NASA’s investigation into damage found on the heatshield of the Artemis Mission’s Orion module two years ago has concluded that the technique used to re-enter Earth’s atmosphere meant gas became trapped in the shield’s outer ablative material, causing concerning cracks.
On Thursday, the aerospace org announced that it concluded that if the module changes its re-entry method, the spacecraft will be safe for crewed flight without a redesign. Accordingly, it announced new target launch dates for its Artemis II crewed test flight and Artemis III crewed lunar landing.
Both dates slipped around seven months – to April 2026 and mid-2027 respectively – to provide time to address the Orion environmental control and life support systems.
As for the heat shield, NASA determined the gasses generated inside the heat shield’s Avcoat material were unable 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,” the org added.
Post-mission Orion heatshield from Artemis I mission. Photo: NASA – Click to enlarge
Avcoat was developed in the 1960s and used on the Apollo missions to protect spacecraft as they re-entered Earth atmosphere. It’s a resin-based material reinforced with silica fibers made by Textron Defense Systems and is embedded into a honeycomb-shaped structure attached to the spacecraft’s exterior. The honeycomb holds the material in place and provides structural integrity during re-entry.
NASA explained that the coating is designed to char and wear away as it heats up during re-entry, to protect Orion and its future crew from re-entry temperatures of nearly 5,000° Fahrenheit (2760° C).
To understand the cause of damage to the first Orion flight, NASA conducted over 100 tests at different geographically dispersed US facilities. They provided around 200 Orion Avcoat samples for detailed sampling of the shield, reviewed imagery and data from spacecraft sensors, and conducted ground testing and analysis.
Researchers also replicated the effects of Orion’s entry into the atmosphere on Avcoat material inside the Arc Jet facilities at NASA’s Ames Research Center in California. The Arc Jet facilities simulate extreme condition like high-speed friction and intense heat that spacecraft experience. The lab can create a supersonic airflow by generating high temperatures using electric arcs.
Eventually, they found that the major cause of the trapped gas was the module’s method of re-entering the atmosphere – a skip guidance entry technique. As its name suggests, the method allows a spacecraft to “skip” off the upper layers of the atmosphere, similar to the technique used to skip a pebble across the surface of water.
“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 re-enter for final descent under parachutes to splashdown,” explained NASA.
The technique provides flexibility, as it extends the spacecraft’s ability to adjust its flight path, ensuring a more precise landing. It also helps manage the thermal load during re-entry by distributing heat and reducing the risk of overheating.
The Arc Jet simulation of the event proved that between the dips in the atmosphere, heat dropped externally but thermal energy remained within the Avcoat, leading to an accumulation of gasses that had nowhere to escape from within the charred material.
“Because the Avcoat did not have ‘permeability,’ internal pressure built up, and led to cracking and uneven shedding of the outer layer,” determined the space agency.
Flight data showed that the damage caused by the temperature fluctuations would not have affected any crew – the cabin temperature remained a cruisy and steady mid-70s Fahrenheit (around 24° C) temperature. Thermal performance of the heat shield was actually deemed to exceed expectations.
NASA concluded that the Artemis II heat shield “can keep the crew safe during the planned mission with changes to Orion’s trajectory as it enters Earth’s atmosphere.”
While some might find the unexpected behavior on the heat shield worrisome, the Artemis I mission did exactly what it was intended to do –testing systems before humans are at risk on a future mission.
“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,” reiterated NASA deputy associate administrator Amit Kshatriya.
He added that the heat shield investigations help ensure a full understanding of the cause and nature of the issue, as well as risk. ®
