On Saturday NASA plans to fly the second of three X-43A unmanned experimental vehicles designed to test hypersonic flight technologies, notably air-breathing scramjet engines. (The first X-43A was lost in June 2001 when its booster rocket flew out of control and was destroyed just a few seconds into the flight.) However, this flight could be one of the last opportunities in the foreseeable future for hypersonic flight research, at least outside of the Defense Department. Should the second X-43A fail, many insiders consider it unlikely that the last vehicle will ever fly. Regardless of the outcome of the X-43A, though, there’s no clear future for hypersonic flight research in NASA. The agency is refocusing its research on programs directly related to the new exploration initiative, and last week NASA officials confirmed that they have cancelled the X-43C, the follow-on to the X-43A. NASA will continue hypersonic research, officials said, but when–and if–any future vehicle will perform test flights remains uncertain.