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Thermal Protection and Non-Destructive Evaluation
08.04.05
 
Many of Langley's technical discipline areas have been tapped to safely return the Shuttle to flight, including aerodynamics, aero-thermodynamics, structures and materials, systems analysis and engineering.

Langley researchers have demonstrated non-destructive methods for detection of flaws in the Shuttle External Tank foam.

Image above: Langley researchers have demonstrated non-destructive methods for detection of flaws in the Shuttle External Tank foam. Credit: NASA

These technical strengths have primarily been focused on achieving a better understanding of the Shuttle's heat shield, or Thermal Protection System (TPS) - what can make the TPS fail, how to inspect the TPS without harming it, how to repair the TPS on orbit and when it is safe to fly even with minor damage.

NASA Langley has:
  • Contributed to a better understanding of the material properties of the foam that fell from the Shuttle External (fuel) Tank.
     
  • Contributed new ways of detecting problems in the TPS for both the External Tank and the Shuttle Orbiter using advanced nondestructive examination techniques.
     
  • Developed physics based models describing the damage caused by debris striking the Orbiter wing leading edge and heat shield tiles.
     
  • Developed concepts to inspect and repair the Reinforced Carbon-Carbon (RCC) panels on the Orbiter wing leading edge and supported efforts to repair tile damage.
     
  • Run wind tunnel tests to ensure that minor damage (cavities) and repairs to tiles or the wing leading edge will not cause a heating problem when the Shuttle returns to Earth.
     
High-speed impact testing of Shuttle External Tank foam

Image above: Langley researcher places a sample of foam like that on the Shuttle External Tank into a crushing device to determine how the foam reacts when it strikes something at high speed. Credit: NASA

Inspecting Without Harming

The Columbia Accident Investigation Board specifically called for developing a nondestructive evaluation (NDE) inspection plan for reinforced carbon-carbon (RCC) areas of the Shuttle, to include the Orbiter's wing leading edge. NDE produces critical information concerning the condition of a structure without harming it, as opposed to destructive testing methods where the structure is damaged in testing and no longer usable. NDE methods can see beneath the surface of a structure.

NDE methods pioneered by Langley have been adopted for ground tests of RCC insulation material on each Orbiter between flights.

Researchers at Langley have helped with the development of a new NDE testing method known as Terahertz imaging being used to detect voids and other flaws in the spray-on foam insulation on the External Tank to prevent the materials' failure during flight. The system can provide three-dimensional information on the foam area being tested. The resulting pictures are high resolution and are produced in real time.