New Artemis 1 schedule uncertainty as NASA EGS ready to continue SLS Booster stacking

by Philip Sloss

The NASA Exploration Ground Systems (EGS) program at Kennedy Space Center (KSC) in Florida is prepared to continue integration of the vehicle for the Artemis 1 lunar mission, but space agency and contractor management for the EGS, Orion, and Space Launch System (SLS) programs are monitoring the status of hardware elements that will be needed to complete the process for a launch scheduled for November 2021.

EGS and prime test and operations contractor Jacobs started the integration process during Thanksgiving week by placing the two foundational pieces of the vehicle, the SLS aft booster assemblies, on Mobile Launcher-1 (ML-1) in the Vehicle Assembly Building (VAB).

With the base of the launch vehicle standing on the Mobile Launcher, the next step is to begin stacking the other eight motor segments of the Boosters on top of them, but uncertainty about the availability of the SLS Core Stage and the Orion spacecraft elements for stacking means that the schedule is still fluid. EGS Operations is keeping tabs on the Core Stage Green Run and a reported avionics box issue with Orion, but plans were still in place to continue with booster stacking next week.

Aft booster assemblies stacked on the Mobile Launcher

The right-hand aft assembly of the SLS solid rocket booster (SRB) was lifted into VAB High Bay 3 overnight November 23 into November 24, about three days after the lift of the left-hand aft assembly. “Both of our aft assemblies are sitting down on the ML right now,” Erik Tormoen, NASA EGS Operations Project Engineer, said in a December 1 interview. “They’re going through some different fitments on the aft end of the aft assembly; they’re doing shoe retainers, which are clamps that hold down the shoes as we like to call them.”

SLS Booster prime contractor Northrop Grumman shipped all 10 of the motor segments from their Promontory facility in Utah to KSC at the beginning of the summer. The two aft motor segments received the majority of the stacking preparation work in the Rotation Processing and Surge Facility (RPSF). Each aft segment was connected to the other major booster assembly hardware pieces in side-by-side build up stands inside the RPSF’s Rotation building.

Credit: NASA/Kim Shiflett.

(Photo Caption: The two SLS aft booster assemblies for the Artemis 1 vehicle in the Rotation building of the RPSF on November 17, ready to begin stacking. The aft segment, aft skirt, and nozzle extension are put together in the two build-up stands in the RPSF. The aft assemblies are also outfitted with Core Stage attachment hardware, cabling for electrical and data connections, and additional thermal protection before the assemblies are ready for stacking.)

After the segments were offloaded from their shipping rail cars, they were separately mated to an aft skirt already placed into the build-up stand, an exit cone nozzle extension, and an attachment ring and struts to connect to the Core Stage. The aft booster assemblies were also outfitted with electrical and data wiring, test instrumentation, and additional thermal protection system (TPS) material before stacking operations began on November 19 when the left-hand assembly was picked up and transported to the VAB for stacking on the Mobile Launcher.

The boosters, with their pre-loaded solid propellant, are the most massive element of the Orion-SLS vehicle, and the weight of the system rests on the aft skirts which sit on eight vehicle support posts (VSP) of the ML, four per booster. The aft skirts were lowered onto the VSPs with “shoes” already attached for mating, and those were then fitted with retainers.

“The aft assembly comes with these shoes already on and when launch occurs at T-0 the shoe stays behind,” Tormoen explained. “It’s a way to control the T-0 liftoff point.”

“That shoe is adhered to the aft skirt and is also bonded and has an electrical bond strap that is on there. That is the designed separation point. So what we do is we bolt that shoe to the ground and when we have lift off that separates [the aft skirt from the shoe].”

“We’re putting on shoe retainers which are clamps that hold that shoe down so that it doesn’t leave with the booster at T-0,” he added. “That’s a bolt on assembly.”

Tormoen also noted other support equipment and umbilical attachments being performed on the aft assemblies now that they are standing on the Mobile Launcher. “We’re going around the VSPs and installing various hardware and then we’re going to go into the different ground umbilicals that we have,” he said.

Credit: NASA/Glenn Benson.

(Photo Caption: One of the four aft skirt corners of the white-painted right-hand aft booster assembly is lowered down onto a corresponding vehicle support post (VSP) of the Mobile Launcher on November 24. A grey, unpainted “shoe” is attached, along with the yellow ground support equipment. When the vehicle lifts off, the shoes will remain with the VSP.)

At the VSPs, “We’re adding HYTORC nuts. Basically these are hold-down nuts that go on top of a threaded stud that basically is just for rollout.”

The booster structural hardware, the segment cases and booster assemblies and aft skirts, are Shuttle assets; in contrast to the Shuttle system, SLS aft skirts are not released pyrotechnically at liftoff. The hold-down nuts are only required for ground winds when the vehicle is being moved outdoors and will be removed at the launch pad. “[It’s] for the vehicle and the ML to [roll to] the pad to help stabilize wind loads and stuff like that,” Tormoen said.

“We’re [also] in the works right now for installing blast shields that go over the hold down area where the VSPs are, the Vehicle Support Posts. The blast shields will go down and protect the spherical balls that the booster segments are sitting on.”

The boosters also have two umbilicals to provide electrical and purge services to the aft skirts. “We have an electrical umbilical, the Aft Skirt Electrical Umbilical (ASEU), and we have the Aft Skirt Purge Umbilical (ASPU),” Tormoen said.

“Obviously the first one is in charge of doing a lot of the electrical connections. We have some flight termination system connections, we have the separation/launch release system (LRS), they get their arm and fire signals from the vehicle through that umbilical.”

“That system, LRS, is responsible for releasing the vehicle as it lifts off the ML,” he explained. “And then the ASPU is basically a flex hose that has been tested and tested and tested again to make sure it functions and it provides the GN2 that inerts the aft skirt area in the aft assembly. So that’s a high volume heated gaseous nitrogen purge.”

Stacking the rest of the segments

The other eight motor segments that are filled with solid rocket propellant went through a shorter process when they were offloaded from their shipping rail cars in the summer. “After they come off the rail car, they do get some inspections, detailed inspections of the grain inside, that’s only done in the horizontal,” Tormoen said.

“There are a few things that are done there, making sure that the hardware is delivered as designed, and then inspecting for any foreign object debris or any kind of contamination. And then basically we put our blue label on — if you will — in paperwork and say ‘it’s ready to go.'”

Credit: NASA/Kim Shiflett.

(Photo Caption: The other eight loaded SRB motor segments for Artemis 1 are shown the Surge 2 building of the RPSF on November 17. The two forward segments are in the background, distinguished by their domes on top, and the two center-center segments are the ones that have most of the NASA “worm” logo on them. The circular wire bundles clearest in the foreground are for instrumentation to collect data during an integrated modal test of the vehicle to be conducted next year in the VAB.)

“We [have] for this launch put on some modal sensors. Basically, they are accelerometers, and we’re trying, eventually, as we stack the vehicle, to understand the modal dynamics of the vehicle during rollout and during the entire integration process,” he added.

All eight segments were placed vertically on transportation pallets and moved to the Surge 2 building of the RPSF after that work was complete.

The next segment to be processed will be the first case-to-case field joint assembly.  When the go-ahead is given, a transporter will drive out to the Surge 2 building, pick up the pallet with the left aft center segment, and drive it to High Bay 4 of the VAB.

“The first thing to do is to bring the segment across the way from the RPSF to the VAB, High Bay 4, and then locate and set down that pallet and the segment in the middle or where ample space is allowable,” Tormoen said. “We are doing a lot of shuffling around and making sure that the right space and the right proximities of all the hardware is achieved in High Bay 4.”

The next set of steps are to prepare the ground support equipment (GSE) for a crane to lift the segment off the pallet with a 384 beam. “The 384 beam is the lifting beam that connects to the forward end of the segment,” Tormoen noted.

Tormoen described that process as “lifting up the 384 beam, taring out the weight on the load cells, making sure everything reads zero, making sure all the systems on that load beam and on the SSET (SRM Stacking Enhancement Tool), which is an enhancement tool for stacking, are working correctly.”

“[We’re also] giving cursory checks to the segment’s condition as it sits [on the pallet and] removing the weather covers. A lot of preps go into making sure the segment is ready to be lifted.”

The four-point 384 lifting beam has a tang interface to allow it to attach to the top clevis end of a segment for lifting. “We’re using the pins as a part of the beam and connecting through where the same flight pins go in to keep the segments together,” Tormoen explained. There are two tangs at each of the lifting beam’s four quadrants where it is pinned to the top of the segment at its clevis end.

Credit: NASA/Chris Swanson.

(Photo Caption: Attached to a 384 lifting beam at the top, an inert center segment is suspended on one of the VAB heavy cranes above a “slap” stand during practice sessions in January 2020 in the VAB. EGS and Jacobs are ready to carry out the stacking preparations on the live Artemis 1 motor segments beginning next week. A final inspection of the bottom, tang end of the segment will be performed in High Bay 4 before the motor is lifted for mating.)

Once a segment is attached to the beam and the crane, it is lifted off the transportation pallet and positioned over a “slap stand” to allow a final, pre-lift inspection of the tang end on the bottom.  “[It] is a piece of GSE that acts like a safety net,” Tormoen explained. “It’s not actually used to hold the segment up, it’s just there in case the segment were to drop while we have people working in and under a suspended load.”

“What you’re doing in that area is you’re doing your inspections, you’re looking inside the joints, you’re looking at the metal and the surfaces for FOD and debris, you’re looking to make sure the joint is in not only visible alignment with the drawings and the condition it’s supposed to be in at the time, but you’re also looking at the profile of the joint and making sure everything is how it should be after storage.”

Tormoen said that in parallel with one group looking at the tang on the bottom of the segment to be lifted for mating, other people are rechecking the condition of the other half of the field joint already stacked on the ML. “You’re also looking at the clevis end or the forward side of the segment that you’re mating to in High Bay 3,” he said.

“So you’re doing the same kind of thing, you’re looking in the clevis, you’re looking for FOD, you’re looking at the condition of the propellant and all the surrounding materials. Something that we always do at KSC is before we mate something together we’re inspecting both sides.  Last look: this is the last time you’re going to see it, so [we’re] documenting and ensuring that it’s to print,” he added.

Before the segment is lifted, a rolled-up, plastic enclosure is secured around the case above the mating hardware. “We attach a static enclosure around the segment, and that’s done in High Bay 4 in this case,” Tormoen said. “During Shuttle we used to do all this in the Transfer Aisle, but we’re doing that in High Bay 4 now. That definitely alleviates a lot of the traffic that needs to go on.”

Then the crane lifts the segment and moves it from High Bay 4 over to High Bay 3. “We go up and over, and we all call it ‘up and over,’ and it happens on an off-shift when people don’t have to show up for 9-5 type of work,” he said.

“When we finally get in range [at about] the three feet mark [between the segments], then we establish our enclosure. We pull that enclosure away from the top side segment, and we build the enclosure. There’s pipes and everything that goes around and stands up this enclosure.”

Credit: NASA/Kim Shiflett.

(Photo Caption: The inert center segment is positioned above an inert aft booster assembly during a final run-through practice on the Mobile Launcher in September. EGS and Jacobs will configure the live Artemis 1 center and forward segments with the rolled up plastic enclosure seen attached here. When paired with the bottom half seen already staged on the extendable work platforms, the enclosure provides an environmentally controlled work area to perform the segment-to-segment mating.)

“And so now we’re in a visibly clean environment where we have conditioned air, we are wearing bunny suits and flame-retardant coveralls, and we’re controlling that area now, this is a critical process just prior to mate,” Tormoen added. “We’re also fitting the segment with sensors that let us know the position of each side of the circle, four quadrants, and we’re also measuring the circularity of the segments to double-check our math.”

“The [SLS Booster] element folks have planned these two segments to go together. It’s not the other two segments; it’s not any old segments. It’s these two segments need to go together, and that’s based off of circularity and the shape of the segment. The shape of the segment is not perfectly circular, nothing in physics and life are perfect shapes.”

After the circularity of the upper tang end suspended on the crane and lower clevis end stacked on the ML are measured, Tormoen said a fixture is installed to assist the mating of the field joint. “After we say ‘yup, double-checked it’ and these segments are going to go well together then we put on our FJAF (Field Joint Alignment Fixture),” he said.

“Basically this is a ‘shoe-in’ in it’s simplest format. It goes ahead of the segment joint and as you come in with the mating joint from the top down, it’s shoeing-in this segment to the receiving segment.”

The fixture also tells the team performing the mate that the hardware is staying aligned straight as the new segment being added is very slowly lowered down. “It’s so slow; I believe it’s like six-thousands of an inch,” Tormoen said. “It’s so slow that you look at it and you can’t tell it’s moving, but it is.”

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