Variable Thrust, Multiple Start Hybrid Motor Solutions for Missile and Space Applications

Abstract

Energy management in missile systems can provide substantial performance advantages, especially for modern missiles capable of all-aspect engagements. Energy management in upper stage propulsion systems allows for the same propulsion system to be used for a variety of payloads and orbits. The objectives of the study were to assess throttling capabilities and novel fuel concepts for hybrid motors. Experimental studies were conducted using 90% hydrogen peroxide (HP) with a variety of unique fuels in both direct injection and catalytic bed injection approaches. Performance efficiencies ranged from 91% to 100% and the combustion in all tests was smooth with the highest level of combustion roughness reaching only 0.6% of the steady state pressure. These hybrid motor tests also displayed the expected connection between the oxidizer flux level and the time required to ignite the fuel grain with higher flux levels resulting in lower ignition delays. Substantial throttling capabilities were demonstrated. Throttle-down tests analogous to a powered vertical landing exhibited a 10:1 throttling ratio with stable combustion across the entire range. Boost/Sustain/Boost thrust profiles representative of tactical solid rocket motors were tested with 75%, 50%, and lower sustain-to-boost chamber pressure ratios with rapid throttle-up achieved following the sustain period. To add multiple-start capability to a hybrid motor without reliance on a catalyst bed or separate ignition system, fuel grains catalytic with the oxidizer were investigated. Test fires of these fuel grains in the hybrid motor test article exhibited regression rates 2.5 times higher than the highest regression rates realized with the uncatalyzed polyethylene fuel grains.