Two-Mode Active Thrust Modulation of a Solid Propellant Rocket Motor

Abstract

An active thrust modulation system of solid propellant motor was proposed and verified experimentally. Candidate propellants have a self-quenched property at intermediate pressure, while they can deflagrate at lower and higher pressure. Appropriate selection of throat diameter presents two combustion modes in the same motor geometry. Propellant with 73 % oxidizer content had demonstrated successfully two-mode active thrust modulation. The propellant with 75 % oxidizer content was examined. While the specific impulse showed little difference from 73 % AP propellant, the thrust density of 75 % AP propellant motor became high. The higher burning rate and the narrowed self-quenched pressure range made the thrust modulation a little difficult. An effect of a negative catalyst LiF was discussed. Slight addition of the catalyst had an effect to widen the intermediate self-quenched pressure range, but little effect to suppress the pressure amplitude in regulating the low mode pressure. More motor combustion tests are needed to confirm its availability.