Resistojet rocket

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A resistojet is a way of propulsion that provides thrust by heating a (typically non-reactive) fluid. Heating is usually achieved by sending electricity through a resistor. For example, take a hydrazine thruster and remove the nozzle. Route the exhaust to a heat exchanger. Heat that heat exchanger with a heavy duty filament (very much like a flood light). Then release the heated exhaust through a nozzle. The specific impulse will be increased by about 50%.

A good analogy to resistojet would be "space heater attached to a water hose".

Resistojets have been flown in space, and do well in situations where energy is much more plentiful than mass, and where propulsion efficiency needs to be reasonably high but low-thrust is acceptable.