SLS continues post-hurricane cleanups and prepares for Core Stage Green Run valve repair

by Philip Sloss

NASA and Boeing continued troubleshooting issues with the Space Launch System (SLS) Core Stage found during summer Green Run testing while cleanup from the mess created by Hurricane Zeta continued in the greater New Orleans area. The hurricane plowed through NASA facilities in the area on the evening of October 28, causing roof and siding damage at the Michoud Assembly Facility (MAF) in New Orleans East and knocking out power across a wide part of the metro region.

Boeing is the prime contractor for the SLS Core Stage and is conducting the Green Run test campaign at the Stennis Space Center in nearby Southern Mississippi; NASA believes they have identified the cause of an intermittent fault with a liquid hydrogen (LH2) prevalve and are preparing to perform repairs. Stennis was also hit by Zeta, but saw less intense conditions than MAF as the storm weakened racing inland and the space agency is still hoping to complete the final Green Run tests by the end of the year.

SLS production work has resumed at MAF as the second Core Stage nears major assembly milestones, but the damage assessments are also continuing.

Core Stage production continues at MAF alongside facility damage survey.

Zeta rapidly intensified prior to making landfall in Louisiana near New Orleans on the evening of October 28, with winds in the center of the storm almost reaching Category 3 level. Winds over one-hundred miles per hour were measured in the area when the storm roared directly through the Michoud area and NASA’s assembly facility on the east side of the city; however, the facility was closed well before the storm’s arrival and only a ride-out crew was on-site at the time.

“NASA’s initial assessment of the impact of Hurricane Zeta at the agency’s Michoud Assembly Facility in New Orleans has revealed some damage to the outside of buildings including roofs,” the agency said in a statement provided by Craig Betbeze, NASA Communications Lead for the Michoud Assembly Facility. “Fortunately, there were no injuries to NASA employees.”

“There is no damage to Space Launch System (SLS) rocket or Orion spacecraft hardware being manufactured at the factory. Michoud is currently open. NASA programs and tenants at the facility are working while teams at Michoud make temporary repairs, continue to assess damage and plan for more permanent repairs.”

The historic Vertical Assembly Building (VAB) at MAF, Building 110, again took a significant storm hit with roofing and siding being ripped off. The VAB at MAF has been used to assemble NASA rockets since the Saturn era; it is one of the tallest and most exposed at the facility and has seen similar damage from previous record hurricanes and a tornado in February, 2017.

Credit: NASA/Eric Bordelon.

(Photo Caption: Temporary covers are being placed over siding damage to Building 110 at MAF in this image from October 29, the day after Hurricane Zeta passed directly through NASA’s facility. The hurricane brought estimated winds of around 100 miles per hour to the area, ripping roofing and siding off this and other buildings there.)

Widespread power outages in the greater New Orleans area caused by the storm have taken time to resolve, which has also slowed down recovery efforts.

Prior to the direct hit from the hurricane, Boeing was separately outfitting the five major elements of Core Stage-2 at MAF.  The elements will be integrated to become the second Core Stage flight article which will support the Artemis 2 test flight sending an Orion spacecraft and its first crew around the Moon.

Structural assembly of the elements, the forward skirt, the liquid oxygen (LOX) tank, the intertank, the liquid hydrogen tank, and the engine section, was completed in 2019 and work since then has concentrated on outfitting them with all their rocket equipment.  The two propellant tanks are currently being coated with corrosion and thermal protection before completing their outfitting; in parallel, shelves, wiring, computer equipment, and fluid tubing are being installed inside the other elements.

Automated foam sprays of the LOX tank domes were performed in mid-October, a first for the program. Spray-on foam insulation (SOFI) for the first Core Stage propellant tanks was applied manually to the domes after the barrels were sprayed automatically by a robot in Cell N of Building 131 at MAF.

Development work to fully automate the dome sprays was completed early this year and will help reduce SOFI application time for the propellant tanks by several weeks. Following trimming of the foam, the LOX tank will be moved out of Cell N and the LH2 tank will take its place for its SOFI sprays.

Before the SOFI can be applied, the propellant tanks get a coat of primer applied to the bare aluminum alloy exterior; the liquid hydrogen tank was completing those primer applications in Cell P at the end of the Summer.

Standalone work on the forward skirt is expected to be finished first; internal outfitting of the element was nearing completion and in October preparations were underway to begin functional testing of the subassembly. The functional checkout of its systems, which include the SLS flight computers, will be the final milestone to complete before the forward skirt is ready for stacking with the upper part of the rocket.

The first mating of stage elements is the forward join that brings together the completed LOX tank and intertank with the forward skirt. With the foam sprays and trimming mostly complete on the LOX tank, it will now be outfitted with its internal liquid propellant level sensor mast assembly and the sump on the aft dome. For the second SLS test flight, the propellant tanks of the stage will also have additional development flight instrumentation (DFI) sensor islands similar to the ones on the first flight Core Stage.

While the LOX tank is being prepped for the forward join, work is continuing to finish laying out a similar set of wire harnesses, tubing, shelves, and computer avionics inside the intertank. When that is complete, the intertank will go through a similar functional checkout of its systems to verify it is ready for stacking.

Once those three pieces of the stage are ready for the forward join, that vertical stacking operation will take place in integration cells in Building 110.  NASA currently projects the forward join to occur early next year.

Work will continue in parallel on the LH2 tank, the engine section, and the boattail assembly. Once standalone work on the LH2 tank is completed, it will be mated to the forward join later in 2021.

Standalone integration of all the equipment in the engine section continues. The four thrust vector control (TVC) platforms that hold most of the hydraulic system hardware are being outfitted, orbital tube welding is being performed for the different fluid and propellant systems, and recently the two sections of the LOX downcomers were installed. Work to outfit the boattail assembly is also continuing.

When engine section standalone work is completed, it will be mated to and integrated with the boattail assembly before finally joining the rest of the stage.

Prevalve repairs may allow final Green Run tests by the end of December.

Boeing was planning to conduct the final two, big Green Run tests in November, but the schedule was put on hold before Zeta’s appearance by issues with one of the LH2 prevalves and the thrust vector control (TVC) system. The issues were reported in October but were discovered during earlier Green Run testing in the summer.

NASA and Boeing have been focused on troubleshooting the faulty LH2 prevalve while it remained installed on the vehicle and in a November 6 blog post, NASA said they now understand the cause of the problem. “Engineers have inspected the valve, understand the reason it is not working properly, and plan to repair the valve while the core stage remains in the B-2 test stand,” the status update said.

“Following a successful repair, the team plans to conduct the Green Run wet dress rehearsal and hot fire testing before the end of the year.”

There are a total of eight prevalves on the Core Stage which help deliver the fuel and oxidizer propellants to the RS-25 engines via separate feedlines in the engine compartment, four LOX prevalves and four LH2 prevalves. The valves are closed during propellant loading while the Core Stage tanks are being filled and prepared for engine start and then opened just before ignition to flow fuel and oxidizer from the tanks to the engines until just after Main Engine Cut-Off (MECO).

Credit: NASA/Steven Seipel.

(Photo Caption: Image of the Core Stage-1 LH2 tank (left) and the engine section/boattail (right) in May, 2019, at MAF. The four LH2 prevalves can be seen extending out from the tank’s aft manifold. An issue with one of the valves has been identified and Boeing will be making repairs over the next few days.)

The problem with the engine four LH2 prevalve was intermittent; troubleshooting appears to have narrowed the problem down to a clutch mechanism. Following repairs and assuming retesting is successful, preparations for the Wet Dress Rehearsal and the Hot-Fire could resume.

Access platforms are still in place inside the engine section to support the prevalve troubleshooting and repair work; once the repairs pass retesting the prevalve will need to be closed out again for the big Green Run tests; closeouts may include reapplying foam and running some additional subsystem checkouts to reverify the overall LH2 systems. After that, it will take several days to disassemble the two-level platform in the engine compartment and remove it in pieces.

Stennis saw similar fallen trees and power line damage from Hurricane Zeta, but by the time the eyewall hit Stennis, the storm had been weakened by more land interaction. Hurricane-force winds were measured in the B-2 Test Stand, but those were lower than winds recorded while Zeta passed through New Orleans and MAF. “We maxed [wind speed] at approximately 75 mph (miles per hour), which was at about two-thirds the height of the stand,” Valerie Buckingham, NASA Stennis News Chief reported.

Both the B Test stand and the Core Stage installed in one of its two test positions escaped damage from Zeta.

Lead image credit: NASA/Eric Bordelon.



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