Reinforced Carbon-Carbon

RCC fabrication begins with a rayon cloth graphitized and impregnated with a phenolic resin. This impregnated cloth is layed up as a laminate and cured in an autoclave. After being cured, the laminate is pyrolized to convert the resin to carbon. This is then impregnated with furfural alcohol in a vacuum chamber, then cured and pyrolized again to convert the furfural alcohol to carbon. This process is repeated three times until the desired carbon-carbon properties are achieved.

To provide oxidation resistance for reuse capability, the outer layers of the RCC are converted to silicon carbide. The RCC is packed in a retort with a dry pack material made up of a mixture of alumina, silicon and silicon carbide. The retort is placed in a furnace, and the coating conversion process takes place in argon with a stepped-time-temperature cycle up to 3,200º F. A diffusion reaction occurs between the dry pack and carbon-carbon in which the outer layers of the carbon-carbon are converted to silicon carbide (whitish-gray color) with no thickness increase. It is this silicon-carbide coating that protects the carbon-carbon from oxidation. The silicon-carbide coating develops surface cracks caused by differential thermal expansion mismatch, requiring further oxidation resistance. That is provided by impregnation of a coated RCC part with tetraethyl orthosilicate. The part is then sealed with a glossy overcoat. The RCC laminate is superior to a sandwich design because it is light in weight and rugged; and it promotes internal cross-radiation from the hot stagnation region to cooler areas, thus reducing stagnation temperatures and thermal gradients around the leading edge. The operating range of RCC is from minus 250º F to about 3,000º F. The RCC is highly resistant to fatigue loading that is experienced during ascent and entry.

The RCC panels are mechanically attached to the wing with a series of floating joints to reduce loading on the panels caused by wing deflections. The seal between each wing leading edge panel is referred to as a T-seal. The T-seals allow for lateral motion and thermal expansion differences between the RCC and the orbiter wing. In addition, they prevent the direct flow of hot boundary layer gases into the wing leading edge cavity during entry. The T-seals are constructed of RCC.

Since carbon is a good thermal conductor, the adjacent aluminum and the metallic attachments must be protected from exceeding temperature limits by internal insulation. Inconel 718 and A-286 fittings are bolted to flanges on the RCC components and are attached to the aluminum wing spars and nose bulkhead. Inconel-covered cerachrome insulation protects the metallic attach fittings and spar from the heat radiated from the inside surface of the RCC wing panels.

The nose cap thermal insulation ues a blanket made from ceramic fibers and filled with silica fibers. HRSI or FRCI tiles are used to protect the forward fuselage from the heat radiated from the hot inside surface of the RCC.

During flight operations, damage has occurred in the area between the RCC nose cap and the nose landing gear doors from impact during ascent and excess heat during entry. The HRSI tiles in this area are to be replaced with RCC.

In the immediate area surrounding the forward orbiter/ET attach point, an AB312 ceramic cloth blanket is placed on the forward fuselage. RCC is placed over the blanket and is attached by metal standoffs for additional protection from the forward orbiter/ET attach point pyrotechnics.