July 08, 2013
For the Pentagon's advanced research agency, blazing a trail in hypersonics has proved problematic. Now a decade-long program to demonstrate technology for prompt global strike is being wound down, with some hard lessons learned but no flight-test successes.
In its place, the U.S. Defense Advanced Research Projects Agency (Darpa) plans to switch its focus to shorter, tactical ranges and launch a hypersonics “initiative” to include flight demonstrations of an air-breathing cruise missile and unpowered boost-glide weapon. If approved, the demos could be conducted jointly with the U.S. Air Force, which is eager to follow the success of its X-51A scramjet demonstrator with a high-speed strike weapon program.
Darpa's original plan for its Integrated Hypersonics (IH) project was to begin with a third attempt to fly the Lockheed Martin Skunk Works-designed HTV-2 unmanned hypersonic glider, after the first two launches in 2010 and 2011 failed just minutes into their Mach 20 flights across the Pacific. This was to be followed by a more capable Hypersonic X-plane that would have pushed performance even further.
The original plan drew sharp criticism from Boeing executives, who viewed the proposed program as a thinly veiled excuse to fund a third flight of Lockheed's dart-like HTV-2, which they consider unflyable. In laying out its revised program plan, Darpa makes no mention of any political lobbying against the HTV-2, but acknowledges a third flight would not make best use of its resources for hypersonic research.
Instead, as the Pentagon refocuses on China as a threat, Darpa is looking to work with the Air Force to demonstrate hypersonic weapons able to penetrate integrated air defenses and survive to strike targets swiftly, from a safe distance. Air-breathing and boost-glide weapons present challenges different to each other and to HTV-2, but the agency believes the lessons learned so far will prove valuable.
Key take-aways from HTV-2, says Darpa program manager Peter Erbland, include that the U.S. “has got kind of lean” in hypersonics competency as investment has declined from the heady days of the X-30 National Aero-Space Plane, and that “we have to be careful assuming our existing design paradigms are adequate” when developing a new class of hypersonic vehicles.
The HTV-2 sprung some surprises on its two failed flights, first with aerodynamics then with hot structures. Working out what happened “required us to mine all the competency in hypersonics that we have,” he says, and took a team assembled from government, the services, NASA, the Missile Defense Agency, industry and academia.