Efficient and reliable space transportation systems are fundamental to the future success of routine scientific, commercial and strategic space missions. RBCC (rocket-based combined cycle) comprising rocket, ramjet and scramjet engines is a propulsion technology that offers promise for reusable space launch systems owing to advantages over traditional propulsion in various aspects including efficiency and flexibility. However, the viability of RBCC-powered access-to-space requires careful consideration and its assessment represents a challenge to conventional design approaches due to the highly complex and coupled characteristics of the system associated with multi-mode propulsion and multi-stage launch. This study has been undertaken to examine the performance of a conceptual RBCC-based TSTO (two-stage-to-orbit) system and identify the key requirements and design factors to achieve space launch via this system. Multi-objective design optimization has been conducted with respect to important design criteria by means of evolutionary algorithms assisted by surrogate modeling and trajectory optimization. The influence of RBCC engine characteristics particularly in terms of performance and operation as well as the scaling of the vehicle and propulsion on the overall performance of the TSTO system and its feasibility has been quantified and examined. Furthermore, a comparative study with a rocket-only-based TSTO system has also been conducted, verifying the advantages of the RBCC-based TSTO system. The results highlight complex aerodynamic characteristics for both concepts as well as highly nonlinear propulsion characteristics for the RBCC-based concept.
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