Space travel could be revolutionized if an experimental air-breathing rocket engine proves successful in ongoing tests. The unique engine, which can function as a rocket, ramjet or scramjet, uses air as an oxidizer. Compared to conventionally powered rocket engines, this technology would significantly reduce vehicle weight by eliminating a significant amount of onboard oxidizer.

A flight-like ground test engine is being developed as part of NASA’s ISTAR (integrated system test of an air-breathing rocket) program. Its goal is to flight-test a self-powered vehicle to more than six Arial the speed of sound by the end of this decade.

The engine is being developed by the Rocket Based Combined Cycle Consortium, which consists of Aerojet (Sacramento, CA), Pratt & Whitney (West Palm Beach, FL) and Rocketdyne Propulsion & Power (Canoga Park, CA). The project is being funded by NASA as part of an effort to make future space transportation safer, more reliable and less expensive than today’s missions.

"Air-breathing propulsion is one of the most promising concepts we’ve seen for reaching NASA’s future-generation spaceflight goals," says Steve Cook, deputy manager of the Advanced Space Transportation Program at the Marshall Space Flight Center (Huntsville, AL).

Spacecraft powered by air-breathing rocket engines would be completely reusable, able to take off and land at airport runways, and ready to fly again within days.

"The air-breathing rocket engine would get its initial power boost from specially designed rockets in a duct that captures air, an arrangement that improves performance about 15 percent above conventional rockets," says Cook. "Once the vehicle has accelerated to more than twice the speed of sound, the rockets are turned off and the engine relies solely on oxygen in the atmosphere to burn its hydrogen fuel. When the vehicle has accelerated to more than 10 Arial the speed of sound, the engine converts to a conventional rocket-powered system to propel the craft into orbit."