The Columbia tragedy has been attributed to ingress of hot plasma into a breach in the wing leading edge upon re-entry. High temperature materials chemistry and thermodynamics of interactions of the re-entry plasma with components of the wing leading edge were used to evaluate possible failure mechanisms. An answer to the following question was sought: Could any correlation be made between time, temperature, and altitude at which deposits inside the wing leading edge occurred to aid in establishing a sequence of failure events? In this presentation, wing leading edge materials are described: reinforced carbon-carbon panels, attachment hardware, and the insulation on the attachment hardware. Possible melting reactions, material reactions with the plasma, and reactions between components within the wing leading edge are described. Results from simple laboratory furnace simulations are described. Correlations with actual deposits found on the interior of the recovered RCC panels were made. Scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction analysis, electron microprobe and wavelength dispersive spectroscopy were used to analyze the debris deposits and laboratory material. The left hand wing evidence showed longer breach duration through heavier deposits and eroded RCC panels. Deposits of resolidified metal and resolidified ceramic insulation on the interior of the wing leading edge proved particularly valuable in delineating temperatures and an understanding of the sequence of events which led to the tragedy. A lower limit to the maximum temperature experienced within the wing leading edge (1800°C) was established based on melting temperature of the ceramic insulation. No correlation to altitude could be made since the environment was relatively oxidizing for the re-entry trajectory conditions considered. Layering within the deposits provided information about the sequence of events.

Acknowledgments. NASA-Glenn: Jim Smialek, Don Humphrey, Dave Hull, Ralph Garlick, Jim Smith, Terry McCue, Leslie Greenbauer-Seng. NASA-Marshall: Sandeep Shah, James Coston, Greg Steele