"Photo Description:" With the X-43A and its booster rocket tucked under its right wing, NASA's venerable B-52B mothership climbs out after takeoff on its final research mission. "Project Description:" The high-risk, unpiloted X-43A flights are the first actual flight tests of an aircraft powered by a scramjet engine capable of operating at hypersonic speeds (above Mach 5, or five times the speed of sound). The X-43A is powered by a revolutionary air-breathing supersonic-combustio n ramjet or "scramjet" engine.