NASA's X-43A (Hyper-X) test vehicle currently holds the record for the fastest aircraft.  Back in November 2004, it achieved a speed close to Mach 10 (12,000km/hr or 7,000mph).  That's well into the hypersonic range, which starts at Mach 5.

For the Air Force and U.S. Armed Forces, it's highly desirable to develop hypersonic aircraft.  Such designs could offer strikes in under an hour from the U.S. to anywhere in the world.  Many in the armed forces view hypersonic strike-craft as a potentially game-changing weapon in the fight against terrorism.

On Tuesday the Defense Advanced Research Projects Agency (DARPA) tested a new design, the HTV-2.  The HTV-2 is classified as a hypersonic glider.  To get it up to its extreme target speed of Mach 20, it is first launched to the edge of space aboard a Minotaur IV Lite solid fuel rocket.  

Once at the edge of space the craft detaches and screams down towards its target.  Its thin wedge-shaped body is designed to produce greater lift.  It is protected against the extreme heat  it will encounter by carbon-carbon material used in the body, the same material used in carbon brakes and Space Shuttle tiles.

On Tuesday the craft embarked on its first test flight, launching from Vandenberg Air Force Base in California.  The craft was to fly across the Pacific Ocean before landing at its target, Kwajalein Atoll, a tiny island in a chain of islands northeast of Australia known as the Marshall Islands.  Kwajaleien is approximately 4,800 miles from VAFB.

Launching on its 30 minute journey everything seemed to be going perfectly.  The craft boosted to near-space, then detached successfully.  It hurtled towards Earth, performing the prescribed maneuvers as it went.  And according to DARPA spokeswoman Joanna Jones it "achieved controlled flight within the atmosphere at over Mach 20" -- a new world record.

Then at nine minutes, during the final stages of maneuvers disaster struck.  Something happened and the craft abruptly stopped responding to the Air Force.

That set back may spell trouble for the cash-strapped hypersonic test program.  The hypersonic strike-craft are currently competing with two other technologies.  One alternative is to repurpose ballistic missiles to carry non-nuclear payloads.  However, this runs the risk of nuclear nations mistaking the missile for a nuke and initiating a counter-strike.  

Another option is to use a modified cruise missile that can travel at Mach 5 or Mach 6.  This program, like the hypersonic glider, seems promising, but has been dealt a setback, with tests pushed back from December 2009 to May 2010.

Still, despite the setback the glider may be the best option, if DARPA can fine-tune its design. Dr. Mark Lewis, the former chief scientist of the Air Force, comments, "There’s always a concern that a conventional warhead on an ICBM might be confused with a nuclear device - what can you do to prove otherwise? With a high lift vehicle, your trajectory would be so different that no one would likely confuse it with something more sinister."

The HTV-2 is only the second major experimental aircraft to launch in the last two weeks.  Last week the X-37B unmanned space shuttle was launched by the Air Force into orbit on a super-secret mission.