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

Atomic-oxygen undercutting is a potential threat to vulnerable spacecr aft materials which have atomic-oxygen protective coatings. Such under cutting is due to the atomic-oxygen attack of oxidizable materials at microscopic defects in the protective coatings. These defects occur du ring fabrication and handling, or from micrometeroid and debris bombar dment in space. An aluminized-polyimide Kapton multilayer insulation s ample that was located on the leading edge of the Long Duration Exposu re Facility has been used to study low Earth orbit atomic-oxygen under cutting. Cracks in the aluminized coating located around vent holes pr ovided excellent defect sites for the evaluation of atomic-oxygen unde rcutting. The experimentally observed undercut profiles were compared to predictions from Monte Carlo models for normal incident space ram a tomic-oxygen attack. The shape of the undercut profile was found to va ry with crack width, which is proportional to the number of oxygen ato ms entering the crack. The resulting profiles of atomic-oxygen undercu tting which occurred on the aluminized-Kapton sample indicated wide un dercut cavities in spite of the fixed ram orientation. Potential cause s of the observed undercutting are presented. Implications of the unde rcutting profiles relevant to Space Station Freedom are also discussed .