The United States military loses contact with an unmanned plane designed to be able to reach any global target in one hour. The hypersonic Falcon HTV-2 was on a test flight.

The problems with the test flight are an embarrassment to the US Defence Advanced Research Projects Agency (Darpa), particularly because almost the same thing happened on the first test mission for the unmanned craft in April.

The plane, designed to be the fastest ever, lost contact with ground control soon after being launched from a base in California on Thursday.

It left Vandenberg Air Force Base in California and separated from its launch vehicle successfully. The arrow-headed plane was expected to separate from its rocket near the top of its ascent and then glide back to earth, reaching hypersonic speed before plunging into the Pacific ocean.

But Darpa said that its monitoring stations lost contact with the aircraft around half an hour into the flight.

“Downrange assets did not re-acquire tracking or telemetry. HTV-2 has an autonomous flight termination capacity,” the organisation said via social networking site Twitter.

The plane is part of plans from the United States Department of Defense to build what it calls a “prompt global strike” capability, enabling it to hit global targets within an hour with conventional or nuclear warheads. It is capable of gliding down from the upper atmosphere at 20 times the speed of sound.