NASA and Space Launch System core stage prime contractor Boeing are working to finish activating new production facilities at the Kennedy Space Center, to complete and deliver the next two units by the end of 2026. After summertime engine section hardware deliveries, the two SLS processing cells in the Space Systems Processing Facility are filled for the first time, and Boeing is preparing to check out new tooling in the Vehicle Assembly Building for the final assembly of the third and fourth stages.
While the Artemis II schedule is on hold due to decisions about what to do with the Orion spacecraft’s existing base heatshield, the mission’s SLS core stage will be installed in the new vertical platforms and tooling in VAB High Bay 2. The plan for next year is to begin the final assembly on the Artemis III unit; for now, the new VAB facility will allow Boeing to finish traveled work on the Artemis II stage while waiting to hear when stacking that vehicle might begin.
Ambitious production goals for the next two years
Boeing’s Space Launch System (SLS) engine section workshop in the Space Systems Processing Facility (SSPF) is now at capacity, with the units for Artemis III and Artemis IV set up in side-by-side processing cells there. Assembly of the welded barrel and bolted thrust structure is still completed at the Michoud Assembly Facility (MAF) in New Orleans. Following transportation to the SSPF at Kennedy Space Center (KSC), all the fluid tubing, wiring, and equipment is installed inside and tested, and then the unit will be moved to VAB High Bay 2.
The engine section will be joined to the upper four elements in the new vertical tooling to complete the final stage assembly. Boeing still assembles the upper “four-fifths” of the core stage — the forward skirt, liquid oxygen (LOX) tank, intertank, and liquid hydrogen (LH2) tank — at MAF in New Orleans. Beginning with the third unit, that will be transported to the VAB at KSC for bolting with the engine section, installation of the RS-25 engines, and final testing and checkouts.
Engine section hardware for Core Stage-3 and Core Stage-4 was delivered to KSC in early September. The boattail fairing and base heatshield for the Core Stage-3 engine section were transported to the SSPF first, with the Core Stage-4 engine section temporarily stored in the VAB Transfer Aisle.
Boeing started SLS engine section integration in the SSPF in December 2022, with the third unit that is assigned to the Artemis III launch vehicle. Integration or outfitting of the stage reached a point in production where the boattail could be bolted to the bottom of the engine section structure. That needed to be completed first, and the Core Stage-3 unit was relocated from Footprint 7 in the SSPF high bay to the adjacent Footprint 5 for that work.
Credit: NASA/Cory S Huston.
(Photo Caption: The engine section for Core Stage-4 approaches the SSPF airlock on Oct. 15. The arrival of a second unit brings Boeing’s SLS worksite in the SSPF to capacity.)
In the middle of that relocation and mating work, Hurricane Milton suspended operations at KSC in October. “We’re down a couple of weeks because of the hurricane,” Steve Wofford, NASA SLS Stages Element manager, said in a late October interview with NSF.
“We didn’t have any hardware damage or any facility damage, but it takes several days to secure for the hurricane, then you’re down for a couple of days when the hurricane is doing its thing, and then it takes you a couple of days to clean up and resume operations and then you turn around and you’re down two weeks.”
On Oct. 15, the week after Milton passed, the Core Stage-4 engine section was moved from the VAB to the SSPF airlock. A week later, pictures released by NASA taken on Oct. 21 show the unit being lifted off of its transportation tooling and moved into Footprint 7, where it will go through a similar set of integration tasks that its predecessor just did.
The space agency released another set of pictures taken on Oct. 30 of Boeing’s two SLS processing cells, showing the two engine sections being processed side-by-side.
The current, high-level forecast for the big Core Stage-3 subassemblies — the upper “four-fifths” and the engine section — is to complete them by the end of next summer so they can be mated in the VAB and then finish final assembly by the end of 2025. “The hydrogen tank aft join, we’re currently forecasting to finish that in early summer of 2025,” Wofford said.
“The forward join is scheduled to complete also in mid-Summer. And then that puts our estimated ship date for the top four-fifths from MAF to KSC in late summer of ’25.”
Wofford noted that the engine section is expected to move to the new VAB final assembly facility in High Bay 2 first. “We lost a couple of weeks [to the hurricane], [but] we’re currently scheduled to move the combined engine section/boattail to the VAB in July of next year,” he said. “And then handover to EGS will be December of 2025.”
Progress on the Artemis III core stage hardware at MAF was slowed in 2023 by an issue with one of the weld tools, which delayed assembly of the LOX tank until the beginning of this year. A new issue with equipment that performs the robotic application of spray-on foam insulation (SOFI) to the large propellant tanks is the latest challenge to the plans to complete the stage by the end of 2025.
Credit: NASA/Steven B. Seipel.
(Photo Caption: The Core Stage-3 liquid hydrogen tank is backed out of Cell P at MAF on May 20. It was moved next door to Cell N to the right for foam sprays, but issues with production equipment have delayed those robotic foam applications.)
“We’ve lost a little bit of time on that due to a tooling issue on the rotation apparatus in that cell at MAF and those repairs are underway,” Wofford explained. “They’ve held us up on that but we’re working on that pretty hot and heavy, and we hope to get into that really soon.”
“As far as MAF hardware goes on Core Stage-3, the LH2 tank is my critical path. Of course, you know, the engine section is always the overall critical path, but due to the tooling issue, [the] LH2 tank is my MAF critical path now.”
The acreage and the domes of the LOX and LH2 tanks are sprayed in an automated process in Cell N of Building 131 at MAF. A similar, robotic process is used to first apply a coat of primer to the metal skin of the tanks next door in Cell P. The tanks are installed in special Rotation, Assembly, and Transportation Tools or RATTs for both sprays. Those tools are tied into the spraying process to synchronize the rates of rotation and spray application.
The LH2 tank was moved from Cell P to Cell N on May 20, after its primer coat was completed; however, the foam sprays are still on hold until those repairs are made, and the cell is again ready. The LOX tank was behind the LH2 tank in production, but it will soon be headed into Cell P for its primer.
Once that is complete, both tanks need to be processed in Cell N. The LOX tank would then be connected to the intertank and forward skirt as a part of the “forward join” milestone.
The intertank and forward skirt for Core Stage-3 are going through standalone functional testing, but the integration of those elements is largely complete, and they are waiting to progress into the forward join when the LOX tank is ready.
After its foam sprays, the LH2 tank will now be connected to an engine section simulator as a part of the “aft join.”
Then the forward and aft joins will be connected with the bottom of the intertank being bolted to the top of the LH2 tank to form the “four-fifths” subassembly.
The December 2025 delivery date for the Artemis III core stage is tied to the current target launch date for the mission of September 2026, but that date could change if Artemis III is delayed again.
VAB High Bay 2 final assembly facility nearing activation
Core Stage-3 will be the first unit to be completed in VAB High Bay 2 but plans to install the Artemis II core stage in the new platforms and tooling built by Futuramic have come full circle. When the core stage KSC production site expansion was announced in December 2022, Core Stage-2 was expected to be delivered to KSC in mid-2023 and VAB High Bay 2 was expected to be completed in the fall, which would have provided an opportunity to install the stage before Artemis II stacking.
By the time that Artemis II was delayed to September 2025 in January, stacking was expected to be underway before the High Bay 2 facilities would be ready; however, Artemis II stacking was again delayed, this time from the end of the summer to the end of 2024 or later. High Bay 2 is now approaching activation, and the core stage isn’t likely to be mated to the Artemis II SRBs until after New Year’s.
Credit: NASA/Adeline Morgan, Boeing (inset, upper left).
(Photo Caption: Core Stage-2 is fitted with lifting equipment in late October in preparation for installation into the new VAB High Bay 2 platforms (inset, left), possibly late this year.)
“First of all, the Boeing and Futuramic teams have done a remarkable job on the high bay tooling, and it’s really been proceeding just like clockwork, it’s beautiful,” Wofford said. “We’ve been carrying [Core Stage-2] processing in the vertical as an opportunity in the schedule and it looks like we will get to realize that opportunity.”
“We’ve got a production readiness review for the High Bay 2 tool [in the last week of October] and then we will look forward to the certificate of completion in mid-November.”
Even though stacking of the boosters in High Bay 3 is on hold, workers in the VAB attached a lift spider to the top of the core stage at the end of October, in preparation for breaking the stage over from horizontal to vertical, and then lifting it into High Bay 2 instead of High Bay 3.
Wofford noted that some work, particularly on a fully assembled core stage, is easier to perform while it is in a vertical orientation. “We can do stuff in the [VAB] Transfer Aisle in the horizontal, but you’ve got to rig up platforms to be able to do it, and it’s hard to react to whatever contingencies might arise,” he explained.
“So, if you’ve got some out-of-sequence work that you have to do, then you’ve got to figure out how to do that in the horizontal. Or if you have to remove and replace something, then you have figure out to do that in the horizontal.”
“When you’re in the vertical, you’ve got the platforms already there, in situ, so you just walk up and do it, and it’s much, much better,” he added. “So, the earlier you can do it in High Bay 2 is better than waiting until you get stacked in High Bay 3 and doing it over there.”
“That’s what High Bay 2 does for us, and we’re pretty excited about it.”
The High Bay 2 final assembly cell will also allow traveled work on the stage to be performed ahead of eventual SLS integration, which now looks like it won’t be completed until well into 2025. “We are going to do whatever processing in the vertical that we can, including traveled work, in High Bay 2, using that new tool, so it will afford us some schedule opportunity,” Wofford said.
Working to certify production restart of Shuttle MPS hardware, not just RS-25s
SLS was created in a 2010 political compromise between the Obama White House and the 111th Congress, which mandated that the launch vehicle design maximize the use of existing Space Shuttle and Constellation program hardware and infrastructure. The obvious Shuttle and Shuttle-derived SLS elements are the solid rocket boosters and the Space Shuttle Main Engines, renamed RS-25 engines in their adaptation and upgrade to fly on SLS.
However, the core stage also directly and indirectly reuses some Shuttle Orbiter main propulsion system (MPS) hardware, including hydraulic system parts. “If you’ve got good, heritage hardware sitting on the shelf then you want to go use it until that supply is exhausted,” Wofford said.
Credit: NASA/Michael Democker.
(Photo Caption: RS-25 Engine 2062 is installed into engine position 3 on Core Stage-2 last September at MAF. The thrust vector control actuators in the engine 4 position that the stage uses to move the engines can be seen in the foreground, right.)
SLS expends all its hardware during launch to place Orion on a trajectory to the Moon, and after a few core stages are built, the program will use up the Shuttle program inventory. Production of RS-25 engines was restarted for SLS and is also underway for the less visible MPS hardware.
The most immediate need to restart production is for the hydraulic thrust vector control (TVC) actuators that gimbal the RS-25 engines and the recirculation pumps that keep the hydraulic fluid moving through each of the four systems on the stage during propellant loading. Each of the four engines has two TVC actuators (a pitch and a yaw actuator) and each of the four hydraulic systems has one recirculation pump.
“We’ve exhausted the Shuttle inventory of [TVC] actuators and [recirculation] pumps on Core Stage-1 and 2,” Wofford noted.
Both of those were “direct reuse” hardware; like the RS-25 engines, the hydraulic actuators and recirculation pumps were flight-proven units that flew in the engine compartment of the Shuttle orbiters and now are flying in the SLS core stage engine section serving the same functions. The core stage also uses Shuttle solid rocket booster hydraulic pumps in each hydraulic system.
“We’ve got suppliers onboard [that are] designing and manufacturing and testing those replacement hardwares,” Wofford said. “Moog is onboard building us the new actuators and we have a proposed design for the new main pump for Core Stage-7, but we don’t have a supplier on board for that, just yet.”
Other MPS and TVC stage elements use modified Shuttle hardware, like the Core Auxiliary Power Unit (CAPU). In contrast to the Shuttle Orbiter auxiliary power unit assembly, which was driven by a hydrazine gas generator, the CAPU is driven by tapped-off gaseous hydrogen from the stage’s autogenous re-pressurization system during RS-25 engine mainstage; prior to engine start, the CAPU is driven by a ground-based gaseous helium spin-start system.
“The improved CAPU, what we call the iCAPU, ‘i’ standing for ‘improved’ is going to phase in on Core Stage-4. We’ve got Collins Aerospace on board to make that under contract for Boeing and they’re progressing well with the design and performing piece-part, subcomponent-level [development] testing and analysis.”
“We also have other new production components, like the circulation pump and the actuators and the iCAPU controller that are progressing through their designs and they’re on track to support the production need dates,” Wofford added.
Although not as visible as the effort to recertify RS-25 engine manufacturing and production, with the third and fourth core stage units well into the assembly, the work to certify the restart of heritage and modified heritage Shuttle MPS and hydraulic/TVC components is something to watch.
Artemis IV Core Stage structures in welding tool traffic pattern with first EUS units
Core Stage-4 will fly on the Artemis IV mission, which will be the first launch of the Block 1B SLS upgrade. Block 1B inaugurates the Exploration Upper Stage (EUS), which is optimized for SLS operations and increases its payload performance to the Moon by about 10 metric tons. The SLS boosters and core stage retain their existing designs and implementation for Block 1B.
Now that the engine section for Core Stage-4 is set up in the SSPF, outfitting of that unit can resume in parallel with work on the rest of the stage at MAF. The engine section is typically the long lead of the five major elements, followed by the intertank, forward skirt, and the LOX and LH2 propellant tanks.
Eventually, the engine section will be ready at KSC for its boattail to be attached; assembly of that structure is underway at MAF. “[We] plan to ship to KSC and then mate it with the engine section in early 2026,” Wofford said.
Credit: NASA/Glenn Benson.
(Photo Caption: The Core Stage-4 engine section is seen on Oct. 30, now set up in SSPF Footprint 7, which is one of two Boeing SLS worksites there.)
The intertank for Core Stage-4 remains in its structural assembly jig at MAF. NASA and Boeing only have one set of integration tooling for the intertank and forward skirt, and those are currently occupied by the Core Stage-3 units until they are moved into a stacking cell for the forward join, now forecast for next year.
The next step for the intertank structure is for the TPS foam sprays of its exterior in Building 114, Cell G. “It’s planned to move into Cell G at the end of the year, in December,” Wofford added.
The other elements of the Artemis IV core stage unit were waiting for the availability of the Vertical Assembly Center (VAC) weld tool. Boeing is also working on EUS development and was performing confidence welds in the VAC during the summer. Now that those are complete, NASA and Boeing were looking at how to optimize the “traffic pattern” through the tool between core stage and EUS flight and test articles.
“We’ve got a good problem in that we had a lot of hardware being crammed through one factory,” Wofford said. “It’s a problem, but it’s a good problem to have.”
“We’ve got two core stages in progress [at MAF] right now and we’ve got EUS-1, so three major flight articles on two product lines cramming through the same set of assets, so we’ve got to figure that out. Boeing has got a good factory model that we are working through runs with them now to figure out exactly when you do what through the various cells and all the various tools.”
The plan now is to finish the forward skirt welds this month, in November. Two rings need to be welded to the top and bottom of the barrel element.
Then the LH2 tank domes and barrels would follow. “The hydrogen tank for Core Stage-4 is scheduled to complete its weld in the VAC in December of this year, and then the LOX tank is planned to finish welding in spring of ’25,” Wofford noted.
He said that the goal is for a summer 2026 shipment of the completed “four-fifths” for Core Stage-4 to KSC. That would be followed by final assembly with the engine section and delivery of the completed stage to Exploration Ground Systems by the end of the fall of 2026.
Beginning fifth core stage work under existing contract, commercial SLS contract “under study”
Boeing has completed and shipped the two core stage units under the initial SLS Stages contract with NASA and the two currently have a contract in place to build the third and fourth units; however, the contract situation after that is cloudy.
NASA has been studying SLS sustainability and/or affordability since the beginning of the decade in an attempt to bring down the cost of the program to the U.S. government. As recently as 2023, NASA had planned on awarding an Exploration Production and Operations Contract (EPOC) to Deep Space Transport, a joint venture between Boeing and Northrop Grumman this year; however, that hasn’t happened.
“EPOC is still under study by NASA Headquarters,” Wofford noted.
Credit: Philip Sloss for NSF.
(Photo Caption: From left to right, the Core Stage-4 and Core Stage-3 intertanks are seen at MAF in October 2023.)
Except for Stages, all the other major program elements have contracts in place that support eight to ten SLS launches. The current Stages Production and Evolution Contract (SPEC) only covers production for four launches, and now that the EPOC situation seems to be in limbo, NASA and Boeing will use SPEC to at least begin production of the fifth core stage unit.
“We’re getting Core Stage-5 production onboard with a task order IDIQ approach,” Wofford explained. “IDIQ stands for indefinite delivery, indefinite quantity. So, what that means is it’s an expedited way that you can get an existing contractor onboard for additional goods or services that the need has arisen for.”
“That’s future stuff that you can’t totally nail down at the time when you let the contract, but it’s a shortcut way of putting new stuff on contract when the need and the definition arises, so then all you have to do is agree on the scope and the price of the work,” he added.
“We’re using what we have to not delay. It’s important, this stuff takes a long time to build, so we’re using the existing contract structure that we have, working with our procurement partners to get the stuff that we need on contract to where we don’t have to rush so much.”
NASA gave Boeing the “authority to proceed” with Core Stage-5 production in October, at the beginning of Fiscal Year 2025. In a follow-up email, NASA public affairs said that the contract actions were completed, but the production work itself would begin in the first quarter of the 2025 calendar year.
As noted earlier, the engine section is the long lead element. The long lead materials are already at on-site at MAF and production will begin with welding the barrel panels and assembly of the bolted thrust structure in separate tools.
(Lead image: From left to right, the engine sections for Core Stage-4 and Core Stage-3 are seen in the Space Systems Processing Facility on Oct. 30. Credit: NASA/Glenn Benson.)
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