By Adam Levine

Military researchers conducting the flight of the fastest unmanned aircraft ever launched said Thursday an "anomaly" caused a lost contact with the vehicle nine minutes into its flight. The plane is believed to have crashed in the Pacific at some point along the planned flight path, according to a statement from the Defense Advanced Research Project Agency (DARPA), which conducted the test.

The Falcon Hypersonic Test Vehicle (HTV-2) had successfully separated from the launch vehicle and was performing "glide phase" maneuvers meant to test its aerodynamics when contact was lost, according to an 11 a.m. (ET) Twitter post from DARPA. A tweet, at 12:30 p.m. said downrange trackers were unable to relocate the HTV2 but the vehicle "has an autonomous flight termination capability".

The vehicle was launched by a Minotaur IV rocket from Vandenberg Air Force Base in California, before separating and re-entering the atmosphere over the Pacific. The launch, originally slated for Wednesday but then scrubbed because of weather, was not broadcast live.

This was the second run for the craft. In April 2010 ended with the aircraft crashing into the Pacific after a loss of contact nine minutes into the flight. But those nine minutes provided some key information about flying 22 times faster than a commercial jetliner.

Thursday's flight was to test control and communications capabilities, as well as heat resistance and other effects of hypersonic flight. The nine minutes of data demonstrated that launching the aircraft was mastered but they continued to be stymied in controlling the vehicle at Mach 20 speed.

"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," said Air Force Maj. Chris Schulz, the DARPA program manager.

DARPA's goal is to create the capability of reaching any target in the world in less than an hour.

The triangular wedge of zoom is capable of reaching Mach 20 – approximately 13,000 miles per hour – according to DARPA. At such speeds in Earth's atmosphere, friction subjects the vehicle to temperatures of more than 3,500 degrees Fahrenheit.

As DARPA said on the HTV-2 site, at that speed "air doesn't travel around you – you rip it apart."