Abstract: An electrothermal thruster includes an electrical heater comprising a copper pipe surrounded by a co-axial tubular copper jacket, and a resistance heated chamber cooperating to heat and decompose liquid fuel which flows into the pipe to effect a gaseous discharge through a propelling nozzle. The jacket has a closed end soldered to the pipe which is supported from the open end by wires. The pipe, jacket and wires constitute the secondary winding of a transformer. The primary winding is of toroidal form round an annular core disposed co-axially about the pipe within the jacket. Induced current in the secondary causes heating of the pipe in turn heating fluid therein.