NASA and Boeing working on optimizing SLS stage production at MAF

NASA’s Space Launch System (SLS) program and Stages prime contractor Boeing are collaborating on optimizing the production areas at the Michoud Assembly Facility (MAF) in New Orleans. The final assembly of the second Core Stage is underway as work expands to cover the production of multiple Core Stages and Exploration Upper Stages (EUS) for the SLS Block 1B vehicle.

SLS and Boeing started a long-term factory optimization plan at the end of 2019; among the changes is a reorganization of the layout of production areas to increase work efficiency. The initial goal for SLS is to reach a delivery rate of one Core Stage and one EUS every year, which will require simultaneous assembly and outfitting of three builds of each unit.
Expanding engine section production work

The initial development contract for SLS Stages included fabrication, manufacturing, and assembly of the first two Core Stages and a set of structural test articles. Most of those Core Stage hardware structures like barrel panels, gore panels, and ring segments were on hand at MAF by 2017 as NASA’s SLS Program and Stages prime contractor Boeing focused on developing an overall process to build Core Stages at the same time as they were learning how to build the first one.

The first Core Stage build was completed in early January 2020, years later than expected; Boeing was already applying some lessons learned from the production of the first flight article to the second, but NASA and Boeing began discussions about how to optimize production in December 2019. “That’s when we started talking about it, and then right before COVID hit is when we presented our plan to NASA,” Jennifer Boland-Masterson, director of Boeing operations at MAF, said in a March 18 interview.

“The whole factory optimization is going to take about five years to get through, so it’s not an instantaneous ‘hey, we’re going to move these three things and then we’re done,'” she explained. The whole point of factory optimization is to make sure the product flows through the factory in the most efficient way possible and also to allow us to use the synergies of the teams for like products.”

“So, for example, tanks, we would like tanks to be together. We have what’s called forward structures, which is your intertank and your forward skirt; we’d like them to be together.”

Credit: NASA/Steven Seipel.

(Photo Caption: The boattail assembly for Core Stage-2 sits in the left foreground of this March 2021, image with the Core Stage-2 engine section across the aisleway in the right background. After standalone work was completed, the boattail flight hardware was moved to allow its workstand tooling to be relocated. NASA and Boeing are clearing areas adjacent to the current engine section integration tooling to set up a second set and possibly a third to allow two or three engine sections to be outfitted simultaneously.)

The Core Stage engine section is the most complicated element of the stage and takes the most time to put together inside and out; with the goal of eventually delivering one Core Stage every year, the work area where the engine compartments are built is being expanded to support simultaneous production of multiple builds.

“Engine section is an incredibly complex portion of the vehicle, and no doubt about it there’s a lot of [work hours] that go into getting that particular section completed,” Chandler Scheuermann, a Manufacturing and Production manager in the NASA SLS Program’s Stages element, said. “As we look into future [delivery] rate discussions and where the SLS Program is headed as far as vehicles per year, things of that nature, we’ll have to pay special attention to how we treat engine section integration, structural assembly, those things.”

“Our engine section is on the critical path, [so] we need to have multiples in progress at one time versus one at a time so that we can meet the manifest to launch,” Boland-Masterson said.

One of the first steps in the plan was to create more floor space in the current engine section work area. As major elements and subassemblies for Core Stage-2 have completed their standalone production work, Boeing has started rearranging the location and layout of existing tooling on the factory floor.

“Our engine section area used to have [tooling for] our boattail, our engine thrust structure, our engine [section] structural [jig], engine section integration, and then forward skirt,” Boland-Masterson said in mid-March. “We have decided that for optimization the forward skirt needed to move [to the] intertank area and we have just completed that tooling move. Now that area is opened up to expand our engine section integration because we need multiples of that.”

“We’ve also moved our engine section thrust structure [tooling], which was right next to the engine section structural piece,” she added.

“[We] moved it across the aisleway so now it has its own home, to allow for more flexibility in that engine section area. And then the boattail [tooling] is the one we’re in process of moving, and that’s going to be moving across the aisleway, too.”

“We moved the forward skirt to the other end of the factory so we have the space for that expansion and then on the other side of the main aisle is where we’ve got the [subassembly] feeder lines, basically feeding the engine section integration cells,” Ben Birkenstock, NASA’s Manufacturing and Production Lead for SLS Stages, said.

NASA and Boeing are still working through the future layout of the engine section work area, but one of the goals is to provide more room for people to move around in the area, including more room for foot traffic in between obstacles on the floor. “We have [what] we call ‘guard dogs’ where we protect our wiring because we have to have extension cords and stuff [running on the floor] to our [work] location, we’re going to make sure that as we do the new layout we have more room to do the things that we need to do versus scrunching it together,” Boland-Masterson noted.

Credit: NASA/Michael DeMocker.

(Photo Caption: The Core Stage-2 forward skirt is lifted off its integration tooling on February 19. The move was done early to allow the blue tooling to be relocated to another part of Building 103 as an early action in the evolving factory optimization plan. The space vacated by the tooling will be used in the future to build multiple Core Stage engine sections simultaneously; currently, only one can be processed, and the Core Stage-2 element can be seen in the lower left background within the current engine section integration tooling.)

The Core Stage-2 engine section is still in its integration phase, where fluid tubing is being welded to the structure, brackets and wire harnesses are being bolted and clamped, and large subassemblies like thrust vector control (TVC) platforms and helium pressure vessels are being installed. NASA and Boeing have started procuring additional sets of the tooling, from work stands to access kits, to get ready to build more than one engine section at a time.

“The current plan is to have two with the option for three for engine section integration,” Birkenstock said. “It’s a modular design that is in review right now and being procured as well as two engine section thrust structure build-ups.”

Those “feeder lines” of large subassemblies are built up on the other side of the aisleway from the engine section integration area. The optimization plan envisions those offline subassembly areas building subassemblies across multiple builds.

“[Things] like TVC platform build up, and helium tanks, and all that work is done on the other side of the aisle, but it feeds those three cells for integration,” Birkenstock said. Forward work on the optimization plan is to see if enough throughput can be achieved without as much extra integration tooling.

“Also compartmentalized into that is figuring out different ways, unique ways that we can sequence integration as well,” Scheuermann noted. “Not only in the integration-specific work area but also are there other opportunities for us to work more in subassembly so that we can integrate assemblies as a whole as we get better and better at doing those things.”

How much additional tooling will be purchased and employed depends in part on the delivery rate that NASA and Boeing can agree on. Boland-Masterson said that NASA and Boeing have gone through the different options for different delivery rates; however, finalizing the terms of a “production and evolution” contract, including delivery rates, is still in negotiation.

Boeing is also modifying new versions of engine section tooling based on lessons learned from the first Core Stage build. A new internal access platform kit for the engine section integration was recently put in use in the later stages of integration for the Core Stage 2 engine section.

“We have kind of two different versions of the [tooling for the] upper deck in the engine section,” Ashleigh Caison, Boeing SLS Propulsion Engineer, said. “We have one that’s used primarily before things like the [TVC] platforms get flown in that lets us get better access to that small tubing, some of the harnesses kind of high up in the engine section we want to get done and out of the way first.”

“Our brand new access kit is basically a copy of [the first], but they’ve made some improvements and modifications to make it a little bit better, a little safer, just based on our lessons learned. That really gives us the ability to take out little sections to put in big things like the feedlines or helium tanks, so you don’t have to take out the entire access kit out and put it back in every time; you can just take out certain pieces.”

Overall plan for Core Stage and EUS

The long-term factory optimization plan also has to account for the production of Core Stages and Exploration Upper Stages, which will both be needed beginning with the fourth SLS vehicle. Practices and procedures for EUS production are still being developed as Boeing begins assembling the structures for the first upper stage.

Tooling in the factory, especially for welding structures, is shared between the upper and lower rocket stages and the optimization plan has to factor that traffic in. “We have a very integrated schedule for both,” Boland-Masterson said. “For affordability, [we] share as much as we can between Core Stage and EUS.”

“So our weld tools absolutely we do a lot of sharing. We look at how to utilize [them] 24 hours a day, we look at efficiencies, innovations, [and] we make sure we eliminate [as much] downtime as possible.”

Credit: NASA/Michael DeMocker.

(Photo Caption: One of the eight panels that make up the engine section barrel for Core Stage-3 is lifted into the Vertical Weld Center (VWC) at MAF on January 7. The VWC is one of the welding tools that Boeing and NASA modified to support building 8.4-meter diameter structures for the SLS Core Stage and EUS.)

Boland-Masterson said Boeing’s team that operates the tooling and handles the flight hardware also works on both vehicles and the size of the contractor workforce is stable. “I would tell you that we have not really grown that much, whether it’s Core Stage or EUS,” she said. “We have done a lot of cross-training.”

“We want to have a bench and also to take those lessons learned. By keeping the same team going to Core Stage and EUS you get the benefit of ‘I’ve already done this once’ or ‘I’ve seen something very similar to that’ so you can take those lessons learned and apply them.”

“Technicians that just did the weld for the [interstage weld confidence article] for EUS were the same ones that weld for Core Stage, so it’s not relearning the machine or the tools; they already know how to [use them],” she added. “That gives us a lot of benefits and that’s what we’re doing.”

Besides COVID, other changes have occurred since planning started. Northrop Grumman was utilizing floor space at MAF for production of the upper stage of their OmegA launch vehicle; after the National Security Space Launch (NSSL) Phase 2 launch service procurement, the program was canceled, and the floor space is not being utilized.

“Even from December of 2019 when we partnered together to say this is what we’d like the factory to look like, we have gotten smarter, we’ve learned some things, and so we’ve made adjustments,” Boland-Masterson said. “We haven’t fully defined what we’re going to do [yet].”

“That [OmegA decision] was a change. ‘This area has become available; what changes do we need?’ So I will tell you that with any optimization, what it started to look like and how it will end will evolve.”

Core Stage-2 forward join underway.

As the Core Stage-2 build reached milestones earlier in 2021, it enabled some of the factory optimization work to begin in preparation for the Core Stage-3 and Core Stage-4 builds. In addition, the top three elements of the rocket stage completed their individual, standalone builds and are being connected at MAF.

Major join 1 of Core Stage-2, also known as the forward join, will first see the bolting together of the forward skirt, the LOX tank, and the intertank in Cell D of Building 110. The intertank was moved into the stacking cell at Michoud on March 19. After completing its own outfitting, the liquid oxygen (LOX) tank was rolled into Building 110 on April 23 and lifted into place on top of the intertank on April 28.

The forward skirt, which was the first element finished late in 2020, will go on top of the LOX tank last. Structural connection of the three forward join elements will not complete the operation; once the structures are connected, even more outfitting work is ahead for the mated assembly while it remains in Cell D.

Credit: NASA/Michael DeMocker.

(Photo Caption: The Core Stage-2 liquid oxygen tank is lowered on top of the intertank in Cell D of Building 110 at MAF on April 28. The structures of the two elements were bolted together to start the integration process between them, which also includes electrical and fluid connections that still need to be done.)

Power, data, and feedline connections will be made between the three elements to begin turning the bolted structure into a functioning machine. Foam closeouts of the two mated flanges will also be started while the forward join is in Cell D.

After vertical connections and integration work is completed in Cell D, the forward join will be rotated back to horizontal and moved to Area 47/48, the final assembly area in Building 103, to continue preparations for the next major join with the liquid hydrogen (LH2) tank.

The LH2 tank was moved into Cell N in Building 131 on May 6 for automated application of its spray-on foam insulation. The tank is lying in ground support equipment that ties into a robotic system that rotates the tank while spraying guns apply the material to the outside of the tank.

The long barrel of the tank is sprayed first, followed by the two hemispheric domes on each end. The latter operation was automated for the first time for Core Stage-2, which will end up saving a lot of production time.

“That was a big deal for us because [for the] first tank we hand-sprayed those domes and it took us a couple of months to do the spray and then to trim it all down,” Michael Alldredge, NASA SLS TPS Subsystem Manager, said. “Even though we asked for as generous a tolerance as we could get from our design team they can’t give us plus or minus a foot, right? So you’d sand and measure it, sand and measure it.”

“When we got the automated dome spray set up, from a test standpoint and then validated that process and then used it in production, we took what was a couple of months and crammed it into about ten minutes, which was amazing for us and the product worked well, the system worked well, we were very happy with the output,” Alldredge said.

Lead image credit: NASA/Michael DeMocker.

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