Reinforced Carbon-Carbon (RCC)

Reinforced Carbon-Carbon, or RCC, is the tough gray material that protected the hottest, most stressed parts of the Space Shuttle as it slammed back into the atmosphere. It is a heat shield and a structural skin rolled into one.

Quick facts

• What it is: A composite (a material made from two parts working together) of carbon fibers held in a carbon matrix – hence “carbon-carbon.” Also called C/C or CFRC.
• Heat it survives: Roughly 1,510 C (2,750 F) at the Shuttle’s wing leading edges, within a surrounding environment reaching about 1,650 C (3,000 F). Carbon-carbon keeps useful strength above 2,000 C, and RCC’s quoted operating range runs from about -250 F to 3,000 F.
• Weight: Around 1.6-1.98 grams per cubic centimeter – much heavier than the Shuttle’s silica tiles.
• On the Shuttle: Each orbiter wing carried 22 RCC panels, roughly 1/4 to 1/2 inch (6.4-12.7 mm) thick.
• Cost: Famously expensive, on the order of $100,000 per square foot to produce.

What it is and how it works

Reinforced Carbon-Carbon is built up in stages. Carbon cloth (originally a graphite rayon fabric) is layered with a phenolic resin – a kind of glue that hardens with heat – then cured in an autoclave (a high-pressure oven). The part is then pyrolized: heated until that resin breaks down into pure carbon. Workers repeatedly soak it with a carbon-yielding liquid such as furfuryl alcohol and re-pyrolize it, a process called densification that fills voids and builds a dense, all-carbon body.

There is one problem: bare carbon would simply burn up in the hot, oxygen-rich plasma (superheated, electrically charged gas) of reentry. So the outer surface is converted to silicon carbide and sealed with a treatment called TEOS to block oxygen from reaching the carbon underneath.

Here is the key difference from the Shuttle’s familiar white and black tiles. The tiles mostly insulate, slowing heat down. RCC instead tolerates the heat directly. Its all-carbon structure stays strong at temperatures that would melt metal, and it radiates heat away from its glowing surface. Its low thermal expansion means it barely changes size as it heats, so it resists thermal shock – the cracking that happens when one part is scorching and another is cooler. That is why it can serve as both the heat shield and the load-bearing skin of a sharply curved, heavily stressed edge. Those panels withstood aerodynamic loads up to about 800 pounds per square foot.

Why it matters

The nose and wing leading edges of a returning spaceplane face the worst of both worlds at once: the highest heating and the highest aerodynamic forces. Ordinary insulating tiles could not survive there. RCC could, flight after flight, which is a big reason the reusable Space Shuttle was possible at all.

Its weakness is just as important a lesson. RCC is wonderfully strong in heat but brittle and poor at resisting impacts. In 2003, the loss of Space Shuttle Columbia (mission STS-107) was traced to a chunk of insulating foam from the External Tank that struck and breached an RCC panel (panel 8) on the left wing’s leading edge during launch. On reentry, superheated plasma poured through the breach and destroyed the wing from the inside, killing all seven crew members. The disaster drove major changes in foam handling, on-orbit inspection of the leading edges, and research into repairing RCC in space.

Where it is used and notable examples

• Space Shuttle orbiter: The RCC nose cap, chin area, and the 22 wing-leading-edge panels per wing – the classic spaceflight use of the material.
• Columbia (STS-107): A breached left-wing RCC panel, caused by foam impact during ascent, led to the orbiter’s destruction – the most consequential RCC-related event in spaceflight history.
• ICBM reentry vehicles: Carbon-carbon was developed in part for the nose cones and heat shields of intercontinental ballistic missile warheads, an early driver of the technology.
• High-performance brakes: The same carbon-carbon family appears in Formula One brake discs (standard since the late 1970s) and in aircraft brakes, such as those on Concorde.
• Later spaceplanes: Newer reusable vehicles often use alternatives – the X-37B uses a lower-cost leading-edge material called TUFROC rather than classic RCC – reflecting RCC’s high cost and poor impact resistance.

Because it is heavy, costly, and easily damaged by impacts, RCC was reserved only for the small, hottest, most highly loaded zones, while lighter silica tiles and blankets covered the rest of the orbiter. A tougher relative, carbon-fiber-reinforced silicon carbide (C/SiC), is used where more durability is needed.