First SLS LVSA ready for Artemis 1, second in production

by Philip Sloss

Second flight unit in production at MSFC

Production of the second LVSA for the Artemis 2 launch continues at MSFC. “The second one we have already started on, it’s actually in fabrication now over in 4755,” Higginbotham said. “We’re actually starting to weld up some of the plates for the forward end of the cone.”

Less than three years ago, a second flight unit was not expected to be needed. Production of the LVSA for Artemis 1 was considered a “one-off” because SLS had expected to move immediately from Block 1 to a Block 1B configuration, replacing the largely off-the-shelf ICPS made by United Launch Alliance with a larger, in-house designed Exploration Upper Stage (EUS) on the program’s second launch.

EUS was officially authorized and funded in 2016, with work on other Block 1 elements like the LVSA discontinued. This changed in early 2018 when Block 1B launches were deferred by the United States Congress to build a second Mobile Launcher specifically dedicated to Block 1B.

Credit: NASA/Jared Lyons.

(Photo Caption: Personnel at the Michoud Assembly Facility (MAF) in New Orleans finish loading Core Stage ground support equipment (GSE) on Pegasus on July 23. A lift spider and two self-propelled modular transporters (SPMTs) joined the LVSA for the remainder of the trip to KSC; they will eventually be used to support Core Stage stacking operations at the launch site in Florida.)

The new Mobile Launcher (ML-2) eliminated the immediate need to perform a three-year long conversion of ML-1 from supporting Block 1 to Block 1B, also keeping it available to fly Block 1 launches while ML-2 construction and EUS development continued.

At the time of that particular change in direction, two additional Block 1 missions were envisioned: the Orion Exploration Mission-2 (EM-2) and Science Mission-1 (SM-1) to launch the Europa Clipper spacecraft to Jupiter. Subsequently, in 2019 the White House started a five-year race to land U.S. astronauts on the Moon by the end of 2024 and EM-2 became Artemis 2 under the newly-renamed lunar program architecture.

The White House also wants to move Europa Clipper off SLS and NASA reassigned the third SLS flight to the multi-launch Artemis 3 mission, with the last liftoff sending another Orion spacecraft and crew to cislunar space before the end of 2024 to meet a commercially-launched lunar lander and accomplish the primary goal of the Artemis program.

With the agency focused on landing astronauts on the Moon again, two more LVSA units were needed in support and NASA negotiated with Teledyne Brown on the second unit and started the process to build a third.

Production of the second unit will incorporate lessons learned from the first build, but Higginbotham indicated that changes would be fine-tuning of procedures rather than ones larger in scope. “For the most part it is pretty much a rebuild,” Higginbotham said. “That’s not to say that as we go further to the right [there] may be some changes, but right now it’s probably one of the least affected structures that we built on the program I would think.”

Application of the SOFI to the LVSA structure is a manual process using a formulation that can be applied at room temperature by hand using a portable dispenser and spray gun. At that point in the process of the first build, the unit was still considered one-of-a-kind, which made the LVSA one the largest “manual sprays” ever done.

Now that additional units will be produced, Higginbotham said that the program reconsidered automating the foam sprays for LVSA. “When we went through looking at building further articles we actually looked at doing a move to another building to see if we could [make] the application process of the TPS simpler and easier,” he noted.

“The decision pointed in the direction to stay where we were currently at and to actually apply it by [hand] as opposed with an automated machine. The tradeoffs and the money that it would cost to automate the process just didn’t prove it out based on the number of articles that we plan to build.”

“I think we’ll continue to do that and of course the key is having the certified people that can actually do the application of the TPS,” he added. “We’ve got that process pretty well defined and you obviously make some improvements the second, third time around but I think the first time went exceptionally well.”

Credit: NASA/Tyler Martin.

(Photo Caption: Workers at MSFC spray foam insulation on the LVSA in Building 4707. For the LVSA, the foam’s main purpose is to provide thermal protection from ascent heating.)

To assemble the LVSA structure, two sets of eight panels are first welded together separately into forward and aft cones. The top ring for the forward cone is machined from a solid forging. Due to its larger circumference, the aft ring consists of multiple segments that are welded together.

Friction-stir welding (FSW) is used to put together the structure, with conventional FSW used for the panels and self-reacting FSW for the circumferential welds for the rings to the cone halves and then for the forward to aft cone weld.

Currently, the forward cone panels are being welded. “The panels where we’re actually doing the friction-stir welding right now [is] the vertical welds in the vertical weld tool,” Higginbotham said. “I haven’t been out there, so I have to rely on email but we’re on about the seventh panel of the forward cone.”

“You’ve got eight panels on the forward cone and you’ve got eight on the aft so right now we’re working on the ones for the forward cone and then we’ll do the aft after that and then you’ve got the circumferential welds that’ll be done by the robotic weld tool. Those rings are being prepped as well in parallel so a lot of that primary structure will be built certainly by the Fall time-frame, so it’s coming together and looking good right now.”

As with activities around the country and the world, work to finish the first LVSA and build the second was interrupted by the current coronavirus pandemic. Currently, MSFC is the only NASA center still in Stage 4 of the agency’s COVID-19 response framework.

To continue, a work plan to resume work on the LVSAs was approved. “Obviously when [the center] went from a Stage 3 to a Stage 4 basically they only let essential personnel out there,” Higginbotham said. “We did what we call a site return to work plan such that we could have small groups of people going out to carry out essential activities.”

“For the most part the majority of us have been working from home, but we had two activities, one was the start of the welding activities in [Building] 4755 for flight unit two and then the remainder of activities for flight unit one over in 4649.”

“[For] flight unit two the situation there is the tooling where they did the friction stir welding,” he added. “That is actually quite a bit bigger equipment that’s in the high bay type environment.

“It’s not as labor-intensive so it allows people to spread out and to follow the safety protocol in an easier manner. So we worked through that and we only have the essential personnel that’s out there, we’re still in this shutdown at the center.”

“Everything is really progressing nicely, we had a status review with our management this morning and the welding is going quite well,” Higginbotham noted. “It’s under a bit of a tight schedule that we’re trying to make some time up on and we’re actually showing that we’re able to do that right now, so it’s a feather in the cap of all the employees doing that during a particularly difficult time.”

The program has reviewed the work schedule and still believes that the current working date for delivery of the second unit is achievable. “For Artemis 2, the date that we’re working to right now is the end of May of 2022, that’s kind of what we call our hardware ready date,” Higginbotham said.

“When we say hardware ready, that’s basically when we feel like we’re ready to accept it or do what we call a transfer of ownership from the contractor, the [U.S. government document] that we refer to as the  ‘DD 250’ (DD Form 250).  It’s very analogous to what we went through last week [with the first flight unit] because we did a DD 250 when we took the ownership when it vacates 4649 and it starts its trip down to the Cape, that’s when NASA takes over the hardware.”

Third flight unit raw materials ordered

Higginbotham said that the process for the third flight unit, aimed at the SLS flight at the tail end of launches for the Artemis 3 mission, has started. “We’ve started the long-lead materials for the flight unit number three,” he said.

Actual hands-on work as a part of the production process won’t begin for several months after the initial order, because it takes that long to acquire enough raw materials to start fabricating parts of the structure. “You could have six, eight months depending on the material that you’re procuring to actually get that on order and to get that in place, so the actual fabrication doesn’t start until another six to eight months down the road,” Higginbotham noted.

“With the types of aluminum alloys we’re procuring which is typically 2195 aluminum lithium and then some of the 7000-series aluminums for the rings themselves, it’s just a somewhat unique material that just takes a little bit longer to put on order and to actually get and receive in hand. All that occurs on the front end and so that’s where we are for the flight unit three, we’ve started the procurement of what we call the long lead material and that’s primarily your aluminum products that we use for the shell of the structure.”

Animation showing the ICPS carrying Orion shortly after separation from Core Stage and LVSA. Credit: NASA.

The LVSA is a Block 1 element and the long-term direction of the SLS vehicle is still being debated between the White House and Congress. The Trump Administration wants to cancel development and construction of the Block 1B vehicle and infrastructure and stick with the Block 1 vehicle as an Orion-only crew launcher.

That would mean continuing production of stage adapters for the ICPS upper stage. Some groups in Congress want to speed up Block 1B development and eventually complete transition to the Exploration Upper Stage-based configuration, which would hasten the end of LVSA builds.

For now, any units beyond the third one require action from Washington, D.C. “We don’t have any current direction or guidance as far as a fourth unit and we certainly don’t have anything on contract, so if that were to come about that would be a unique situation that we would have to address,” Higginbotham said.

Current law requires SLS to launch Europa Clipper; unless Congress modifies four-year old language, go ahead for an LVSA to support that launch would be needed soon. “I had the question the other day if we were to build a fourth article, what time would we need to get started on it and that would probably be toward the end of this year, so it would be upon us pretty quick if the agency decided to go that route,” he added.

Lead image credit: NASA/Fred Deaton.

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