.

The New Wave: Specialized and Smallsat Propulsion Companies

The satellite industry has been completely reshaped by the “smallsat” revolution. The rise of CubeSats (satellites built in 10-cm units) and constellations of small, 100-500 kg satellites has created a brand new market. These satellites can’t use the large, power-hungry engines from the legacy players. They need tiny, low-power, and – most importantly – cheap and mass-producible propulsion systems.

This demand has fueled a new generation of innovative startups, each with a different technical approach to solving the smallsat propulsion problem.

Busek Co. Inc.

Based in Massachusetts, Busek is a US research and development company that has been a quiet innovator for decades. It’s often the “skunkworks” behind many advanced government projects.

• Key Technologies: Busek develops almost everything: Hall thrusters, gridded ion engines, and electrospray thrusters.
• Products & Missions:
  • BHT-series Hall Thrusters: Busek has a wide range of Hall thrusters. A BHT-200 thruster was used on NASA’s LISA Pathfinder mission. They are also providing 6-kW Hall thrusters for the Gateway PPE, alongside Aerojet Rocketdyne’s AEPS.
  • BIT-3 Ion Engine: This is a small, 3-cm gridded ion engine. One of these flew on the LISA Pathfinder mission, where it was used as a micro-propulsion system to make incredibly fine, non-vibrating adjustments to the spacecraft’s position, a test for future gravitational wave observatories.
  • Electrospray: Busek is also a leader in electrospray technology, providing tiny thrusters for CubeSats that require precision pointing.

Phase Four

A California-based startup, Phase Four’s entire identity is built around a single, disruptive idea: getting rid of the cathode.

• Key Technologies: Radio Frequency (RF) Plasma Thruster.
• Products & Missions:
  • Maxwell: This is Phase Four’s flagship product. It’s a “cathodeless” thruster. Instead of using a cathode (a sensitive, life-limiting component) to generate electrons, Maxwell uses RF antennas to beam energy into the propellant, turning it into a plasma. The company argues this “electdeless” design is far simpler, more reliable, and easier to manufacture in large volumes. It also claims the technology is more “propellant-agnostic,” meaning it could one day run on propellants other than xenon. It has been successfully flown on several commercial smallsats.

Exotrail

This French startup has a holistic business model. It doesn’t just sell thrusters; it sells mobility.

• Key Technologies: Miniaturized Hall thrusters and orbital transfer services.
• Products & Missions:
  • ExoMG Hall Thrusters: A family of small, low-power Hall thrusters specifically designed for the smallsat market (from 10 kg to 250 kg satellites). They are compact, modular, and designed for mass production.
  • spacevan: This is Exotrail’s “space tug” or Orbital Transfer Vehicle (OTV). A spacevan is a small, self-propelled spacecraft that launches on a large SpaceX rideshare mission. It carries a “manifest” of smaller customer CubeSats. After the rocket drops everyone off in a generic orbit, the spacevan uses its own ExoMG thrusters to taxi the CubeSats to their precise, custom orbits. This “last-mile delivery” service is a new and growing part of the space economy.

Enpulsion

An Austrian company, Enpulsion has rapidly become a dominant player in the CubeSat market with its unique take on FEEP technology.

• Key Technologies: Field-Emission Electric Propulsion (FEEP) using a liquid metal propellant.
• Products & Missions:
  • IFM Nano: This is Enpulsion’s breakthrough product. It’s a tiny, coffee-mug-sized thruster that uses indium as propellant. The indium is kept solid, heated into a liquid, and then its ions are extracted and accelerated using the FEEP process.
  • Innovation: Enpulsion’s real innovation is its manufacturing. It was one of the first companies to design its thrusters for mass production, with a clean, modular design. This allowed it to service the growing constellation market, and its thrusters have been selected for numerous CubeSat missions, including by OneWeb.

Accion Systems

A Boston-based company spun out of MIT, Accion has a different approach to electrospray.

• Key Technologies: TILE (Tiled Ionic Liquid Electrospray).
• Products & Missions:
  • TILE Thrusters: Accion’s systems use a safe, non-toxic, non-pressurized “ionic liquid” as propellant. Their thrusters are not tiny engines but flat, postage-stamp-sized chips covered in microscopic emitters.
  • Modularity: The “Tiled” name is the key. A satellite designer can “tile” these chips together. Need a little thrust? Use two chips. Need more? Use eight. This Lego-like modularity offers extreme design flexibility. The TILE systems have flown on several demonstration missions and are providing propulsion for satellites in LEO.

ThrustMe

Another French innovator, ThrustMe made history by solving one of the biggest economic and logistical problems in electric propulsion: the propellant.

• Key Technologies: Iodine-fueled electric propulsion.
• Products & Missions:
  • NPT30-I2: This is a gridded ion thruster system, but with a revolutionary twist. Instead of using xenon – which is rare, expensive, and must be stored in heavy, high-pressure tanks – it uses iodine.
  • Why Iodine is a Big Deal: Iodine is cheap and abundant. More importantly, it’s solid at room temperature. It can be stored as a dense, inert solid block (like a bar of soap) with no high-pressure tank needed. When the thruster needs to fire, it just gently heats the iodine, which sublimates directly into a gas, ready for ionization. This radically simplifies the satellite design, saving mass, volume, and cost. ThrustMe was the first company in the world to successfully demonstrate an iodine thruster in space, and the technology is now being widely adopted.

Momentus

Momentus is a US company that, like Exotrail, is focused on the “space tug” business model, enabled by a unique and very “green” propulsion technology.

• Key Technologies: Microwave Electrothermal Thruster (MET) using water as propellant.
• Products & Missions:
  • MET: The Momentus engine uses plain water. It injects water vapor into a chamber and then blasts it with microwaves, heating it into a plasma and expelling it for thrust. Water is the ultimate “green” propellant: it’s cheap, abundant, safe to handle, and stable.
  • Vigoride: This is the company’s orbital transfer vehicle, which uses the water-based MET. Vigoride is designed to provide “last-mile” delivery services, carrying customer satellites from a main rocket’s drop-off point to their final destinations. The company has flown several Vigoride missions.

Bellatrix Aerospace

An Indian company, Bellatrix highlights the global nature of the NewSpace propulsion market. They are developing a full suite of propulsion systems.

• Key Technologies: Microwave Plasma Thrusters and Hall thrusters.
• Products & Missions:
  • Microwave Plasma Thruster: Similar to Phase Four’s concept, Bellatrix is developing a thruster that uses microwaves to create the plasma, aiming for high reliability and a long lifetime.
  • Hall Thrusters: The company also has a line of more conventional Hall thrusters and is developing its own Sagar orbital transfer vehicle, showing that the “space tug” model is a worldwide trend.

Rocket Lab

Known primarily for its Electron rocket and Rutherford chemical engines, Rocket Lab has quietly become a major player in satellite components and propulsion.

• Key Technologies: Hall thrusters and chemical propulsion for its satellite bus.
• Products &Missions:
  • Photon: This is Rocket Lab’s satellite bus, or “chassis.” It’s an all-in-one package (power, communications, propulsion) that customers can buy to build their satellite around. Photon is designed for flexibility. While some versions use the company’s chemical Curie engine for rapid maneuvers, the Interplanetary Photon models designed for deep space missions (like the CAPSTONE mission to the Moon) have been equipped with third-party Hall thrusters. Rocket Lab has also been developing its own in-house Hall thruster systems to bring this capability under its own roof, recognizing its importance for future missions.

The Market Landscape and Future Trends

The in-space propulsion market is split. The “legacy” market is driven by high-value, billion-dollar GEO satellites and government science missions. The “new” market is driven by the sheer volume of small satellites and constellations.

The Rise of Satellite Constellations

This is the single biggest driver of the electric propulsion industry. Megaconstellations like Starlink, OneWeb, and Amazon’s Project Kuiper require thousands of satellites, each of which needs its own engine.

These satellites are in low Earth orbit, where there is still a tiny amount of atmospheric drag. Without propulsion, they would fall back to Earth in a few years. EP is essential for:

1. Orbit Raising: Moving from the low launch orbit to the higher operational orbit.
2. Station Keeping: Firing the thruster periodically to counteract drag and stay in the correct orbit.
3. Collision Avoidance: Maneuvering to dodge space debris or other satellites.
4. De-orbiting: At the end of its life, the satellite must use its thruster to safely lower its orbit and burn up in the atmosphere, preventing it from becoming dangerous space junk.

This has created a need for “assembly line” production of thrusters, moving away from the old model of building a few exquisite, hand-built engines per year.

The “Last-Mile” Economy

The “space tug” or Orbital Transfer Vehicle (OTV) model, pursued by companies like Exotrail and Momentus, is a direct result of efficient EP. Rideshare rockets are cheap but drop all their passengers at the same “bus stop.” An OTV powered by a Hall thruster or MET can then efficiently deliver each satellite to its precise, custom orbit, a service many satellite operators are willing to pay for.

The Search for New Propellants

Xenon, the historic propellant of choice, is rare and its price is volatile (it’s also used in medical imaging and semiconductor manufacturing). This has driven a massive R&D push for alternatives:

• Krypton: Cheaper than xenon, but less efficient. SpaceX’s use of it for Starlink proved it was “good enough” for a LEO constellation.
• Iodine: The game-changer from ThrustMe. It’s solid, dense, and cheap.
• Water: The “green” option from Momentus.
• Argon: Another noble gas that is very cheap and abundant, but more difficult to ionize. It’s a key area of research for next-generation, high-power thrusters.

Summary

Electric propulsion has evolved from a niche, experimental technology for exotic science missions into the backbone of the modern space industry. It is the key enabling technology that makes satellite megaconstellations economically viable, extends the life of commercial satellites by years, and opens up the solar system to new, complex exploration.

The market is defined by a healthy tension between established aerospace giants and a vibrant, fast-moving startup scene. Legacy companies like Aerojet Rocketdyne and Safran continue to push the boundaries of high-power systems for flagship missions like the Gateway. At the same time, innovators like ThrustMe, Phase Four, and Enpulsion are radically redesigning the thruster itself – using new propellants, new manufacturing methods, and new physics – to serve the explosive demand for smallsats. Together, they are building the engines for a new, mobile, and permanent economy in space.