Guy Norris/LOS ANGELES
The first hypersonic X-43A test vehicle, designed to demonstrate the use of an airframe-integrated scramjet (supersonic ramjet), is expected to be delivered to NASA in July.
The 3.6m (11ft)-long X-43A forms the core of NASA's Hyper-X programme. This is aimed at proving the use of air-breathing engine technologies to increase the payload capacities of future hypersonic aircraft (faster than Mach 5) and reusable space launchers.
The overall shape of the X-43A, built by MicroCraft of Tullahoma, Tennessee, resembles that of the defunct National Aero-Space Plane, which was designed around the same scramjet propulsion concept. The forebody is shaped to generate shock waves which compress the air entering the scramjet intake mounted below the fuselage. Hydrogen-based fuel is injected into the scramjet and combusts spontaneously on contact with the oxygen in the compressed air.
The X-43A will be attached to a modified Orbital Sciences-built Pegasus booster and air launched from NASA's Boeing B-52 near San Nicolas island off the California coast. The first of three planned flights is expected around the end of January, says Hyper-X deputy programme manager Don Gatlin. The second of the three X-43A vehicles is scheduled to arrive at NASA's Dryden Flight Research Centre a month after the planned first flight.
Mounted on the nose of the Pegasus, the X-43A will drop from the B-52 at between 18,000ft and 20,000ft, from where it will be boosted to around 45,000ft. From here, it will climb more gradually to around 100,000ft before separating from the Pegasus.
After 30s, and once the flightpath has stabilised, NASA plans to open the cowl covering the intake which is closed for the boost phase. The scramjet will then operate for 7s to demonstrate forward thrust in flight. NASA plans to achieve Mach 7 with the first two flights.
Following the scramjet test, the cowl will be closed again and the engine shut off. The X-43A will go into a high-speed manoeuvring glide, during which it will collect up to 6min of hypersonic aerodynamic data.
"We will get data on stability at Mach 6, 5 and 4 before it goes subsonic and we lose it," says Gatlin. NASA will not recover the vehicle, and its earlier plans to fit landing gear and re-orientate the flightpath towards San Nicolas island have been abandoned.
The M7 flights will cover about 1,000km (700nm} in 500s. The M10 flights are expected to cover 1,570km in roughly the same time. During the M10 flight, due around September 2001, the aircraft will travel at about two miles/s, or the equivalent of 7,200mph at sea level. Data from the five-year Phase I scramjet technology validation programme are expected to be contribute to a second programme which would involve the construction and testing of a larger, reusable hypersonic X-plane.
Source: Flight International
