US military officials have lost contact with the fastest plane ever built during a hypersonic test flight over the Pacific on Thursday.
The Falcon HTV-2 was launched aboard a rocket from Vandenberg air force base in California, on what at first appeared to be a flawless mission.
But after separating from the rocket at the edge of space and beginning its return to Earth, the aircraft went silent during the gliding stage of the test flight, when it was due to perform a series of manoeuvres as it hurtled through the atmosphere.
Officials at the US Defence Advance Research Projects Agency (Darpa) announced they had lost communication with the speeding craft at 4.21pm BST, 36 minutes into the flight.
The unmanned "hypersonic technology flight" had been expected to reach a top speed of Mach 20, or 13,000 mph, and withstand temperatures of 2,000C caused by the ultrafast flow of air around the aircraft.
At that speed, the plane could travel from London to Sydney in less than an hour and cross the US mainland, from New York to Los Angeles, in 12 minutes.