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.
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