Prior to workplace closures, SLS was making good progress ahead of opening missions

by Philip Sloss

Prior to the shut down of work last month in response to the coronavirus disease 2019 (COVID-19) pandemic, NASA’s Space Launch System (SLS) Program was working towards milestones for its first two launches. At Stennis Space Center in Mississippi, Core Stage prime contractor Boeing was getting ready to do powered checkouts of the first flight article ahead of the two major tests in the Stage’s Green Run campaign there. Subsystem testing in support of readiness for the Green Run test and for the Artemis 1 launch was also being performed at the Marshall Space Flight Center (MSFC) in Alabama and in Florida.

Protecting the NASA and contractor workforce from COVID-19 outbreaks suspended work at Stennis, Marshall, and also the Michoud Assembly Facility (MAF) in New Orleans, where Boeing was moving from the structural assembly of the second Core Stage flight article into integration activities in March.

In other parts of the United States, some hands-on work does continue with almost everyone else working from home; solid rocket booster (SRB) and upper stage hardware for Artemis 1 is being processed and for Artemis 2 is in production.

When it is safe to return, NASA and Boeing will also resume work repairing a leftover Core Stage liquid hydrogen tank. The tank was originally a part of the hardware built for the first flight, but it was set aside in 2017 after a post-welding anomaly was discovered. After research and testing, plans are in place after return to the worksite to fix the welds and eventually proof test the tank. If the repairs pass testing, the tank is earmarked for the Core Stage-3 build.

Green Run status

The element of the Artemis 1 hardware that has the longest schedule of work remaining, the critical path, is Core Stage-1. The program’s first flight article also doubles as the test article for the program’s Core Stage Green Run test campaign, where for the first time a working stage is activated, fueled, and fired.

The stage is bolted into the B-2 position of the B Test Stand at Stennis, following its arrival there in mid-January. The Green Run campaign includes tests as a part of initial development to field the first launch vehicle and following installation into the stand a modal test was completed at the end of January.

From that point up until work was stopped in mid-March as a part of the response to COVID-19, Boeing was working towards the next major milestone of powering up the stage in the B-2 stand with their ground control system. Boeing is finishing the development of its Core Stage Controller that will conduct the stage and stand systems and infrastructure through a systematic activation and checkout.

Credit: Philip Sloss for NSF.

(Photo Caption: Core Stage-1 in the B-2 Test Stand at Stennis on February 10. In the lower right, a liquid hydrogen barge is docked at the stand. Barges will supply the cryogenic liquid hydrogen and oxygen to fill the stage’s propellant tanks for the two biggest tests in the Green Run campaign, a Wet Dress Rehearsal tanking test and a hot-fire test firing of the stage.)

Powering the stage up with the Stage Controller and checking out how they behave individually and as a team leads into the two crucial tests at Stennis, a Wet Dress Rehearsal (WDR) to fuel the stage for the first time and a hot-fire test to fire it while held down in the stand for a flight-duration of eight minutes.

Boeing was nearing completion of the prerequisites to begin testing, which culminates in a broad test readiness review (TRR) to get concurrence to proceed into the powered up stage checkout. “On the stand itself for Core Stage-1 we were prepared to do power-up testing which is our first big vehicle test when we had the stand-down order,” John Shannon, Boeing’s Vice President and Program Manager for SLS, said in an April 10 interview . “When we return to normal operations it will take about three days to configure the vehicle back and then about ten days to complete all the work to set up for power-on testing.”

“So when we get the go we’ll be two weeks from powering up the vehicle for the first time on the stand and the Stage Controller is a big part of that.”

Stennis is a federal city, with dozens of tenants from government to private enterprise; although some national security and other work categorized as essential continues on site, NASA-related work is on hold. “We do have a small number of people that are what we call a rideout crew at both Stennis and MAF,” Shannon noted.

“We’ve secured all the hardware prior to leaving the site and we send those people back generally every other day unless there’s severe weather like we’re expected to have this weekend and they check on the hardware and the purges and just the general condition to make sure that everything is in good shape.” MAF was moved to Stage 4 of the agency’s COVID-19 response framework at the same as Stennis on March 19; like Stennis NASA-related work at MAF is suspended, but some activity continues on other work that is considered essential.

Credit: NASA/Joel Kowsky.

(Photo Caption: NASA Administrator Jim Bridenstine is given a tour of engine access platform on the B-2 Test Stand on February 10, surrounded by the SLS Core Stage RS-25 engines and the base heat shield of the stage’s boattail. The administrator is standing under the manhole of the boattail, one of multiple access doors leading into and providing work access to the engine section and boattail of the stage.)

Boeing’s Stage Controller system takes the role at Stennis for the Green Run that the launch processing system under NASA’s Exploration Ground System (EGS) takes at the Kennedy Space Center (KSC).

“The team is making really good progress, they’ve already completed all the work for what we call Phase 1, which is all of the test activities up to Wet Dress,” Shannon said. “In Phase 2, they’re just about done with it and ready to get back into verification as soon as we can get back on the site at Marshall.”

“Stage Controller work is done in two locations,” he added. “All of the qualification testing is done at the lab in Florida, they are still working and making good progress.”

“The verification work is performed at Marshall and that work has been stopped although we are able to go in. We are sending in a team next week to calibrate all the different sensors and such in the facility so that when we get back to work we won’t be stopped for any calibration issues.”

Verification testing of the Stage Controller avionics and software at Marshall for the Green Run campaign was being performed integrated with the Core Stage’s avionics and software, supplied by Boeing and NASA, respectively. A second set of avionics racks like the ones installed on the B-2 Test Stand is set up in the Software Integration Lab at MSFC connected to the System Integration Test Facility’s Qualification (SITF-Q) ring, where a representative set of Core Stage vehicle computer hardware and software is set up.

Phase 1 of the Stage Controller software has passed its own TRR for power-up testing when activities at Stennis can resume. The Phase 2 version of the software is being tested with the Green Run Application Software (GRAS) that NASA developed and runs on the stage’s three flight computers.

The Stage Controller sits between the stage and the stand infrastructure for Green Run, providing a command and control and monitoring interface to the team managing test operations from the B-2 test control center. It is designed to orchestrate the WDR and hot-fire countdowns, issuing sequences of commands to the stage and test stand, relaying operational parameters for stage and test stand systems to the test team, and monitoring and enforcing test commit criteria for critical operational parameters.

Credit: NASA/Joel Kowsky.

(Photo Caption: NASA Administrator Jim Bridenstine tours the engine access platform level of the B-2 Test Stand at Stennis on February 10. The first working article of the SLS Core Stage is being used for the Green Run test campaign there before traveling to KSC to be the first flight article. The nozzles of the four RS-25 engines are covered by yellow bags.)

When the workforce comes back to work at Stennis and what approaches to take bringing people back together for work are still to be determined. “I don’t think it’s going to be a step-function where we just all show up back to work and things go back to normal,” NASA SLS Program Manager John Honeycutt said on April 10.

“There’s going to be some startup periods and things that we have to do to continue to protect the workforce as we potentially move from a Phase Four environment to a Three and then back to a Two.”

Due to the priority placed on Artemis program goals which have a fixed deadline, resuming work at Stennis, MSFC, and MAF is critical to scheduling. “We have prepared plans for all options starting with a normal return to work all the way down to just having a skeleton crew for critical path operations with the majority of the workforce staying in that telework role,” Shannon said.

“We’ll just see what the conditions are around the site and what NASA’s position is for how many people we can put back on the floor or on the test stand when we get to that point.”

Artemis 1 preparations

Depending on COVID-19 restrictions at other worksites, development and processing work in preparation for the Artemis 1 launch is continuing. The first SLS element completed was the Interim Cryogenic Propulsion Stage (ICPS) produced by United Launch Alliance (ULA), who delivered the stage from their Decatur, Alabama, assembly factory to Cape Canaveral in March, 2017.

The ICPS is a version of the Delta Cryogenic Second Stage (DCSS) customized for NASA by ULA; following arrival at Cape Canaveral Air Force Station (recently renamed Cape Canaveral Space Force Station) in 2017, the stage was processed at the company’s Delta Operations Center (DOC) and then turned over to NASA EGS in July, 2017, to wait for launch processing. Now that the launch date for Artemis 1 has slipped into 2021, the stage was returned to the DOC last month for periodic maintenance.

Credit: NASA/Kim Shiflett.

(Photo Caption: The ICPS for Artemis 1 leaving the Delta Operations Center in July, 2017, for storage at KSC. The stage was recently returned from the Space Station Processing Facility to the DOC for periodic inspections and maintenance.)

“It was more convenient for us to move it from where we had it stored at the Space Station Processing Facility over to the Air Force side where the Delta Operations Center is,” Honeycutt explained. “We made that move and we’ve been going through a series of checkouts and inspections and updates for ICPS.”

“All the DCSSs that have flown in the ULA fleet have always had continual minor upgrades and so this is really just a part of a normal operational flow so that we can do some minor testing and maintenance as we get ready to move to flight. They’ve got all the tools they need to do the work down there and it just wasn’t practical for us to do the maintenance work in the SSPF and so it’s going to stay in the DOC until it’s needed.”

SLS Booster prime contractor Northrop Grumman continues to prepare the Artemis 1 hardware for launch preparations. “For the Booster activities, those continue to go on out in Utah as well as at the Booster Fabrication Facility (BFF) at KSC,” Honeycutt said. “We’ve found a way to continue to support the work that’s going on at the Booster Fabrication Facility to minimize the impacts there primarily through social distancing and providing the touch labor workforce with the appropriate protective equipment to stay safe.”

Northrop Grumman has completed the production of sets of five-segment solid rocket motors (RSRMV) for both Artemis 1 and Artemis 2 at their Promontory facility north of Salt Lake City. Each of the two Solid Rocket Boosters (SRB) for an SLS vehicle are composed of the five motor segments plus a forward and aft assembly that includes avionics, hardware for attachment to the Core Stage, and a hydraulic thrust vector control (TVC) system.

The assemblies are being completed in the BFF at KSC and the SLS Program is working with the EGS in Florida on when to ship the Artemis 1 motor segments from Utah to the launch site. “We’re going to have to figure that out in working closely with the Exploration Ground folks, we’re continually talking to them,” Honeycutt said.

“It’s on hold now given the COVID-19 situation but where we’re headed is we’re ready to deliver them, we want to do what makes sense from a timing perspective as to when the EGS folks need them. That’s one of those things that will be impacted by the virus and how we roll out of that but from the SLS perspective we’re ready to deliver as soon as we understand the need date at Kennedy.”

The aft exit cones for the boosters were shipped from Utah to Florida late last year.

The latest estimate was that the motor segments could be transported in June. “It’s a real time call, it needs to precede the Core Stage delivery by a few months,” Mike Bolger, NASA EGS Program Manager said in December. “We’ve got to see how things go at Green Run.”

Credit: Northrop Grumman.

(Photo Caption: Technicians finish adding photogrammetry markings to one of the forward motor segments for the Artemis 1 boosters in 2017. The segments remain in storage at Northrop Grumman’s Promontory facility in Utah, but NASA plans to transport them to KSC for launch preparations later this year.)

“We’ll actually get into our ML (Mobile Launcher) preps and we’ll actually start to get into our stacking ahead of Core Stage, so it’s a real time call. In theory, we’ve got a year clock and that’s exactly why they’re keeping an eye on that.” The segments have a time limit of about a year that they can remain stacked, so the SLS and EGS programs are trying to synchronize the timing of stacking and of shipping before that with the Core Stage schedule.

Additional development testing was being performed at Marshall prior to its shut down on March 27. Qualification testing of individual Core Stage subsystems and together in integrated sets was continuing before the shutdown.

Structural qualification testing at Marshall was nearing completion at the time. “We had one additional test case that we needed to run on that LOX (liquid oxygen) tank per the plan and then we were going to have a discussion relative to a similar type final test where we do the test at a higher load,” Honeycutt said.

A structural test article (STA) for the Core Stage LOX tank was the final of four STAs to be subjected to a series of load cases in test stands at MSFC to verify that the structure had at least a factor of safety of 1.4 as required.

“Probably the biggest one is we’ve shut down the activities in the Software Integration Lab and the System Integration Test Facility (SIL/SITF) as well as the Software Development [Facility] Lab,” Honeycutt noted.

“We’re looking at ways to safely to get back into the facility with a small number of people and the correct PPE (personal protective equipment), get in there, and do some calibration on Stage Controller there so we’re up and ready to go. There are going to be some impacts from discontinuing the work in the SIL/SITF when we went to Phase 4.”

“The software development folks they’ve moved along,” he added. “They’ve been able to make some good progress in this virtual environment and we’ve worked with our Safety and Mission Assurance (S&MA) folks who provide our quality support for all the inspections that we need to do and we have those verification activities that the quality folks do in parallel with the software developers and the testing that they do and so we’ve been able to work through that and find ways to do that verification quality oversight work in a virtual environment.”

The Core Stage hydraulic thrust vector control (TVC) system was also going through subsystem qualification testing in separate labs at Marshall. “The other big ones that we’ve backed out of is the work that we were doing on the speed control valve for the Core Stage Auxiliary Power Unit (CAPU),” Honeycutt said.

“We had that going on at two areas in our Component Development [Area] facility and also in our Thrust Vector Control lab. The team was ready to move out on the work when Phase 4 hit and so that’s an area that we’ll have to spin back up and where we’ve been impacted.”

The issue with the CAPU speed control valve came up during TVC qualification testing at Marshall last year. “It’s basically a poppet that lets pressurized fluid go through the APU to the turbine wheel,” Shannon explained back in January.

“The failure that we had was the poppet got cocked in there and let flow go through which was going to overspeed the CAPU turbine except the CAPU controller shut it down when it sensed that. It had a lot of time on it, probably the equivalent of five flight cycles on it when that happened. We were kind of debating on whether a stronger spring that kind of pushes that poppet back into place is warranted or not.

“We’re still going through some qual tests and some debate on that,” he said at the time. “Back then when we were looking at it, weren’t sure if we were going to have to do some inspection or something on the CAPU. We’ve since then determined that no, we do not need to.”

Credit: NASA/Eric Bordelon.

(Photo Caption: The Core Stage-2 (CS-2) liquid oxygen (LOX) tank is moved into Building 103 on March 16. The tank is covered with a coat of primer for corrosion protection. At the very far left, a part of the CS-2 liquid hydrogen (LH2) tank can be seen in Area 6.)

“In talking about whether we needed to do something on the speed control valve or not, if we did it would be a very small component that there’s this one bolt that is required to remove that speed control valve if we wanted to swap out the spring.”

The issue was discussed back at the time the four RS-25 engines were being installed in the Core Stage at MAF last Fall; space in the engine compartment is even more cramped than in the Shuttle orbiter boattail and there was some initial discussion about whether engines needed to be moved out of the way for access. As it turned out, Shannon said that wasn’t necessary for a few reasons.

“We took all the measurements and determined that we could get a CAPU out through the manhole between all four engines if that was really required,” he noted. “If we did do something it would be a very small fix to the CAPU, to that speed control valve to replace the spring, and then if we had some other issue that came up during qualification testing and we had to remove the CAPU then we could get it out through the manhole itself and there was zero reason to ship without an engine in place to give you access.”

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