At the base of Orion are 186 blocks of a material called Avcoat; they are individually attached to provide a protective layer that allows the spacecraft to survive the heating of atmospheric reentry. Analysis after the Artemis I mission found that this Avcoat material was “impermeable,” essentially meaning it could not breathe. During reentry, gases became trapped in the heat shield, leading to cracking.
After considering several options, including swapping the heat shield out for a newer one with more permeable Avcoat, NASA decided instead to change Orion’s reentry profile. For Artemis II, it would return through Earth’s atmosphere at a steeper angle, spending fewer minutes in the environment where this outgassing occurred during Artemis I.
This largely worked, but there were some downsides. According to Hill, the new reentry profile reduced the vehicle’s “downrange” capability from 4,800 nautical miles to 1,775 miles. Downrange capability is the distance a spacecraft can travel, relative to the Earth’s surface, from the point of atmospheric reentry. A longer downrange is useful for finding a suitable splashdown site when weather conditions change, and it can give mission planners more options for return trajectories from the Moon.
For Artemis III and beyond, NASA is moving to a more permeable Avcoat material, which should allow them to reenter Orion without char loss and bring back a much larger downrange capability, Hill said.
Panel also impressed by NASA’s leadership
Toward the end of the safety panel’s meeting on Monday, a few members made some striking comments about their experiences working with NASA this year. For long-time listeners to meetings of the Aerospace Safety Advisory Panel, which is distinctly independent from NASA and tasked with identifying safety issues, these were eye-opening statements.