Boeing completes first NASA SLS engine section, getting ready for final Core Stage mate

by Philip Sloss

Final pre-mate work on ‘four-fifths’ of the stage

The changes to the final assembly plan applied earlier this year allowed work on the rest of the stage to continue in parallel. The forward join that includes the upper three elements of the forward skirt, liquid oxygen (LOX) tank, and the intertank, was attached to the liquid hydrogen (LH2) tank over the Memorial Day weekend in late May.

Since then work on the mated, upper “four-fifths” of the stage has progressed to point where it is basically ready for the engine section mate.

“We’ve maxed out our work content for the feedlines and the press lines,” Craig Williams, Boeing’s Core Stage Integrated Product Team Director, said. “The passive roller stands and the rotation equipment that we sit the vehicle on is maxed out in terms of weight and how much work we can do and still hold that article from a weight standpoint and a center of gravity standpoint.”

Credit: NASA/Jude Guidry.

(Photo Caption: Boeing Director of Operations at MAF Jennifer Boland-Masterson shows NASA Administrator Jim Bridenstine the nearly two-hundred foot long front end of the Core Stage on August 15. The partially-assembled major protuberances on the -Z side of the Core Stage can be seen, including one of the two LOX feedlines, two tank pressurization lines above it, and the lighter-shaded area below it where a large section of the systems tunnel was attached on August 17. Acreage foam in this part of the LH2 tank was machined down where the base plates of the tunnel will sit and rows of studs are seen that will help fasten the plates.)

The LOX tank rides up front in the Core Stage, around one-hundred, fifty feet above the engines, so two, large-diameter feedlines run from the bottom of the tank that sits inside the intertank, down opposite sides on the exterior of the LH2 tank, and then into the engine section. Those long lines are connected in sections, attaching both to each other and to fixtures on the LH2 tank that hold them in place.

As Williams noted, work is complete on the sections of the LOX feedline that could be installed prior to putting the whole stage together. The remaining pieces will be connected from the bottom of the stage towards the top.

“[It’s] critical that we have the engine section installed,” Williams said. “That first feedline, the stub out from the engine section to that feedline number two we call it, it’s critical that we install that one first and then connect to feedline two through five.”

“Then that’ll leave six and seven which go up into the intertank as the last to install and that gives us the max flexibility of the BSTRAs (ball-strut tie-rod assemblies) in the feedline assembly to maneuver it into place,” he added. “It’s a much riskier operation to install the engine section one last, so the preferred production method is to do that engine section feedline first.”

The current segment of work inside the now-cramped volume of the intertank is also complete. After the LH2 tank was mated to the forward join, the volume in the intertank was largely consumed; however, an access kit was installed inside to complete several internal connections.

Credit: NASA/Eric Bordelon.

(Photo Caption: The top ‘four-fifths’ of Core Stage-1 in early August, top on the right and bottom of the left. From left to right, the four join elements are the LH2 tank, intertank, LOX tank, and forward skirt. The lighter-shaded rings roughly delimit the elements. Since they were physically bolted together in late May, technicians have worked to interconnect all the services that will run between the elements on the inside and outfit additional services that will run on the outside of the stage. In the foreground, a Boeing technician can be seen working on one of two pieces of the systems tunnel cover plates.)

“For the intertank work volume that access kit was completely installed and the required work is all complete,” Williams noted. “We’re in the process right now of removing that access kit to allow us to go to the next stage of operations and [by] that I mean [we] have to have that kit out to rotate the vehicle.”

The front of the stage needs to be rolled ninety degrees from its current orientation for the engine section mate. It was rotated most of the way for one more major installation first.

“We’re taking out the intertank platform right now and this weekend we will be rotating that four-fifths of the rocket to what we call fourteen degrees up,” Williams explained on August 14. In that orientation, the footprint of the systems tunnel is pointed straight down at the floor.

“That will allow us to roll in the aft systems tunnel assembly that sits on that independent tool,” he noted. “We’ll air pallet that over and we’ll install the aft system tunnel on the hydrogen tank starting Saturday and that’s the last amount of weight we can put on the system with those passive roller stands and the T-RATT the rotation and transportation tool.”

Core Stage subassemblies are often held in Boeing’s Rotational Assembly and Transportation Tools (RATT); the T-RATT is a Transitional RATT that they modified for more flexibility in handling different subassemblies in different phases of the assembly/production process.

Williams subsequently noted that the long section of the systems tunnel on the LH2 tank was attached as planned on August 17 and since then the team is completing the full mechanical installation. The sections are staged with wire harness runs and tubing on a base plate that is fastened to the spray-on foam insulation (SOFI) on the outside of the stage. Cover plates will subsequently fit over the top of the tunnel.

Williams added that work connecting the installed systems tunnel sections will continue while the top of the stage waits for the engine section mate. “There was an interim rotation in there, to go from the fourteen degrees, if you will, to ninety, to allow for further system tunnel work to be done,” he said on Thursday.

The ninety-degrees up orientation is basically back to the orientation the stage was in during the Summer. “That rotation in there just allows extra work to happen during this time until the engine section is ready — wire harness routings, small-diameter tube installations, and then some TPS or foam ramps that we’re actually looking for the possibility to eliminate based on requirements,” he said.

“The final rotation to mate the engine section is at zero degrees and we’ll place that in that position when the engine section is ready to come back from 110.”

Preps for final mate

Now that all parties have signed off on the functional test results, there’s a lot of preparation work to do before the front of the engine section can be rotated and connected to the back of the LH2 tank. Not only do the intricacies of the test equipment, controlled work area platforms and fixtures, and scaffolding have to be cleaned up and moved out of the way, but there’s final quality inspections to do.

“What we’re trying to do is make sure we have all of our mechanical assembly type work done on the inside of the volume,” McGee explained prior to the review. “So two things before we start pulling out stands, internal stands and the external stands. We have to finish the break of configuration, so we’d have to say ‘ok, we’re ready to turn off our equipment and move it all back, does everybody concur with that?'”

“Once we get that then we’d be free to start disconnecting, and then to have what we call ‘shakedowns,'” he noted, referring to a protocol of Defense Contract Management Agency (DCMA) final quality inspections of the inside of the element while there is still well-established access.

“So we have internal Boeing and also government DCMA shakedowns, which is really going into the volume and looking to say ‘ok, we’re done with this work statement,'” McGee explained. “This is your last chance to come in and really look at everything before we go horizontal and mate, so that latter part of that work has to take place after the break of configuration.”

Credit: NASA/Eric Bordelon.

(Photo Caption: A view from up high in the Core Stage final assembly area at MAF, Area 47/48, in early August. In the left background, the engine section/boattail sit in one of the tools developed to support the revised assembly of the remaining pieces of the stage. The hardware was positioned along the back of Area 47, and the support team work area is seen in front, with a ring of gray and white ground test equipment around the work stand in between. Already approaching two-hundred feet in length, the rest of the stage consumes most of the Area 48 footprint on the right.)

While the results of the different functional tests were being reviewed, some configuration and TPS work also continues on the engine section and boattail.

“There’s four vents that go on the inside of the engine section, these are vents that keep rainwater out and bugs and all that kind of stuff and so those are kind of the last few things to put in,” McGee noted mid-month. “We may have already finished this.”

“Right in front of the vent is what we call the haz gas tube, which is the system inside the engine section to sniff for any hazardous gases that are building up in the engine section volume while you’re either at Stennis or on the launch pad, so we are just buttoning up a few things like that. Other work that we’re doing in there is installing Green Run hardware, there are some cameras that are in there and wires for Green Run sensors, we’re finishing up that work.”

“We’re also doing some RT-455 [applications], the ablative material on the outside, trying to get all of that work done while we’re finishing up with our functional testing,” McGee added. “It’s hand-applied stuff that you can mold and shape.”

“It cures and then you come back later and shave it down to profile,” he explained. “So it’s a material that goes over like fastener heads and structural joints where the cork can’t really adhere to a nice, smooth surface.”

In addition to the inspections and removal of access platforms and other non-flight equipment, there will be a few final tasks to complete. The temp-installed LH2 propellant tubing, the four individual engine feedlines and the fill and drain line, will also have to braced for all of the upcoming shipping and handling of the engine section — first by itself around the factory, then with the rest of the stage on the trip to Stennis, and finally being lifted up into the B-2 Test Stand.

Credit: NASA/Eric Bordelon.

(Photo Caption: The engine section/boattail is rolled on its new transportation tool April 1 to its current parking spot in Area 47/48. After platforms and stands are broken down and moved out of the way, SPMTs will pick up the tool again and move it back to Building 110 to begin the sequence of activities to mate it with the rest of the stage.)

“To go horizontal with the LH2 feedlines detached from the hydrogen tank, we’ve had to manufacture some tooling struts that tie the LH2 feedlines over to the primary structure and hold those in place during transportation,” McGee said. “So we’ve got to put that in and then we’ll be ready to start pulling out the internal access stands.”

McGee also noted one of the tasks is to connect lines to pressurize the propellant tanks for transportation.

“To transport the Core Stage we have to pressurize the LOX and the LH2 tanks, so one of the last things that we do is hook up those lines to the press systems and then run those over to the access door, where we have a pressure panel that is mounted to the access door,” he said.

“So just a handful of little things like that that we’ve got to do before we start pulling out the scaffolding. When you see the stands all coming out of there, you’ll know we’re really, really close to getting ready to roll over to Building 110 for the rotation.”

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