Design of an Airbreathing Second Stage for a Rocket-Scramjet-Rocket Launch Vehicle

The most promising alternative to rockets for improved access to space involves staged systems using airbreathing propulsion. With scramjet technology improving, a number of airbreathing assisted access-to-space vehicle concepts have recently been proposed, including a three-stage rocket-scramjet-rocket launch architecture for payload masses on the order of 100 kg. This article presents a design methodology developed for the airbreathing second stage of such a system. This methodology uses multidisciplinary design optimization with simplified methods for the calculation of vehicle aerodynamics, propulsion, and mass. It has been applied to the design of a reusable scramjet-powered winged cone vehicle with a near-term Mach 6–12 hydrogen-fueled scramjet for propulsion. Through the manipulation of five vehicle design parameters, including the size and position of the engines, and flying the vehicle along constant dynamic pressure trajectories, a configuration was developed to maximize payload mass fraction to low Earth orbit. The mass of the whole system was 11.3 t, and that of the airbreathing vehicle was 4625 kg, delivering a 211 kg payload to low Earth orbit. This corresponds to an overall payload mass fraction of 1.87%. This methodology supplies a useful framework for developing a better understanding of the key drivers for airbreathing hypersonic accelerators.