Two hypersonic vehicle prototypes developed by the Defense Advanced Research Projects Agency and the Air Force are due to fly by the end of the year, the agency’s director said May 1.

One vehicle is part of the hypersonic air-breathing weapon concept, or HAWC, program. The other is the tactical boost glide, or TBG, effort, said Steven Walker.

“We’re on track for both to have flights … before the calendar year ends,” he told reporters during a breakfast meeting in Washington, D.C. However, that might be questionable because once “you actually get into the building of these things and qualifying the hardware, … things tend to slip.”

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