Moisture Absorption Characteristics of the Orbiter Thermal Protection System and Methods Used to Prevent Water Ingestion

This paper describes the Orbiter silica tile thermal protection system (TPS); the inherent moisture, absorption problems associated with low-density, highly porous insulation systems; and methods used to minimize and/or prevent water ingestion into the TPS tile. The test programs associated with developing water repellent agents for the tiles, application technique development, flight test program results, and material improvements are discussed.