Failure analysis of a thermal tile on the space shuttle Columbia

Abstract

Several high-temperature reusable surface insulation (HRSI) tiles from the space shuttle Columbia were analyzed for their response to the catastrophic events during re-entry. The analysis of the HRSI tile focused on the outer surface, which was composed of silica tile with a reaction-cured glass (RCG) coating, and the inner surface strain isolation pad, which is bonded to the tile using a room-temperature vulcanizing silicone adhesive. Light optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to evaluate the tile surfaces. The tiles were found to have a heavily damaged outer surface, with much of the top RCG coating eroded by impact from shuttle debris and/or plasma flow during the shuttle’s breakup and re-entry. The RCG experienced slumping and the silica exhibited melting and glassification due to temperatures exceeding the glass transition temperature and the anticipated tile operating temperatures. Deep cavities present in the material were found to contain metal particles that are not normally present and suggest impact with shuttle debris. Silicone adhesive degradation was also found. The slumping of the silica, the degraded adhesive, and the erosion of the tile contributed to a complex process during which the individual tile delaminated from the shuttle airframe.