1 American Institute of Aeronautics and Astronautics Current State of High Speed Propulsion: Gaps, Obstacles, and Technological Challenges in Hypersonic Applications Timothy A. Barber, * Brian A. Maicke, † and Joseph Majdalani ‡ University of Tennessee Space Institute, Tullahoma, TN 37388 The object of this study is to canvas the literature for the purpose of identifying and compiling a list of Gaps, Obstacles, and Technological Challenges in Hypersonic Applications (GOTCHA). The significance of GOTCHA related deficiencies is discussed along with potential solutions, promising approaches, and feasible remedies that may be considered by engineers in pursuit of next generation hypersonic vehicle designs and optimizations. Based on the synthesis of several modern surveys and public reports, a cohesive list is formed consisting of widely accepted areas needing improvement that fall under several general categories. These include: aerodynamics, propulsion, materials, analytical modeling, CFD modeling, and education in high speed flow physics. New methods and lines of research inquiries are suggested such as the homotopy-based analysis (HAM) for the treatment of strong nonlinearities, the use of improved turbulence models and unstructured grids in numerical simulations, the need for accessible validation data, and the refinement of mission objectives for Hypersonic Air- breathing Propulsion (HAP). Nomenclature AHI = Australian Hypersonic Initiative ASALM = Advanced Strategic Air Launched Missile ASSET = Aerothermodynamic Elastic Structural Systems Environment Tests BGRV = Boost-Glide Reentry Vehicle CFD = Computational Fluid Dynamics CONUS = Contiguous US CRV = Crew Return Vehicle DARPA = Defense Advanced Research Projects Agency DLR = German Aerospace Center EHA = European Hypersonic Association ELV = Expendable Launch Vehicle FALCON = Forced Application and Launch from CONUS FIRE = Flight Investigation of Reentry HCV = Hypersonic Cruise Vehicle HiSTED = High Speed Turbine Engine Demonstrator * Graduate Research Assistant, Mechanical, Aerospace and Biomedical Engineering Department. Member AIAA. † Graduate Research Assistant, Mechanical, Aerospace and Biomedical Engineering Department. Member AIAA. ‡ H. H. Arnold Chair of Excellence in Advanced Propulsion, Mechanical, Aerospace and Biomedical Engineering Department. Senior Member AIAA. Fellow ASME. 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 2 - 5 August 2009, Denver, Colorado AIAA 2009-5118 Copyright © 2009 by authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.