Origin and Development of Ablator for Space Shuttle External Tank

THE SPACE SHUTTLE EXTERNAL FUEL TANK (ET) is covered with a Thermal Protection System (TPS). The TPS materials are designed to prevent structural overheating during ascent/descent and maintain good quality cryogenic propellents until main engine cut off.

The primary TPS materials consist of a nonmetallic rigid foam and a composite ablator. These materials and processes were developed through an evolutionary procedure, driven by changing requirements, definitions, and progressively increasing delivery rates. The evolution, from contract start in 1973 to the present, is reviewed.