The Defense Advanced Research Projects Agency is taking to the sky again, this time to run what it say will be the second and final test of its hypersonic Falcon aircraft which is capable if hitting speeds up to Mach 20 or about 13,000MPH.

The Falcon Hypersonic Technology Vehicle 2 is scheduled to launch Wednesday between 7:00am - 1:00 pm PDT from Vandenberg AFB, Calif., aboard an Air Force Minotaur IV rocket which delivers the Falcon to a starting point high in the atmosphere where its engine ignites and if all goes well it will blast through the air for about a half hour, DARPA says.

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Mastery of three key technical challenges stands between the DoD and long-duration hypersonic flight: Aerodynamics; Aerothermal effects; and critical guidance, navigation and control, DARPA says.

DARPA describes the Falcon as a "data truck" with numerous sensors that collect data in an uncertain operating envelope. For its second test flight, engineers adjusted the HTV-2's center of gravity, decreased the angle of attack flown, and will use the onboard reaction control system to augment the vehicle flaps to maintain stability during flight operations, the agency stated.

The first flight of the Falcon in 2010 "collected data that 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."

From the HTV-2 first flight DARPA said it:

Deployed largest number of sea, land, air and space data collection assets in support of hypersonic flight test

Maintained Global Positioning System (GPS) signals while traveling 3.6 miles per second

◦Validated two-way communication with the vehicle

Verified effective use of the Reaction Control System (RCS)

While it helped move the program forward, about nine minutes into its first test 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, DARPA said.

"Assumptions about Mach 20 hypersonic flight were made from physics-based computational models and simulations, wind tunnel testing, and data collected from HTV-2's first test flight-the first real data available in this flight regime at Mach 20," said Air Force Maj. Chris Schulz, HTV-2 program manager in a statement. "It's time to conduct another flight test to validate our assumptions and gain further insight into extremely high Mach regimes that we cannot fully replicate on the ground."

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