In deep-space travel, sometimes the most important “hardware” is a few inches of material that only matters for minutes. The Artemis II mission will orbit four astronauts around the Moon and return them to Earth, thus re-establishing the human lunar trajectory that has not been flown in over half a century. The Space Launch System and Orion spacecraft combination has already been considered a cathedral-sized instrument that has been assembled, inspected, and transported with meticulous choreography. But the argument that is gaining the most attention is not about engines or navigation but about what happens at the very end: Orion’s return through Earth’s atmosphere.
The concern began with the Artemis I mission, where the Orion spacecraft landed in 2022 with an unusual pattern of damage. NASA later clarified that gases produced inside the ablative Avcoat material on the Orion spacecraft were not able to vent, leading to a buildup of pressure until the material broke and spewed charred material. NASA explained this process in a statement in December 2024 regarding the Artemis I mission, where it stated that gases produced inside the Avcoat material were not able to vent.
With a manned mission, the issue is obvious: heat shields are not designed to shed chunks. Charlie Camarda, a former astronaut and heat shield designer, has wondered why the same heat shield will be used on the Artemis II mission, saying, The way we’re going to solve this problem is too much analysis and not enough design. Dan Rasky, a former NASA employee and heat shield materials specialist, was blunter about the level of risk involved: “The reason this is such a big deal is that when the heat shield is spalling or you have big chunks coming off even if the vehicle isn’t destroyed, you’re right at the point of incipient failure now. It’s like you’re at the edge of the cliff on a foggy day.”
The counterpoint offered by NASA is not that the phenomenon was not recognized, but that it was recognized, replicated, and defined. This was achieved through the integration of sensor data, sampling, and a lot of ground testing, including simulated re-entry conditions in arc jet facilities. In these tests, the relationship between the cracking and the build-up of heat in skip re-entry and the differences in permeability in Avcoat was determined. One of the major internal determinations was that areas of higher permeability did not crack, which supported the controlling variable of permeability.
The controversial engineering decision is the solution. Since the Artemis II heat shield had already been designed and implemented before any Artemis I missions, NASA decided not to make any major changes to the hardware for this mission but instead to change the “environment” in which the shield operates: the entry path. “Based on the data, we have decided NASA unanimously and our decision-makers to move forward with the current Artemis II Orion capsule and heat shield, with a modified entry trajectory,” said former administrator Bill Nelson. “We won’t go as high on that skip, it’ll just be a loft,” explained Artemis flight director Rick Henfling.
An independent review panel was established in 2024 to review the investigation, and, as the chairman of the panel Paul Hill has since explained, no contrarian view was found in the final recommendations. Hill said that the panel debated “sentence by sentence” until a consensus was reached, although Hill also admitted that there were disagreements at first about whether the heat shield should be allowed to fly as intended. Hill also noted a complication that made the debate more urgent: the Artemis II shield was produced to be more impermeable than the Artemis I shield, in order to accommodate bond verification procedures, although low permeability is at the heart of the problem of cracking.
Those in favor of the flight plan point to margins and layers. Former astronaut Danny Olivas, who was part of the investigation, said, “Will the heat shield crack? Yes, it’s going to crack,” although he also claimed that the Orion has redundant protection for Avcoat. The present NASA administrator, Jared Isaacman, was confident about the change in the trajectory: “We have changed our re-entry trajectory. We have regained our margin of safety, and I feel very good about that with Artemis 2.”
What is presented here is a very modern crisis in human space exploration: whether it is to change the equipment, or whether it is to change the way the equipment is used. Artemis II is ready to provide an answer to this question in the only place that finally matters on the edge of space and air, with a crew on board.
