Preparing the adaptor – LVSA readies for SLS debut

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NASA is getting ready to apply spray-on foam insulation (SOFI) to the outside of the Launch Vehicle Stage Adapter (LVSA) that will fly as a part of the Space Launch System (SLS) launch vehicle on Exploration Mission-1 (EM-1). The LVSA is a roughly thirty feet by thirty feet conical spacer structure that connects the top of the SLS Core Stage with the Interim Cryogenic Propulsion System (ICPS) upper stage that will fly on EM-1.

LVSA:

Built by NASA and prime contractor Teledyne Brown Engineering, the LVSA will shortly begin preparations at the National Center for Advanced Manufacturing in Building 4707 at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, for a few months of foam application work.

Following some additional work at Marshall, the LVSA will be shipped to the Kennedy Space Center (KSC) in Florida next year.

The flight article is the second unit completed; the first unit, a structural test article, was used in integrated structural tests at Marshall this year with the other elements that connect the Orion spacecraft with the ICPS and the SLS.  In Building 4707 at Marshall, a clean area is ready for the foam application work to take place.

NASA and Teledyne Brown recently completed major welding of the LVSA at the Advanced Weld Facility at Marshall.  The structure is primarily made up of sixteen 2195 aluminum alloy panels.

“2195 panels [and] 2219 rings,” noted Jon Street, manufacturing lead for the LVSA in the Marshall engineering directorate.  “That’s a segmented ring on the bottom [and] a solid forging that’s machined into a ring at the forward end.”  (2219 is another aluminum alloy that is used extensively on the SLS Core Stage structures.)

Due to its dimensions, the adapter had to first be welded into two cones, forward and aft, which were then welded to complete the structure.

“I don’t have a tool that can get twenty-eight feet tall,” Street added. “We build the forward cone first with vertical welds and there are eight of them. It takes about five weeks to do it.  Basically what we do is we weld up seven of the joints and then we have to measure it to figure out the final arc length for the top and bottom that we need to do to maintain a cone.

“That takes about a week of scanning and analysis.  Then we trim that last one and we weld it.  So once you make that cone, you’re stuck with that cone, so the top and the bottom diameter has to be [correct].”

“I build it like a cake — I take the forward off, reconfigure the tool, and then I build the aft, and it’s a cone, so I’m trying to hit a target diameter, but I’m not trying to get too small or too short, either.  So I’ve got to manage all that.”

“Once we weld those two together, I want to make sure the flange is centered — the axis to the top of the cone — and then once I weld that bottom, I trim that middle joint area, and load the top cone on, and then start trimming until I get the two pieces where I need it.  Because you have to have the panels fairly flat — you cannot have ‘step’ in it.”

“The cone part of it that people have trouble with is if I trim it to meet a diameter, I could trim it so it’s too short.  You can’t weld it unless you get the two diameters right so the biggest challenge was maintaining axial center and parallelism.”

The panels were welded using conventional friction stir welding, while the circumferential welds of the rings to the top and bottom used self-reacting friction stir welding.  The rings at the top and the bottom of the adapter, also called flanges, are structural attach points to other parts of the launch vehicle.

The bottom flange is essentially identical to the flanges that will be on the Core Stage elements and will be bolted to the top flange of the Forward Skirt during vehicle integration in the Vehicle Assembly Building at the Kennedy Space Center in Florida.  The adapter’s top flange will attach with a frangible joint assembly to the ICPS.

During flight, the Orion-ICPS stack will separate from the Core Stage at the LVSA top flange, with the LVSA remaining attached to the Core Stage.

TPS foam application:

Unlike the static testing of the STA done on the ground, the flight unit needs thermal protection from the atmospheric heating it will see during ascent, so it received a coat of primer in preparation for applying spray-on foam insulation on top of that.

“There’s some pretty high heat loads in some places,” Mindy Nettles, the SLS manager for the LVSA said about the requirement for insulation.  “We don’t have any cryo exposure, it’s just the ascent heating.”

Once work begins, the first task is to prepare the surface, beginning with cleaning.

“The first thing that we’ll do is a solvent wipe.  We’ll wipe down the whole hardware with a…cleaner that we use for these substrates,” Michael Frazier, branch chief for the Non-Metallic Materials Division in Marshall’s Materials and Processes Lab added.

Next, the weld lands where the panels were joined together side-by-side and top-to-bottom will be painted with primer.

“The panels came pre-primed and then we’ll just fill in the weld lands,” Amy Buck, thermal protection system expert in Marshall’s Materials and Processes Lab, said.  “We will roll that material on with just paint rollers — that’s why we tried to minimize the area that we had to do.

“So the panels were pre-primed with a spray process and then we’ll do the rolling process on the weld lands.  And then once we get all that done we’ll start the foam application.”

“We have a very skilled crew of technicians that are ready to do this job.”

The type of spray-on foam used on the LVSA will be manual spray.  Although similar in chemistry, each of the three foam application processes used on SLS hardware has its own formulation.

Besides the manual spray foam, there is a robotically-sprayed foam (also called “auto spray”) that is used at the Michoud Assembly Facility in New Orleans on the barrels of the large Core Stage propellant tanks, and a pour foam that is used for hardware with more complex shapes, like Core Stage propellant feedlines and valves.

The manual spray foam was chosen for the LVSA for a few reasons.

“This is one of the largest manual sprays that’s ever been done,” Buck explained.  “We don’t have the equipment to do the automatic spray in this facility.  The automatic equipment we have here at Marshall is much smaller so we had to go back to a manual process to do the larger article here.  So we’ll split it into sections and do a section at a time.”

“This manual spray foam that we have here is more robust as far as the temperatures and humidities that you can apply it in,” Frazier added.  “We can apply that at room temperature.  The robotically-applied foam that goes on the [Core Stage propellant] tanks [requires] a temperature and humidity controlled booth to do that operation.

“They are sprayed at much higher temperatures, environment-wise, and much lower humidities than what we’re able to do here with the manual spray foam.  [Manual spray] gives us more range, more capability for applying foam.”

Additionally, since the SLS Block 1 vehicle is only planned to be flown once, producing this stage adapter is a “one-off” job, as is the foaming operation for it.

The sprays will be done by hand; two technicians standing up on a lift will alternate using a hand-held spray gun.

“We have a portable dispense unit that will carry the foam materials,” Buck said.  “There will be two component materials that stay separate until [they get] to the gun.  And so when they come together in the gun it will go straight onto the substrate and then react and rise.  So it actually starts immediately when it gets into the gun.”

The materials will stay on the ground with hoses for each running up to the gun where they are combined.

“It will be one spray gun, two guys operating one gun,” Buck explained.

“They’ll switch off as they go up. The material that’s in the two drums will stay on the ground along with the actual pumping equipment will also be on the ground and the material will then go through hoses up.  There will just be two guys and a hose with the gun.”

The team has been practicing for the work by spraying on a test panel.

“We have one of the panels — one sixteenth of the full article — over in our other development facility and we’ve been spraying on it so that we can get everything right,” she explained.  “We’re spraying the whole acreage and then down here where this ramp is, where it goes towards the [bottom] flange, we will actually spray part of that, too.

“So our spray foam technicians have been working on how to make that ramp from a manual process in a net spray, so they won’t have to go back and shave [the foam] to get that ramp.  They’re going to build it up as they spray the article.”

For the LVSA, the technicians will spray alternating strips on one panel at a time.

“[For] this particular operation we’re going to mask off sixteen vertical strips, because that’s about the limit that the guy can do in the cart that he’s going to be up in,” Frazier explained.  “So we mask off everything but those strips that we’re going to be working on.  We’ll spray that strip and then we’ll remove the masking.”

“We’re actually going to alternate a space over so we don’t get overspray onto the article next to it. And then after we do those sixteen alternating sprays, then we’ll come back and do the ones that are in between.

“We use what we call a tie-coat — you actually have to prep that surface of the foam that you did spray.  You cut it and then you tie-coat it, it’s an adhesive material that you put in there.  You let that dry and then you spray foam into those other alternating sixteen segments that you have.”

As they build up the foam, they will use a tool to measure until they reach the specified thickness.

“We have a dualscope gauge, which is an eddy current gauge,” Frazier noted.  “We actually touch the surface of the foam and it can read the distance to the metal that is behind it on the substrate.”

The work is planned to take a few months.

“We will have the article through December working on it, to spray it,” Buck said.  “We have about two months of foam work and about a month of primer.”

Like house painting, most of the time involved is getting set up to do a spray.

“There’s more time spent probably prepping the hardware and getting it ready than is [spent on] the actual operation of putting the foam and the paint on.  It’s more masking and removing and curing, letting stuff go through the normal process and then checking the thicknesses.  There’s a lot of [work besides] just applying the material to the hardware.”

Next Steps:

After the foam application is complete, the LVSA will be moved to another area for additional work.

“When we’re through, then we’ll move to another building, that’s taller and we will attach the frangible joint assembly,” Nettles said.  “Teledyne Brown will then finish up some work on the interior of the cone, some internal platforms that have to be used for work to get to the cryo propulsion stage (the ICPS) and then we will board the Pegasus barge and go to the Cape.”

Nettles said the barge trip for the adapter from Marshall to Kennedy is currently planned for the summer of next year.

The LVSA will eventually take its place on the rocket in the VAB at Kennedy, when it is stacked on the Core Stage.  It will be lifted up into High Bay 3 and positioned on top of the Forward Skirt, where workers on an elevated platform on Level E will install 360 bolts around the circumference where the flanges on the two pieces meet.

The same type of manually sprayed foam will then be used to “closeout” the bolted flanges.

Some time later, the ICPS will be lifted into the High Bay 3 integration cell and attached to the frangible joint assembly on the top of the LVSA.

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