Electric Propulsion

Electric propulsion uses electrical power to accelerate a propellant. It produces much higher exhaust velocity than most chemical systems, so a spacecraft can obtain a given total impulse with less propellant. The trade is low thrust: manoeuvres that take minutes with chemical propulsion may require days or months with an electric thruster.¹

Electric propulsion normally consumes reaction mass. The term describes how energy is added to the propellant, not a propellant-free drive.

Operating principles

Three broad mechanisms are used:

• Electrothermal thrusters, including resistojets and arcjets, heat a gas electrically before expanding it through a nozzle.
• Electrostatic thrusters, including gridded-ion, Hall-effect, field-emission electric propulsion and electrospray devices, accelerate charged particles through an electric field.
• Electromagnetic thrusters, including pulsed-plasma and magnetoplasmadynamic devices, use interacting electric and magnetic fields to accelerate plasma.²

An operational system includes more than the thruster. It needs propellant storage and feed, a power-processing unit, control electronics, electrical and thermal interfaces and, for many ion systems, a neutraliser that prevents the spacecraft accumulating charge. Gimbals may steer the thrust vector. Plume interactions with solar arrays, sensors and surfaces can constrain placement and operation.

Mission uses and limits

Electric propulsion is used for station keeping, orbit raising, drag compensation, collision avoidance, space tugs and long-duration interplanetary missions. NASA’s Psyche spacecraft, for example, uses Hall thrusters to accelerate ionised xenon with electric and magnetic fields.³

Its efficiency is useful when propellant mass dominates a mission, but electrical power, heat rejection and manoeuvre time then become limiting resources. Low thrust also means the trajectory changes continuously during a burn; mission planning cannot always approximate the manoeuvre as an instantaneous velocity change. Electric propulsion is generally unsuitable for launch from Earth’s surface because it cannot overcome gravity with adequate thrust.

Xenon is a mature propellant for ion and Hall thrusters, but its price and supply have encouraged alternatives. Iodine can be stored without a high-pressure tank and was demonstrated in orbit in 2021.⁴ That demonstration did not remove all integration risks: ESA work continues to examine iodine’s material compatibility and plume interactions.⁵

UK capability

Britain has both established and emerging work in electric propulsion. QinetiQ ion-propulsion technology has mission heritage. In 2026 Magdrive opened the DEEP laboratory at Harwell with UK Space Agency support; its two-metre vacuum chamber and plasma diagnostics are available to other UK firms and researchers.⁶ UKSA has also funded Magdrive metal-plasma propulsion and Southampton-led Hall-thruster work with Pulsar Fusion.⁷

Those investments show active national capability and ground development. Public sources do not yet establish flight heritage for Magdrive’s current system or full validation of the Southampton/Pulsar 10 kW design, so neither should be described as an operational flight product.

References

Footnotes

1. European Space Agency, Electrifying spacecraft propulsion. ↩

2. ECSS, ECSS-E-ST-35-01C: Liquid and electric propulsion for spacecraft. ↩

3. NASA Jet Propulsion Laboratory, Psyche spacecraft. ↩

4. Rafalskyi et al., In-orbit demonstration of an iodine electric propulsion system, Nature 599 (2021). ↩

5. European Space Agency, Use of iodine as a propellant for Hall-effect thrusters. ↩

6. UK Space Agency, Investment in a new electric-propulsion laboratory. ↩

7. UK Space Agency, To Mars and beyond; UK Space Agency invests £17 million. ↩