A Hall-effect thruster is an electric rocket engine that ionises a noble gas — usually xenon or krypton — and accelerates the ions electrostatically for gentle, extremely efficient thrust. It is the workhorse of modern satellite propulsion, flying on thousands of constellation satellites.
Understanding Hall-Effect Thruster
How the Hall current works
The thruster's magic is a magnetic field strong enough to trap light electrons but far too weak to deflect heavy ions. Electrons emitted by a cathode drift into the annular discharge channel and get caught circling it — the Hall current. Propellant gas fed into the channel collides with these circling electrons and ionises. The ions, barely feeling the magnetic field, are accelerated out of the channel by the electric field at up to 20 km/s. A fraction of the cathode's electrons leaves with the beam to neutralise it, keeping the spacecraft electrically balanced.
Hall thrusters vs other propulsion
| Type | Specific impulse | Thrust | Best for |
|---|---|---|---|
| Chemical (bipropellant) | ~300–450 s | kN class | Launch, fast transfers |
| Hall-effect thruster | 1,500–3,000 s | 20–600 mN | Orbit raising, station-keeping |
| Gridded ion thruster | 2,500–4,000+ s | 20–250 mN | Deep-space missions |
| Cold gas | ~60–80 s | mN–N | Simple attitude control |