The Space Shuttle thermal protection system (TPS)
is the barrier that protects the Space Shuttle Orbiter during the searing 1650°C (3000°F) heat of atmospheric re-entry. A secondary goal is to protect from the heat and cold of space while on orbit. The TPS covers essentially the entire orbiter surface, and consists of seven different materials in varying locations based on amount of required heat protection needed. The one we are going to look at are the black HRSI tiles (High-temperature reusable surface insulation.) HRSI tiles (black in color) provide protection against temperatures up to 1260 °C. There are 20,548 HRSI tiles
which cover the landing gear doors, external tank umbilical connection doors, and the rest of the orbiter's under surfaces. They are used in areas on the upper forward fuselage, parts of the orbital maneuvering system pods, vertical stabilizer leading edge, elevon trailing edges, and upper body flap surface as well. They vary in thickness from 2.54 cm (one inch) to 12.7 cm (five inches), depending upon the heat load encountered during reentry.
The black coating on the tiles is Reaction Cured Glass (RCG) of which tetrasilicide and borosilicate glass
are some of several ingredients. RCG is applied to all but one side of the tile to protect them and to increase the heat sink properties.