AVCOAT
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AVCOAT 5026-39 is a NASA code for several versions of a specific ablative heat shield material originally created by Avco for the Apollo program. It is composed of silica fibers in an epoxy novolac resin. The original AVCOAT was used for the Apollo Command Module heat shield. A reformulated version was used for the initial Orion heat shield and later for a redesigned Orion heat shield.
AVCOAT 5026-39 is a NASA code for several versions of a specific ablative heat shield material originally created by Avco for the Apollo program. It is composed of silica fibers in an epoxy novolac resin. The original AVCOAT was used for the Apollo Command Module heat shield. A reformulated version was used for the initial Orion heat shield and later for a redesigned Orion heat shield.
Artemis I heat shield performance
After the Artemis I Orion capsule was recovered, inspection showed unexpected loss of material from the heat shield. NASA undertook an exhaustive and complex analysis of the loss, and was finally able to report on it and announce recommendations after two years, on December 5, 2024. The conclusion was that the damage was initiated by spalling caused when gas trapped within the shield heated and then expanded when external pressure was reduced, blowing pieces out of the shield. This occurred during the reentry "skip" maneuver, which had a different heating and cooling profile than simpler direct-entry profiles.
Later Artemis missions
Based on the Artemis I analysis, NASA decided to use the already-installed identical heat shield for the Artemis II mission, but to fly with a different re-entry profile that would not allow the external pressure to be reduced. Since the Artemis III shield was not yet installed, NASA chose to change the AVCOAT formulation for it. This revised formulation will not trap gasses within the shield, and this in turn allows the capsule to use the preferred reentry skip maneuver. NASA press conference with extensive description of AVCOAT history and details
Text derived from https://en.wikipedia.org/w/index.php?oldid=1370322649 under CC BY-SA 4.0; modifications have been made.