ATOMIC-OXYGEN UNDERCUTTING OF LONG-DURATION EXPOSURE FACILITY ALUMINIZED-KAPTON MULTILAYER INSULATION

Atomic-oxygen undercutting is a potential threat to vulnerable spacecraft materials which have atomic-oxygen protective coatings. Such undercutting is due to the atomic-oxygen attack of oxidizable materials at microscopic defects in the protective coatings. These defects occur during fabrication and handling, or from micrometeroid and debris bombardment in space. An aluminized-polyimide Kapton multilayer insulation sample that was located on the leading edge of the Long Duration Exposure Facility has been used to study low Earth orbit atomic-oxygen undercutting. Cracks in the aluminized coating located around vent holes provided excellent defect sites for the evaluation of atomic-oxygen undercutting. The experimentally observed undercut profiles were compared to predictions from Monte Carlo models for normal incident space ram atomic-oxygen attack. The shape of the undercut profile was found to vary with crack width, which is proportional to the number of oxygen atoms entering the crack. The resulting profiles of atomic-oxygen undercutting which occurred on the aluminized-Kapton sample indicated wide undercut cavities in spite of the fixed ram orientation. Potential causes of the observed undercutting are presented. Implications of the undercutting profiles relevant to Space Station Freedom are also discussed.