Closed-Loop Thrust and Pressure Profile Throttling of a Nitrous-Oxide HTPB Hybrid Rocket Motor

Abstract

Hybrid motors that employ non-toxic, non-explosive components with a liquid oxidizer and a solid hydrocarbon fuel grain have inherently safe operating characteristics. The inherent safety of hybrid rocket motors o ers the potential to greatly reduce overall operating costs. Another key advantage of hybrid rocket motors is the potential for in ight shutdown, restart, and throttle by controlling the pressure drop between the oxidizer tank and the injector. The proposed research designs, develops, and ground tests a closed-loop throttle controller for a hybrid rocket motor using nitrous oxide and hydroxyl-terminated polybutadiene as propellants. The research simultaneously developed closed-loop throttle algorithms and lab scale motor hardware to evaluate the delity of the throttle simulations and algorithms. Initial open-loop motor tests were performed to better classify system parameters and to validate motor performance values. Deep-throttle open-loop tests evaluated limits of stable thrust that can be achieved on the test hardware. Open loop tests demonstrated the ability to throttle the motor to less than 10% of maximum thrust with little reduction in e ective speci c impulse and acoustical stability. Following the openloop development, closed-loop, hardware-in-the-loop tests were performed. The closed loop controller successfully tracked prescribed step and ramp and with a high degree of delity.