Long term production dependent on establishing a manifest, production line
The sole-source justification document for the future contract notes the projection that there would typically be three units being processed at MAF simultaneously in different phases of production. “Each CS (Core Stage) takes 16 months to procure and receive long-lead materials and another 36 months to manufacture, test, and deliver to the Kennedy Space Center,” the Justification for Other than Full and Open Competition (JOFOC) of the Stages Production and Evolution Contract says.
“With a planned manifest and launch cadence of one flight per year, the Government needs to have three CS in production at any given time.”
Simultaneous production of the first and second cores took place at MAF with welding and bolting of the structures for Core Stage-2 going on in and around final assembly of Core Stage-1. With part of the process improvements applied and more in development to applied downstream in the production, Boeing believes that they can optimize production with their current infrastructure to get to a higher delivery rate than one per year.
“Three years is a pretty reasonable estimate for how long it takes to build a Core Stage,” Shannon said. “So once we get the pipeline fed at the very beginning, it’s about a three year process and we think we’ll be, with the current tooling we have, on about eight month centers if that’s what NASA wants to go fly.”
(Photo Caption: The Core Stage-1 forward join is rotated to horizontal in the Building 110 aisle in April, 2019. In the background left, the Core Stage-2 liquid oxygen (LOX) tank was going through post VAC weld processing in Cell A. Boeing completed welding of Core Stage-2 structures in 2019 in parallel with Core Stage-1 final assembly operations in Building 110.)
NASA’s future plans, especially beyond Artemis 3, aren’t clear. An eight-month cadence would amount to three Cores being delivered every two years instead of two; contracts for future production of the other main elements of the launch vehicle, the Northrop Grumman SLS Boosters and Aerojet Rocketdyne’s RS-25 engines would also have to be synchronized to a desired flight rate and NASA has not said as an agency whether it wants to fly SLS any more than once a year.
Boeing is looking to reduce the three-year long production timeline for a given Core, but the delivery rate would be based on how frequently the authority to proceed on the next vehicle in the manifest is given by the agency. “That is the way to make this an affordable program is to have a well-planned out manifest that we understand exactly when to go deliver and we can set up our supply chain for that and we have not done that yet,” he said.
“I have a fairly large design engineering team that I’m going to find other things for them to go do like EUS (Exploration Upper Stage) and some other things, but that whole vehicle was put together [by] two hundred and fifty techs (technicians),” he added. “It’s a wildly complex vehicle, it’s a [Space Shuttle] ET plus an orbiter aft plus an IU (Instrument Unit) ring for Saturn V and it was put together by two hundred and fifty techs and about four hundred engineers and other people that were down here and if you think about that it’s remarkable and if we can skinny down and start building the vehicles with a team of about that size it’ll very rapidly become a very affordable Core Stage.”
Extra structural, mass margins could help future production
The future contract is being called a “production and evolution” contract because it is expected that there will be some smaller-scale updates to the vehicle design. Based on full-scale ground testing NASA and Boeing are already seeing some possibilities to fine tune the vehicle structure even before the vehicle flies for the first time.
The structural qualification articles welded together at MAF and assembled into STAs are identical structurally to the first and second flight articles. Loads testing is complete for three of the four the STAs built and preliminary results indicate that the vehicle has a structural margin above the 1.4 factor of safety required by the program.
STAs were built for four of the five major structural elements of the stage; the engine section STA was delivered first followed by one for the intertank, the liquid hydrogen (LH2) tank, and the liquid oxygen (LOX) tank. The baseline test series already completed for the engine section, intertank, and LH2 tank STAs was augmented by a final “margin test” to apply a selected loads case above the required safety level to the test article to evaluate how much additional margin there is.
The most recent margin test on the LH2 tank STA was the most extreme conducted so far. In the test performed on December 5, buckling loads that were 260 percent of the maximum expected in flight (equivalent to a 2.6 factor of safety) were applied to the STA for over five hours while it was pressurized with nitrogen gas before the structure first buckled and then fully ruptured on one side ten minutes later.
(Photo Caption: The Core Stage LH2 tank STA ruptures after initial structural failure in a margin expansion test conducted on the night December 5 at the Marshall Space Flight Center in Huntsville, Alabama. Following standard structural testing, the tank was intentionally tested to failure in the margin test. Preliminary results show that the structures have margin well above required safety levels and Boeing and NASA are looking at possible changes to help optimizing future builds and vehicle performance.)
Shannon noted that the additional margin seen in the preliminary results from the structural testing and elsewhere may also help with future production. “This first Core Stage looks like it’s going to end up being about 7000 pounds lighter than our design requirement, so that gives you a little more than three tons of additional capability, which is great news,” he said.
“Very early in the program some design decisions were made to reduce mass and through this testing we were able to identify areas that have too much mass and through the production we’re able to identify areas that we made it really hard to produce because we were trying to reduce mass. One of that comes most quickly to mind is some of the intertank panels. All eight of them are a different design because they have to carry different kinds of loads.”
“If we can add three or four hundred pounds of mass to the intertank panels, I can make them much more producible and much easier to assemble and we’ve already talked to NASA about that,” he explained. “They are in agreement and there’s some other areas that we’ve learned through the testing both in the primary structure and the secondary structure we’ve got a lot of excess capability and it makes a lot of sense to go and change that as we’re building the next set to be able to increase even more the amount of mass we can get up to space.”
“So it will be an iterative process; some of it we’ll add mass to make it more producible, some of it we’ll take mass based on what we learned from the structural testing,” he added. The desire is to phase in some of those changes beginning with the third build, with a caveat given the third Core would be pointed at the mission with the hard New Year’s Eve 2024 deadline.
“We won’t let that affect the schedule, but we’re still fairly early in the procurement of the parts for Core Stage-3 so we have the opportunity to make some of those changes,” Shannon said.
Core Stage-2 schedule adapting to efficiencies and big picture
Boeing’s current schedule forecast is to have the second Core ready for delivery in about two years. “Our plan right now is to get Core Stage-2 out in March of ’22, we have probably six months of margin in that schedule and that’s well ahead of the need date,” Shannon said.
After deciding to retain a Green Run test campaign for the first Core Stage last Summer, NASA also decided to drop plans to execute a similar test series on the second one, which bought back several months of schedule; the plan now is for the second vehicle to be delivered directly from MAF to the Kennedy Space Center. Under new Associate Administrator for the Human Exploration and Operations Mission Directorate (HEOMD) Doug Loverro schedules for Artemis 1 and Artemis 2 are being re-envisioned, so the relationship between the Core Stage delivery date and an Artemis 2 launch date isn’t known.
Artemis 2 (formerly Exploration Mission-2) is planned to be the first crewed flight of both the Orion spacecraft and SLS. Although the second build is progressing more efficiently, Boeing is using the extra time to apply additional lessons learned; there’s also the matter of the Green Run for the first Core.
(Photo Caption: The Core Stage-2 intertank is lifted into Cell G at MAF in early August, 2019. The production team recently completed the first of two phases of application of spray-on foam insulation (SOFI) and was preparing for the last. After the TPS is applied to the outside of the barrel and trimmed, the element will be moved to Area 55 for standalone integration.)
“Some of it is we’re not going to be super-efficient on Core Stage-2 for a while here because a good third of the team will be at Stennis working through Core Stage-1 hot-fire and we won’t have that lien on the program for future Core Stages,” Shannon explained. “The other thing [is] we could have it done a little bit earlier but we’re early to overall program need even in the Spring of ’22.”
“So we have gone back and some of the lessons we’ve learned since the second one is going to be a crewed vehicle we’re making some changes on things like wiring harnesses and brackets and tubing and things like that. “Parts that we already had delivered for Core Stage-2 we’re sending some of that back to incorporate lessons learned in Core Stage-1. That kind of artificially expands your schedule, right?”
“We would not do that if we were under the gun to get it out earlier but we’ve got some time to be able to incorporate those [changes] so that the vehicle that we fly for the first crewed flight has all of the lessons learned, things that we would like to fix that we learned out of the build for Core Stage-1. So the way I would say it is we have some extra time, we’re taking some extra time.”
The final assembly plan for the first Core Stage was changed in the Spring of 2019 to get back several months of lost schedule time. By designing new support equipment to enable the remaining sections of the stage to be connected horizontally, the first Core was able to be delivered a few weeks ago; however, horizontally connecting the engine section to the rest of the rocket did orphan a set of tasks.
Work to fully connect the LH2 lines running from the propellant tank to the four RS-25 engines and to ground loading and storage facilities was deferred until the first Core is vertically installed in the test stand at Stennis. That was an acceptable compromise given the time crunch to finish the first build, but with more time to think about it Boeing has come up with a plan to implement when they get there with the second build.
“They’ve actually figured out a way now and a tool they can use — this is that same team, they’re really good — where we can actually do all of the build horizontally,” Shannon said. “We can even do the LH2 lines, we can do that horizontal integration to the LH2 tank.”
“So all of the work that we’re traveling to Stennis now, that’ll all be done and we’ll have a completed vehicle for Core Stage-2 going to the Cape even with the horizontal build.”
(Photo Caption: The Core Stage-2 engine section in its structural assembly jig at MAF on December 9. The element has subsequently been moved out of the jig to an adjacent work area, suggesting that major structural assembly is complete.)
The structural assembly for Core Stage-2 is largely complete. The LOX and LH2 tanks were welded last year and are going through post-assembly verifications and preparations to begin TPS applications.
“The LOX tank for CS-2 is still a few months out from any of our processes and by that I mean any of the automated priming which would then precede the TPS applications for the cryo tanks,” Alldredge noted on January 8, the rollout day for the first Core. “The intertank itself is actually in the process of getting insulated right now over in Cell G. With the intertank we’ve got to fill all the grid pockets with foam and then trim all that back and then we do our acreage spray over that.
“So we’ve finished all the pockets, we have some work being done right now from our cork team up around the SRB (Solid Rocket Booster) fittings, then the wire harness team is doing some wire routing and things like that. Once they finish that which should have been yesterday or today and we get all that sold off, we’ll then go into preparations for that acreage spray.”
The forward skirt has already completed its external TPS application and is set up in its integration stand. Just down the aisle, the engine section has been moved from its structural assembly jig to an adjacent area where integration work can begin.
Lead image credit: NASA/Eric Bordelon.