Why Orion’s heat shield problems give Jared Isaacman the perfect justification to cancel all of SLS/Orion
Damage to Orion heat shield caused during re-entry in 2022,
including “cavities resulting from the loss of large chunks”
In yesterday’s press conference announcing new delays in NASA’s next two SLS/Orion Artemis missions to the Moon, agency officials were remarkably terse in providing details on why large chunks of Orion’s heat shield material broke off during its return to Earth in 2022 during the first Artemis mission. That damage, shown to the right, is one of the main reasons for the newly announced launch delays.
All they really said was that the damage was caused during re-entry, the atmosphere causing more stress than expected on the heat shield.
Today NASA finally released a more detailed explanation.
Engineers determined as Orion was returning from its uncrewed mission around the Moon, gases generated inside the heat shield’s ablative outer material called Avcoat were not able to vent and dissipate as expected. This allowed pressure to build up and cracking to occur, causing some charred material to break off in several locations.
…During Artemis I, engineers used the skip guidance entry technique to return Orion to Earth. … Using this maneuver, Orion dipped into the upper part of Earth’s atmosphere and used atmospheric drag to slow down. Orion then used the aerodynamic lift of the capsule to skip back out of the atmosphere, then reenter for final descent under parachutes to splashdown.
[Ground testing during the investigation showed] that during the period between dips into the atmosphere, heating rates decreased, and thermal energy accumulated inside the heat shield’s Avcoat material. This led to the accumulation of gases that are part of the expected ablation process. Because the Avcoat did not have “permeability,” internal pressure built up, and led to cracking and uneven shedding of the outer layer.
In other words, instead of ablating off in small layers, the gas build-up caused the Avcoat to break off in large chunks, with the breakage tending to occur at the seams between sections of the heat shield.
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