NASA's Marshall Space Flight Center and Rocketdyne recently completed one hour of testing on this air-breathing rocket. Photo: NASA/MSFC

Engineers developing air-breathing rocket propulsion technology achieved an important milestone in May. NASA's Marshall Space Flight Center in Huntsville, Ala., and its industry partner, Rocketdyne of Canoga Park, Calif., this month completed one hour of testing on an air-breathing rocket -- or rocket-based, combined cycle -- engine at the General Applied Sciences Laboratory (GASL) in Ronkonkoma, NY. The 3,600 seconds of test time on the ground testing engine represent the most time accumulated on any rocket-based, combined-cycle engine.

NASA is developing technology for air-breathing rocket engines that could help make space transportation safe, reliable and affordable for ordinary people. Powered by engines that "breathe" oxygen from the air, the spacecraft would be completely reusable, take off and land at airport runways, and be ready to fly again within days. The engines would get their initial take-off power from specially designed rockets, called air-augmented rockets, that boost performance about 15 percent over conventional rockets. When the vehicle's velocity reaches twice the speed of sound, the rockets are turned off and the engines rely totally on oxygen in the atmosphere to burn the hydrogen fuel. Once the vehicle's speed increases to about 10 times the speed of sound, the engine converts to a conventional rocket-power mode to propel the vehicle into orbit.

In reaching the one-hour testing milestone, engineers have demonstrated performance of the engine in all of its operating modes and transitions between the various modes. The next step is definition of flight-weight structures and engine systems required for in-flight demonstration of this advanced propulsion system. Development of air-breathing rocket propulsion technology is managed by the Marshall Center's Advanced Space Transportation Program. NASA's industry partners in this effort are Rocketdyne; Aerojet Corp. of Sacramento, Calif.; and Pennsylvania State University of University Park.