Although the flight did not last as long or hit the mach 6 speed anticipated, Boeing’s Huntington Beach cutting edge research unit—Boeing Phantom Works—today achieved a major milestone in sustained hypersonic flight. After seven years in development, the X-51A WaveRider, built by the local Boeing team, achieved mach 5 in a 200 second test flight over the Pacific Ocean.

The Boeing team built the airframe, while Pratt & Whitney Rocketdyne built the craft’s supersonic combustion ramjet (scramjet) motor. According to a Boeing statement, “The longest previous hypersonic scramjet flight test, performed by a NASA X-43 in 2004, was faster, but lasted only about 10 seconds and used less logistically supportable hydrogen fuel.”

Here is the explanation of a scramjet from Wikipedia:
“A scramjet (supersonic combustion ramjet) is a variation of a ramjet distinguished by supersonic combustion. A scramjet, like a ramjet, essentially consists of a constricted tube through which inlet air is compressed by the high speed of the vehicle, a combustion chamber where fuel is combusted, and a nozzle through which the exhaust jet leaves at higher speed than the inlet air.
Most jet engines use a fan-style compressor to squeeze air into the engine, then spray fuel into the compressed air and ignite it to produce thrust as it exits the engine through an expansion nozzle. A scramjet uses the speed of the aircraft to compress the air, so very few moving parts are needed to operate it. In particular there is no high-speed turbine, as in a turbofan or turbojet engine, that is expensive to produce and can be a major point of failure.”

In a statement, Boeing called the test flight “the longest supersonic combustion ramjet-powered flight in history -- nearly three and a half minutes at a top speed of Mach 5.”

Originally, the flight was supposed to last five minutes and hit mach 6. Boeing reported “The unmanned aerial vehicle was released from a U.S. Air Force B-52H bomber off the southern California coast around 10 a.m. today. It flew autonomously for more than 200 seconds, powered by its Pratt & Whitney Rocketdyne supersonic combustion ramjet (scramjet) motor, as it transmitted telemetry data to ground stations. Something then occurred that caused the vehicle to lose acceleration. At that point, the X-51A was terminated as planned.”

The experimental program is not without its critics. According to the Wikipedia article, “Some notable aerospace commentators such as Henry Spencer and Jim Oberg have gone so far as calling orbital scramjets "the hardest way to reach orbit", or even "scamjets" due to the extreme technical challenges involved.”

But, Boeing was undaunted by the shortcomings of today’s test flight. "The technology proven today is something The Boeing Company has worked on for the past seven years," said Alex Lopez, vice president of Advanced Network & Space Systems, a division of Boeing Phantom Works. "It is thrilling to be a part of history and advance hypersonic science to the next level. Boeing is looking forward to transitioning the technology to operation in the near term, but for now, we are exhilarated.”

Likewise, the Air Force offered unqualified praise for today’s test. "We are ecstatic to have accomplished many of the X-51A test points during its first hypersonic mission," said Charlie Brink, X-51A program manager with the Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio. "This gives us huge confidence. We built four test vehicles to get a successful flight, and we hit many of our goals right out of the gate, the first time around.”

The X-51A was carried aloft under the left wing of an Air Force Flight Test Center B-52H Stratofortress that took off from Edwards Air Force Base. It was released while flying at approximately 50,000 feet over the Point Mugu Naval Air Warfare Center Sea Range. Four seconds later, a solid rocket booster from a U.S. Army tactical missile accelerated the X-51A to about Mach 4.5 before it and a connecting interstage were jettisoned. The X-51A's engine ignited on a mix of ethylene and JP-7 jet fuel. After a short period, the X-51A ran exclusively on JP-7 jet fuel. The flight reached an altitude of about 70,000 feet and an approximate speed of Mach 5.

Onboard sensors transmitted data to both an airborne U.S. Navy P-3 Orion and to ground systems at Point Mugu, Edwards, and Vandenberg Air Force Base before the X-51A was terminated. The team will review the data from today's test before scheduling additional flights with the three remaining test vehicles.

"This is a new world record and sets the foundation for several hypersonic applications, including access to space, reconnaissance, strike, global reach and commercial transportation," said Joe Vogel, Boeing director of Hypersonics and X-51A program manager.