The scope of this work is twofold: first, to perfect the exergy approach to the design and optimization of aerospace propulsion systems; second, to develop a modular simulation tool in order to analyze potentialities and limits of different configurations of a scramjet engine. The vehicle is considered a “flying control volume” and is treated as a Large Complex Energy System (“LCES”) to which systems balances (mass, energy, exergy) are applied to calculate the relevant losses for each one of its elementary devices. An energy and exergy analysis of a hydrogen-fueled scramjet is presented and discussed as a first application of the procedure that shall be extended to the analysis of different scramjet-configurations, fueled by H2-alternative fuels: an exergy-based performance comparison can consequently complement an energy and thrust-based analysis. All calculations have been performed with CAMEL ® , an “in-house” modular process simulator code for energy conversion processes.