Multidisciplinary Design Optimization of a Two-Stage-to-Orbit Reusable Launch Vehicle with Ethanol-Fueled Rocket-Based Combined Cycle Engines

A fully reusable two-stage-to-orbit launch vehicle with ethanol-fueled rocket-based combined cycle (RBCC) engines has been studied in Japan as a promising option for future space transportation system. In this paper, a conceptual design study of such a vehicle is conducted using multidisciplinary design optimization (MDO) techniques in order to clarify a technology goal for related technology development activities. An MDO framework composed of coupled analysis disciplines (vehicle geometry, mass property, aerodynamics, propulsion, and trajectory) is constructed. In particular, consideration is given to the development of a simplified numerical model for evaluating the airframe-propulsion integration that can be incorporated into MDO studies, in contrast to costly CFD simulations. Vehicle design and ascent trajectory are then simultaneously optimized with the aim of minimizing the gross mass of the mated vehicle (booster and orbiter). The gross mass of the obtained optimal design is 581 t for the assumed mission of transporting an 800 kg payload into a low Earth orbit. A detailed inspection of the solution reveals that an external nozzle of the engines enhances not only the propulsion performance, but also longitudinal static stability of the vehicle during hypersonic flight.