NASA EGS, Jacobs preparing SLS Core Stage for Artemis 1 stacking
The Core Stage of NASA’s first Space Launch System (SLS) vehicle arrived at the Kennedy… The post NASA EGS, Jacobs preparing SLS Core Stage for Artemis 1 stacking appeared first on NASASpaceFlight.com.
The Core Stage of NASA’s first Space Launch System (SLS) vehicle arrived at the Kennedy Space Center (KSC) and was moved into the Vehicle Assembly Building (VAB) on April 29. The stage is now in the hands of KSC’s Exploration Ground System (EGS) program and prime test operations and support contractor (TOSC) Jacobs.
The long-awaited milestone allows EGS and Jacobs to work towards putting the whole Orion/SLS vehicle together and beginning months of testing to get it ready for the launch of Artemis 1. The stage is now in the low bay of the VAB, where some “traveled” work from the recently-completed Green Run design verification campaign will be performed in parallel with preparations for stacking with the new launch vehicle’s Solid Rocket Boosters (SRB), which are already in place on the Mobile Launcher in VAB High Bay 3.
Critical path to mate
Two major milestones were recently passed in April. First, Core Stage prime contractor Boeing completed the Green Run design verification campaign on the first flight article, Core Stage-1, at the Stennis Space Center in Mississippi. The stage was delivered to KSC on April 27 and is now sitting in the VAB.
Just before arrival, the SLS Core Stage team completed the Element Acceptance Review (EAR) for Core Stage-1 on April 26. The review board covered current status and documentation products, and at the conclusion of the review, the Artemis 1 flight article was officially transferred from Boeing to EGS for launch processing.
The next major milestone is to get the stage mated to the SLS Boosters, which are assembled on Mobile Launcher-1 in the High Bay 3 integration cell of the VAB. For now, the stage is still the primary critical path for the schedule of work to get ready for the Artemis 1 lunar orbit mission.
Mating the Core Stage to the Boosters is the next big, highly visible milestone, but moving the stage into launch position also opens up major job paths that EGS and Jacobs can then work on simultaneously.
“I think for us it really comes down to what are the critical path priorities,” Andrew Shroble, Integrated Operations Flow Manager for Jacobs, said. “There’s a lot of parallel work that’s going to be happening once we stack and get the Core Stage mated to the Boosters.”
“There’s a huge goal to get the whole vehicle stacked, there’s another huge goal to get connectivity and be able to power up as soon as you can to troubleshoot and get through any challenges we’ll have there, and then you have a lot of work that has to happen to get ready for the tests down the line like the Integrated Modal Test (IMT).”
“If we run into an obstacle or we have a non-conformance issue, then we move onto the next priority, so you’re keeping all these critical paths moving forward at all times. If you run into a kink, you move onto the next.”
(Photo Caption: Core Stage-1 is set down on “skid beams” in the VAB on April 29 after offload from the Pegasus Barge. Engineers will install ordnance and make Thermal Protection System (TPS) repairs before the vehicle is repositioned in the VAB for lift operations to mate it with the SLS Boosters.)
The stage is still resting in its Multi-Purpose Transportation System (MPTS) carrier, where the remainder of the work while it is horizontal will be done. “When we roll the Core Stage into the low bay, we’ll set it down onto these skid beams which basically distribute the load [across the] floor in the low bay,” Shroble said on April 29 just before the stage was rolled into the VAB.
“The primary objective in the transfer aisle in the horizontal position is to get those areas that are inaccessible once we go vertical in High Bay 3.”
The stacking, high-bay cells in the VAB are positioned on the east and west ends of the building, with a transfer aisle that runs north-south in between them. The low-bay area extends out from the high bay area on the south side of the building.
Before it can be rolled from the low-bay to the northern part of the transfer aisle in between the high bays and hooked up to cranes for the lift up into High Bay 3 for stacking, there are a few jobs that can best be performed on the stage in its current configuration. The first task for EGS and Jacobs was to do receiving inspections of the stage.
“We’ll go right into receiving inspections,” Shroble said. “As part of the NASA handover, to our contract [terms], we have to do full external inspections for any damage and non-conformances that would need to be addressed.”
The major job originally planned while the stage was horizontal in the VAB Transfer Aisle was installation of the components of the Flight Termination System (FTS). For its first launches, SLS will use the traditional FTS, which would be manually activated by Cape Canaveral Range Safety to terminate an off-nominal launch.
Following the receiving inspections, EGS and Jacobs will begin installing the Core Stage parts of the FTS. “They’re going to install the linear-shaped charges, the S&As (Safe and Arm Devices), the CRDs (Command Receiver/Decoders) as well,” Nathalie Quintero, Boeing SLS Launch Operations Aerospace and Systems Engineer, said. “That’s all part of the FTS that’s going to be installed here.”
The FTS assemblies will be installed inside the systems tunnel of the Core Stage, which runs almost the entire length of the element along its exterior. Cover plates will be removed to attach the components to the cable trays inside.
(Photo Caption: The -Z side of the Artemis 1 Core Stage is highlighted as self-propelled motorized transporters (SPMT) roll the stage and its carrier into the VAB on April 29. The lighting in the image highlights the long systems tunnel that runs almost the length of the stage and the different cover plates currently installed. The plates with a more glossy appearance are non-flight covers installed for the recently completed Green Run test campaign; all the plates will be removed to install FTS components inside, and only flight covers coated with foam will later be reinstalled.)
The work was planned for this point in the processing flow because there is better access to the tunnel and the work area now while the stage is horizontal. “The nominal planning was to go install FTS ordnance into the systems tunnel,” Shroble explained.
Installing the components would be more difficult to do once the stage is vertical and encircled with several levels of platforms. “The linear shaped charges and the FCDC (Flexible Confined Detonating Cord) lines, [it’s difficult] to be able to take a ten or twelve foot linear-shaped charge and walk that up and be able to secure that into the systems tunnel,” Shroble said.
“So once we get through receiving inspections, we’ll gain access to the systems tunnel. We’re going to pull all the tunnel covers off, expose the systems tunnel, [and] we’ll have the ordnance delivered and pre-staged.”
“Then that team will come in, install the LSCs, install the FCDC, and then final securing, make sure that connectivity is good, and then they’ll [re]install the tunnel covers,” he added. Once the FTS work is done, that prerequisite to move into stacking preparations would be complete.
Recent schedule forecasts had projected a couple of weeks for the FTS work, but more post-Green Run refurbishment work on the stage was brought from the Green Run at the Stennis Space Center to Kennedy. Some of that “traveled” work needs to be done before stacking the stage and could take another couple of weeks to complete.
With the additional traveled work from Stennis, the current forecast for mating the Core Stage to the Boosters is the end of May, beginning of June.
Extra traveled TPS work
Some of the refurbishment of the Core Stage thermal protection system (TPS) was moved to the KSC task list while it is still horizontal. In addition, to optimize the remainder of the schedule to Artemis 1, post-Green Run refurbishment work that didn’t need to be done at Stennis was deferred until after arrival at KSC.
This allowed the stage to be removed from the B-2 Test Stand at Stennis, transported to Florida, and moved indoors inside the VAB. Similar to the work deferred from Stennis, any refurbishment work that doesn’t need to be done while the stage is horizontal will be deferred to later in the launch processing flow; however, there are some TPS inspections and repairs that need to be done now.
(Photo Caption: Core Stage-1 is rolled off the Pegasus barge at KSC on April 29. In the top middle of the images are two dark areas around the intertank to LH2 tank flange where the spray-on foam insulation (SOFI) closeouts need to be repaired. In addition, the plan is to repair areas of the Core Stage TPS while the stage is in its current horizontal orientation, especially areas that would be inaccessible after it is stacked vertically with the SLS Boosters.)
“We’ve got a laundry list of things to do and it’s being split up between the Boeing team and the Jacobs team on how we’re going to handle it and try to smartly put the resources out there in the most efficient way possible,” Michael Alldredge, NASA SLS TPS Subsystem Manager, said. “The work is being broken down into access constraints.”
There are areas around the outside of the stage that are easier to access right now than they will be after it is mated to the two boosters. In particular, after the boosters are attached, they will physically restrict access to external areas on the sides of the Core Stage.
The boosters will block the 90 and 270 degree locations around the 360-degree circumference of the stage, so any repair locations that would be made hard or harder to reach would be candidates to tackle now. “Once you stack [it is difficult] getting to the 90 and the 270 side because of the Boosters, so the work is being prioritized such that we do the things that we have to do in the Transfer Aisle and then everything else I believe will go in [HB-3],” Alldredge said.
“We have some repairs to do like on the LH2-Intertank flange,” he noted. “So we’re going to have to dress up and reinsulate the portions of that where we can get to it from the sides.”
The flanges are where the five major structural elements of the Core Stage are bolted together during assembly. Then, a specific formulation of spray-on foam insulation (SOFI) is manually applied to cover the area to keep as much ambient heat from the outside away from the cryogenic propellants in the two tanks.
Some cracks were expected to develop in some areas of the foam during Green Run propellant loading and unloading at Stennis, especially during the first full tanking cycle, which occurred on December 20 during the second Wet Dress Rehearsal. “We had the full duration Wet Dress and then we cold-soaked for two and a half, three hours, which is a long time to sit,” Alldredge said.
(Photo Caption: A graphic showing the SLS vehicle configuration with the different points around the circumference of the Core Stage. The Boosters attach at the 90 and 270 degree locations; TPS repair work in those areas is being prioritized since they will be inaccessible after the Boosters and Core are mated.)
Alldredge noted that the flange where the bottom of the intertank bolts to the top of the LH2 tank is where most of the damage was seen. “We did see a number of cracks that did show up there, some of which didn’t get any worse as we got into Hot-Fire #1 and then Hot-Fire #2, and some of which did get a little bit worse,” he said.
“You see a lot of dynamic energy right there in and around that flange, and so we did pick up a good bit of cracks there, which is not uncommon. We expected that to be a potential, and it showed itself.”
The more visible TPS damage seen during the two static test-firings was to the bottom of the stage on its base heatshield, but that traveled work can be scheduled for later in the processing flow in parallel with the critical path processing of the assembled SLS vehicle. “We should have very good access to the base heat shield after the Core Stage is vertical and integrated with the boosters in HB-3,” Alldredge noted.
“Overhead access will make operations less risky compared to operations in-and-around the main engines with the vehicle in the horizontal orientation.”
Delivery to KSC follows a month of post-Green Run engine refurbishment.
The SLS Core Stage was the final major Artemis 1 component to arrive at KSC, which will enable EGS and Jacobs to complete launch preparations. Artemis 1 will be the first joint mission of all three of the Exploration Systems Development division programs, and in addition to launching and flying together for the first time, most of the elements will be making their maiden voyage.
The Core Stage Green Run Hot-Fire that was completed on March 18 at the Stennis Space Center was the final major standalone development test. The stage departed the test facility on April 22 in the agency’s Pegasus barge following a month of refurbishment. After both test-firings at Stennis, the four RS-25 engines needed to be refurbished immediately afterward. There was more work to do after the full-duration firing on the second attempt.
“[The] first one took 19 days to say we were done and that we were ready for cryos,” Bill Muddle, Lead RS-25 Field Integration Engineer for Aerojet Rocketdyne, said. “From an engine perspective [it took] 19 days to turn around, 29 for the second one.”
“But the 29 [days] was from when we shutdown to when we were ready to transport, so we had covers and closures [to install], closeout inspections, other things that we had to go do, so it added a little more time on there. All the shipping configuration checks, too.”
(Photo Caption: The four Aerojet Rocketdyne RS-25 adaptation engines lead the way as Core Stage-1 is backed out of the Pegasus Barge at KSC on April 29. All four engines are modified Space Shuttle Main Engines (SSME) that served the Shuttle Program as far back as the 1990s; the top two engines as seen in this image helped power the final Shuttle launch almost ten years ago.)
In the case of the turnaround after the abbreviated hot-fire test in January, the same engine drying had to be performed, but the refurbishment period was shorter because the engines were going to be fired again in the same place and because of the shorter firing time. “We had looked at the requirements in what we call a short-duration hot-fire,” Muddle said.
“We went through all those requirements, and we actually pared it down a little bit. We still pretty much looked at everything we looked at on the second hot-fire, but the second hot-fire we looked at it in more detail.”
Some nozzle tube repairs are typically needed after the engines are fired for full-duration, and there wasn’t as much work to do after the abbreviated first firing. “On the first one we had to fix one engine, on the second one we had to fix all four,” Muddle noted.
The four engines in the Core Stage are returning to KSC for the first time in almost a decade after being stored at Stennis Space Center for several years. During their Space Shuttle Program service, the engines were refurbished between flights at KSC; Muddle started working on Space Shuttle Main Engines (SSME) for Rocketdyne in 1988 and moved to Florida the next year. “I call them my children,” he said. “So my children are coming home.”
Now that the flight hardware is in the hands of EGS and Jacobs, Aerojet Rocketdyne and Muddle will be in an oversight role for Artemis 1. “EGS is going to take it over, but Aerojet Rocketdyne will come in, there is some transportation reconfiguration that we have to go do on the engines to get into flight [configuration], so that’s about the only work that Aerojet Rocketdyne has [left] to do.”
Next step: lift preps
Once the work in the low-bay transfer aisle is completed, the self-propelled motorized transporters (SPMT) will again pick up the MPTS carrier with the Core Stage on board and roll them into the north transfer aisle between the VAB’s high bays, where the stage will be prepared for the lift “up and over” into High Bay 3 for mating to the Boosters.
“[We’ll] get into preps for lift, dual-crane operations, going through the spider integration, connecting the aft lifting equipment with the 175-ton crane on the aft end and then basically we’ll do a horizontal lift, remove the GSE (Ground Support Equipment), do a breakover, [and then] we have some leveling to do before we lift into the high bay,” Shroble said.
The spider, or lift spider, is an identical lifting fixture unit to the one used at Stennis for the whole Green Run campaign. The unit at Stennis was disconnected from the Core Stage before it was rolled onto the barge and after it had been rotated or “broken over” from vertical to horizontal.
The second unit was delivered to KSC when the Core Stage Pathfinder stopped through in 2019 for shipping and handling practice, and will again be used to take the Core Stage back to a vertical orientation for attachment to the SLS Boosters. The massive spider is too heavy to leave hanging, cantilevered off the front end of the stage for very long, so the load will be shared between different ground support equipment.
The first piece is the Transportation Interface Fixture (TIF) that will be used to hold the 45,000-pound, yellow-painted spider while it is moved into place and bolted to the top end of the stage. “The ability for the stage to be able to handle that load without any potential damage to the hardware is why they implemented this fixture,” Shroble said.
“Right now we have the spider sitting in the transfer aisle, so we’re going to connect that to a crane, lift it up, break it over into a vertical position and actually attach it to the TIF. We’ll then disconnect the crane so now the TIF and spider are integrated [and] they’re ready to then be relocated where we can then install the spider to the Core Stage.”
“Once we install it to the Core Stage [and] they get a set number of pins in, then they actually connect the overhead crane. So there’s a switchover, [the crane will] basically take over the load before fully disconnecting the TIF, and now the full load is actually somewhat distributed into the ground support equipment.”
In addition to one of the overhead cranes taking up some of the spider’s weight, Shroble said the SPMTs will also be used for support underneath. “What they’ll do is they’ll take the SPMTs and assume some of the load, so it’s kind of like a three-point lift in a way where you’ve got the TIF, you’ve got the overhead crane, and you’ve got the SPMTs supporting to kind of try to lessen the load on the hardware,” he explained.
The lift operations will be very similar to the practice with the Pathfinder in 2019. One of the two 325-ton cranes will be attached to the spider on the front of the Core Stage, and the 175-ton crane will be attached to lift points on the engine section structure.
“The 175-ton crane is our transfer aisle crane that runs north and south, that’s going to be used for the aft, and then the 325 number two crane goes [west and east] between High Bay 3 and High Bay 4, so that’s our primary crane used for lifting flight hardware and stacking operations,” Shroble added. “So we break over with both of those cranes into a vertical position.”
“All the load will be assumed by the 325 number two [crane], and they’ll have slack in the transfer aisle 175-ton crane, and then they’ll disconnect that. And then after they level [the Core Stage] with the master link which is connected to the spider, they then fly it up and be able to lower it down and mate it to the Boosters.”
Lead image credit: Philip Sloss for NSF.
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