ShuttleTiles

Takeoff

The [|thermal protection system] consists of various materials applied to the outer surface of the [|orbiter] to protect the orbiter at extreme temperatures, primarily during the re- [|entry] into the atmosphere. These materials are the last defense before the aluminum and graphite epoxy shell. During re- [|entry], the [|TPS] materials perform in temperature ranges from minus 250 F in the cold soak of space to [|entry] temperatures that reach nearly 3,000 oF. Because the [|thermal protection system] is installed on the outside of the [|orbiter] skin, it establishes the aerodynamics over the vehicle in addition to acting as the heat shield. The [|TPS] is a passive system consisting of materials selected for stability at high temperatures and weight efficiency. These materials are as follows: 1. __ [|Reinforced carbon-carbon] __ (RCC) is used on the [|wing] leading edges; the nose cap, including an area near the nose cap on the lower surface, and an area around the forward orbiter/external tank structural attachment. [|RCC] protects areas where temperatures exceed 2,300 oF during [|entry]. 2. Black __ [|High-Temperature Reusable Surface Insulation] [| (HRSI) tiles] __ are used all over the orbiter; there are nearly 20,000 of these tiles on the orbiter. They do not encounter the most extreme temperatures but must withstand some heat. The [|HRSI] tiles protect areas where temperatures are below 2,300 oF. 3. Black tiles called __Fibrous Refractory Composite Insulation__ (FRCI) were developed later in the [|thermal protection system] program. [|FRCI] tiles replace some of the [|HRSI] tiles in selected areas of the [|orbiter]. There are nearly 3,000 FRCI tiles on the shuttle, primarily in areas of high heat. FRCI tiles are mostly used on the base of the shuttle; this is where the highest heat is encountered. 4. __Low-Temperature Reusable Surface Insulation__ (LRSI) white tiles are used in selected areas of the orbiter; such as the vertical tail and upper wing. These tiles protect areas where temperatures are below 1,200 oF. The tiles are white since while in orbit the shuttle encounters extremely low temperatures and the white surface provides better thermal characteristics when the temperature is below 0 oF. 5. __Advanced Flexible Reusable Surface Insulation__ (AFRSI) blankets were developed after the orbiter Columbia was built. AFRSI blankets consist of sewn __composite__ quilted fabric insulation that is sandwiched between two layers of white fabric that are sewn together to essentially form a quilted blanket. [|AFRSI] blankets were used on [|Discovery] and [|Atlantis] and replaced the vast majority of the [|LRSI] tiles. Columbia had the AFRSI blankets added after its seventh flight. Each orbiter has about 1,900 square feet of AFRSI blankets. The advantages to the AFRSI blankets to LRSI tiles are that they are more durable, less fabrication, less installation time and costs, and a weight reduction. These blankets are used in areas where the temperature does not exceed 1,200 oF. 6. White blankets made of coated __Nomex__ [|Felt Reusable Surface Insulation] are used on the upper [|payload bay doors], and portions of the upper [|wing] surface. These blankets are used in areas where the temperature does not exceed 700 oF.

[|REINFORCED CARBON-CARBON]
The reinforced carbon-carbon tiles are produced by impregnating a __graphitized__ rayon cloth with a phenolic resin. Basically, this cloth is filled with some juice. The cloth is then placed in an __autoclave__ for curing. After being cured, the cloth is __pyrolized__ to convert the resin to carbon. The cloth is then impregnated with furfural alcohol in a vacuum chamber, then cured and pyrolized again to convert the alcohol to carbon. The process is repeated three times until the desired carbon-carbon properties are achieved. Then, to ensure that the carbon-carbon material won’t __oxidize__ the outer surface is coated with 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 then placed into a furnace, and the coating is converted while in argon with a stepped-time-temperature cycle up to 3,200 oF. A __diffusion__ reaction occurs between the dry pack and carbon-carbon which causes the outer layers of the carbon-carbon to convert to silicon carbide (a whitish-gray color) without increasing the thickness. The silicon carbide coating protects the carbon-carbon surface from oxidation. But, the silicon-carbide coating can and mostly will develop surface cracks caused by differential __thermal expansion__ mismatch, requiring further oxidation resistance. So the material must end up with the same thermal expansion or it will break. This is provided by impregnating a coated [|RCC] part with tetraethyl orthosilicate. The part is then sealed with a glossy overcoat. The [|RCC] laminate is better than a sandwich design because it is light in weight and rugged. The operating range of [|RCC] is from minus 250 oF to about 3,000 oF, practically the same range as the orbiter encounters in space and during re-entry. The [|RCC] tile is resistant to __fatigue loading__ that is experienced during [|ascent] and re- [|entry].