NASA pinpoints cause of Orion heat shield char loss

NASA pinpoints cause of Orion heat shield char loss
by Clarence Oxford
Los Angeles CA (SPX) Dec 06, 2024

NASA engineers have identified the technical cause behind the unexpected char loss on the Artemis I Orion spacecraft's heat shield during its return from the Moon. The issue arose from trapped gases within the ablative material of the heat shield, leading to pressure buildup and cracking.

Orion's heat shield, made with Avcoat material, experienced uneven shedding of its charred outer layer as gases generated during reentry were unable to escape. "Our early Artemis flights are a test campaign, and the Artemis I test flight gave us an opportunity to check out our systems in the deep space environment before adding crew on future missions," said Amit Kshatriya, deputy associate administrator, Moon to Mars Program Office, NASA Headquarters. He added that the investigation ensures a comprehensive understanding of the risks involved before sending humans to the Moon.

Key Findings and Investigations

A systematic approach was employed to identify the root cause, including detailed analysis of samples, spacecraft sensor data, and ground-based testing. During the Artemis I mission, Orion used a skip guidance entry technique, which increased flexibility in landing locations by leveraging aerodynamic lift and atmospheric drag. The unique reentry dynamics slowed the heat shield's char formation process, allowing internal gas pressure to build, causing cracks.

Laboratory simulations at NASA's Ames Research Center replicated Artemis I's entry conditions. Tests revealed that under reduced heating rates observed during the mission, the Avcoat material retained thermal energy, leading to cracking and material loss.

Although pre-flight tests simulated more intense heating scenarios, these conditions allowed permeable char formation and efficient gas venting. Enhancements to testing facilities post-flight enabled better replication of Artemis I's conditions, validating the observed phenomena.

Flight data confirmed that crew safety was not compromised. Temperatures within the crew module remained stable, well within acceptable limits. Engineers determined the Artemis II heat shield could be safely used with adjustments to entry procedures.

Comprehensive Analysis Process

The investigation drew expertise from multiple NASA divisions and external partners, employing tools like non-destructive evaluation and advanced thermal testing. "We took our heat shield investigation process extremely seriously with crew safety as the driving force behind the investigation," said Howard Hu, manager, Orion Program, NASA's Johnson Space Center.

Approximately 200 samples were removed from the Artemis I heat shield for analysis. Permeable regions of Avcoat, identified pre-flight, did not experience char loss, supporting the hypothesis that venting eliminated pressure buildup.

A robust testing campaign included thermal, aerodynamic, and permeability evaluations at facilities nationwide. These efforts confirmed the technical cause and validated predictive models of heat shield behavior during reentry.

In spring 2024, an independent review team, led by aerospace safety expert Paul Hill, assessed NASA's investigation. The review supported NASA's conclusions on the heat shield's behavior and identified no safety concerns for future missions.