As efficient as air-breathing rockets are, they can't provide the thrust for liftoff. For that, there are two options being considered. NASA may use turbojets or air-augmented rockets to get the vehicle off the ground. An air-augmented rocket is like a normal rocket engine, except that when it gets a high enough speed, maybe at Mach two or three, it will augment the oxididation of the fuel with air in the atmosphere, and maybe go up to Mach 10 and then change back to normal rocket function. These air-augmented rockets are placed in a duct that capture air, and could boost performance about 15 percent over conventional rockets.
Further out, NASA is developing a plan to launch the air-breathing rocket vehicle by using magnetic levitation (maglev) tracks. Using maglev tracks, the vehicle will accelerate to speeds of up to 600 mph before lifting into the air.
Following liftoff and after the vehicle reaches twice the speed of sound, the air-augmented rockets would shut off. Propulsion would then be provided by the air-breathing rocket vehicle, which will inhale oxygen for about half of the flight to burn fuel. The advantage of this is it won't have to store as much oxygen on board the spacecraft as past spacecraft have, thus reducing launch costs. Once the vehicle reaches 10 times the speed of sound, it will switch back to a conventional rocket-powered system for a final push into orbit.
Because it will cut the weight of the oxidizer, the vehicle will be easier to maneuver than current spacecraft. This means that traveling on an air-breathing rocket-powered vehicle will be safer. Eventually, the public could be travelling on these vehicles into space as space tourists.
The Marshall Center and NASA's Glenn Research Center in Cleveland are planning to design a flight-weight air-breathing rocket engine in-house for flight demonstration by 2005. That project will determine if air-breathing rocket engines can be built light enough for a launch vehicle.