Earlier this year, NASA announced it had postponed the manned Artemis 2 swing of the moon until September 2025, a practice run in preparation for the 2026 Artemis 3 mission, which will land astronauts near the moon’s south pole.
One of the reasons given for the ten-month delay was to understand the heat shield data on return Artemis 1which sent an uncrewed Orion capsule to lunar orbit and back.
Engineers analyzed data from that shakeout cruise, which began with a NASA launch Space launch system mega rocket on November 16, 2022.
The 25-day Artemis 1 mission ended on December 11, 2022, with the Orion capsule splashing down under parachutes into the Pacific Ocean off Baja California.
Related: The 10 most beautiful images from NASA’s Artemis 1 moon mission
A thrilling return
Orion’s heat shield assumed the reentry speed of 40,000 km/h that day and ably protected the capsule. But soon afterward, NASA and contractors began grappling with the discovery that the ablative heat shield belonged to Orion went differently than predicted.
Some areas of the expected charred material disappeared in a way that was not predicted by computer models and soil tests. Also, slightly more release of the char material occurred during reentry than expected.
Orion’s heat shield features the same ablative material, called Avcoat, that was used during the Apollo program late 1960s and early 1970s. However, the construction process for the heat shield was changed from the Apollo-era method.
Vintage Apollo
While Avcoat is a vintage Apollo, the manufacturing process for Orion’s 21st century thermal protection system was changed.
According to Lockheed Martin, the company is leading Orion’s heat shield development process: “instead of workers filling 300,000 honeycomb cells one by one with ablative material, then heat-setting the material and machining it into the right shape, the team now produces Avcoat blocks – just under 200 – that are pre-processed to into their positions and bonded in place to the heat shield’s carbon fiber skin,” the aerospace company said website explains.
This process allows Avcoat to be applied in just a quarter of the time and also saves money, according to the company.
Cause
Post-flight inspection of the Artemis 1 Orion heat shield showed an unexpected loss of pieces of char from the spacecraft. NASA has literally focused on understanding the cause of Avcoat’s charring and cracking.
“We designed and executed a building block ground test approach using remote test facilities,” NASA’s Orion program office told Space.com.
The first series of tests began in the summer of 2023 and ended in a final series of tests in December 2023. “We expect to determine the cause this spring,” the NASA office said.
Simulation testing
Those Orion heat shield tests involved the Laser Hardened Materials Evaluation Laboratory, a unique facility operated by UES, a BlueHalo company in Dayton, Ohio, and managed by the Air Force Research Laboratory. This laboratory conducts thermal simulation tests equipped with high-power lasers.
Tests were also conducted at the Arc Jet Complex at NASA Ames Research Center in California’s Silicon Valley. Arc beam tests are performed on thermal protection material with plasma simulating the intense heat generated during the plummeting atmospheric reentry of the Orion capsule.
In turn, Lockheed Martin has worked with NASA to organize a core team of engineers to investigate and understand the cause of the loss of carbon dioxide and what should be done to prevent similar events on future flights, Blaine Brown said , Orion Spacecraft Mechanical Systems. Director at the company.
“Over the past year, the Lockheed Martin team, along with NASA, has been very busy producing test articles and supporting re-entry environmental testing in various NASA and industry test chambers,” Brown told Space.com.
These tests have provided a wealth of information for the research team, Brown said. “Lockheed Martin has also provided analytical expertise to demonstrate acceptable thermal margins to support the flight rationale for the Artemis 2 mission.”
Related: NASA’s Artemis Program: Everything You Need to Know
Heat shield malfunctioning
Last year the Orion program office was at NASA Johnson Space Center in Houston responded to a Space.com request for comment about the heat shield hiccups.
“We expect the material to disappear at a temperature of 5,000 degrees Fahrenheit [2,760 degrees Celsius] the spacecraft encounters during a return via the Earth’s atmosphereand to see charring of the material due to a chemical reaction, but we did not expect the small pieces to come loose, rather than being taken away,” the NASA office said.
There was a healthy margin of new Avcoat left, and cabin temperature data remained at expected levels, so if the crew had been on board they would not have been in danger, the program office statement said.
NASA said a special investigation will include planned tests, detailed analyses, extensive heat shield sampling and review of data from sensors to assess what the Orion capsule experienced upon reentry.
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Avcoat changes?
Is it possible that changes to the Avcoat are required?
“It is too early in our testing and analysis to arrive at any potential recommendations or solutions that address further char liberation,” the NASA office responded in its 2023 communiqué.
It’s possible that the Artemis 1 heat shield phenomenon is simply inherent to this heat shield, the agency said at the time.
Moreover, it could be what NASA would expect when the capsule returns the moon“but we are informed by the data,” the Orion project office said, adding that “our teams want the confidence that we have the best possible heat shield to fly people in the future.”