When it comes to hypersonic flight, going fast is a given. It's how long that speed can be maintained that matters to the team of engineers behind a test flight scheduled for Tuesday off the Southern California coast.
The X-51A Waverider (pictured, above) will be carried under the wing of a B-52 scheduled for take-off from the Air Force Flight Test Center at Edwards Air Force Base. The vehicle will be dropped from the B-52 and -- if all goes as planned -- soar for about 300 seconds at about Mach 6 before spashing down in the Pacific Ocean.
A successful test of the unmanned aircraft would mean the WaveRider traveled for twice as long as any aircraft ever has at that speed. It also would provide more data about the applications of hypersonic flight, such as increasing quick-strike military capabilities and reaching space.
Hypersonic flight is usually defined as beginning at Mach 5 -- about 3,600 mph. A Boeing 747's typical cruise speed at 35,000 feet is about 570 mph.
During Tuesday's test, the B-52 will carry the WaveRider to about 50,000 feet over the Pacific Ocean. After the vehicle drops from the aircraft, a solid rocket booster will push the WaveRider to its hypersonic speed.
The first Waverider test flight occurred in May 2010. After it was released from a B-52, the vehicle accelerated to about Mach 5 for approximately 140 seconds.
The test was the longest of its kind by 10 seconds. TIME magazine called the craft one of the top-50 inventions of 2010.
During another test in June, the WaveRider shut down after a lapse in airflow to its jet engine.
The WaveRider project is a collaboration involving Boeing, Pratt and Whitney Rocketdyne, U.S. Air Force Research Laboratory and the Defense Research Projects Agency (DARPA).