NASA is set next week to unveil the Artemis II crew that will sojourn around the Moon, now eyed for November 2024. The four-person team would make the trek secure in their Orion spacecraft – the first piloted spacecraft to travel to the Moon, or beyond low Earth orbit, since Apollo 17 in December 1972.
But there appears to be a tad more look-see at the results of the uncrewed Orion on its Artemis I flight last year. Orion’s heat shield took on the 25,000 miles per hour re-entry, but NASA and contractors are wrestling with the results.
The heat shield features the same ablative material called AVCOAT used in Apollo lunar outings and return-to-Earth missions. However, the building process has changed, according to Lockheed Martin that fashioned Orion’s thermal protection system.
“Instead of having workers fill 300,000 honeycomb cells one by one with ablative material, then heat-cure the material and machine it to the proper shape, the team now manufactures AVCOAT blocks – just fewer than 200 – that are pre-machined to fit into their positions and bonded in place on the heat shield’s carbon fiber skin,” the aerospace firm’s website explains. That process is a timesaver in putting on the AVCOAT – about a quarter of the time.
As NASA stated, pre-Artemis 1 liftoff: “The primary goals for Artemis I are to demonstrate Orion’s systems in a spaceflight environment and ensure a safe re-entry, descent, splashdown, and recovery prior to the first flight with crew on Artemis II.”
So what’s up with the Orion heat-shield and how concerned is NASA?
Heat shield hiccups
Inside Outer Space contacted the Orion program office at NASA Johnson Space Center for comment regarding the heat-shield hiccups.
“During Artemis I post-flight inspection, engineers observed variations of Avcoat material across the appearance of Orion’s heat shield. Some areas of expected charred material ablated away differently than computer modeling and ground testing predicted, and there was slightly more liberation of the charred material during re-entry than anticipated,” the program office stated.
“We expect the material to ablate with the 5,000 degrees Fahrenheit the spacecraft encounters on a re-entry through Earth’s atmosphere, and to see charring of the material through a chemical reaction, but we didn’t expect the small pieces that came off, versus being ablated,” the NASA statements adds.
“We don’t know yet exactly how much was liberated, which is why we’re analyzing the data, but there was a healthy margin remaining of virgin Avcoat, and temperature data inside the cabin remained at expected levels, so if crew were on board they would not have been in danger,” explains the program office statement.
What kind of efforts, testing, are underway to try to understand what happened?
NASA responded that there are 186 blocks of Avcoat and their team is looking at each block. “We have a dedicated investigation underway that includes planned testing, detailed analysis, extensive sampling of the heat shield, and review of data from sensors.”
Data was collected from images and videos from the Orion’s spacecraft’s re-entry. Those are being correlated with the heat shield sensors onboard Orion, “then looking at our computer models to see how we can understand what we experienced on re-entry,” the Orion program office said.
“We’ve extracted samples from the heat shield, which will be X-rayed, and we’re also getting a more precise understanding of how much Avcoat is still remaining on the heat shield—which is significant,” the NASA statement continues. “As we get all these pieces of information together, we’ll arrive at an assessment to determine what additional testing is needed in finding the root cause or to better understand the phenomenon.”
Is it possible that changes in the Avcoat may be needed?
“It’s still too early in our testing and analysis to arrive at any potential recommendations or solutions that address additional char liberation,” NASA responded. “It’s possible the phenomenon may just [be] part of what the heat shield is, and what we would expect as we return from the Moon, but we’ll let the data inform us.”
Lastly, the NASA Orion program office stated: “We’ll continue to protect for variations that could happen during re-entry as we want to ensure we have significant margin against the various types of uncertainties that might occur as the spacecraft re-enters the atmosphere. Our teams want the confidence that we have the best heat shield possible to fly humans going forward.”