Final assembly started in September
NASA and Boeing completed checkout and validation of the engine section with its boattail fairing in late August, and the aft compartment was moved to Building 110 a few days later. After non-flight work platforms and equipment were removed and quality control inspections were completed, the element was lifted and broken over from its vertical standalone assembly orientation to the horizontal orientation of the rest of the stage in mid-September.
After being secured to ground support equipment, the engine section and boattail were rolled back to the final assembly area, Area 47/48, where the top of the engine section barrel was bolted to the bottom flange of the liquid hydrogen tank a few days later. Area 47/48 is a dual position area and after the stage was fully mated in Area 48, it was picked up and moved across the floor to the Area 47 position in late September for the rest of final assembly work.
(Photo Caption: The horizontal engine section/boattail assembly rolls out of Building 110 on September 14 after breakover activities, headed to the final assembly area for mating to the rest of Core Stage-1. A pair of Boeing’s indoor Self-Propelled Modular Transporters (SPMT) carried the flight hardware on its modified Core Stage RATT driven remotely by nearby technicians.)
The stage was then rotated ninety degrees along its long axis to the engine install orientation. After re-establishing internal and external work access platforms to the rest of the stage, Boeing then worked through the first half of October to thread an intricate set of work platforms through openings in the boattail to support installing the engines.
NASA reviews ahead of shipment
While Boeing still has a lot of testing to complete, NASA is also conducting reviews to coincide with completion of assembly and shipment to Stennis. “We just kicked off this week what we call FCA/PCA, that’s a functional configuration audit and a physical configuration audit, and that’s a review of the engineering and the build paperwork and the non-conformances associated with it,” Williams noted.
“That’s a two-week effort and there’s about thirty-ish NASA folks down here for the next ten days going through those build records and those non-conformance records and test records, showing that the intent of the design was met throughout the build, and that’s one element of it.”
“Then there’s a couple of others,” Williams added. “There’s a TRR, Transportation Readiness Review, that NASA will hold and that we’ll participate in but NASA has transportation duties, so they’ll take ownership of it in the aisle there in [Building] 110 and they’ll move it to the barge and move it up and place it in the stand and DD1149 it (a U.S. government requisition and invoice/shipping form) back to Boeing to go conduct Stennis operations and test.”
(Photo Caption: The fully assembled Core Stage-1 structure in the Area 48 position of final assembly on September 30. Additional support tools were removed from under the two mated flanges not yet treated with spray-on foam insulation (SOFI). Passive roller stands and other RATTs were previously connected in the area of the primer green colored stripes around the LH2-engine section flange (foreground left) and LOX-intertank flange (background right) seen here. With all the platforms removed, the two remaining stage RATTs were picked up by SPMTs and moved from the Area 48 footprint to the Area 47 footprint (left to right, towards the camera) to complete most of final assembly and prepare the stage for engine installations that began in mid-October.)
“And then there’s a pre-ship review which we call the readiness review for shipment and that’s about a week before shipment,” Williams said. “We’re finalizing the schedule for that as we shore up this exact date in December.”
“That will [review] some elements of the acceptance data package, it’ll have a reconciliation status, it’ll have our non-conformance status, any open work that would be in consideration to move to Stennis, and verification objective status and a whole bunch of other health and well-being of the vehicle status if you will.”
There’s also the destination side of the trip. “Concurrently ongoing with that there’s the whole readiness of Stennis,” Williams noted. “So there’s a production readiness review and test readiness review set of sessions that are ongoing saying that Stennis is ready to receive the vehicle and start testing.”
“Of course modal testing is the first thing that happens there the first few days the vehicle arrives.” Modal tests are being conducted during the development phase of the different Exploration programs to collect data on the structural dynamics of elements of the SLS, Orion, and ground systems like the Mobile Launcher.
When the Core Stage arrives at Stennis, Green Run testing begins with the modal test. “Right when you come off the barge and you really go to hang that thing on the crane the modal test is one of the first few activities done before placement into the stand,” Williams added.
(Photo Caption: The engine section/boattail assembly is parked outside the Area 48 final assembly area on September 14 before beginning mating operations with the rest of the stage. The final assembly connections that will be completed once the Core Stage is installed in the B-2 Test Stand at Stennis can be seen on the aft end of the LH2 tank. Four LH2 prevalve assemblies and one fill and drain valve assembly stick out of the aft manifold of the LH2 tank. The feedlines that run from the prevalves to the engine inlets and the line that runs from the fill and drain valve to the Tail Service Mast Umbilical will be connected at Stennis.)
After the stage is fully bolted into the stand vertically and access re-established inside, the last assembly tasks orphaned by the change early this year to finish final assembly all in the horizontal orientation can be completed. New hardware and procedures were devised to allow all the other vertical assembly tasks to be performed horizontally, saving several months of schedule and maintaining the opportunity to finish assembly this year.
The major exception that couldn’t be completed horizontally were the liquid hydrogen (LH2) lines in the engine compartment. The four individual engine LH2 feedlines and the fill and drain line were installed in the engine section and secured in early September for the rest of final assembly at MAF and eventual transport to Stennis, even before the element was mated to the rest of the stage.
Once the stage is locked down in the stand, those lines can be fully connected and the remainder of the FIFT check out completed. “We’ll complete the feedline installation, the fill and drain line installation, and then there’s some other tubing, some electrical lines that run up off the feedlines that we’ll close out and then we have some TPS final closeout activities there as we test those areas,” Williams said.
“Those [FIFT] tests would come in right when make the mate [at Stennis], then we would go into a leak check and you would want to make sure you were sealed and passed the leak rate,” he explained. “The other testing that would be included other than those four feedlines and the fill and drain line, there’s some small-diameter tubing installations there so we would do a leak check for those tubing installs and then there’s those final electrical connections that we would have to make, so we would do a sensor channelization verification test.”
“Everything from the engines will have been connected here so we developed a system [and] put in blank-off plates in the lines themselves that allow the engine testing to be done here, in terms of the installation,” he added. “The planned production work that we’re doing up at Stennis now in the vertical position there’s only about ten percent of the FIFT that went to Stennis and that’s associated with the connection of the Boeing side of the interface.”
“The Aerojet side of the interface will be done here.”
Preps for shipment after functional testing
As the FIFT wraps up, pre-shipment work on the stage will increase. “We’ll leave open the intertank and the obviously the engine section aft of the SRB (Solid Rocket Booster) ring and the forward skirt because we’ll need access for testing,” Williams said.
“Once those elements of testing are complete for that given volume, then we’ll start extracting the internal access kits and close those out.” Before the platforms can be removed, official quality control inspections and documentation of the internal configuration will be completed.
(Photo Caption: Engine 2056 in the number two position on the left and Engine 2045 in the number one position on the right are seen in this image taken looking up at them from the Building 103 floor at MAF on October 30. The final two engines were installed into the lower positions seen in the foreground here in early November. Multi-Layer Insulation (MLI) blankets will be attached from clips around the base of the engine nozzles to the larger circular openings to protect the engine powerheads and the inside of the engine section from heating during the Green Run test-fire and later on during the Artemis 1 launch.)
“We’ll do a shakedown/walkdown, we’ll do a FOD (foreign object debris) verification check, we’ll do closeout photos, everything associated with the need to declare that volume complete and ready to closeout and then we’ll put those access doors on, ready it for shipment, and basically the last thing we’ll do is take off the ground umbilical plates, the four ground umbilical plates,” Williams explained. The ground side plates have been attached to the stage’s vehicle side plates during final assembly at MAF and earlier.
“They come off for cg (center of gravity) of the vehicle and weight for the transportation,” he noted. “They’re actually pretty big, they’re about twelve-hundred pounds apiece, so we take those off for stability of transportation, they’ll be shipped up there as individual items and then one of the first activities we do thereafter placement into the stand is put these plates on at Stennis.”
In addition to closing out the internal volumes of the forward skirt, intertank, and engine section, the exterior of the stage will be closed out for shipment to Stennis and the Green Run campaign, such as installing cover plates over the systems tunnel and engine fairings in the corners of the boattail. “There’s some fairing taping, things like that around the cork area in the boattail, aft end,” Williams said.
“We’ll have to obviously put the fairings on, do some closeout taping there and then the final thing we’d really do would be putting on the MLI (Multi-Layer Insulation) blankets.” The MLI blankets will provide similar thermal protection on the Core Stage as the eyelids and dome heat shields installed around the engines when they were installed in Shuttle Orbiters.
“And then those [blankets] actually they serve as a barrier for the purge in that engine volume, too,” Williams added. “We put like a very small purge in that area just for positive pressure for shipment.”
(Photo Caption: The four RS-25 engines soft-installed in Core Stage-1 on November 7 at MAF. The facets of the boattail fairing facing aft towards the camera here will see higher total heating during a static, full-duration Green Run hot-fire than they would during a launch ascent and extra TPS is being added for the ground test-firing scheduled for next year at Stennis.)
Attaching the engine fairings will require the stage to be rotated. “Right now we’re limited to our ninety-degree [up] orientation in this current configuration until we take the platforms out of the engine section and the intertank, so we need to be done with FIFT and then extract those from the vehicle and then we’re free to rotate it as needed.”
Other exterior TPS closeouts on the stage, such as foam sprays and closeouts, is also being completed during final assembly. During mating of the engine section to the rest of the stage in mid-September, the other temporary passive roller stand (PRS) was removed from under the aft end of the LH2 tank, leaving the stage supported in two Rotational Assembly and Transportation Tools (RATT).
The forward RATT is attached to the front of the forward skirt and the aft RATT is pinned to the structural SRB ring in the engine section, which allowed spray-on foam insulation (SOFI) work to be completed on the mating flanges between the main structural elements of the stage. The forward PRS positioned near the intertank to LH2 tank flange was removed prior to the engine section mate, which provided access to finish the SOFI sprays and trimming/sanding there.
Similarly, access to do SOFI sprays and closeouts on the LOX tank to intertank flange was provided when a RATT connected there was removed after the engine section mate. SOFI sprays and closeouts of the final mated flange between the LH2 tank and the engine section are also in work; although the engine section barrel is largely protected by sheets of cork and a coat of white paint, the flange closeout is with foam.
(Photo Caption: A Boeing technician installs one of three-hundred sixty bolts around the circumference of the LH2-engine section flange on September 17. Prior to shipment, SOFI was used to thermally insulate the area. A manually-sprayed foam is applied to the light-green primer coat seen exposed here. The small cavity behind his hand between the LOX feedline aft reaction structure and the barrel will be filled using pour foam.)
“It’ll actually be the S-180 hand spray foam all the way around except for a handful of places like right behind the downcomers,” Michael Alldredge, NASA SLS TPS Team Lead, explained in September. “The feedlines will have a pour foam solution, and the reason we had to go that way is because if you look at the way the architecture is on the vehicle that cavity behind the feedlines and the engine section wall is so tight that we couldn’t get access to it to spray it so we’re going to a combination of pour and spray around those feedlines.”
At some point during the final closeouts and pre-shipment work, the stage will be moved from the final assembly area in Building 103, Area 47/48, over to the aisle of Building 110, also known at MAF as the Vertical Assembly Building (VAB). That is where Boeing will turn over the stage to NASA, but they won’t quite be done when the stage gets there.
“We have some work to do out there, we’ll have to take it obviously off the roll rings, we’ll have to participate in that transportation to the NASA equipment and we have some final closeouts that we’ll still have to conduct over there,” Williams said. The review to approve shipment of the stage to Stennis would occur once the stage is in the Building 110 aisle.
“We would generally do the review a week before we’re ready to ship which means we’re turning it over in place in that 110 aisle to NASA to move to the barge, so we would have roughly seven days worth of work left that would be the final shipping configuration readiness activities. We’re going to try and do as much work as we can in the 47/48 footprint before we move back to 110.”
(Photo Caption: The Core Stage will be re-oriented again for the barge ride from MAF to Stennis. It will remain in its current orientation (left) used for engine installs and final assembly through the integrated functional testing with the large LOX feedlines at the nine o’clock and three o’clock positions. When placed on NASA’s overland transportation equipment and while riding inside the Pegasus barge, the stage will be oriented with the feedlines at twelve o’clock and six o’clock positions.)
“Obviously it’s just a much better environment for us,” he noted. “As you can imagine if you were here this week, 110 is pretty darn cold.”
Although it has some air conditioning and ceiling fans, Building 110 is not environmentally controlled as a whole, and the high-temperature controls aren’t as effective when the Michoud area is under an overnight freeze warning as it was once last week. Williams said some of the final work may move from Area 47/48 to Building 110.
“It depends on where we’ll be from a process perspective, [there’s] a little bit of dynamics there and we planned it that way,” he explained. “We’ll try to do it where we’re most efficient and best themally-suited from an environment perspective but if pressures tell us we need to go back, we can with some work content.”
Lead image credit: NASA/Jared Lyons.