Artemis III SLS stacking advances as Orion results confirm trajectory fix

Teams at NASA's Kennedy Space Center have pushed Artemis III Space Launch System hardware another step forward, stacking the next pair of solid rocket booster segments inside the Vehicle Assembly Building while Core Stage-3 engine work and early Artemis IV processing also continue. The progress comes as NASA's Aerospace Safety Advisory Panel (ASAP) reviewed post-flight analysis of Orion's Artemis II heat shield, confirming that a modified reentry profile sharply reduced the Avcoat char-loss seen after Artemis I. Four of five booster segments now stacked NASA completed mating of the center segments on the twin five-segment SLS solid rocket boosters for Artemis III. Teams have since begun stacking the forward center segments on top of those, leaving only the forward assemblies to complete each booster stack. Photographs from the base of Mobile Launcher 1 looking up the boosters also show the Tail Service Mast Umbilicals missing their quick-disconnect plates. Officials had previously indicated that leaks found on those interfaces during Artemis II processing could prompt a design change for a firmer seal. The missing plates may reflect that work, or they may simply be part of the post-Artemis II refurbishment of the launcher. Either way, the configuration is likely to become clearer as Artemis III stacking continues. Inside the VAB, teams have also completed installation of all four RS-25 engines on Core Stage-3. That milestone opens the remaining outfitting work needed before the stage can be transferred onto Mobile Launcher 1 between the two boosters. Artemis IV hardware arrives as well While most of Core Stage-4 remains in production at the Michoud Assembly Facility in New Orleans, its engine section has been in processing at Kennedy for years. This past week, NASA's Pegasus barge delivered the last major piece still needed for that section: the boattail. Artemis IV: Boattail section for SLS being offloaded from Pegasus at KSC.https://t.co/2y8guyW0pi pic.twitter.com/R04Vgb67bM — NSF – NASASpaceflight.com (@NASASpaceflight) August 31, 2026 The boattail attaches to the engine-section barrel and provides aerodynamic support for the RS-25 engines in flight. Its arrival keeps Artemis IV hardware moving in parallel with Artemis III stacking. NASA is targeting a 2028 lunar landing on Artemis IV, a schedule that will require continued hardware flow of this kind. Artemis II heat shield: fewer than 10 percent of Artemis I's char-loss sites Artemis II lifted off April 1, becoming the first crewed Artemis flight and the first human mission around the Moon since 1972. It flew with the same class of Avcoat heat shield already installed when post-flight inspection of Artemis I revealed unexpected char loss. The issue was not a large void or obvious gap. It was permeability. During reentry, Avcoat heats, gasifies, and ablates. Heat also soaks deeper into the material, so lower layers continue generating gas while the outer layers are still in the same process. If those outer layers are too permeable, gas from below cannot escape. Pressure builds and can blow out the upper layers, a process known as spallation, or char loss. Artemis I used a skip reentry: Orion dipped into the atmosphere, shed a large amount of speed, then used lift to skip back out before the final descent and Pacific splashdown. That profile created two problems for the heat shield. The longer exposure gave more time for gas to build in deeper layers. The skip also interrupted gasification at the outer surface while residual heat kept the inner layers generating gas that could no longer vent. NASA chose not to remanufacture the already-installed Artemis II heat shield, which would have delayed the mission. Instead, it flew a non-skip, steeper reentry. That path imposed higher heat loads but kept heat from soaking as deep, and it shortened the time available for pressure to build. Recovery images made the difference visible immediately. After nearly five months of analysis, NASA presented the results to the Aerospace Safety Advisory Panel. Panel member Paul Hill, a former NASA flight director and MOD Director, said Artemis I's heat shield had more than 100 spallation sites. In contrast, Artemis II had only nine, a reduction of more than 90 percent from changing the entry profile alone. The trade is operational. Skipping the skip shortens the distance from entry interface to splashdown and reduces the area NASA can target, cutting mission-planning flexibility. To restore skip-entry capability, NASA has changed Avcoat manufacturing so that the material is more permeable and can vent gases rather than trap them. That process change will fly first on Artemis III next year and will be used on subsequent Orion heat shields. The VAB work now underway is the next test of whether that hardware cadence can keep Artemis III and IV on their intended paths. Featured Image: NASA.