Artemis Reentry

heat shield The Orion heat shield from the Artemis 1 mission, whose erosion led to a lengthy investigation that has significantly delayed Artemis 2. (credit: NASA) Artemis reentry by Jeff Foust Monday, December 9, 2024 In January, NASA announced delays in the next Artemis missions to the Moon. Artemis 2, which had been scheduled to launch by the end of the year, was pushed back to September 2025, which resulted in a similar slip in Artemis 3 to September 2026. NASA blamed the delay on several technical issues with the Orion spacecraft, including unexpected erosion of the heat shield seen on the Artemis 1 mission in late 2021 (see “Twenty years of chasing the Moon”, The Space Review, January 15, 2024.) “There was a lot of little links in the error chain,” Kshatriya said, “that accumulated over time that led to our inability to predict this in ground tests.” NASA provided few significant updates in the months that followed, sticking to the September 2025 launch date for Artemis 2 even as the slow pace of launch preparations suggested a delay. In late October, NASA officials said that the agency had determined the root cause of the heat shield erosion, but declined to provide details, saying they would wait until after determining how to address the problem for Artemis 2 before disclosing more details. (NASA even avoided releasing images of the heat shield; the only photographic evidence of the erosion came in a report by the agency’s inspector general.) What corrective action NASA decided to pursue would determine when Artemis 2 could fly. If NASA decided it could just change the reentry profile of Orion, the spacecraft could fly as-is with a modest delay. However, if the heat shield needed to be replaced, a much longer delay—perhaps a year or more—might be in store. On Thursday—ten years to the day after Orion first flew on the short EFT-1 mission, launched on a Delta IV Heavy—NASA finally announced the outcome of the heat shield investigation and its implications for Artemis 2. During a briefing at NASA headquarters announced on less than 24 hours’ notice, agency leaders said Artemis 2 would be delayed again, now to April 2026, even while avoiding the worst-case scenarios. “We were able to recreate the problem here on Earth, and now we know the root cause,” NASA administrator Bill Nelson said. “This has allowed us to devise a path forward.” That root cause was linked to the “skip entry” used by Orion when it reenters, dipping in and out of the atmosphere to bleed off energy. “We have since determined that while the capsule was dipping in and out of the atmosphere as part of that planned skip entry, heat accumulated inside the heat shield’s outer layer,” said deputy administrator Pam Melroy. The created gases inside the heat shield that could not escape, “and led to cracking and uneven shedding of that outer layer.” The issue, said Amit Kshatriya, deputy associate administrator of NASA’s Moon to Mars Program Office, was linked to the permeability of the heat shield material, called Avcoat. “The permeability of the Avcoat material is essential,” he said, something that only became clear when looking at portions of the heat shield that did not suffer the cracking and loss of char material. “The acreage of the heat shield was not uniform in terms of its permeability,” he said. “There were places where it was actually more permeable than the rest, a small percentage. In those places, we did not witness in-flight cracking. That was the key clue for us.” He blamed several factors, including changes in the formulation of Avcoat and “dissolution of the understanding” of how to make it over the decades since its use on Apollo. There was also a change in the geometry of the blocks of Avcoat material as applied to the heat shield. “There was a lot of little links in the error chain,” he said, “that accumulated over time that led to our inability to predict this in ground tests.” “We can either change the material to mitigate the issue or we can change the environment,” he said. For later Artemis missions NASA will take the former approach, with efforts underway to produce Avcoat with the desired permeability. For Artemis 2, though, “we can safely and with high degrees of success control that entry environment” with the same heat shield. That revised trajectory will limit the “skip” part of the reentry, where the reduced heating causes gas to build up without the charring that allows the gas to be safely released. “We need our commercial and international partners to double down to meet and improve this schedule,” Nelson said. “We want to constrain the downtrack, the period from which the vehicle hits the entry interface down to where aerothermal loading stops,” Kshatriya said. That will be reduced to 1,775 nautical miles (3,287 kilometers). “I wanted 1,776 nautical miles because, if we’re going to fly in the first part of 2026, we could have celebrated the 250th anniversary at the same time. That would have been elegant, but engineering said I couldn’t do that.” heat shield A closeup of a portion of the heat shield shows cracking and erosion. (credit: NASA) That has implications for landing trajectories to ensure the capsule comes down in the preferred location off the coast from San Diego. That also affects launch availability. “In order to constrain yourself to 1,775 [nautical miles], you basically lose the tails of every launch window,” he said. “About 50% of the window is cut out.” With that assessment of the heat shield issue complete (which, agency officials said, was reviewed by an independent committee that agreed with the root cause), NASA is moving ahead with preparations for Artemis 2. NASA had been holding off the start of stacking of the Space Launch System solid-rocket booster segments, which begins a clock on their certified lifetime. “As soon as we walked out of the administrator’s executive council today, we gave direction to the team at EGS [Exploration Ground Systems] to start moving the aft-center segments over,” Kshatriya said. “That will start, essentially, tomorrow.” On Artemis 1, the certified lifetime of the boosters once stacking of the segments started was 12 months, but that was extended to closer to two years before the rocket finally launched. While stacking is starting now, launch is still 16 months away. “The theoretical concern is that, because of the compression on the seals and the interfaces, you could have propellant grains migrate from the inner liner and cause issues,” he said. However, with the ability to monitor the segments, and the experience of Artemis 1, he said NASA was confident that the booster lifetime can be extended. “I believe we can get between 18 and 24 months pretty comfortably.” The delay in Artemis 2 to April 2026 pushes out Artemis 3, which is now scheduled for mid-2027. Nelson said he would be pushing the various companies involved in SLS, Orion, the Human Landing System, and spacesuits to accelerate their work in a long-shot bid to move up the missions. “We need our commercial and international partners to double down to meet and improve this schedule,” he said, describing meetings with company executives “sometimes unannounced” at their facilities to impress upon them “a shared sense of urgency, and I think we have that.” briefing NASA administrator Bill Nelson, deputy administrator Pam Melroy, associate administrator Jim Free, and Artemis 2 commander Reid Wiseman discuss plans for Artemis 2 and the future of the program at a December 5 briefing. (credit: NASA/B. Ingalls) Will Artemis 2 ever fly? The timing of the announcement raised eyebrows given the impending change in administrations and, with it, new leadership at NASA. Officials argued the decision was made now to avoid any further delays. “To the greatest extent possible, we certainly want to defer any decisions about starting or ending programs,” Melroy said. “We’re on a day-for-day slip. We had to make this decision. If you’re waiting for a new administrator to be confirmed and a team to come up to speed on this technical work that we’ve all been tracking very closely, I think that would actually be far worse to defer it.” She added that agency leadership wasn’t able to brief the incoming Trump Administration ahead of the public briefing since the Trump transition team had not named an agency review team for NASA. However, the day before, President-elect Trump announced his intent to nominate Jared Isaacman as NASA administrator. Both the timing of the announcement and Trump’s choice took many by surprise. Previous administrations have traditionally waited until after inauguration to nominate a NASA administrator: the first Trump Administration waited more than seven months before nominating Jim Bridenstine, for example. Isaacman blamed “excessive consolidation among defense and aerospace players” for the problems NASA and others, like the Pentagon, have faced on programs. Isaacman, meanwhile, was on virtually nobody’s radar as a potential candidate to lead the agency. The billionaire founder of payment processing company Shift4 is best known to the space community as the commander of the Inspiration4 and Polaris Dawn private astronaut missions flown on SpaceX Crew Dragon spacecraft. Those missions, which Isaacman funded, included the first commercial spacewalk that Isaacman performed on Polaris Dawn in September. “Jared’s passion for Space, astronaut experience, and dedication to pushing the boundaries of exploration, unlocking the mysteries of the universe, and advancing the new Space economy, make him ideally suited to lead NASA into a bold new Era,” Trump stated in his announcement (capitalization in original.) Isaacman has said little since last week’s announcement about his plans for the agency, but he does have a significant paper trail—or, rather, social media trail—of statements on space topics outside of his own missions. That included, in October, endorsing an op-ed by Bloomberg founder Michael Bloomberg critical of NASA’s Artemis campaign, including SLS and Orion. “There are government boondoggles, and then there’s NASA’s Artemis program,” Bloomberg wrote. Artemis, he argued, “has so far spent nearly $100 billion without anyone getting off the ground, yet its complexity and outrageous waste are still spiraling upward. The next US president should rethink the program in its entirety.” “These points are not new, and I agree with most of them, but it’s great to have someone like Mike, with a loud voice, educating people on topics they may not be as familiar with,” Isaacman wrote in a social media post about Bloomberg’s commentary. Isaacman blamed “excessive consolidation among defense and aerospace players” for the problems NASA and others, like the Pentagon, have faced on programs. Even before Isaacman’s nomination, there was widespread speculation that the incoming administration would at least revisit Artemis, in particular programs like SLS, Orion, and the lunar Gateway. Musk’s current influence with Trump heightened that speculation, and the selection of Isaacman to lead NASA—which still requires Senate confirmation in the new year—further supports it. At last week’s briefing, though, agency leaders said they believed they were giving the incoming Trump Administration a firm plan to return humans to the Moon using SLS and Orion, along with SpaceX’s Starship lunar lander. “I think we are handing to the new administration a safe and reliable way forward for us, which is to go back to the Moon, get there before China, to have a presence in cislunar, which is important to our country other than NASA, and to be on the way of Moon-to-Mars,” Nelson said. “I think we’ve got that wrapped up with a bow and I think it’s on its way.” He seemed unconcerned that the next administration might, for example, replace SLS and Orion with Starship, a topic that prompted questions along those lines at the briefing. “Are they going to axe Artemis and insert the Starship? First of all, there is one human-rated spacecraft that is flying and has already flown beyond the Moon, farther than any other human-rated spacecraft, and that’s the SLS combined with Orion,” he said. “We have a large decision behind us,” Wiseman said of the Orion heat shield. “A lot of the uncertainty has been removed.” “I expect that this is going to continue,” he said of the current architecture. “I don’t see the concern that your question raises—although it’s a legitimate question—that you’re suddenly going to have Starship take over everything.” NASA, of course, won’t be able to cancel SLS and Orion without the support of Congress, including members from states and districts heavily invested in those programs. The attempt by the Obama Administration in 2010 to cancel the Constellation program ultimately led to the end of that program, but Orion continued, as did a shuttle-derived rocket in the form of SLS. It does, though, offer uncertainty about whether and how those key elements of Artemis will continue. One of the participants at the briefing was Reid Wiseman, the astronaut commanding Artemis 2. “We have a large decision behind us,” he said of that decision to proceed with the mission using the current heat shield but new reentry technique. “A lot of the uncertainty has been removed.” However, there is now uncertainty, not about how Artemis 2 will fly, but if it will even get off the ground in anything like its current form. Jeff Foust (jeff@thespacereview.com) is the editor and publisher of The Space Review, and a senior staff writer with SpaceNews. He also operates the Spacetoday.net web site. Views and opinions expressed in this article are those of the author alone.