NASA's X-43A Hyper-X mishap investigation board has concluded that the 2 June2001 hypersonic test attempt failed because of a deficient vehicle control system stemming from modelling inaccuracies.
The failure sequence began seconds after the X-43A, mounted on the front of an Orbital Sciences Pegasus booster, was dropped from the NASA Boeing B-52 mothership over the Pacific test range. As the vehicle began a planned pitch-up towards an altitude of 95,000ft (29,000m), the booster began to experience roll oscillation. At 13.5s after release, and at 22,000ft, the starboard elevon suffered structural overload and the vehicle began to fly out of control. The booster was destroyed 48.6s after release.
NASA says "major contributors to the mishap" included modelling inaccuracies in the booster fin actuation system and aerodynamics, and "insufficient variations of modelling parameters. The flight mishap could only be reproduced when all of the modelling inaccuracies with uncertainty variations were incorporated in the analysis."
A second attempt to test air-breathing hypersonic propulsion at Mach 7 will be made with the second X-43A around October or November.
Source: Flight International
