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Estimates of upper bounds on ightMach number for scramjet-powered vehicles operating on liquid hydrocarbon fuels assuming either equilibrium or frozen nozzle chemistry are presented. For an axisymmetric missileshaped vehicle, these upper bounds lie between Mach 9 and 10. Nomenclature A = area C D = drag coef cient C T g = gross engine thrust coef cient C TN = net vehicle force coef cient ER e = effective fuel-air equivalence ratio M = Mach number p = pressure q = dynamic pressure ® = angle of attacḱ c = fuel combustion ef ciencý KE = inlet kinetic energy ef ciency Subscripts c = combustor des = design i = inlet geometric max = maximum ref = reference w = wall 0 = freestream 1-5 = engine stations (see Fig. 1)

A history of high-speed airbreathing propulsion ramjet engines and their respective vehicle and weapon systems developed under the support of the U.S. Navy is presented. These include surface-and air-launched subsonic combustion ramjets, supersonic combustion ramjets (scramjets), and mixed-cycle ramjet/scramjet/rocket engines intended primarily for missile applications for ight speeds from Mach 2 to Mach 8. A summary of the development of the joint Department of Defense/NASA-sponsored National Aerospace Plane is also presented. Nomenclature= freestream 1-6 = engine stations (Fig. 1

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