Solid production – Booster segments readying for opening SLS launches

by Philip Sloss

Orbital ATK recently provided a peek at current production of Space Launch System (SLS) booster segments at their Promontory Propulsion Systems facility in Northern Utah. Work on the segments for the first two SLS launches continues and is on track to ship hardware to the launch site when needed. The last segment for the first launch, Exploration Mission-1 (EM-1), was recently loaded with solid fuel in mid-June and work on all the EM-1 segments should be complete by the beginning of November.

EM-1 propellant casting complete, but still work to do:

The Orbital ATK Promontory facility includes testing and production areas and prior to a qualification test of their abort motor for the Orion Launch Abort System (LAS) this month, a tour was provided of a couple of SLS booster production areas where hardware for the first two SLS launches was seen in different stages of production.

The SLS boosters are composed of five-segment solid rocket motors (RSRMV); for SLS, two boosters are attached to opposite sides of the liquid, cryogenic Core Stage.

The SLS booster consists of the RSRMV motor, along with the forward assembly that includes the nose cone and forward skirt that houses avionics and the aft assembly that includes the aft skirt that houses the booster thrust vector control (TVC) hardware.

Fully assembled, the SLS booster reaches a length of 177 feet. They retain much of the forward and aft assembly hardware unchanged from its Shuttle heritage.

Solid propellant was cast into the tenth and final booster segment for EM-1, the EM-1A center/center segment earlier in the week of the LAS test. (The left booster is also referred to as EM-1A, the right booster EM-1B.)

Completion of propellant casting is a milestone in work for the EM-1 segments, but there are still several steps to complete before they are ready to go to the Kennedy Space Center (KSC) in Florida to be stacked for launch.

“From the time we put propellant in. to the time we’re complete with final assembly. is about three months [of work],” Jeff Foote, Orbital ATK’s Vice President of NASA Programs, said in an interview with at the Promontory facility.

“We go through an NDE – non-destructive inspection – and then there’s about two months of hardware assembly including thermal protection. Right around first of November we’ll have all the segments for EM-1 completed at the plant here.”

Currently, work on three of the ten segments is complete.

The RSRMV is an evolution of the Space Shuttle Reusable Solid Rocket Motor (RSRM) design; originally selected to be the first-stage of the Constellation Program’s Ares I Crew Launch Vehicle, after Constellation was cancelled the design was adopted for SLS in 2011.

The Shuttle RSRM had four segments: the forward, forward-center, aft-center, and aft segments. The RSRMV adds an additional center-center segment in the middle of the motor, stretching its length from over 126 feet to almost 156 feet. The motor cases are a little over 12 feet in diameter.

EM-2 segments in production:

Even as the EM-1 segments are going through final preparations in the production process, work has started on much of the hardware that will fly on the second SLS launch, Exploration Mission-2 (EM-2).

The empty steel cylinders that make up the five segments come through the insulation area where the tour made a stop to show some of the work there. Most of the segments consist of two cylinders that are joined at a factory joint. At KSC, the loaded segments are attached together at a field joint.

The cases are prepared in the insulation area up to the point where they are ready to have propellant cast into them. The empty case cylinders arrive from Orbital ATK’s Clearfield facility, which is also located in the greater Salt Lake City area.

Almost all of the cases have flown on several previous Space Shuttle missions, were used in ground static tests, or both. The used, disassembled segments are refurbished at Clearfield.

“So it comes in from Clearfield [and] we bring it in[to the insulation work area],” Norman Kay, Orbital ATK Manufacturing Engineer said during the tour.

“We have booth where we wash it, we have another one where we grit blast it – that preps the surfaces inside and out. And then we bring those into the other building here [in the area]. We paint the outside and then we apply Chemlok, which is an adhesive, on the inside of it, and then on the Chemlok is where we lay up the rubber [insulation].”

Kay explained there are multiple layers to the insulation between the case walls and the propellant.

“We put the Chemlok on the metal and then we put an initial layer of rubber [insulation] on – it varies based on our performance factors and requirements all through each segment,” he said.

“And then on top of that we put another layer of Chemlok, which is the barrier coat, and then a thin cap ply. Then once we have all that, we put a liner on it and that kind of is the interface between the actual insulation and the propellant.”

During the tour (a full set of photos and videos are available in L2), the two cylinders for one of the EM-2 forward segments were seen stripped to the bare metal. Those are just beginning the assembly and production process and will be joined with a forward dome before the outside coat of paint and inside coat of adhesive are applied.

A total of five segments were seen in the insulation area during the tour, including two center segments and two aft segments. The process of lining the inside of the cases is done in several stages, with the cases going into vertical pits for applications of Chemlok and drying and set on horizontal stands in between.

“We have four pits here,” Kay added. “One is used for [the] dry cycle, one is used for when we [initially] bring it in, we paint the outside and we apply the Chemlok on the inside of the bare metal. The next one is used for when we put the barrier coat on, the second layer of Chemlok on top of the first insulation. And then the last pit there is when we apply the liner.”

The facility also has a large autoclave where the bonds between the layers are cured.

“What we do is we’ll lay up the rubber and then – same you would do as for a composite – we’ll put all the bleeder-breather material on [the segment], we’ll put a bag [on], we’ll pull it under vacuum, we’ll put it in the oven, and we’ll cure it,” Kay noted.

Propellant loading for the first EM-2 segment is planned to start after the Fourth of July holiday.

“We cast at about one a month, plus or minus with holidays, about one segment a month. That fits with plant operations and program needs,” Foote added.

EM-1 work in final assembly:

With all of the EM-1 segments through propellant casting, they are making their way through the production process to the final assembly area, which was also the last stop on the tour.

Shortly before the tour arrived there, the second of two aft segments (EM-1B) was delivered after several weeks of the NDE X-ray inspections.

Richard Wilkey, Operations Team Supervisor for Orbital ATK, explained there is still a lot of work to do on the segments after they are loaded with propellant.

“[After casting] it comes right up the hill here for [propellant] trim, then it goes to X-ray, and then [it comes] down here.”

The segments are moved around on specialized decks that sit on air bearings and one of the first tasks in final assembly as they are transferred from one deck to another is to take measurements of the weight and center of gravity.

After that, they are moved to a series of processing bays for installation of the additional flight hardware.

“We float them in[to] these work cells and then these floor sections extend out so we can access the top of the motor,” Wilkey said. “In this bay we bond the systems tunnels, then we float them over to this bay and install all the ring hardware.”

The systems tunnel runs the length of the motor to provide a sheltered place for cabling that runs from the forward skirt of the booster to the aft skirt and the linear-shaped charge for the thrust termination system. The ring hardware is ground support used for handling the segments. Installation of instrumentation is also performed in the final assembly area.

The forward and aft segments require additional assembly work.

“The forward and aft segments get stood up [to] vertical for nozzle and igniter install,” Wilkey noted. “So they stand up in these elephant stands and we install the nozzle and igniter vertically.”

One of the EM-1 forward segments was seen during the tour returned to horizontal position, having already had its igniter installed through a hole at the apex of the forward dome. The igniters are also assembled in the final assembly area before installation into forward segments.

To mate the motor nozzle to the aft segment case, those segments are rotated upside-down. Up on the third level of the processing bay, the nozzle is lowered down to the aft dome where the pieces are bolted together.

Work to finish this task on the EM-1A aft segment was almost complete, but it was still in the vertical stand during the tour. It will be followed by the EM-1B aft segment that had just arrived in final assembly.

At the end of the process, the outside of the segments are scrubbed, given a fresh coat of cosmetic white paint, and then the black imagery reference markings are applied.

Completed segments are moved from the final assembly area into storage units at Promontory, where they will wait until they are needed at the launch site.

“There’s less environmental conditioning than what we have here, so we’ll ship them when the ground segment (Exploration Ground Systems) is ready to start processing and stack,” Foote explained.

When they are called for stacking in Florida, each segment will be put back on the road transporter and driven down to rail car containers, where a train will take the segments from Promontory to KSC.

(Images: Orbital ATK and L2, via Philip Sloss. Additional renders by L2 Artist Nathan Koga. The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*))

(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here: //

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