Unmanned Falcon Hypersonic Technology Vehicle 2 can travel from London to Sydney in less than an hour

By the time you finish reading this sentence, the Falcon HTV-2, the fastest plane ever built, could have flown 18 miles. It would get from London to Sydney in less than an hour, while withstanding temperatures of almost 2,000C, hotter than the melting point of steel.

At 3pm BST on Thursday , the US Defence Advance Research Projects Agency will launch the Falcon Hypersonic Technology Vehicle 2 on the back of a rocket from the Vandenberg Air Force Base in California. If all goes to plan, engineers will launch the Falcon HTV-2 to the edge of space, before detaching the plane and guiding it on a hypersonic flight that will reach speeds of 13,000mph (about 20 times the speed of sound) on its return to Earth.

The Falcon started life in 2003, part of a US military research project to build a plane that could reach (and potentially deliver bombs to) any part of the world in less than an hour.

The plane has been tested in computer models and wind tunnels, but they can only simulate speeds up to Mach 15 (11,400mph). A real test is the only way to determine if the plane will remain flying at high speeds.

Thursday's flight will also test the carbon composite materials designed to withstand the extreme temperatures the plane will experience on its skin and also the navigation systems that will control its trajectory as it moves at almost four miles per second.

The design and flight pattern of the plane has been tweaked since an aborted test flight in April last year. Nine minutes into that mission, which succeeded in flying for 139 seconds at Mach 22 (16,700mph), the onboard computer detected an anomaly and ordered the plane to ditch into the ocean for safety reasons.

Unlike most other rocket launches, this one will not be shown live online, though it will be possible to follow the plane's progress via tweets from @DARPA_News.