The Falcon Hypersonic Technology Vehicle 2 (HTV-2), shown in this artist's conception, is an unmanned, rocket-launched, maneuverable aircraft that glides through the Earth's atmosphere at incredibly fast speeds close to Mach 20 (approximately 21,000 kilometres per hour). (DARPA/Associated Press)

An unmanned hypersonic glider developed for U.S. defence research into super-fast global strike capability was launched atop a rocket early Thursday but contact was lost after the experimental craft began flying on its own, the Defense Advanced Research Projects Agency said.

There was no immediate information on how much of the mission's goals were achieved.

The launch from Vandenberg Air Force Base, 210 kilometres northwest of Los Angeles, was the second of two planned flights of a Falcon Hypersonic Technology Vehicle-2. Contact was also lost during the first mission.

Shaped like the tip of a spear, the small craft is part of a U.S. military initiative to develop technology to respond to threats at 20 times the speed of sound ("Mach 20") or greater, reaching any part of the globe in an hour.

The HTV-2 is designed to be launched to the edge of space, separate from its booster and maneuver through the atmosphere at around 21,000 kilometres per hour before intentionally crashing into the ocean. Sound travels in air at around 1200 kilometres per hour, but it travels more slowly at high altitudes (such as near the edge of space), where the air is thinner.

Defense analyst John Pike of Globalsecurity.org wasn't surprised with the latest failure because the hypersonic test flight program is still in its infancy.

"At this early stage of the game, if they did not experience failures, it's because they're not trying very hard," he said.

Pike said it's possible for engineers to still glean useful information about what worked and what didn't, despite the flight ending prematurely. The key is to analyze what happened in the final five seconds before contact was lost.

DARPA used Twitter to announce the launch and status of the flight.

Rocket launch and separation successful

The agency said the launch of the Minotaur 4 rocket was successful and separation was confirmed. It next reported that telemetry — the transmission and measurement of data from the glider — had been lost.

"Downrange assets did not reacquire tracking or telemetry," the agency added. The craft has "an autonomous flight termination capability," it noted.