Design and development of a low power laboratory resistojet

Resistojet thrusters are categorized as one of electrothermal engines which are capable of operating both at high and low power levels based on their design and the mission imposed requirements. High power
resistojets operate at a power level of 0.5 - 1.5 kW and a specific impulse of 300 – 350 s using Hydrazine or Ammonia as propellant. The development of such engines commenced in early 1960's. However, with
respect to the growing interest for the smaller satellites, low power systems are currently of more interest as they can operate at a power level of below 100 W producing thrust up to 100 mN with a specific
impulse of up to 100 s based on the choice of propellant. The propellant can be almost any compressed- or liquefied-gas as long as it is
compatible with the high-temperature operating condition. Resistojets operating at low power and using liquid propellants have become attractive propulsion options for small satellites. Therefore, for
the first time in west Asia and Iran, a laboratory model resistojet has been designed and developed to operate at low power levels of 15 – 50 W using a liquefied-gas as propellant. The paper describes the design and development of a butane resistojet of nominal power level of 15 –
50 W, producing near 50 mN of thrust at a specific impulse slightly below 70 seconds. The butane is stored in liquid form in the tank and converts to gas as it emerges. Then, it is heated to a maximum temperature of 350°C while flowing through heaters inside the thruster. It is finally accelerated inside a micro-machined steel convergent-divergent nozzle
with a 0.4 mm throat and approximately 250:1 area ratio. The thrust measurement tests were carried out on a cantilever beam test stand measuring the thrust using a high-precision load-cell inside a 1 × 2.5 m
vacuum chamber at a pressure of near 3 Pascal.