Resistojets

Resistojets are a form of electric propulsion used on spacecraft. They generate thrust by passing electric current through resistive heating elements that heat a propellant. The heated gas expands through a nozzle, producing thrust. Compared with chemical rockets, resistojets use electrical energy to heat the propellant rather than storing chemical energy, and they typically provide low to moderate thrust.

Principle and propellants: The heater elements transfer heat to the propellant, which can be a gas such as nitrogen, helium, ammonia, or a monopropellant; the hot gas is expelled through a nozzle. They operate at tens of watts to several kilowatts and provide thrusts from millinewtons to newtons. Specific impulse is modest relative to other electric propulsion, often in the hundreds of seconds.

History and use: Developed in the 1950s–1960s, resistojets were used for satellite attitude control and orbital maneuvers. They offered a simple, robust option and were implemented on some early spacecraft. Over time, ion and Hall thrusters became more common for high-efficiency propulsion, but resistojets remained of interest for small spacecraft and educational demonstrations due to their simplicity.

Advantages and limitations: Advantages include simplicity, compactness, and minimal moving parts; limitations include lower efficiency and thrust density compared with modern electric propulsion, as well as thermal management challenges. Resistojets are often considered for low-power, reliable propulsion applications where high specific impulse is not required.

See also: electric propulsion, arcjet, ion thruster, Hall-effect thruster.