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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.

US military loses contact with hypersonic aircraft

US military scientists lost contact with an unmanned hypersonic experimental aircraft on its second test flight, officials said.

The Falcon Hypersonic Test Vehicle 2 (HTV-2) successfully separated from its rocket but lost contact shortly into its "glide phase".

The plane is designed to travel at Mach 20, or 20 times the speed of sound.

The Falcon project is part of the US defence department's plans to develop a rapid-strike weapons system.

A hypersonic plane could potentially enable the US military to hit targets anywhere in the world in under an hour.

Highly complex

The HTV-2 - shaped like the tip of a spear - took off atop a Minotaur IV rocket from Vanderberg Air Force Base in California early on Thursday.

It was propelled to the edges of space where it then separated from the rocket.

The aim by engineers was that it would glide back to Earth at 13,000mph (21,000km/h) - enduring temperatures in excess of 3,500F (2,000C) - before plunging into the Pacific Ocean.

The Defense Advanced Research Projects Agency (Darpa), which is funding the HTV-2 programme and overseeing the tests, said more than nine minutes of data was collected "before an anomaly caused loss of signal".

"Initial indications are that the aircraft impacted the Pacific Ocean along the planned flight path," Darpa said in a statement on its website.

An HTV-2 plane was first tested last year, and ended with the craft crashing into the Pacific after the military lost contact with the glider nine minutes into the flight.

However, the flight still managed to return 139 seconds of aerodynamic data at a velocity between 17 and 22 times the speed of sound, Darpa said.

"We know how to boost the aircraft to near space," Maj Chris Schulz, the programme manager, was quoted as saying on Darpa's website.

"We know how to insert the aircraft into atmospheric hypersonic flight. We do not yet know how to achieve the desired control during the aerodynamic phase of flight. It's vexing; I'm confident there is a solution. We have to find it."

Maj Shulz said a team of experts would now analyse the flight data and expand "our technical understanding of this incredibly harsh flight regime".

Some analysts say a second uncompleted flight could force Darpa to rethink the entire project, the BBC's Marcus George in Washington reports.

kostmayer wrote:Maybe Moonraker stole it.