HYPERSONICS: THE NEXT GREAT LEAP; The next paradigm shift in aircraft technology will be based on hypersonics, air-breathing aircraft able to travel at five times the speed of sound or more. (Air-breathing is a key aspect. Rockets have to carry their own oxygen to burn their fuel, which means that for the same payload, a rocket must be larger than an aircraft.) Everyone is interested. The Air Force imagines manned bombers than can strike targets halfway around the world in one-fifth of the time the B-2 needs. NASA wants to replace the shuttle with a large hypersonic aircraft that would climb to the edge of space and then launch a rocket-driven "second stage" into orbit. The Navy wants anti-ship cruise missiles that travel at five times the speed of sound. The Army wants a ground-launched missile that could hit a mobile Scud launcher (detected by satellite or a recon drone) before it could reach a hide site. The Air Force, NASA, DARPA, the Navy, and the Army are working together to establish a road map to reach this technology. The Air Force has already begun a project to build a scramjet (supersonic combustion ramjet). The X-43A is to fly next June on hydrogen-fueled scramjet engines. The X-43A should reach Mach-7 and may eventually reach Mach-10. The X-43B will use the new ISTAR engine. This has a pure rocket engine to reach Mach-2.5, at which point the engine would convert into a ramjet and accelerate to Mach-5, at which point the engine would convert into a scramjet and climb to Mach-7. The advantage of this system is that the same aircraft could switch its engine back into a rocket to climb into orbit once it ran out of atmosphere to burn. Later, the X-43C would test a hydrocarbon scramjet, and the X-43D may reach Mach-15 on pure hydrogen. Critics fault the Air Force, however, for failure to establish a strict system of analyzing hypersonic systems.--Stephen V Cole