Evaluation of Near-Term Air-Breathing Engine Concepts for Spaceplane Acceleration Missions Designed for Ground Take-Off

Abstract

Based on the booster stage of the DSL TSTO-concept with separation Mach number range 2.7 to 3.5, the results of a parametrical investigation of air-breathing engine types will be described in this paper. Basic demand for the propulsion system is full operability from take-off to separation. Same air mass flow at sea-level conditions and similar levels of cycle temperatures are assumed for all investigated types. Due to the overall system lay-out hydro carbon fuels will be used. Investigated engines include turbojet and turbofan with afterburner in a single or two spool configuration. Additionally a turbo-rocket with storable propellants is considered. The influence of engine pre-cooling by water injection or CH4-heat exchanger is moreover examined. An expander cycle simular to Japanese ATREX-type is finally evaluated. In a separate approach the efficiencies of the main propulsion components air-intake and thrust nozzle are regarded. The number of intake ramps is varied for external and mixed compression character. Axial-symmetric and 2D-nozzle configurations are modified in mechanical complexity and for the maximum exit area. A combined numerical engine performance calculation, and a simulation of the, for all engine types fixed DSL-trajectory, deviver the propellant mass. This procedure is followed by a preliminary design of the complete air-breathing engine, including the air-intake and the nozzle. Using a fast analytical design-tool built on structural mechanical as well as empirical relationships, an engine mass estimation is performed, enabling the application of advanced material technology. Evaluation of concepts regards the sum of fuel and engine mass normalized by the system take-off weight.