Hypersonic vehicle terminal velocity improvement considering ramjet safety boundary constraint

Abstract

The air-breathing ramjet is an essential power plant to improve the terminal velocity of hypersonic vehicles. The high-performance requirement of ramjet makes it operate close to the safety boundary, and the optimization of the terminal velocity of vehicle is faced with challenges. An integrated flight/ propulsion model considering thrust and safety performance is constructed, and the trajectory optimization method for the whole flight phase operating process of hypersonic vehicles with multiple performance optimization indicators and complex safety constraints is studied. Moreover, the trajectory optimization results of the whole flight phase for CAV-H and X-43A (powered/unpowered) plans are compared and analyzed, and the dive-acceleration-climb strategy can improve the maneuverability of the vehicle in the ramjet operating phase. Furthermore, the terminal flight velocity of the vehicle in the powered plan is increased from 363.60 m/s to 943.57 m/s under the effect of ramjet. In addition, the trajectory optimization results of vehicle with different geometrical configurations of the ramjet are compared under safety constraints. The results show that the variable geometry ramjet enables the vehicle to increase its terminal velocity by up to 9.73 % with respect to the fixed geometry engine. Hypersonic vehicle terminal velocity is effectively improved by considering ramjet variable geometry adjustment.