The orbiter's nose cap is fabricated as one piece while each of the wings has 22 seperate RCC panels and T- seals on the leading edge. Each panel is affixed to the orbiter's skin by mechanical attachments. About 70 percent of an orbiter's external surface is shielded from heat by a network of more than 24,000 tiles formed from a silica fiber compound. More advanced materials such as Flexible Insulation Blankets have replaced tiles on some of the upper surfaces of the orbiter. LRSI is still used on the upper surface of the forward fuselage above the crew windows and on some parts of the OMS pods.
Tiles vary in size, thickness and density.
LRSI tiles are larger and thinner, generally 8 inches square and from 0.2 to 1 inch thick. The thermal properties of the tiles are dependent on their very high purity. The manufacture of both types of tiles begins with fibers of pure white silica refined from common sand. The fibers are mixed with deionized water and other chemicals and poured into a plastic mold where excess liquid is squeezed out of the mixture. Lockheed Space Operations Co. Then, they are sintered in a 2,350 degrees F oven.