NEAR-OPTIMAL PROPULSION-SYSTEM OPERATION FOR AN AIR-BREATHING LAUNCH VEHICLE

A methodology for determining the near-optimal operation of the propul sion system of hybrid air-breathing launch vehicles is derived. The me thod is based on selecting propulsion-system modes and parameters that maximize a certain performance function. This function is derived fro m consideration of the energy-state model of the aircraft equations of motion. The vehicle model reflects the many interactions and complexi ties of the multimode air-breathing and rocket engine systems proposed for launch-vehicle use. The method is used to investigate the optimal throttle switching of air-breathing and rocket engine modes, and to i nvestigate the desirability of using liquid-oxygen augmentation in air -breathing engine cycles, the oxygen either carried from takeoff or co llected in flight. It is found that the air-breathing engine is always at full throttle, and that the rocket is on full at takeoff and at ve ry high Mach numbers, but off otherwise. Augmentation of the air-breat hing engine with stored liquid oxygen is beneficial, but only marginal ly so.