First NASA SLS Core Stage rolls out – Ships to Stennis

by Philip Sloss

First build took longer than expected

Getting to this historical first Core Stage rollout milestone for the SLS program took much longer than expected. “When we came out of the Critical Design Review in ’15, we expected to have the rocket built really by the end of ’17 so we’re about two years late and Boeing completely owns that,” Shannon said.

Although the Core Stage looks from the outside like a longer Space Shuttle External Tank and employs existing Space Shuttle engines, NASA’s design is all new. The agency took apart the Shuttle’s liquid propulsion elements, taking its external liquid propellant tanks and components inside the back end of Shuttle orbiters, rearranging them, and bringing in newer equipment, avionics, and brand new software.

The side-mounted Shuttle elements were stretched, bulked up, and redesigned as an inline rocket stage, which meant the new design would require an all-new manufacturing infrastructure. Issues constructing and activating the large Vertical Assembly Center welding tool delayed work verifying the new welding processes.

“We basically just had an empty factory form and I think there was a mindset that ‘they got a facility, they got a design, why can’t they just build the rocket and get it out?’,” NASA SLS Program Manager John Honeycutt said on rollout day.

Credit: NASA/Eric Bordelon.

(Photo Caption: NASA took ownership of Core Stage-1 from Boeing for transportation. The NASA MPTS rolls the rocket stage towards the agency’s Pegasus Barge on January 8. NASA will transport the stage to Stennis, lift it up into the B-2 Test Stand there, and position it over the holddown posts before handing over control back to Boeing.)

“The issues that caused us to be two years late were associated with the new tooling that we used to weld the vehicle together and some issues that we had with that process,” Shannon explained. “We had never done friction stir welding for material that was that thick and we learned some lessons from that and I’m happy to say the second Core Stage went together flawlessly with no issues so we’ve gotten past that problem.”

“The other issue that I think caused us some difficulty was we really underestimated the complexity of building the engine section, which is the bottom of the rocket that holds all of the propulsion elements and all of the TVC and hydraulic elements,” Shannon added.

“The agency and the program were frustrated due to the lack of progress and our inability to hold schedule,” Honeycutt said. “That said though I’m fully aware that we were — and I’m going to use [John Shannon’s] words — we’re building the system to build a lot of these Core Stages and we’re putting the system together in parallel with building the first one.”

“That’s not normally the way we do things. We had a flat budget, we didn’t have this big development spike, so we worked really, really hard to be as efficient as we could.”

Switching transporters to go outdoors

Once the stage was mostly inside Building 110, the primary work was to transfer it from Boeing’s indoor transportation equipment to NASA’s outdoor equipment. Two Boeing RATTs were holding the stage and their set of Manufacturing, Assembly, and Operations (MAO) Self-Propelled Modular Transporters (SPMT) were used to pick up the whole system and move it to different factory locations.

NASA’s Multi-Purpose Transportation System (MPTS) is designed for outdoor conditions, larger loads, and terrain that isn’t necessarily flat. Building 110 is the original high-bay assembly building at MAF and it has two heavy cranes that were used to pick up and hold the stage while the transporters were swapped.

Credit: NASA/Jude Guidry.

(Photo Caption: The RS-25 engines installed in Core Stage-1 straddle a pole in the Building 110 aisle at MAF as the rocket was backed in on New Year’s Day.  The engine-mounted heat shield (EMHS) blankets were installed on the left two engines, but it was decided to bag the right two engines and install their blankets when the stage is vertical at Stennis.)

The team had to wait for a couple of days for good enough weather to start that process. “Since we were going to have two days of rain, we moved New Year’s Day, parked it, and we straddled this pole with engines and then we just worked a few last minute things that could get done in 110,” Gertjejansen explained.

“Then two days later when the weather was good we moved it out.” The RATTs have a two-piece roll ring that holds the stage and the top half of those was first removed.

“The first use of the cranes was taking the roll rings off,” she said. “Then we had to install brackets on the engine section. One of the things that we did in [Area] 47 was we installed the brackets on the intertank side.”

“Then they lift the stage up, remove the RATTs and drive in the NASA MPTS.”

As the stage rolled out to the barge its external configuration, mostly TPS, is largely complete. “There is a couple of ‘cats and dogs’, things that we’ve got to take care of but the bulk of all the TPS work that’s going to be done for Green Run is complete for the external,” Michael Alldredge, NASA SLS TPS Team Lead, said.

“There’s a handful more we’ve got that are internal applications.” The internal sprays will help to close out the LH2 lines inside the engine section that will be fully connected and secured once the stage is in the test stand at Stennis.

The team had planned on installing engine-mounted heat shield (EMHS) blankets around all four engines, but deferred some of that until the stage is vertical in the stand. “We had a problem during install because we were in the horizontal because of how heavy they are, the material was trying to fight against us,” Alldredge explained.

Credit: Philip Sloss for NSF.

(Photo Caption: Some of the red temp cover plates for the Core Stage-1 systems tunnel can be seen intermingled with flight plates that are predominantly covered with spray-on foam insulation (SOFI) during rollout on January 8. The lead-in plates on top and bottom are protected with cork and white paint similarly to the engine section where it is needed to protect more against in-flight heating than the cryogenic fuel in the propellant tanks.)

“They’re semi-rigid, they’re multi-layer insulation, but then they bolt to the engine and then up to the frame, the base heatshield frame, and that’s what holds them in place.”

“The guys went and struggled to get two on and they said hey this would be much easier if we could do it in the vertical where gravity is working for us,” Alldredge added. “So what they did is two of them are bagged up for transport, they’re all sealed up and the other two blankets are installed.”

The systems tunnel that runs almost the whole length of the stage on the -Z side looks a little different than it will for launch; for Green Run, some of the covers are temporary. “Knowing that we may see some damage due to hot-fire or handling or just transportation damage in general, there were a number of the systems tunnel covers that we actually put temporary covers on that will then come off once we get to Kennedy and we’ll put the flight covers on,” Alldredge explained.

“All the temporary covers are painted red, that’s how you can identify which ones they are. Some of the covers that are on actually have the flight foam on them as well, so we’ll have a mixed bag what we’ll trade out and what we’ll have to repair.”

With work at MAF complete, the Boeing team is taking a break while NASA transports the stage to the B-2 Test Stand at Stennis but most of them will reconvene there for the Green Run campaign. “We’re taking I would say sixty percent of our final assembly team, sixty to seventy percent, and the rest of them are going back to Core Stage-2 to help build Core Stage-2,” Gertjejansen said.

Lead image credit: NASA/Steven Seipel.

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