One of the main components of the Space Shuttle's thermal protection system for reentry was the layer of tiles on the outside of the orbiter. What, if any, changes were made to the composition of these tiles between the first and last flights of the Shuttle program?
In 1981, each shuttle had more than 24,000 tiles of six by six inch blocks made of silica (high grade sand) and fibres. These are made of silica fibres and chemicals mixed, molded and heated at microwave oven at 2350 degrees, at which temperature the silica fuses to form a high temperature insulator.
In earlier days of the shuttle program, three types of spray on foams were used
- polyurethane foam (BX_250)
- polyisocyanurate foam (NCFI 24_124,NCFI 24_57)
Both of the foams are applied with the blowing agent HCHC-141b
Previously spacecraft used ablative heat shield which usually burnt off and cannot be reused after re-entry and they are very heavy and they are also used in Apollo command module comprised of 0.333 of vehicles weight and they are fragile and can be crush a tiles by hand
After Columbia accident the changes are made to the tiles:
EMITTANCE WASH - (polish) consist of silicon carbide fibres and mixed with strong glue which attachs them to the tiles leading to stiffer bonds and on ground testing indicated that the material has increased the amount of heat that damages the tiles by 70 to 160 degrees
RENFORCED CARBON_CARBON-the light gray material capable of withstanding 1510 degree placed in the leading edges of the wing and the nose cap and 6.4 to 13 mm thick 22 RCC plates are attached to each orbitor
SHUTTLE TILE ABLATOR 54 -it is basically a mixture of room_temperature_vulcanizing rubber, glass microballoons , silicone oil , a fumed silica (Cab-O-Sil) and a catalyst . the technique uses silicone condensation reaction to create silicon rubber which pyrolised during re-entry to a ceramic state
RCC was made from laminated composite material made from graphite rayon cloth and impregnated with phenolic resins and exposed to high temperature (curing) in autoclave and pyrolised to convet the resin to carbon and then impregnated in furfural alcohol in vacuum chamber the heated till the desired properties are achieved