Tweeting a Mach 20 Test Flight

The Defense Advanced Research Projects Agency, DoD's skunk works, vowed to try again after the second test flight of an aircraft that flies 22 times faster than commercial airplanes, the Falcon Hypersonic Technology Vehicle 2, ended early. DARPA had tweeted the event live on Aug. 11.

In its Aug. 9 news release, DARPA explained that the vehicle would fly at 13,000 mph, fast enough to take it from New York to Los Angeles in less than 12 minutes, and had to withstand temperatures above 3,500 degrees Fahrenheit after being launched atop an Air Force Minotaur IV rocket. The launch at Vandenberg AFB, Calif., went fine and more than nine minutes of data was collected before an anomaly caused the loss of signal. DARPA said Aug. 11 that initial indications are that the gliding aircraft fell into the Pacific Ocean along the planned flight path.

"Here's what we know,”"said Air Force Maj. Chris Schulz, DARPA's HTV-2 program manager. "We know how to boost the aircraft to near space. 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."

"Prior to flight, the technical team completed the most sophisticated simulations and extensive wind tunnel tests possible. But these ground tests have not yielded the necessary knowledge. Filling the gaps in our understanding of hypersonic flight in this demanding regime requires that we be willing to fly," said DARPA Director Regina Dugan. "In the April 2010 test, we obtained four times the amount of data previously available at these speeds. Today more than 20 air, land, sea, and space data collection systems were operational. We'll learn. We'll try again. That's what it takes."

Data from the first flight in April 2010 "demonstrated advances in high lift-to-drag aerodynamics; high temperature materials; thermal protection systems; autonomous flight safety systems; and advanced guidance, navigation, and control for long-duration hypersonic flight," according to the release, which described the flight this way: Approximately nine minutes into the flight, telemetry assets experienced a loss of signal from the HTV-2. The vehicle's onboard system detected a flight anomaly and engaged its onboard safety system, prompting the vehicle to execute a controlled descent into the ocean.

"Wind tunnels capture valuable, relevant hypersonic data and can operate for relatively long durations up to around Mach 15. To replicate speeds above Mach 15 generally requires special wind tunnels, called impulse tunnels, which provide milliseconds or less of data per run," Schulz said prior to the second flight. "To have captured the equivalent aerodynamic data from flight one at only a scale representation on the ground would have required years, tens of millions of dollars, and several hundred impulse tunnel tests. And even then, we wouldn't know exactly what to expect based solely on the snapshots provided in ground testing. Only flight testing reveals the harsh and uncertain reality."

More information about the second test flight is available at this website.

Posted by Jerry Laws on Aug 11, 2011

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