The X-43A was a hypersonic aircraft test program that NASA flight-tested successfully in 2004. Carried aloft by NASA's Boeing B-52B, the tiny, unmanned X-43A -- only 14 feet long and shaped rather like a surfboard -- was mounted on a modified Pegasus booster that accelerated the vehicle to a speed where its little scramjet engine could work and the X-43A could fly under its own power. Part of NASA's larger Hyper-X program, the X-43A reached a speed of Mach 9.8 in atmospheric flight. Here, the NASA B-52B takes off carrying the second of three X-43As on its Pegasus rocket. Credit: NASA Dryden Flight Research Center
