Space Shuttle Tiles
Here is a CNN article (Feb. 3, 2003) about the space shuttle tiles. It indicates that the tiles are made of a silica fiber compound, a material derived 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. They are then baked in the nation's largest microwave, in Sunnyvale, California, and fused in a 2,350 degree oven.
A NASA note written in 1997 indicates that their value is between $1000 and $4000, although they are not for sale.
A materials chemistry article states that "the tiles consist of fine glass fibers organized in an open cellular pattern, so that tiny spaces account for 95% of their volume".
Through his contacts with NASA, Harry Nelson, Director of the John Deere
Planetarium from 1968 to 1988, acquired a couple of space shuttle tiles.
The photo above shows one of them. It measures 15 x 15 x 6.5 cm. Its
mass is 266 g so its density is 0.18 g/cm3.
The following paragraphs are from a book called "The Space Shuttle Operator's Manual" published in 1982 (ISBN 0-345-30321-0).
|The black areas on the Orbiter are covered with blocks or
tiles of varying size and thickness. These are called
"high-temperature reusable surface insulation", or HRSI
tiles. HRSI tiles protect areas where temperatures are between
650°C (1200°F) and 1275°C (2300°F).
On Columbia, white tiles cover the forward fuselage, outer wing areas, pods, and the stabilizer. Called "low-temperature reusable surface insulation", or LRSI, these tiles are used where temperatures are between 370°C (700°F) and 650°C (1200°F).
Columbia's cargo-bay doors, fuselage sides, upper wing surfaces, and aft areas of the OMS pods are covered with a Nomex felt material. These areas remain below 370°C (700°F) during flight.
Altogether, nearly 32,000 HRSI and LRSI tiles cover Columbia. No two tiles are alike and each must be installed by hand. Both types of tiles are made from extremely pure (99.5%) sand. The sand is crushed into very small silica fibers and added to a ceramic binder. This mixture is fired to produce the blocks. They are machined to the proper size and shape, then the black or white coating is applied to their outer surfaces. The coating is made from a high-strength refractory glass.
An aluminum structure like that of the Orbiter flexes and bends slightly in flight. The TPS (thermal protection system) tiles covering the vehicle must be very close together. On the underside, the largest allowable gap between tiles is only 0.065" (1.6 mm). These glass-covered silica tiles are rather brittle and cannot flex or bend without breaking. To let the structure flex while keeping the TPS rigid, Nomex felt pads are sandwiched between the tiles and the structure. This way, the structure can move without moving the tiles. The pads and the tiles are attached with a thin layer of a room temperature vulcanizing silicon adhesive.