X-43 hits Mach 9.6

There are two things to know about the X-43A. First, it used an experimental engine called a scramjet, in which the supersonic speed of the vehicle itself compresses the air that the vehicle's engine, in turn, uses to generate hypersonic (faster than Mach 5) flight. In addition, the vehicle essentially surfs on the supersonic shock wave it creates.

Second, the X-43A flew really, really fast. One of the unmanned test vehicles reached Mach 6.8 (nearly 5,000 miles per hour) in March 2004, and the second reached Mach 9.6 (roughly 7,000 mph) in November of that year. By contrast, the manned SR-71 Blackbird, used for many years by the U.S. Air Force, had a top speed of just more than Mach 3.