An efficient performance analysis method is developed to evaluate potential airbreathing/rocket propulsion systems for advanced technology single-stage-to-orbit launch vehicles. Evaluated are tradeoffs between airbreathing, rocket, and concurrent airbreathing/rocket propulsion in maximizing payload delivery to orbit for a given ascent flight trajectory. With the analysis method, several modes of airbreathing/rocket propulsion are compared to a baseline "airbreather alone" propulsion system in terms of fuel/propellant required to attain orbital velocity. Concurrent airbreathing/rocket propulsion shows a reduction in fuel/propellant consumption over straight airbreather to rocket propulsion transition. The optimal switch point (staging) is identified for the transition from airbreathing to rocket propulsion.Nomenclature engine throttle ratio coefficient of lift drag force, N stoichiometric fuel-air ratio PS/W, fuel specific energy, m/kg controller transfer function vehicle transfer function gravity constant, 9.807 m/s 2 height above sea level, m airbreather specific impulse, s rocket specific impulse, s gain in guidance law lift force, N = vehicle mass, kg ; specific excess power, m/s dynamic pressure, kPa radius from Earth's center, m = Earth radius, 6,356,766 m = vehicle reference area, m 2 = distance down range from launch point, m = thrust, N = flight velocity, m/s = vehicle payload, kg = airbreather/rocket fuel combined flow rate, kg/s = airbreather air flow rate, kg/s = airbreather fuel flow rate, kg/s = rocket propellant flow rate, kg/s = angle of attack, radians = factor in exponential altitude density relation = flight-path angle, rad = denotes an increment = time constant in guidance law, s = fuel-to-air equivalence ratio = atmospheric density, kg/m 3
