NASA
NASA officials declared the Artemis I mission a success in late 2021, and it's hard to argue with that assessment. The Space Launch System rocket and Orion spacecraft performed nearly flawlessly on an uncrewed flight that took it around the Moon and then back to Earth, paving the way for the Artemis 2 mission, the program's first crewed mission.
But one thing engineers saw on Artemis I that didn't quite match expectations was a problem with the Orion spacecraft's heat shield. As the capsule reentered Earth's atmosphere at the end of the mission, the heat shield diminished or burned up in a different way than the computer models predicted.
A larger amount of charred material than expected exited the heat shield during Artemis 1's return, and the way it exited was somewhat uneven, NASA officials said. Orion's heat shield is made of a material called AFCOT, which is designed to burn up as the spacecraft plunges into the atmosphere at 25,000 mph (40,000 km/h). Upon its return from the Moon, Orion encountered temperatures of up to 5,000 degrees Fahrenheit (2,760 degrees Celsius), hotter than what the spacecraft sees when it reenters the atmosphere from low Earth orbit.
Despite the heat shield problem, the Orion spacecraft landed safely in the Pacific Ocean. Engineers discovered uneven charring during post-flight inspections.
There are no answers yet
Amit Kshatriya, who oversees Artemis mission development at NASA's Exploration Division, said Friday that the agency is still searching for the root cause of the heat shield problem. Managers want to make sure they understand why before moving forward with Project Artemis II, which will send astronauts Reed Wiseman, Victor Glover, Christina Koch and Jeremy Hansen on a 10-day trip around the far side of the moon.
It will be the first time humans have flown close to the Moon since the last Apollo mission in 1972. In January, NASA announced that the launch of Artemis 2 would be postponed from late 2024 until September 2025, largely due to the unresolved investigation into Heat shield issue. .
“We are still in the middle of our investigation into the performance of the Artemis 1 heat shield,” Kshatriya said Friday in a meeting with a committee of NASA's advisory board.
Engineers conducted sub-scale heat shield tests in wind tunnels and jet installations to better understand what led to the uneven charring on Artemis I. “We are getting closer to the final answer as to this cause,” Kshatriya said.
NASA officials previously said it was unlikely they would need to make changes to the heat shield already installed on the Orion spacecraft for Artemis II, but they did not rule it out. Redesigning or modifying the Orion heat shield on Artemis II would likely delay the mission by at least a year.
Instead, engineers are analyzing all the possible paths the Orion spacecraft could fly when it reenters the atmosphere at the end of the Artemis 2 mission. Aboard the Artemis 1 spacecraft, Orion flew a reentry bypass trajectory, dove into the atmosphere, then It jumped back into space, then made a final descent into the atmosphere, like a rock jumping across a pond. This profile allows Orion to make more precise landings closer to rescue teams in the Pacific Ocean and reduces gravitational forces on the spacecraft and the crew riding inside. It also divides the heat load on the spacecraft into two phases.
The Apollo missions flew in the direct re-entry profile. There is also a re-entry mode available called ballistic reentry, in which the spacecraft flies through the atmosphere without guidance.
Charred material began to fly out of the heat shield in the first phase of the reentry process. Engineers are investigating how the reentry skip profile affects the performance of the Orion heat shield. NASA wants to understand how Orion's heat shield will perform during each of Artemis II's potential reentry paths.
“What we need to do is say to the analysis teams: OK, whatever the constraints are, what can we afford?” Kshatriya said.
Once officials understand what caused the heat shield to char, engineers will determine what type of trajectory Artemis II needs to fly upon return to minimize risks to the crew. Next, managers will look to build what NASA calls flight justifications. Essentially, this is the process of convincing themselves that the spacecraft is safe to fly.
“When we put it all together, we either have a justification to fly or we don't,” Kshatriya said.
Assuming NASA approves the rationale for an Artemis 2 flight, there will be additional discussions about how to ensure Orion's heat shields are safe to fly on downstream Artemis missions, which will have high-speed re-entry profiles as astronauts return from lunar landings.
Meanwhile, preparations aboard the Orion spacecraft for Artemis II continue at NASA's Kennedy Space Center. The crew and service modules for Artemis II were integrated together earlier this year, and the entire Orion spacecraft is now inside a vacuum chamber for environmental testing.