EDWARDS, Calif. — The Artemis II astronauts are scheduled to return Friday from their trip to the moon. When they do, they will slam into Earth’s atmosphere at over 32 times the speed of sound — and will do so using a reentry technique that has yet to be tested in real-world scenarios.
In 2022, NASA sent the uncrewed Artemis I test mission to the moon. As it pierced through the Earth’s atmosphere on return, the capsule suffered unexpected damage to its heat shield, prompting NASA scientists to rethink what’s needed to keep the homeward-bound Artemis II astronauts safe.
There’s been a ton of work done to prepare for this moment — but the reality is, scientists won’t know exactly how the heat shield will behave until they test it in a bona fide reentry.
That’s why a team of NASA and Department of Defense scientists and test pilots stand at the ready to collect detailed data on how the heat shield performs as the capsule streaks through the sky, turning the atmosphere around it into a bright fireball about half as hot as the surface of the sun before splashing down off the coast of San Diego.
Test pilots stationed at Southern California military bases will take turns chasing the capsule in a complex, high-speed relay: first a NASA business jet, then a Navy surveillance aircraft, followed by another NASA jet, and finally a NASA weather research aircraft. Crews on the ground will monitor the Artemis II capsule and send those test pilots precise speeds and coordinates to hit as they follow the fireball in the sky. Meanwhile, researchers in the back of the planes will track the capsule with telescopes and sensors.
Center Director Bradley C. Flick, left, gives project manager Robert Navarro a high five at the NASA Armstrong Flight Research Center on Edwards Air Force Base on March 18.
(Genaro Molina / Los Angeles Times)
“It’s an exciting job threading the needle multiple times,” said Robert Navarro, project manager at NASA’s Armstrong Flight Research Center in Edwards, Calif., which is in charge of the critical third segment of the relay. “It has to be precise, simply because of the short window of time that they need to collect that data. They have to be exactly right on the mark.”
After splashdown, a separate Armstrong Flight Research Center team will collect a fortified sensor affixed to the exterior of the capsule that is designed to study the heat shield up close.
“I’m really excited that my team is a part of such an important mission,” said Patty Ortiz, deputy project manager for the capsule sensor project at the center. “Having worked on it since 2019, it’s definitely a full-circle moment for me.”
The center has pushed the limits of human flight for decades — and collected a lot of data doing so.
“We consider our airplanes flying labs — we’re going to go do things that maybe haven’t been done before,” said Brad Flick, who retired as director of the center March 20 after nearly four decades at the research facility.
Armstrong Flight Research Center project manager Robert Navarro walks past a Gulfstream III airplane that will be used in the Artemis II mission.
(Genaro Molina / Los Angeles Times)
In the 1960s, engineers at the Flight Research Center helped design and test a mock-up of the Apollo lunar landing vehicle that Neil Armstrong used for landing practice on Earth before he flew to the moon. (The center was later renamed after him, the first person to walk on the lunar surface.)
The center has been preparing to study the Artemis II reentry for years, but the work became even more important after NASA discovered issues with the heat shield after the Artemis I test mission.
NASA guided the Artemis I capsule to first only graze the Earth’s atmosphere before briefly popping back up into space, then completing the final reentry. This novel approach reduced the forces that astronauts would experience on reentry and helped NASA to more precisely maneuver the capsule to its landing point in the Pacific — regardless of where or when it comes back from the moon.
That mission seemed like a success, but when crews began inspecting the heat shield on the bottom of the uncrewed capsule after splashdown, they noticed a problem.
After NASA’s Orion spacecraft was recovered at the conclusion of the Artemis I test flight and transported to NASA’s Kennedy Space Center in Florida, its heat shield was removed from the crew module inside the Operations and Checkout Building and rotated for inspection.
(NASA)
The heat shield is designed to slowly erode (or “ablate,” in NASA parlance) away during reentry to keep conditions in the capsule livable while the air a few inches away can reach nearly 5,000 degrees Fahrenheit: The outside layer of the shield routinely heats up, then sloughs off in the form of gas and pieces of char, which carry that heat away from the capsule as they disperse into the atmosphere around the capsule.
The problem with Artemis I was that the new reentry approach NASA had attempted seemed to disrupt this ablation process.
Because Artemis I went back into space between the first dip into the atmosphere and the final reentry, there was a brief respite in its heat exposure — that meant that the hot interior of the heat shield kept producing gases, but the exterior was no longer shedding material fast enough to allow those gases to escape. Pressure built up, which cracked the heat shield and ultimately resulted in larger pieces chipping off during the final reentry.
NASA scientists determined that had a crew been onboard, they would have survived — but they didn’t want to expose the Artemis II astronauts to unnecessary risk.
That left two options: First, replace the already-built Artemis II heat shield with a new design in the works that could handle the reentry path attempted with Artemis I. Second, change the reentry path to skip the first dip into the atmosphere and just go straight in to eliminate the conditions that created the problem in the first place.
The agency ultimately deemed replacing the Artemis II heat shield too much of a logistical headache and opted for the latter, simpler approach. On Friday, NASA astronauts will put that decision to the test. Armstrong Flight Research Center scientists are standing by to watch.