Electric space propulsion

Also known as Electric propulsion, Ion propulsion, Ion thrusters, Hall-effect thrusters, Solar electric propulsion

Electric space propulsion uses electrical power, usually from solar arrays, to accelerate a gas such as xenon out of a spacecraft. It uses far less propellant than chemical rockets for the same change in speed, but its thrust is very small, so it works over months or years.

CommercialDemonstratedReviewed 22 Oct 2026
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

In plain language

A chemical rocket pushes a spacecraft by burning fuel very quickly. It gives a strong push for a short time and uses a lot of fuel. Electric propulsion works the other way round. Solar panels supply electricity that turns a small amount of gas into charged particles, and electric fields then throw those particles out of the back of the spacecraft at very high speed. Each particle carries little momentum, so the push is gentle.

That gentle push is the trade-off. Because the gas leaves so fast, a small amount of propellant can change a spacecraft's speed by a large amount over time. NASA's Deep Space 1 used a xenon ion engine that ran for more than 16,000 hours and consumed more than 70 kg of xenon. Dawn used ion engines to move between two large bodies in the asteroid belt, and BepiColombo uses them to reach Mercury.

Technical explanation

Electric thrusters ionise a propellant, usually xenon, and accelerate the ions with an electric field. Thrust equals the mass flow rate of propellant multiplied by its exhaust velocity. Because the same impulse needs much less propellant when the exhaust is faster, electric propulsion has a high specific impulse. The cost is that the power needed for a given thrust is large, so the thrust is small. ESA gives an exhaust velocity of 50,000 m/s for the T6 ion thrusters on BepiColombo, which it describes as 15 times greater than conventional chemical rocket thrusters. The same thruster has a maximum thrust of 250 mN.

Two main families are flown. Gridded ion thrusters accelerate ions through a set of electrically biased grids. Hall-effect thrusters use a radial magnetic field to trap electrons in an annular channel, which ionises the propellant and produces the accelerating field. The 2001 NASA Glenn report on Deep Space 1 describes a xenon ion engine rated at 2.3 kW that provided primary propulsion and two-axis attitude control. Dawn used three ion engines with a maximum engine power of 2,500 W, according to DLR's mission description.

The main engineering limits are power, propellant and lifetime. Thrust-to-power is low, so spacecraft need large solar arrays. BepiColombo has twin 15 m solar arrays. Xenon costs more than krypton and its supply is limited, and ESA identifies xenon availability as a key issue for mega-constellations. Krypton is cheaper, but a 2019 Spaceflight Now report says it gives less thrust efficiency. ESA runs the ARTES AT Kr project to develop krypton-operated thrusters for that market.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Demonstrated Shown in a published experiment, test or shipping product.

Deep Space 1's 2.3 kW xenon ion engine provided primary propulsion and two-axis attitude control, operated for more than 16,000 hours and consumed more than 70 kg of xenon propellant.

Sources: [1] · Article text

Deep Space 1 launched from Cape Canaveral on 24 October 1998 to test 12 advanced, high-risk technologies, and was retired on 18 December 2001.

Sources: [2] · JPL mission summary

Dawn used three ion engines and entered orbit around Vesta on 15 July 2011 and around Ceres on 6 March 2015; the mission ended on 1 November 2018.

Sources: [3], [4] · JPL mission page; DLR ion propulsion page

Dawn's ion propulsion let the spacecraft spiral down to an altitude of about 210 km (130 miles) during its orbit around Vesta.

Sources: [3] · JPL mission page

Reported, unverified Stated by a company or team but not independently confirmed.

BepiColombo's four 22 cm T6 ion thrusters run on xenon, with a maximum thrust of 250 mN and an exhaust velocity of 50,000 m/s, which ESA says is 15 times greater than conventional chemical rocket thrusters.

Sources: [5] · Article text · medium confidence

In November 2018, ESA said the BepiColombo ion thrusters would operate continuously for about three months to optimise the trajectory, with arrival at Mercury expected about seven years later.

Sources: [5] · Article text · medium confidence

Starlink satellites use Hall thrusters that run on krypton. A 2019 Spaceflight Now report says krypton costs less than xenon but gives less thrust efficiency, and that most satellites using Hall thrusters consume xenon.

Sources: [6] · Hall thrusters and propellant sections · medium confidence

ESA's ARTES AT Kr project aims to optimise a krypton-operated cathode for the PPS X00 thruster, names xenon availability as a key issue in the mega-constellation segment, and states that all elements are in place to claim TRL6 maturity for the krypton cathode. The project page gives no quantitative krypton efficiency figure.

Sources: [7] · Project description and status · medium confidence

Limitations and open problems

  • Thrust is very small. ESA gives a maximum thrust of 250 mN for BepiColombo's T6 thrusters, and says they will fire continuously for about three months to shape the trajectory.
  • Electric thrusters need large electrical power. BepiColombo has twin 15 m solar arrays, and Deep Space 1's engine was rated at 2.3 kW.
  • Xenon is expensive and its supply is limited. ESA identifies xenon availability as a key issue for mega-constellations.
  • Krypton is cheaper than xenon but gives lower thrust efficiency, according to a 2019 Spaceflight Now report. The sources reviewed here give no verified efficiency percentage for krypton on the same thruster.
  • Flight heritage is for a small number of missions and constellation satellites; the sources reviewed here do not give verified cost, mass or reliability figures across the market.

Possible future uses

Speculative

Ideas, not predictions. None of these has been demonstrated.

  • Electric tugs that move cargo or large structures between orbits over many months, reusing one propulsion stage for repeated trips.
  • Electric propulsion for crewed deep-space missions, where long transit times are an acceptable trade for lower propellant mass.
  • Krypton-fuelled thrusters for small satellites in very large constellations, if qualification and efficiency gaps close.

Timeline

  1. 24 Oct 1998Deep Space 1 launches from Cape Canaveral to test 12 advanced, high-risk technologies, including its xenon ion engine. Sources: [2], [1]
  2. 18 Dec 2001Deep Space 1 is retired after its ion engine had operated for more than 16,000 hours. Sources: [1], [2]
  3. 15 Jul 2011Dawn, using solar-electric ion propulsion, enters orbit around the asteroid Vesta. Sources: [3]
  4. 6 Mar 2015Dawn enters orbit around the dwarf planet Ceres. Sources: [3]
  5. 1 Nov 2018Dawn mission ends, listed by JPL as the end of mission date. Sources: [3]
  6. 16 Nov 2018ESA reports in-flight commissioning and test firings of BepiColombo's four T6 ion thrusters in the week of 16 November 2018. Sources: [5]

Related breakthroughs

Glossary

Specific impulse
A measure of how efficiently a thruster uses propellant, roughly the thrust delivered per unit of propellant used per second. Higher values mean less propellant for the same impulse.
Gridded ion thruster
An electric thruster that ionises a gas and accelerates the ions through a set of electrically charged grids.
Hall-effect thruster
An electric thruster that uses a magnetic field to trap electrons in a channel, which ionises the propellant and accelerates the ions.
Millinewton (mN)
One thousandth of a newton, a unit of force. Electric thrusters typically produce forces measured in millinewtons.

Sources

  1. government report
    Deep Space 1 Ion Engine Completed a 3-Year Journey
    James S. Sovey, Michael J. Patterson, Vincent K. Rawlin et al.. NASA Technical Reports Server (NASA Glenn Research Center), in Research and Technology 2000, 1 Mar 2001. Accessed 22 Oct 2026.
  2. other
    Deep Space 1
    NASA Jet Propulsion Laboratory, Publication date not stated. Accessed 22 Oct 2026.
  3. other
    Dawn mission page
    NASA Jet Propulsion Laboratory, Publication date not stated. Accessed 22 Oct 2026.
  4. other
    Dawn: The ion propulsion system
    German Aerospace Center (DLR), Publication date not stated. Accessed 22 Oct 2026.
  5. other
    Electric blue thrusters propelling BepiColombo to Mercury
    European Space Agency, 16 Nov 2018. Accessed 22 Oct 2026.
  6. other
    ARTES AT Kr - Electric Propulsion Technologies Operating on Krypton Propellant
    European Space Agency, Connectivity and Secure Communications, 15 Jan 2025. Accessed 22 Oct 2026.

Revision history

3 changes since this profile was created.

Changes on 22 Oct 2026
Published on owner instruction (loop iteration, research batch 002 and category gaps, 2026-10-22)80cd179
Sources and claims re-checked against originals409337d
Initial profile drafted from primary sourceseaac9eb