A design and analysis computational tool is proposed for simulating unsteady reacting flows in combustor devices used in reusable launch vehicles. Key aspects guiding the development are: (a) accuracy, (b) efficiency, and (c) integration of multidisciplinary techniques. To accurately reflect the physics, the tool must include unsteady, all-speed flow modeling with real-fluid effects and be multidisciplinary, including solid-phase thermal and stress analysis. Efficiency necessitates large-scale parallel computing. Finally, the computational framework must allow an efficient integration of multidisciplinary physics. The key features of the proposed tool are: (1) a rule-based framework called LOCI which automatically handles parallel computing and multidisciplinary algorithm integration; (2) all-speed pressure-based CFD methodology (embedded in a code called STREAM); (3) unsteady flow solver with finite-rate chemistry on unstructured grids; (4) real-fluid modeling (RFM); (5) tightly-coupled multidisciplinary physics, including solid-phase thermal and stress analysis. Phase I work will consist of: (a) implementing unsteady finite-rate combustion capability into LOCI-STREAM and (b) laying the foundation for implementing real-fluid models into LOCI. Phase II will accomplish: (a) integration of real-fluid models into LOCI-STREAM; (b) integration of solid-phase heat transfer and finite element stress analysis with the fluid flow solver. The resulting CFD tool will be called LOCI-STREAM-RFM.