NASA X-43 Hyper-X airplane model. NASA established a multi-year experimental hypersonic ground and flight test program called Hyper-X. The program sought to demonstrate "air-breathing" engine technologies that promise to increase payload capacity or reduce vehicle size for the same payload for future hypersonic aircraft and/or reusable space launch vehicles. Payload capacity was to be increased by discarding the heavy oxygen tanks that rockets must carry and by using a propulsion system that uses the oxygen in the atmosphere as the vehicle flies at many times the speed of sound. Hydrogen will fuel the program's research vehicles, but it requires oxygen from the atmosphere to burn.