An aircraft resembling a shark-nosed missile detached from a flying B-52 bomber and shot above the Pacific Ocean at more than 4,800 km/h in a historic test flight by the US Air Force.
The unmanned X-51A WaveRider sped westward for four minutes, reaching Mach 5.1, or more than five times the speed of sound, before making a planned plunge into the ocean.
It flew for longer than any other aircraft of its kind and travelled more than 425 kilometres, reigniting decades-long efforts to develop a vehicle that could travel faster than a speeding bullet.
A passenger aircraft travelling at such a speed could fly from Los Angeles to New York in less than an hour.
The United States Air Force has been flirting with hypersonic technology for more than half a century with little success. Aerospace engineers say that harnessing technology capable of sustaining hypersonic speeds is crucial to the next generation of missiles, military aircraft, spacecraft and passenger planes.
The X-51A, built and tested in southern California, was powered by an air-breathing engine that has no moving parts.
But the technology had been exceedingly difficult to perfect, until Wednesday's flight.
"It was a full mission success," said Charlie Brink, X-51A programme manager for the Air Force Research Laboratory Aerospace Systems Directorate. "I believe all we have learned from the X-51A WaveRider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight."
The X-51A took off from Edwards Air Force Base, suspended under the wing of the bomber. At about 15,000 metres it was released like a bomb and engaged a solid rocket booster that accelerated it to Mach 4.8 in about 26 seconds. After separating from the booster, the X-51A scramjet engine then lit and sped to Mach 5.1 at 18,200 metres.
The scramjet engine functions through hydrocarbon fuel being injected into the combustion chamber, where it mixes with air rushing through the chamber and is ignited. The X-51A then rides its own shock wave; hence, the WaveRider nickname. After the flight, the 4.3 metre cruiser hit the Pacific Ocean and broke up. There are no plans to recover it.
The X-51A was the last of four such test vehicles originally conceived under a US$300 million programme to demonstrate technology, which began in 2004. None of the other flights went the distance.