Rocket Science: Unexpected Aeroshell Degradation

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The self-peeling (at Mach 20) Falcon HTV-2

Pentagon geeks over at the Defense Advanced Research Projects Agency have blamed last summer’s Falcon Hypersonic Technology Vehicle 2 (HTV-2) flameout on “unexpected aeroshell degradation” (sort of like what can happen to M&Ms under certain conditions).

The $120 million August test over the Pacific ended when “larger than anticipated portions of the vehicle’s skin peeled from the aerostructure” after screaming across the heavens at 13,000 miles an hour — 20 times the speed of sound (and about 20 times as fast as a bullet) — for three minutes.

“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,” DARPA said, summarizing the findings of its independent Engineering Review Board.

It was the second test of such a hypersonic vehicle. “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,” says Air Force Maj. Chris Schulz, the program manager.

The engineering study into the second flight “will inform policy, acquisition and operational decisions for future Conventional Prompt Global Strike initiatives executed by the Office of the Secretary of Defense, Acquisition, Technology & Logistics, Strategic Warfare directorate—the goal of which, ultimately, is to have the capability to reach anywhere in the world in less than one hour,” DARPA says.