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March 27, 2004, Edwards Air Force Base, Calif.—NASA’s experimental X-43 scramjet took off for its second test. It had plenty of help taking to the sky—it was appended to a modified Pegasus rocket booster, attached to a Boeing B-52B. Once the B-52 and the Pegasus had played their part—boosting the X-43 to about Mach 5—the scramjet engine came to life, and shattered a record in the process. The X-43 reached a speed of almost 5,000 mph (Mach 6.8). Though it sustained this top speed for only 11 seconds, it covered a remarkable 15 miles over that time span.

The record-breaking performance vindicated NASA’s Hyper-X scramjet program. Three X-43 prototypes were built—each only 12 feet long and designed for just a single use—and the first failed its test on June 2, 2001, due to a malfunction of the conventional Pegasus booster rocket.

Conventional rockets produce thrust by mixing fuel with oxygen, both of which must be carried into flight.A scramjet engine scoops oxygen directly from the atmosphere, thus greatly reducing the weight of the aircraft. The main obstacle to further development of such engines is the speed at which they operate. Scramjets only function at about Mach 5 or higher, and therefore need to be boosted into flight by a conventional rocket. Once at speed, the scramjet begins pulling oxygen into the combustion chamber, then compressing and igniting it while adding hydrogen fuel.

The record set on March 27, 2004, was surpassed that November by the third and final X-43, which hit a blazing speed of Mach 10— a velocity that, if sustained, would allow a plane to travel from San Francisco to Washington, D.C., in under 20 minutes.


Originally published in the March 2007 issue of Aviation History. To subscribe, click here