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In the last week of May, thousands of square miles of airspace above the Pacific Ocean will be cleared to make way for a skinny, shark-nosed aircraft called the X-51.
The 4-metre-long prototype will drop from beneath the wing of a bomber and attempt to become the first scramjet to punch through the atmosphere at hypersonic speeds for minutes, not seconds.
Like an airliner's jet engines, supersonic combustion ramjets – or scramjets – work by compressing air enough to ignite fuel which drives air out of the back of the engine to provide thrust. It is designed to work at hypersonic speeds – above about 5 times the speed of sound.
A handful of experimental scramjets have flown successfully, reaching speeds as high as Mach 10, but not for long. "No one has successfully flown a vehicle of this nature for more than a few seconds," says Joe Vogel, X-51 programme manager at Boeing. "Our goal is about 300 seconds of powered flight."
The project is a collaboration between several US military agencies and private firms like Boeing that have ideas about how to solve the problems with heat and manoeuvrability that have limited previous scramjet flights.