NASA's 12-foot-long unmanned X-43A hypersonic research aircraft became the first scramjet-powered aircraft to fly freely. Scramjet engines hold the potential to increase payload capacity for future hypersonic vehicles by consuming ambient oxygen for combustion rather than having to carry on oxidizer on board, as rocket engines require. In March 2004, the second X-43A flew at Mach 7, or about 5,000 mph, for 11 seconds, a world record for air-breathing propulsion. That record was surpassed in November 2004, when the third X-43A flight demonstration sustained flight at nearly Mach 10, close to 7,000 mph.
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