Detailed Description
The TPS is a system of different protection types, not just silica tiles. They are in two basic categories: tile TPS and non-tile TPS. The main selection criteria is using the lightest weight protection capable of handling the heat in a given area. However in some cases a heavier type is used if additional impact resistance is needed. The FIB blankets were primarily adopted for reduced maintenance, not for thermal or weight reasons.
Much of the shuttle is covered with LI-900 silica tiles, made from essentially very pure quartz sand. The insulation prevents heat transfer to the underlying orbiter aluminum skin and structure. These tiles are such poor heat conductors that one can hold one while it is still red hot. There are about 24,300 unique tiles individually fitted on the vehicle, for which the Orbiter has been called "the flying brickyard". Researchers at University of Minnesota and Pennsylvania State University are performing the atomistic simulations to obtain accurate description of interactions between atomic and molecular oxygen with silica surfaces to develop better high-temperature oxidation-protection systems for leading edges on hypersonic vehicles.
The tiles are not mechanically fastened to the vehicle, but glued. Since the brittle tiles cannot flex with the underlying vehicle skin, they are glued to Nomex felt Strain Isolation Pads (SIPs) with RTV silicone adhesive, which are in turn glued to the orbiter skin. These isolate the tiles from the orbiter's structural deflections and expansions.
Read more about this topic: Space Shuttle Thermal Protection System
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