(57) An electric thruster for spacecraft propulsion has an ionisation chamber (8), and
inlet (9) for supplying gaseous propellant into the chamber (8) via a valve (7) when
thrust is required, a hollow cathode electron emitter (11) and keeper (12) and an
anode (13) for ionising the propellant by electron collision, an accelerating grid
(16) at one end of the chamber (8), and an alternating voltage supply (201) connected
to the grid (16) such that positive propellant ions and electrons are alternately
accelerated out of the chamber (8) to provide an exhaust beam (17) which gives the
required thrust and has a predetermined net electrical charge (typically zero).
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