a compendium of tech stuff

May 22, 2012

On 8:19 PM by Lalith Varun   No comments

        Resisto-jet is a type of spacecraft propulsion that works by heating the propellant through an external power source to high speed. Heating is usually achieved by passing electricity through a resistor consisting of a hot incandescent filament and thus the name resisto-jet. The thermal energy released is converted into kinetic energy by a nozzle with high expansion ratio. For high exhaust velocity, the pressure and temperature of the gases entering the nozzle must be high, hence efficient heating of the gas is required. As gases are bad conductors of electricity, the thin layer which is in contact with the heater only gets heated and moreover the filament radiates heat to the chamber walls, hence there is a loss in power. To maximize the heat transfer to the gas, a multichannel heat ex-changer is used to bring as much of the gas as possible in contact with the heater.

        An advantage of this thruster is that any propellant that is compatible with materials of the chamber and the heater can be used. Most commonly used propellants are Hydrogen, Helium, Water, Ammonia and Hydrazine. They are relatively uncomplicated and their electrical efficiency is close to 90%. The hottest part of the thruster is the filament itself and hence the service temperature of the filament is the limiting factor. The heat transfer from the filament to the gas also plays an important role in the performance of the thruster. Thus a more efficient heat transfer mechanism is needed to improve the performance of the resisto-jet.

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