Boeing reorganizes its plans by building the second engine section of NASA SLS Core Stage

The main part of NASA's Space Launch System (SLS), the second main stage, will look a lot like the first, but the Boeing master builder has redesigned its structure. The engine compartment, which is the bottom of the five major parts that make up a complete stage, is the most complex part of the launcher.

Boeing has just completed the assembly and control of the first engine section and its cabin fairing extension, while attention was focused on integrating with the rest of Phase 1 and completing the assembly. final, but the engineers learned the lessons from the first. time build and rewrite the script for the second.

Although the fundamental aspects of the assembly and production of the Core Stage-2 engine section remain the same, the better understanding gained going through the entire assembly process has already resulted significant changes in the layout of the work and an improvement in the quality of the results. .

The main integration of internal equipment such as tubes, wiring and electronics will follow the assembly of primary structures, but some of this work has already begun; efforts will continue in successive constructions to refine the production process of the Core Stage, from work on individual elements to final assembly.

Reconstruction of the construction plan

The equipment for Core Stage-2 is being produced in New Orleans, NASA's Michud Assembly Assembly (MAF), while Boeing and NASA are applying lessons learned from the first to the second build. The Core Stage is the new piece of SLS. Although the engines and thrusters of the government launcher predate this one, the scene developed at the beginning of the decade following the end of the Space Shuttle program and the cancellation of the Constellation program.

The stage plays the role of ground support during the launch, playing the same role as Orbiters for the Space Shuttle. The Shuttle multipurpose orbits fulfilled several functions beyond the launch phase of a launch rocket, but that was the only goal of the main phase: there is no need for it. upper element in the space such as orbital maneuvering system modules (OMS), no payload container as in a cargo hold, there are no elements of reentry and landing as the wings of delta, nor of spacecraft crew module.

Although redesigned around the shuttle's liquid propellant tanks, main propulsion system and RS-25 rocket engines, the platen has also been reset to become a larger in-line launcher; development of new construction techniques then put into practice on qualifying items and Core Stage-1 created a difficult learning curve for the first time.

The assembly of the first working engine section ended up being the largest learning curve of construction and Boeing deconstructed and rebuilt the work for the second to improve speed and quality. "We have a new staff here, we have hired staff at this facility, a lot of people have been transferred to this facility," said Todd Nicholson, head of Boeing's integrated products division, "but if you consider it a new workforce, I call it "the factory has learned."

"It has matured and the nonconforming conditions are down compared to the Core Stage-1, which indicates that you have less time to do the red-line in manufacturing engineering. The store must say, "We tried to build it, we ran into a problem. What do you want us to do with this problem? " So that's what I mean by less disengagement on this cycle of nonconforming conditions. "

(Photo: The Core Stage-2 engine section in mid-July in its structural assembly template at MAF Once the structural assembly is complete, the technicians will work on most of the integration phase of the construction. of the element.)

The structure of the engine section is a combination of welded and bolted structures, and an important step in the structural assembly has been the matching of the welded body with the thrust structure on which the engines are mounted. The barrel was welded together from eight panels in the vertical welding center (VWC) to MAF, then an L-ring was welded to the top in the vertical mounting center (VAC); this work was completed in 2017 and the VAC welding was completed at the end of the month of October 2017.

The thrust structure is bolted to the inside of the barrel; the engines will be mounted on this structure on the lower part and the thrust vector control platforms (TVC) (also called MPS platforms) with a large part of the hydraulic system equipment will eventually be mounted on the top. The two pieces were collected at the end of May, but several tasks performed downstream of this work sequence for the first article were advanced for the second.

"So, Core Stage-2, we first and foremost came up with more effective ways to do the job statement," Nicholson explained.

"For example, the thrust structure has a huge amount of tubes and cables, because that's where the engines react in the vehicle. So, we build the thrust structure first, and then we put the barrel on it, right?

"One of the things we wanted to do in Phase 1 of the Core, but we could not do it because of the timing, it was about before I started, it was -Fill our skills to the fullest. all the equipment and subassemblies on this thrust structure, "he continued.

Vito Neal, a welding engineer at Boeing, noted that orbital tube welding had started much earlier in the sequence than when the first section of the engine was integrated.

"Vito is right, we have soldered," Nicholson said. "We called it all" pre-integrate " [work]So we pre-integrated the thrust structure before assembling it. We started installing tubes and all kinds of supports. "

"The most interesting part about this is the most effective part is that you have a lot more access [when] you do not have this barrel on you, "he explained. "A technician who works and who needs help or to ask a question to someone, he does not have to go out completely from the print or the barrel to talk about the manufacturing or quality engineering. "

"He can pretty much just yell at the structure and say" Hey, come here a minute ". [that is] just the human element of efficiency, the number one. "

Even before the first integration work on the thrust structure at MAF, Boeing had already transferred some of the structural assembly tasks of the equipment, returning the match drill work to the supplier.

"For Core Stage-2 and for which we have put in place an initiative, we call it" pre-drilling "our holes," Nicholson said. "We exerted a change in the program to say why not drive it to the manufacturer of the blank, leave enough tolerance on those holes and report back here during the assembly process so that we are not concerned. put an assembly operation on the mechanic and run the risk of hurting him badly, because that is all at the hand. "

"While at the manufacturer, you can install it on a template and use machines to drill these holes, and they are on site. I do not know the numbers of efficiency, but I've seen the graphics and Core Stage-1 to 2, it's at least twice as good, it's astronomically better, and we hope to reap this harvest in the future with Core Stages once. we are under contract with those. "

(Photo caption: The body of the Core Stage-2 engine section is lowered on the thrust structure in the MAF engine section structural mounting jig at the end of May. The cylinder and the ring on the top are welded, the thrust structure is bolted, and the two pieces are assembled in the jig.)

For the Core Stage-1, the thrust structure and barrel were brought together in the MAF structural assembly jig at the start of construction. At this point, the holes for containing the tube supports have been drilled.

"We matched them on the spot," Nicholson said. "It was thought through the Core Stage design phase and you learn things with the first unit. We said that "it takes too much work", which is equivalent to time and we had a lot of mis-matched holes. So engineering had the ingenious idea that we sold the program to pre-drill those holes. the manufacturer of the part. "

"[The] The program has demonstrated due diligence. Engineering had to put together a large commercial study to convince it that it was an investment in time but that it would save you a lot during the assembly and the order, "he explained. "You will only harvest this harvest months later."

"The day we started, the day we started assembling all these pre-drilled pieces, everyone knew it well at the time, because the number of our jobs was increasing exponentially because we all thought back when we did it with Core Stage-1. we would have a poorly matched drill hole and we would sit here to make a nonconformity from the start. [It was] instant return on investment, instant return on investment. "

"The engineers were sitting and saying, see? We told you so.

After the work, Nicholson said the supplier would provide the push structure to MAF after this work: "It's now part of the basic design, all the others will be built this way."

He also noted that not all match holes would be done elsewhere. "There is still some correspondence, but I'm talking mainly about the supports that hold the tubes, the wiring and the spatial geometry on a substructure. We do not see this pre-drilled in the future, we do not see the value of this because of the complexity of the implementation of these parts, they must be perfectly adapted to their implementation. "

Nicholson said Boeing planned to incorporate lessons learned in future developments beyond the fundamental phase 2, for example with cabling. "The next goal we would like to address before the third step is to start the electrical wiring sooner," he said.

"We had a lot of unexpected discoveries with the Core Stage-1 with our electric work statement. We are integrating these lessons into the required engineering and this engineering is currently going through a publication cycle to build these bundles incorporating these lessons. "

"Ideally, I would like to have these harnesses a few months ago. If you go to the interior [the] barrel for the moment, we have pre-filled these cable harness brackets to attach the bundles. I would like, in this mounting position, to go from the front and pre-install these bundles of cables to the maximum. "

For the second version, Nicholson announced the modification of some cables to facilitate management: "We are integrating the lessons learned from the basic phase 1 into the basic phase 2. One of the lessons learned was the production interruptions of our electrical system. cables. "

(Photo: The Core Stage-2 engine section body is stored next to one of the liquid oxygen tank (LOX) domes in February 2018. The barrel body is made up of eight welded panels by friction-stirring and an L-ring above which Vertical weld zones for panels can be considered here as breaks in primer treatment before welding, as well as circumferential weld zones for the ring at the top.)

He gave a hypothetical example: "We have a 75-foot electric cable that goes from one side of the barrel to the other, through the other side of the barrel. It's a lot of work to deploy this cable, set it up and adjust it properly. "

"Well, maybe it's smarter to put a production break in there, so you have something smaller to handle," Nicholson explained. "You can simply manipulate it physically faster, easier, and more easily."

"We implement some of that, we separate it into small pieces, because the more you cut the cable into shorter lengths, the more you have what is called a line loss, your current does not hold up until you reach it. ;at the end. So we're very strategic about these kinds of changes, but we do a little bit. "

In addition to the efficiency gains based on streamlining the workflow, the quality of work improves. More work is completed according to its specifications, which means less time is needed to repair the output, set specifications or both.

"These three big things, which integrate all the lessons learned, attack the electrical system and pre-integrate the thrust structure before the first stage of Core Stage 1, allow us to gain efficiency," said Nicholson. "Our nonconforming conditions, I do not know the number, but we are at light-years, ten times lower than at the first stage."

"And so we expect the Core Stage-2 and forth our efficiency will soar and eventually reach a plateau. What we do not know yet is that we can predict this plateau. "

"Our industrial engineering team is trying to analyze this with all the data from Core Stage-1 and the current data on Core Stage-2 to try to help us understand when can we expect to say & Ok, it's as fast as you can ever build a rocket, "he added. "The story tells me: thirty-two years in this sector, always building for the first time, that's all I did. The story tells me that it will probably be the fourth before we really understand that, but that's just my opinion. . "