sections, full nose caps, or in any number of custom shapes or sizes. , SIRCA had been demonstrated in backshell interface applications, but not yet as a forebody TPS material. AVCOAT AVCOAT is a NASA-specified ablative heat shield, a glass-filled epoxy–novolac system. NASA originally used it for the Apollo command module in the 1960s, and then utilized the material for its next-generation beyond low Earth orbit Orion crew module, which first flew in a December 2014 test and then operationally in November 2022. The Avcoat to be used on Orion has been reformulated to meet environmental legislation that has been passed since the end of Apollo. Thermal soak Thermal soak is a part of almost all TPS schemes. For example, an ablative heat shield loses most of its thermal protection effectiveness when the outer wall temperature drops below the minimum necessary for pyrolysis. From that time to the end of the heat pulse, heat from the shock layer convects into the heat shield's outer wall and would eventually conduct to the payload. This outcome can be prevented by ejecting the heat shield (with its heat soak) prior to the heat conducting to the inner wall. Refractory insulation Refractory insulation keeps the heat in the outermost layer of the spacecraft surface, where it is conducted away by the air. The temperature of the surface rises to incandescent levels, so the material must have a very high melting point, and the material must also exhibit very low thermal conductivity. Materials with these properties tend to be brittle, delicate, and difficult to fabricate in large sizes, so they are generally fabricated as relatively small tiles that are then attached to the structural skin of the spacecraft. There is a tradeoff between toughness and thermal conductivity: less conductive materials are generally more brittle. The space shuttle used multiple types of tiles. Tiles are also used on the Boeing X-37 and in the Dream Chaser and SpaceX Starship designs. Because insulation cannot be perfect, some heat energy is stored in the insulation and in the underlying material ("thermal soaking") and must be dissipated after the spacecraft exits the high-temperature flight regime. Some of this heat will re-radiate through the surface or will be carried off the surface by convection, but some will heat the spacecraft structure and interior, which may require active cooling after landing. Typical Space Shuttle TPS tiles (LI-900) have remarkable thermal protection