Air-Breathing Engines; February 1999; Scientific American Magazine; by McClinton; 2 Page(s)

For years, engineers have dreamed of building an aircraft that could reach hypersonic speeds, greater than Mach 5, or five times the speed of sound. Propelled by a special type of airbreathing jet engine, a high-performance hypersonic craft might even be able to "fly" into orbit-a possibility first considered more than four decades ago. Recently, as the technology has matured and as the demand for more efficient Earth-to-orbit propulsion grows, scientists have begun seriously considering such systems for access to space.

Air-breathing engines have several advantages over rockets. Because the former use oxygen from the atmosphere, they require less propellant-fuel, but no oxidizer-resulting in lighter, smaller and cheaper launch vehicles. To produce the same thrust, air-breathing engines require less than one seventh the propellant that rockets do. Furthermore, because air-breathing vehicles rely on aerodynamic forces rather than on rocket thrust, they have greater maneuverability, leading to higher safety: flights can be aborted, with the vehicle gliding back to Earth. Missions can also be more flexible.