Development of a Specific Impulse Balance for Capillary Discharge Pulsed Plasma Thrusters

Capillary-Discharge-Based (CD), coaxial, electrothermal pulsed plasma thrusters (PPT) are currently under development as a high-efficiency alternative to more traditional ablative PPTs. The major drawback of the traditional ablative PPT is the propulsive efficiency. Even though specific impulses (J) on the order of 1000 s have been achieved with ablative PPTs using electromagnetic acceleration, the propulsive efficiencies of flight-qualified thrusters typically remains below 10%. Capillary discharges are relatively efficient sources of high-density, high-temperature plasmas, which are being developed for a number of applications. The CD operates on a solid propellant ablated from a relatively long tube during a pulsed discharge. Previous performance calculations have suggested that a capillary-discharge-based electrothermal PPT can achieve propulsive efficiencies of 30-40% even without nozzle expansion. Additional studies indicate that nozzle expansion of the high-pressure, high-temperature plasma generated by the capillary discharge will increase the efficiency above 50% [6]. With the potential for vast improvement in efficiency, the capillary-discharge, electrothermal PPT may be a strong candidate for satellite attitude control and station-keeping maneuvers.