Ase ightspeedincreasesinto thehypersonicregime, stagnation pressureand temperatureinsidean airbreathing engine become so great that, for practical structures of acceptable mass, the e ow must pass through the engine at supersonic speeds so as to limit the static pressures, hence the term scramjet (supersonic combustion ramjet ). The classicapplication forthescramjet isto along-rangeairlinerusing hydrogenfueland offeringextended hypersonic e ight. The scramjet is also widely accepted as propulsion for cruise missiles and as a possible complement to the rockets conventionally used for space launchers. The topic of how scramjets may best be used, especially in the near term, is explored. In particular, the advantages are demonstrated of using hydrocarbon fuel such as kerosene in a scramjet-powered second stage of a two-stage-to-orbit aerospace plane. Nomenclature Ai = intake capture area CL = lift coefe cient (referred to planform area ) D = drag f = acceleration g = acceleration due to gravity h = specie c enthalpy L = lift L=D = lift-to-drag ratio .L=D/p = L=D calculated from pressure forces .L=D/v = L=D calculated from pressure lift and the sum of pressure and friction drags M = mach number n = number of shock waves in scramjet intake (Fig. 3) p1 = ambient pressure T = thrust or temperature t = time 1f = gain in acceleration