"Return to Flight" Program
In the wake of the Columbia shuttle accident in February 2003, NASA focused its attention on inspection of the wing leading edge, which was penetrated by a piece of foam insulation from the booster fuel tank. The leading edge is a set of three-layer, reinforced carbon-carbon (RCC) panels. All layers must be inspected for potential defects. However, the shape, porosity and composition of the panels pose a challenge to most conventional inspection technologies. The silicon carbon outer layer of the shuttle protects the carbon-carbon material beneath it from the extreme temperatures, but also complicates inspection of deeper layers. To meet the turnaround time requirements for future shuttle flights, the inspection technique must be capable of inspecting the entire leading edge quickly and accurately.
To ensure the safety of future shuttle flights, NASA needed to
accomplish the following:
Identify suitable technology to inspect the entire leading edge quickly
Establish inspection procedures
Implement the technology for ongoing inspections of the shuttle
Operate in constrained environment
Inspect entire volume of leading edge
Develop uniform procedures and training
Archive entire inspection
After evaluating alternatives, NASA selected TWI to provide equipment and assist in the development of procedures and best practices for thermographic NDT of the shuttle leading edge. The TWI EchoTherm system was modified to accommodate the space and environmental constraints of the inspection facility. The system was designed to operate on a robotic gantry system. Since inspection of the entire structure requires numerous acquisitions, the TWI MOSAIQ software is used to combine the data into a single image. The TSR® processing in MOSAIQ allows detection of deeper or more subtle indications.
NASA successfully implemented the EchoTherm NDT system as the primary inspection method for the shuttle leading edge. To date, the system has successfully identified anomalies in the leading edge that would have otherwise gone undetected. TWI has presented several training courses to NASA personnel and contractors, and continues to provide assistance to the Return to Flight program.