Last May, the X-51A Waverider fired up a scramjet engine and boosted itself to a hypersonic Mach 5. The Air Force was hoping for Mach 6, and, next week, the military will unleash this beast for another flight.
The X-51A Waverider uses a scramjet engine, which uses no moving parts at all but can (hypothetically, at least) achieve speeds anywhere from Mach 12 to Mach 24. Mach 24 is, if you're counting, just north of 18,000 miles per hour, which would get me from my house in SF to the DVICE office in NYC in under 10 minutes, which is only about 8 minutes longer than my normal daily commute from bed to couch.
During the last test, the Waverider managed to achieve Mach 5, but it took longer to get there than engineers had hoped, and the test flight was terminated a minute and a half early. And by "terminated," they mean crashed into the ocean. Data from that flight revealed that the vehicle gets so hot from friction with the air that the engine actually grows in size by nearly an inch, and this (plus other factors) may have caused a seal to fail. The remaining test vehicles have been beefed up to keep this from happening again.
On March 22, an X-51A will be carried up to 50,000 feet slung underneath the wing of a B-52. It will be dropped, and a booster rocket will fire up to get the Waverider up to Mach 4.5, which is when the scramjet kicks in. The booster rocket is jettisoned, and then the X-51A goes hypersonic and we'll see what the vehicle can really do.
Below, you can watch an Air Force video about the previous test, giving more details and footage of the X-51A. And we've also got a gallery full of extra pics of this futuristic vehicle that somehow also exists in the present.
Boeing, via U.S. Air Force