Ion Thrusters: Science Fiction or the Future of Spaceflight?

(Star Wars Fandom, n.d.)

Blazing fast speeds, luminous neon-blue light, and near-perfect efficiency, features once confined to science fiction, but now approaching reality. Thanks to recent technological advances, ion thrusters are now used in modern space missions. Will ion propulsion redefine the future of space travel, or will combustion rockets continue to set the stage?

How Do Ion Thrusters Function?

Firstly, it is essential to clarify that Ion thrusters do not operate in the same manner as their fictional counterparts, which are often depicted as delivering immediate and extreme speeds. Instead, ion propulsion systems are most notably characterized by their very low thrust but exceptionally high efficiency (GlobalSpec Insights, n.d.).

The ion thruster—more specifically, the gridded ion thruster—produces thrust by ejecting ions, which are charged atoms or molecules, at extremely high exhaust velocities. These ions are created by generating a plasma inside the engine, where a neutral gas propellant—most commonly xenon—is bombarded with electrons. This process causes atoms to lose electrons and form positively charged ions. Although the plasma contains both free electrons and positive ions, it remains electrically neutral overall. To generate thrust, the positive ions are extracted and accelerated through a set of charged grids at the rear of the engine; electrons remain inside the chamber to sustain further ionization. As the ions pass through the grids, a high electric potential accelerates them into space at velocities of up to 90 km/s, producing thrust (Fraser Cain, 2018).

Gridded Ion Thruster Diagram (Anthony, 2012)

At first, the high exhaust velocity of ions may sound significant. However, according to Newton’s third law of motion—for every action there is an equal and opposite reaction—the amount of thrust produced depends on both velocity and mass flow rate. Because individual ions have such minuscule mass, even when expelled at very high speeds, the resulting force on the spacecraft is very low. Rather than delivering a large, instantaneous push like a combustion rocket, ion thrusters produce many tiny but continuous impulses, allowing spacecraft to gradually build up speed over long periods of time (cite).

Present Day Status

Historically, gridded ion thrusters were the standard form of ion propulsion. However, over time, advances in technology have led to the development of more modern Hall-effect thrusters. Unlike former gridded designs, Hall thrusters do not rely on physical acceleration grids, eliminating the issue of grid erosion and significantly increasing operational lifespan (Science Workshop, 2023; Princeton Plasma Physics Lab, n.d.).

Hall-effect Ion Thruster Diagram (Princeton Plasma Physics Lab, n.d.)

Similar to gridded ion thrusters, Hall-effect thrusters use a neutral propellant. However, they incorporate an external hollow electron cathode, often referred to as an electron “gun,” which supplies electrons to ionize the propellant and neutralize the exhaust plume. Inside the thruster, strong magnetic fields—up to 500 times stronger than Earth’s magnetic field—trap electrons in a rapid circulating motion around the channel, occurring at frequencies of up to one million times per second. This confinement significantly increases the number of collisions between electrons and the neutral propellant, resulting in the production of a greater number of ions and, consequently, increased thrust. Electrons that lose momentum through collisions are collected by the anode at the back of the thruster before being replenished by the external electron cathode (Science Workshop, 2023)

Currently, NASA has deployed Hall-effect thruster technology across multiple space missions, most recently on the Psyche spacecraft. The aircraft employs solar electric propulsion, where solar panel-generated electricity powers its Hall-effect thrusters, and is equipped with four Hall-effect thrusters that accelerate ionized xenon using electromagnetic fields, producing a faint blue exhaust plume. Although only one thruster operates at a time, it can generate up to 240 millinewtons of thrust. To put that into perspective, that is equivalent to the force felt when holding a single AA battery. To sustain propulsion over its multi-year journey, Psyche carries large reserves of xenon propellant, allowing it apply continuous, efficient thrust for an extended period of time (NASA Science, 2025)

Compared to gridded ion thrusters, Hall-effect thrusters prioritize higher thrust output at the expense of some efficiency, making them better suited for missions that require more practical maneuvering over long durations. In contrast, gridded ion engines focus on maximizing efficiency and exhaust velocity rather than thrust. This distinction highlights how different ion propulsion architectures are optimized for specific mission requirements rather than representing differences in technological maturity (NASA Science, 2025).

While these capabilities are impressive, ion engines are currently confined to the vacuum of space. Their extremely low thrust, the requirement for a near-vacuum—since collisions between expelled ions and air molecules drastically reduce efficiency—their poor power-to-thrust ratio, and their inability to lift off from Earth without the assistance of combustion rockets make ion propulsion impractical for atmospheric flight or launch.

Ion vs Combustion Thrusters

(University of Michigan, n.d.; Szondy, 2018; Tesla Oracle, 2025)

Combustion and ion propulsion systems differ fundamentally in how they produce thrust and where they are most effective. Combustion rocket engines, such as SpaceX’s Raptor 3, generate thrust through combustion, producing forces upwards of around 2.75 million Newtons, which makes them indispensable for launching spacecraft and rapid maneuvers. In contrast, ion propulsion systems—such as the SPT-140 Hall-effect thruster used on NASA’s Psyche mission or the NEXT gridded ion thruster—operate using electrical power from solar panels to accelerate ionized xenon, producing thrust measured in only hundreds of milinewtons. (SPT-140: ~240 mN, NEXT: ~236 mN) (NASA, n.d.-b; NASA, n.d.-a; SpaceX, n.d.).

Since ion thrusters accelerate charged particles rather than combustion, ion thrusters cannot launch spacecraft from earth, and are instead used exclusively in space—this is due to their minimal acceleration even with low mass spacecraft, some achieving 0-100km/h in a span of 4 straight days of continuous acceleration—where their low thrust can gradually build up speed over long periods. Despite this, ion thrusters offer a substantial advantage in efficiency against combustion rockets, enabling them to deliver 90% efficiency, while their combustion counterparts only achieving 35% (Fraser Cain, 2018). This allows ion thrusters to produce more acceleration for the same amount of fuel, where this efficiency is ideal for long-term thrust missions (such as deep space probes and satellite station-keeping) (Space Voyage Ventures, 2025).

Another key difference is operational lifespan. Tests have shown that ion thrusters, much like NASA’s Next engine, demonstrate continuous operation over 48000 hours (~5.5 years) without failure, setting records for endurance in propulsion testing (Tillman, 2013). Further solidifying ion thrusters’ dominance in sustained-thrust space missions. In contrast, combustion rockets are typically designed for short, high-intensity burns, many of which do not even last over a few minutes (NASA, 1966/1975)

Future Possibilities and What to Expect

To increase the thrust produced by ion thrusters, a dramatic increase in available electrical power is required. NASA has explored this challenge in the past. Early plans for the Jupiter Icy Moons Orbiter (JIMO) mission in 2005 proposed the application of nuclear power to drive high-power ion thrusters, replacing solar panels. Although the mission never progressed beyond early planning stages, the concept highlighted the potential of nuclear-powered electric propulsion to provide vastly greater electrical output without sacrificing operational lifespan, given the long endurance of nuclear systems. More recent proposals have also suggested hybrid designs that combine solar and nuclear power, aiming to balance power availability and mission longevity (NASA Technical Reports Server, 2012).

X3 Nested Channel Hall Thruster (University of Michigan, n.d.)

Advances in thruster design further demonstrate this potential. One notable example is the X3 Nested-Channel Hall Thruster, capable of delivering up to 5.4 newtons of thrust—a substantial increase compared to traditional ion thrusters that typically produce thrust measured in millinewtons. While this represents a major step forward for electric propulsion, the X3 has yet to be flown on an operational mission due to its extreme power demands. Whereas most spacecraft can supply only 1-20 kilowatts of electrical power, the X3 requires approximately 100 kilowatts, necessitating either massive solar arrays or a compact nuclear reactor (University of Michigan, n.d.).

Despite these promising developments, several challenges remain. In the vacuum of space, heat dissipation becomes a major issue, as the absence of air prevents convective cooling, causing heat to accumulate within spacecraft systems. Additionally, although modern Hall-effect thrusters reduce wear compared to gridded ion engines, thruster erosion and long-term lifespan under sustained high-power operation are still active areas of testing and research. Until these issues are fully resolved, high-power ion propulsion will remain limited to experimental and specialized missions rather than widespread adoption.

Conclusion 

To answer the question of whether ion propulsion will redefine the future of space travel, or whether combustion rockets continue to set the stage, is that both technologies will play their very own crucial and complementary roles. Combustion rockets remain essential for launch and rapid maneuvers due to their immense thrust; ion propulsion offers unmatched efficiency and long-duration acceleration, making it ideal for deep-space exploration and precise orbital adjustments. As technology advances—through higher-power thrusters, hybrid energy sources, and improved lifespans—ion engines are likely to take on an increasingly prominent role in interplanetary missions, gradually expanding the possibilities of what spacecraft can achieve.

References

Anthony. (2012, December). NASA’s NEXT ion drive breaks world record, will eventually power interplanetary missions. ExtremeTech. https://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

Fraser Cain. (2018, May 16). How do ion engines work? The most efficient propulsion system out there [Video]. YouTube. https://youtu.be/6H0qsqZjLW0?si=xMMzxzNDbgVOqkKF

GlobalSpec Insights. (n.d.). Ion thrusters: Ultra-efficient high-speed spacecraft propulsion. https://insights.globalspec.com/article/10010/ion-thrusters-ultra-efficient-high-speed-spacecraft-propulsion

NASA. (1966/1975). Rocketdyne J‑2 engine. NASA History Office. https://en.wikipedia.org/wiki/Rocketdyne_J-2

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NASA Science. (n.d.). Psyche spacecraft. https://science.nasa.gov/mission/psyche/spacecraft

NASA Technical Reports Server. (2012). NEXT ion propulsion system: Final report (NASA/CR-20120016895). https://ntrs.nasa.gov/api/citations/20120016895/downloads/20120016895.pdf

New Atlas. (2018, January 26). BepiColombo Mercury mission to use ion thrusters. https://newatlas.com/bepicolombo-mercury-ion-thruster/56878/

Princeton Plasma Physics Lab. (n.d.). Electric thrusters. https://htx.pppl.gov/thrusters.html

Science Workshop. (2023, July 14). How Hall Effect Thrusters REALLY work (Step-by-Step) [Video]. YouTube. https://youtu.be/OHRS2pbOGhc?si=9-RK8h2CruzEz8Qe

Space Voyage Ventures. (n.d.). Ion drives. https://spacevoyageventures.com/ion-drives

SpaceX. (n.d.). Raptor engine. Wikipedia. https://en.wikipedia.org/wiki/SpaceX_Raptor

Star Wars Fandom. (n.d.). Destroyer Ion Engine. https://starwars.fandom.com/wiki/Destroyer_Ion_Engine

Tesla Oracle. (2024, August 10). SpaceX fires the Raptor 3 engine for the first time. https://www.teslaoracle.com/2024/08/10/spacex-fires-the-raptor-3-engine-for-the-first-time-and-silences-the-critics

University of Michigan. (n.d.-a). 9-kW magnetically shielded Hall thruster. https://pepl.engin.umich.edu/project/9-kw-magnetically-shielded-hall-thruster/

University of Michigan. (n.d.-b). X3 nested-channel Hall thruster. https://pepl.engin.umich.edu/project/x3-nested-channel-hall-thruster

Wall, M. (2012, February 9). NASA’s ion thruster sets world record for continuous operation. Space.com. https://www.space.com/22916-nasa-ion-thruster-world-record-test.html