Shell Degradation Cause Of DARPA Hypersonic Vehicle Flight Abort
April 22, 2012

DARPA’s Hypersonic Glider Aborted Due To Shell Degradation

An experimental hypersonic glider was forced to abort its 13,000 mph flight over the Pacific Ocean during the summer of 2011 because larger than expected portions of its skin peeled off, officials from the US Defense Advanced Research Projects Agency (DARPA) announced on Friday.

According to the Associated Press (AP), the Hypersonic Technology Vehicle-2 (HTV-2) launched atop a rocket from California's Vandenberg Air Force Base last August 11 as part of research into the development of extremely-fast global strike capability for the Department of Defense.

It was able to reach speeds of up to Mach 20 (20 times the speed of sound) for three minutes before its autonomous flight safety system aborted the flight, landing it in the ocean.

While officials expected some of the vehicle's skin to gradually wear away, an independent engineering review board (ERB) concluded that the unmanned craft shed more than anticipated, creating gaps which caused the vehicle to roll, according to the AP's John Antczak.

Representatives of the agency said that the HTV-2 was able to correct itself on multiple occasions, but the disturbances eventually overwhelmed it, and the excessive aeroshell degradation led to the activation of the craft's Flight Safety Systems and an eventual splashdown into the ocean itself, DARPA said in an April 20 press release.

"Approximately nine minutes into the test flight, the vehicle experienced a series of shocks culminating in an anomaly, which prompted the autonomous flight safety system to use the vehicle´s aerodynamic systems to make a controlled descent and splashdown into the ocean," the defense research organization said.

“The initial shockwave disturbances experienced during second flight, from which the vehicle was able to recover and continue controlled flight, exceeded by more than 100 times what the vehicle was designed to withstand,” added DARPA's Acting Director, Kaigham J. Gabriel. “That´s a major validation that we´re advancing our understanding of aerodynamic control for hypersonic flight.”

Following the ERB review, DARPA said that they will attempt to improve the heat-stress allowances of the HTV-2's outer shell, as well as enhance models for determining thermal uncertainties based on data collected from both the original test flight and the second, most recent one. Ultimately, they said that the goal of the craft is to be able to travel anywhere in the world in less than an hour.

"Data collected during the second test flight revealed new knowledge about thermal-protective material properties and uncertainties for Mach 20 flight inside the atmosphere, which can now be used to adjust our assumptions based on actual flight data and modify our modeling and simulation to better characterize thermal uncertainties and determine how to assess integrated thermal systems," Air Force Major and DARPA program manager Chris Schulz said.

Schulz added that the board's findings will result in "a profound advancement in understanding the areas we need to focus on to advance aerothermal structures for future hypersonic vehicles."