Vehicle concepts for an ejector ramjet combined cycle engine

Abstract

The study looks at air-breathing vehicle concepts from the lower end of the (mission averaged) specific impulse range. The selected concepts are ejector rocket and ejector ramjet rocket combined cycle propulsion systems, which are compared to rocket-only concepts. The use of such engines leads to high propellant mass fractions but also offers the potential of only moderate increase of propulsion system mass. Furthermore, the simple and technologically proven designs of such engines require lower development cost and are likely to result in low production and operational cost compared to other airbreathing vehicle concepts. The study tries to identify if single stage vehicles can obtain the little extra bit of specific impulse required to make them technically feasible as compared to rocket only concepts. Alternatively an identical (sometimes Siamese or biamese) two stage vehicle is assessed, because also for this concept only one vehicle needs to be developed, so development cost remain nearly the same, only operational cost roughly double. A one-dimensional thermodynamic model has been developed for the combined cycle propulsion system. The trajectories are obtained from a mass-point model, in a single plane, with standard atmosphere, Earth rotation and potential gravity field. With a genetic algorithm the vehicle trajectory as well as wing size are optimized for a given target orbit to obtain the lowest possible propellant mass fraction. © 2001 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission.