GRAHAM WARWICK / WASHINGTON DC
Successful Mach 7 mission is crucial to plans to fly vehicle at M10 and for follow-on faster experimental craft
NASA has scheduled its crucial second attempt to fly the X-43A experimental hypersonic vehicle for 21 February at the earliest, but is still analysing an anomaly in a booster actuator controller that could delay the flight. The first X-43A was destroyed in June 2001 when its Orbital Sciences Pegasus booster malfunctioned after air launch from NASA's Boeing B-52.
"There is a high probability the flight will slide into March," says Chuck McClinton, NASA deputy director of the National Aerospace Initiative's high-speed hypersonics pillar. A successful Mach 7 first flight of the unmanned X-43A is crucial to plans for a second flight at M10 later this year, and for a follow-on X-43C capable of accelerating from M5 to M7 and a proposed X-43D capable of M15. The X-43C is planned to fly in 2007, followed by the as-yet unfunded X-43D around 2010.
Loss of the first X-43A was blamed on stability and control modelling deficiencies and the booster has been upgraded for the second flight, including dual actuator motors. The booster will be dropped at 40,000ft (12,200m), compared with 23,000ft on the first flight, to reduce transonic dynamic pressure. Propellant load has been reduced by 1,600kg (3,500lb). The expendable X-43A will be accelerated to M7 then released.
A successful mission is crucial to proving a supersonic-combustion ramjet (scramjet) can be started and operated in flight, albeit for only 10s. The X-43C is intended to demonstrate that a scramjet can generate sufficient thrust to accelerate. Whereas the hydrogen-fuelled X-43A has a copper heat-sink engine, the hydrocarbon-fuelled X-43C will have a flight-weight, fuel-cooled scramjet providing3-5min of powered flight. The proposed X-43D would have a hydrogen-powered, fuel-cooled scramjet capable for running for over 1min and accelerating the vehicle to M15.
NASA has awarded Alliant Techsystems (ATK) a contract to build three X-43Cs, powered by a dual-mode ramjet/scramjet engine developed with Pratt & Whitney. ATK and P&W plan to run a second, flight-weight scramjet ground-demonstrator engine in December. This will represent one of the three engine modules on the X-43C, and will be followed in 2005 by a two-thirds-scale multi-module flowpath demonstrator, complete with inlet and nozzle, and in 2006 by a flight clearance engine.
The first X-43C flight is planned for the third quarter of 2007, followed by the second in June 2008 and third in March 2009. Each vehicle will be air-dropped from NASA's B-52 and accelerated to M5.8 by a Pegasus-derived booster. NASA is looking at ways to recover one or more of the vehicles to assess engine condition.
NASA plans to complete flight testing of an X-43A low-speed model in February, and to follow with flights of a low-speed model of the larger X-43B, now renamed the Reusable Combined-Cycle Flight Demonstrator. Built by Accurate Automation, the turbojet-powered X-43A-LS demonstrated good handling in previous flights, says McClinton, but "roll and pitch control were not well harmonised". Pitch stability margin will be reduced for the next flights. The larger X-43B-LS is powered by two 110,000lb-thrust (480kN) turbojets, built by SWB Turbines, and has canard foreplanes.
Source: Flight International
