Experimental Demonstration of the Vacuum Specific Impulse of a Hybrid Rocket Engine

This paper presents the experimental results of a hybrid rocket engine fired both at ambient pressure and under low-pressure conditions. The hybrid engine includes a catalyst bed and a vortex injector, and it is fitted with ultrasound sensors to measure the instantaneous fuel regression rate. These tests have enabled demonstration of the experimentally achievable specific impulse of the hybrid rocket technology under low-pressure conditions and validated the extrapolation of experimental results at ambient pressure to vacuum pressure conditions. The demonstrated combustion efficiency is above 98%, and the specific impulse is experimentally proven to be above 270 s for a conical nozzle with an expansion ratio of 50.