Airbreathing Acceleration Toward Earth Orbit

Abstract

As flight speed increases, aerodynamic drag rises more sharply than the availability of atmospheric oxygen. The ratio of oxygen mass flux to dynamic pressure cannot be improved by changing altitude. The maximum possible speed for airbreathing propulsion is limited by the ratio of air capture area to vehicle drag area, approximately Mach 6 at equal areas. Simulation of vehicle acceleration shows that the use of atmospheric oxygen offers a significant potential for minimizing onboard consumables at low speeds. These fundamental calculations indicate that a practical airbreathing launch vehicle would accelerate to near steady-state speed while consuming only onboard fuel, then transition to rocket propulsion. It is suggested that an aircraft carrying a rocket-propelled vehicle to approximately Mach 5 could be a realistic technical goal toward improving access to orbit.

Supersonic Multi-Objective Optimization of a Rocket Based Combined Cycle Inlet by Differential Evolution

“…To follow a path similar to the airbreathing flight requirement laid out by Whitehead [8] in Fig. 1.2 of Chapter 1, the freestream velocity (and Mach number) is increased with altitude to allow the oxygen flux needed for airbreathing propulsion.…”

“…RBCC engine flight profile[8,36]. however, as its speed increases it begins to assume a profile closer to other air-breathing vehicles.…”

“…Typically, oxygen fluxes for airbreathing vehicles are around 10 (kg/s)/m 2 [8] and are measured per air capture area. Since density decreases with increasing altitude, an airbreathing vehicle will need to fly faster as its altitude increases.…”

“…Since density decreases with increasing altitude, an airbreathing vehicle will need to fly faster as its altitude increases. Liquid rockets typically have 4 to 10 times as much oxygen flux, measured per vehicle cross sectional area [8]. This leads to different flight profiles as is illustrated in Fig.…”

“…Rocket vehicles take a much steeper trajectory to orbit to avoid atmospheric drag, due to dynamic pressure on the front of the vehicle. Airbreathing engines, however, remain in the atmosphere, to maintain the oxygen flux needed for thrust [8]. By using this atmospheric oxygen, airbreathing vehicles have lower vehicle propellent mass fractions compared to rocket engines.…”