An arcjet is a simple, reliable form of electrothermal
propulsion used to provide brief, low-power bursts of thrust, such a
satellite needs for station-keeping.
A nonflammable propellant is heated, typically changing state from liquid
to gas, by an electric arc in a chamber. It then goes out the nozzle throat
and is accelerated and expelled at reasonably high speed to create thrust.
Arcjets can use electrical power from solar cells or batteries, and any
of a variety propellants. Hydrazine is
the most popular propellant, however, because it can also be used in a chemical
engine on the same spacecraft to provide high thrust capability or to act
as a backup to the arcjet.