As NASA showed off the first assembled Space Launch System (SLS) Core Stage to government stakeholders and media at the Michoud Assembly Facility (MAF) in New Orleans, prime contractor Boeing continued preparations to ship the stage to the Stennis Space Center in Mississippi as soon as they can. While the TV camera “red lights” were on during a live morning broadcast on December 9 at the beginning of “Artemis Day” event festivities held at MAF, similar “test in progress” lights were on around the stage as Boeing and RS-25 prime contractor Aerojet Rocketdyne continued working to complete engine leak checks.



In parallel, NASA and contractor teams at Stennis are wrapping up work at the B Test Stand there so the Core Stage can be installed in the B-2 stage test position there next month. Boeing is now estimating that the Stage “Green Run” test campaign will last up to ten months before the stage will be ready to ship to Kennedy Space Center (KSC) in Florida for final preparations for a 2021 Artemis 1 launch.

The centerpiece of the test campaign is an eight-minute long, flight duration “hot-fire” of the stage in the B-2 stand, which could take place in the middle of the year; however, the extent of repairs and refurbishment of the stage after the first-time firing is an unknown and test managers are bookkeeping two to three months to restore the stage to a safe enough condition to travel to KSC.

At MAF functional testing to verify that the systems of Core Stage-1 are connected and communicating with each other correctly is still in progress, and the tentative date for shipment to Stennis is now just after New Year’s. Once testing is complete, final outfitting of the stage must be completed where it is currently lying in the SLS Final Assembly area, and then it will be moved for loading onto NASA transporters to roll out to the barge and head to Stennis.

Stage shipping preps in parallel with completing functional testing

NASA and Administrator Jim Bridenstine celebrated the completion of the first Core Stage at Michoud on December 9 and while all the working pieces are connected, prime contractor Boeing continues running through a final integrated functional test (FIFT) of the stage.

“We’re in functional testing, so we’ve connected all the major pieces of the rocket, we’re making sure they all talk to each other,” Amanda Gertjejansen, Core Stage-1 Operations Manager for Boeing, said in an interview on December 9. “Once we’re done with functional test we’ve got to prep the vehicle to ship.”

(Photo Caption: Core Stage-1 provides the backdrop as NASA Administrator speaks during a live TV broadcast to begin the “Artemis Day” media event at MAF on December 9. Although assembly of all the mechanical and working parts of the stage is complete, Boeing still has a few weeks of work remaining to finish testing, outfitting, and closeout before the stage is ready to transport to Stennis for the Green Run test campaign.)

As seen during the media event on December 9, the stage is lying horizontally in the Area 47 footprint of the Area 47/48 duplex in Building 103, where Core Stage Final Assembly takes place. With functional testing still underway, the stage is still missing several flight covers and remains surrounded by work stands.

Boeing still hopes to ship the stage from MAF as close to the end of the month as they can, and so the flurry of work to closeout the inside and outside of the stage is overlapping with the functional checks. “It’s got covers, any of the test ports that we’re covering up, some blankets around the engines, some covers across the systems tunnel we button that up,” Gertjejansen said. “We have to back away the stands to do some rotations.”

The stage is currently held in two Rotational Assembly and Transportation Tools (RATT) that allow it to be rotated; however, the stage has been in its current orientation since October to facilitate RS-25 engine installations. “We’re at ninety (degrees) up so we’ll rotate to put the boattail fairings on,” she said.

The bottom of the boattail extends out slightly beyond the twenty-seven plus foot circumference of the stage to accommodate the powerheads of the four engines; the fairings help streamline aerodynamic flow during the early part of ascent. “We’ll put two of [them] on in the orientation it’s in now and then we’ll have to rotate one-hundred eighty degrees and put the other two on.”

The final assembly team is already working on shipping prep tasks where they can. “We’re pulling ahead any we’re calling it ‘final outfitting’ so we’ve been putting on some of those covers now,” Gertjejansen noted. “As we run the [last] test we’re pulling whatever covers go over, this the last time we have to go hook up a connector to this area, we’re putting covers on as we go.”

As an example, she noted on the afternoon of the December 9 media day, “we just finished leak checks and we’ll be looking to start the thermal blankets tomorrow.” With the RS-25 engine leak checks completed, the engine-mounted heat shield (EMHS) blankets can be installed. The blankets provide thermal protection for the engine powerheads and the inside of the engine section and boattail.

(Photo Caption: The covered nozzles of the four RS-25 engines are the most prominent feature of a heavily-obscured tail of Core Stage-1 on December 9. Upstairs on the second level, Andrew Rostron with Aerojet Rocketdyne sits next to Engine 2045 in the number one position, upper right. Boeing and Aerojet completed leak checks of the engines later that day.)

Once all of the outfitting is complete, a pre-ship review will be held about a week before the stage is rolled out to the Pegasus barge for its relatively short water voyage to Stennis. Mark Nappi, Boeing Green Run Test Manager, said in a media question and answer session on December 10 that the tentative schedule for the review was December 28.

That rollout will be the first time the stage has been transported outside and it will be placed in special NASA transportation equipment and moved by remotely-controlled “self-propelled mobilized transporters” (SPMT). Boeing has its own factory transporters for the shorter trips from one indoor work area to another and those will be used one more time to move the stage from its current location a couple of doors down to Building 110 to transfer it over to the NASA transporters.

Green Run outline

At Stennis, Boeing will begin the Stage Green Run for this first working Core Stage article that also doubles as the first flight vehicle. Now planned only to be conducted on this first unit, the test campaign is the first opportunity to run a Core Stage through a series of tests that will help validate analytical models of how the stage’s mechanical and rocket hardware should behave during the phases of the countdown, ignition, liftoff, and ascent to orbit.

“We’re setting up this thing so that we’re essentially going to launch it bolted down, a full flight firing of that Core Stage over eight minutes bolted down,” Nappi said during the December 10th Q&A session. “That’ll satisfy a lot of our design objectives and make sure that that propulsion system is working like it’s supposed to. Then we’ll get it ready after the hot-fire and ship it to Florida.”

“It’s a big deal, it’s a 24/7 operation,” he said. “It’s just an extended launch campaign, actually; right now we (Boeing) probably have a dozen people here. In another thirty days, we’re going to have two-hundred fifty to three-hundred people and we’ll be working around the clock seven days a week, getting this vehicle ready for that hot-fire test.”

The flight-duration “hot-fire” of the stage, while it remains bolted into the B-2 stand, is the final major test in the Green Run Stage campaign; the firing serves as a “Green Run” or acceptance test of the stage, but its primary purpose is to validate analytics that model the stage behavior.

(Photo Caption: Core Stage-1 surrounded by work platforms in the SLS Final Assembly area at MAF on December 9. The lower level provides access to the -Z side LOX downcomer and adjacent systems tunnel. The upper level provides access to the tank repressurization lines and upper umbilicals for the forward skirt and intertank. Another set of platforms spans the +Z side of the stage.)

“The purpose of the Green Run is to satisfy design objectives, so we’ve got really, really good models that are predicting how the vehicle is going to react once we load it with liquid oxygen, liquid hydrogen, and we do the hot-fire,” Nappi explained. “The Green Run is to verify that yeah those models were right, and you only need to do that once and then you can depend on your models for any changes that occur.”

The models also allow engineers to analyze how the stage would behave under a larger set of operating conditions, including outside the currently defined limits. Previously, NASA and Boeing had also planned on conducting an acceptance test of the second Core Stage; however, in the name of schedule the necessity of both months-long Green Run campaigns came into question.

“It’s about ten months to get it all done and if we have a little bit of luck we could get it done a little sooner than that,” Nappi said. If the stage arrives at Stennis in early January, that would put arrival at KSC in the October time-frame next year, implying that the Artemis 1 launch date target would be well into 2021.

A final decision in the summer was to perform the Green Run campaign once on the first flight unit; plans to do the same for the second unit were canceled.

Nappi provided an overview of the Green Run activities at Stennis: “What’s involved once the vehicle gets here is getting it in the stand and this is really a joint effort between Stennis and the NASA Marshall Stages Office and us as a contractor, Boeing, to get that vehicle in position where we can hot-fire it,” he said. “So as soon as we get it in the stand we’ll take about two or three weeks where we’re going to do something called a modal, which is essentially just a response test to see how the vehicle reacts, again matching up those results with the models that we’ve created to make sure that it’s reacting like we expected it to.”

As was practiced at Stennis with the Core Stage Pathfinder, the flight stage will be rolled off of the Pegasus barge that moves it from MAF to Stennis, lifted up with two cranes, rotated from horizontal to vertical, and then the primary test stand derrick crane will install the stage in the stand where it will be bolted down and the crane disconnected.

“From the time the barge gets here it takes about three, four days and then it’ll be in the stand,” Nappi noted.

(Photo Caption: The B Test Stand derrick crane lifts the Core Stage Pathfinder out of the stand’s B-2 position on August 29. After installing Core Stage-1 into the stand in January, the crane will be used to lift the stage up out of the hold-down attachments to perform three separate modal test runs over a period of a couple of weeks. The modal tests are the first of many test cases to be run as a part of the Stage Green Run campaign.)

The modal test measuring the structural frequency response of the Core Stage by itself is three separate test runs where the derrick crane is reattached and the stage is partially lifted out of the stand so it is hanging on the crane to perform the test. “We lift it three times, so we take it, lift it up, do the modal test, put it back in the stand. Do some data analysis, come back again pick it up, do modal, put it back in the stand. Same thing, three times.”

“Once we’re done with modal then we’ll bolt the vehicle down in the stand and we’ll start getting access,” Nappi explained. “We’ve got to get access into the engine section, we have to get access into the intertank, we have to get access into the forward skirt so that we can start configuring the vehicle for test.”

“We also have some work that we’re going to complete from MAF, the LH2 (liquid hydrogen) feedlines still need to be connected so we’re going to have about two or three months worth of work to get those feedlines connected so that when we start our power on testing we’ll have the vehicle in flight configuration.”

The LH2 feedlines and fill and drain line are positioned inside the engine compartment, but can’t be secured while the stage is horizontal. Boeing, with NASA’s concurrence, traded deferring that work to Stennis in order to buy back several months of time at MAF by completing the rest of the stage assembly in the horizontal.



After the LH2 Main Propulsion System (MPS) lines are secured, checked out, and final spray-on foam insulation (SOFI) closeout work completed, the power-up testing will start to verify that the stage is ready to be loaded with propellant and then fired; the cryogenic tanking and test-firing will be firsts for the SLS Program.

“We’ll do what we call power-up testing or confidence testing,” Nappi explained. “This is the first time that this vehicle has been in this stand and has seen the software that we’ve created to run these tests, so we want to take a really slow and methodical set of steps to make sure that that all works together properly so that when we do go do the ‘wet dress’ (Wet Dress Rehearsal) and the hot-fire everything is working like it’s supposed to.”

Special software will run on the stage’s three redundant flight computers to account for the static nature of the eight-minute long test; otherwise, most of the stage’s systems have to perform as they would during a dynamic ascent to orbit insertion. Boeing has also developed the Core Stage Controller (also known as the Stage Controller) package of ground software and avionics that manages that side of the Stennis testing.

“The tests are validating that all of our systems are working, that our avionics systems are working, our hydraulic systems are working, TVC systems are working, our Main Propulsion Systems are all working. We’ll have people in our control room that will be monitoring all their systems as we bring every single black box up and we actuate every valve and we’re checking to make sure that when we send the command that it works and the indications come back and they’re coming back like they’re supposed to.”

“So we’re going to take a couple of months testing everything with the software and the vehicle and the stand to make sure that it works right,” he added. “When we’re done with that we’re going to take a step back and say it’s time to load this vehicle with LH2 and LOX (liquid oxygen) and see how it reacts.”

(Photo Caption: A view of the northern perimeter of the B Test Complex from Level 19 of the B-2 test stand position in December, 2018. The white-colored tubing to the right of the exhaust/water deluge pathway that extends out from the flame buckets of both B-1 (left) and B-2 (right) positions is where LOX will be dumped after it is drained from the Core Stage after the Wet Dress Rehearsal. Any LOX residuals left in the tank following the hot-fire test will also be dumped here. Gaseous oxygen boiloff will be vented out a port on the stage’s forward skirt.)

“We’re going to do what’s called a Wet Dress Rehearsal (WDR), load it with LH2 and LOX, make sure it doesn’t leak, we’re good. We detank it, these guys get us some more commodities so we can load that vehicle again and [then] we come back and we actually run the hot-fire.”

Boeing anticipates a short turnaround from the WDR to the hot-fire; what amounts to a scrub turnaround between the WDR tanking and the hot-fire tanking is driven by the infrastructure at Stennis to supply propellant and other support commodities to the fluid-hungry stage. The cryogenic propellants are supplied to the hydrogen-oxygen test stands at Stennis by barges docked around them.

“Our liquid oxygen barges here, each one of those holds about a hundred thousand gallons of liquid oxygen,” Maury Vander, NASA’s Test Operations Division Chief in the Stennis Engineering and Test Directorate, said. “Those [liquid hydrogen barges] are about two-hundred, forty thousand gallons of liquid hydrogen.”

“The vehicle holds five-hundred fifty thousand gallons of LH and about two-hundred thousand gallons of liquid oxygen so we’ve got enough, but we don’t have enough to try to recycle quickly. We’re making the conscious decision after the wet dress we’re going to discard the LOX and we’re going to drain back the liquid hydrogen so we’ve got to get trucks in here to replenish our barges and that’s what drives the five-day turnaround between wet dress to hot-fire.”

“When we do the wet dress, we’re just basically testing the health of the overall system,” Nappi noted. “Are we getting any leaks? Are the valves working properly? Is it a nominal type of tanking?”

“And detanking — it’s real important to assure that we can detank this vehicle as safely as we tanked that, so those are two real important parts of the test. Then when we do hot-fire you’re essentially just checking your flight readiness of all the main propulsion system and that it’s working properly and we’ll be watching it just like we would on day of launch.”

Following the hot-fire, Boeing has set aside a long period for refurbishing the stage. “It takes about two to three months after hot-fire,” Nappi said. “We haven’t hot-fired it yet so when we’re done we’ll take a step back, we’ll see what needs to be fixed before we put it on the barge.”

“First of all we have to do shipping preps, we have to get the vehicle ready to put on the barge. That’s all known work, we know what kind of preparations need to be made.”

(Photo Caption: A view of the dual-position B Test Stand looking to the south on December 10. The B-2 stage test position is on the left, the single-engine B-1 test position is on the right. Both positions are fed propellants from barges docked around the stand, but the B-1 position has run tanks for the LOX and LH2 propellant commodities. For the SLS Core Stage Green Run propellant tests, the barges will be used to fill the stage and a day tank on the B-2 side will be used to maintain stable replenishment of LOX for the stage.)

“The second piece is the engine refurb, and the third piece is any damage that occurs during hot-fire,” he added. “This thing is going to fire for eight minutes and it’s going to be bolted down.”

“We expect to see some TPS damage and so we’re going to have to repair that, but we don’t have to repair it all here. We can take a lot of that to KSC if we like and do it on a non-interference basis at KSC.”

“So that work is undefined, we don’t know what the damage is going to be yet,” Nappi explained. “We suspect we know where some of it is going to be and we’re preparing for it, but until we know what it is we won’t be able to scope it.”

Aerojet Rocketdyne will refurbish the RS-25s while Boeing works on the rest of the stage. “They’ve come up with a minimal number of days that they need to essentially get the engines refurbished to a point where they’re safe enough to put it on the barge,” Nappi said. “After hot-fire it’s about two months.”

“We’re going to have a lot of instrumentation on the vehicle for this test so that instrumentation has to come off. That’s again known work, we will be able to do that under the envelope of the engines being refurbished,” he added.

There is also ground test instrumentation specific to the modal tests that will be conducted at the beginning of the campaign; Nappi said that instrumentation would be removed immediately after the modal tests are completed.