Trapped gas between bonded blocks cracked the Avcoat coating during skip-reentry on Artemis I, causing material loss at 100+ locations.Source: background

What caused the Artemis I heat shield damage?

Trapped gas built pressure during the skip-reentry manoeuvre, cracking the Avcoat coating.Source: background

Background

Orion's Avcoat heat shield lost material at 100+ locations during Artemis I reentry. NASA identified trapped gas beneath the surface as the root cause: pressure built during the skip-reentry manoeuvre, cracking the coating and ejecting char fragments. No replacement or redesign was possible because the Artemis II shield was already built and installed.

Avcoat is an epoxy-novolac resin filled with silica fibres, designed to ablate (burn away) in a controlled manner during reentry, carrying heat away from the spacecraft. Originally developed for Apollo-era capsules, it was reintroduced for Orion after NASA evaluated multiple thermal protection systems. Unlike the Apollo heat shield (a single monolithic pour), Orion's Avcoat is applied as individual blocks bonded to the heat shield structure.

The block-bonded method may have contributed to the failure: gas can infiltrate between blocks in ways the monolithic Apollo coating did not permit. NASA's mitigation is a steeper direct-descent reentry that avoids the skip manoeuvre, reducing thermal cycling but increasing peak deceleration forces on the crew. The underlying material is unchanged.