An X-51 Path to Hypersonics?

If the Air Force wants to bring hypersonic speed to military systems, it should probably focus on weapons first, said Mark Lewis, University of Maryland professor and former Air Force chief scientist. Hypersonic weapons—loosely defined as those traveling at five times the speed of sound or faster—are relatively attainable, said Lewis at AFA¹s Global Warfare Symposium in Los Angeles last week. The X-51A—an experimental flight vehicle with a supersonic combustion ramjet engine—flew on its own power at Mach 5 for 200 seconds in May 2010. It was launched from a B-52 and is roughly the size and shape of what could be an operational missile, he said. A second X-51 test flight this past June, also from a B-52, was a failure, however, and Lewis lamented what he considers to be USAF’s unduly risk-averse flight-test culture that is “intolerant of failure.” Still, the X-51 is fundamentally different from an operational weapon, so Lewis believes that USAF should push to demonstrate “minutes long” hypersonic flight, while being more willing to take risks—but without committing to dead-end or “bridge too far” technologies.