The first NASA Space Launch System (SLS) Core Stage arrived at the Stennis Space Center in Mississippi onboard the Pegasus barge late last weekend to begin the Stage Green Run test campaign that will take up the majority of the year. The stage was transported from its Michoud Assembly Facility factory after weather postponed the trip for a few days.
The test team at Stennis has prepared the stage to be lifted into the B-2 position at the B Test Stand where activation and full checkouts of the stage will precede its first propellant loading, followed by an eight-minute long firing of the stage and its engines. The amount of time it will take to be ready to conduct the propellant load and hot-fire test will be driven by both how well the stage behaves in the stand during preparations and how favorable weather conditions are at Stennis during the rest of the Winter and the Spring.
NASA and prime contractor Boeing have transferred some of the expected refurbishment work after the hot-fire test to the Kennedy Space Center after the stage is shipped there from Stennis for launch preparations, but estimates when that transport might occur still range anywhere from August to October. The team at Stennis has practiced for all the upcoming testing for months and is ready to begin working on the real rocket now that it is on site.
Weather slows barge trip, will be one of the factors in schedule
Pushed and pulled by tug boats, the agency’s Pegasus barge with Core Stage-1 onboard arrived at the dock for the B Test Stand in the afternoon on January 12 after departing the Michoud Assembly Facility (MAF) in New Orleans early that morning. The first flight article, which will eventually help launch the Artemis 1 mission to the Moon, rolled out of the factory at MAF on January 8.
The rocket was secured on Pegasus a few hours after the rollout, but the trip on the water from MAF to Stennis had to wait a few days for acceptable weather conditions. A weather system brought strong, gusty winds into the area at the end of the week followed by a threat of severe weather early on the weekend.
Even if the barge had arrived at Stennis before the weather system passed through the area, high winds and lightning likely would have delayed the next steps in the process. With favorable weather conditions at arrival, work started within hours to roll the stage off the barge.
(Photo Caption: Tugboats maneuver NASA’s Pegasus barge holding Core Stage-1 into position at the B Test Stand dock on January 12. The day trip on the water from the Michoud production facility to Stennis had to wait for weather conditions to improve after a strong system passed through the New Orleans area the day before. The B Test Complex has a dual position stand; the Core Stage will be installed in the position on the right above the barge.)
The self-propelled modular transporters (SPMT) that rode with the stage and the rest of the NASA Multi-Purpose Transportation System (MPTS) on the barge from Michoud were first unloaded. The remotely-controlled transporters were driven under the support equipment carriers holding the stage, raised them off of the barge attach points, rolled them off of Pegasus onto the tarmac beside the stand, and set them down.
Preparations then began to lift the stage into the stand, following the same outline of steps performed several months ago with the Core Stage Pathfinder when it was at Stennis. A couple of the SPMTs were used to position a fixture holding a lift spider up against the front of the stage.
After the lift spider is attached to the weather cover on top of the forward skirt, the stand’s derrick crane will be attached to the spider and a commercial crane has already been rigged to pick up the back of the stage at two points on the outside of the engine section section barrel. After the stage is disconnected from the MPTS interface structures, the cranes will lift the stage up in its current horizontal orientation high enough to break it over from horizontal to vertical, with the derrick crane on the stand raising the top of the rocket up and the trailing crane helping rotate it to vertical.
As with the practice with the Pathfinder, the stage will be lifted when the weather permits. The plan is to do it at night when wind speeds are typically lower; there are wind limits to safely perform the lift, breakover, and install.
Once the stage is in a vertical orientation, the trailing crane can be disconnected and the stand’s crane will finish the installation, lifting the stage up, pivoting it into the B-2 position of the stand, and lowering it down for install.
(Photo Caption: The curtain at the back end of Pegasus is drawn showing Core Stage-1 inside as the barge is tied to the B Test Stand dock during arrival at Stennis on January 12. Teams at Stennis will be working around the clock to support the Green Run test campaign and work to offload the stage and prepare it for lift and install into the B-2 position of the test stand began within hours of arrival.)
Now that the stage is again off the barge, it will be outside at Stennis for a long time until it is rolled back onto Pegasus at the conclusion of the Green Run campaign. The test stand itself provides lightning protection for the safety of the team and the hardware, but the Core Stage and team working on it are mostly outside in the elements. When conditions deteriorate and become unsafe to remain outside technicians doing work inside, outside, and around the stage on the stand will have to suspend work and take shelter indoors.
The amount of time that weather keeps work from continuing is one of the uncertainties in forecasting how long the test campaign at Stennis will be. “We’ve given NASA a range of possibilities; of course this the first time we’ll be putting cryogenic fluids, the super-cold fluids in the vehicle and we’ll learn some there but if everything went perfectly and we didn’t have any kind of weather issues on the stand that would halt work, if the vehicle performs completely as expected and we didn’t have any refurbishment we’d be out probably in the late Summer time-frame, July/August time-frame,” John Shannon, Boeing’s Vice President and Program Manager for SLS, said.
“Those set of assumptions probably is not reasonable, we’ve tried to look at climatology to determine how many days we think that weather could end up slowing down work on the stand and then we’ve looked at refurbishment — after the vehicle is fired what type of things that we might have to go do,” he added. “Originally we had about three months in the plan for that.”
“We’ve looked harder at that, moved some of it to KSC, it’s down to about a month and a half, so the range I think would be from July/August if everything goes perfectly to an October time-frame if we deal with what would normally be typical weather or typical damage that could happen to things like the thermal protection system (TPS) after that eight-minute firing.”
Development testing leads to first tanking
Core Stage-1 is the SLS Program’s first working article of the sustainer stage that controls the launch vehicle from the end of the countdown to insertion into Earth orbit. The Core Stage Green Run is a testing campaign focused on the stage, not the four veteran engines once called Space Shuttle Main Engines (SSME) and now called RS-25s that are installed in the back.
In contrast to the other elements of SLS that are flight-proven or ground-tested like the RS-25s, the Core Stage is the new piece of the launch vehicle. It started development behind designs and hardware already evolved from the Space Shuttle or the cancelled Constellation program and no working version has yet gone through full-scale testing.
The Green Run of this first working unit is the only planned opportunity to demonstrate a full-duration test run of a Core Stage before the program’s first launch. After debating whether to skip the test campaign last year in favor of abbreviated options to shortcut the schedule, the agency decided to keep the test.
“I think some folks view Green Run as workmanship screening; I don’t view it as that, as a matter of fact that’s not what it is,” NASA SLS Program Manager John Honeycutt said on January 8 when the rocket stage rolled out of the factory. “This Green Run and this Green Run only is for us to learn everything that we can about the Core Stage while we’ve got it here on the ground with us.”
Earlier plans were to hot-fire the first two Core Stage flight articles at Stennis, but the current plan now is to only go through this test campaign once. The second Core would be completed at MAF and shipped directly to Kennedy Space Center (KSC) for the Artemis 2 launch campaign.
A generic “green run” is an acceptance test firing of new rocket engine hardware and the test campaign at Stennis will be capped by a test-firing of the stage; however, the Stage Green Run also refers to the whole development test campaign. “Green Run is a well-choreographed plan for individually activating each of the systems on the vehicle, taking a look at the instrumentation to make sure the vehicle performs as expected, that will culminate in two significant activities,” Shannon explained.
“One is the Wet Dress Rehearsal (WDR) where we’ll put cryogenic oxygen and cryogenic hydrogen in it and at that time we’ll go an exercise all the systems, make sure they work properly. We’ll drain the tank and then we’ll refill it again about a week later after we’ve looked at all the data very closely and do what’s called the hot-fire and right now the plan is for that hot-fire to last just over eight minutes which is the normal mission duty cycle of the Core Stage, so it’ll be a simulated full mission.”
“The Core Stage is a human-rated vehicle [and] NASA has some very specific requirements that we need to fulfill in the design and test and build of the vehicle to show that it is human-rated,” Shannon noted. “Part of that is a full qualification of all of the different components that are used on the rocket, so every single system, avionics box, the wiring, the tubing, the propellant lines, they are taken through a very rigorous qualification series of tests for everything from stress and temperature and fracture.”
“And then after all that is done for the individual components, we will put them together and run through what’s called a final integrated functional test on each of the integrated systems to show that the way that they were placed in the rocket, the way that they work with each other is acceptable. As a result of the human rating it has gone through an extremely rigorous series of tests that will culminate with the Green Run where we do those tests at cryogenic conditions and finally end up with a full mission, duty cycle hot-fire.”
“So by the time we take this vehicle to Kennedy Space Center, it will be an extremely well understood vehicle and we’ll have really high confidence in flying it and for the second flight putting a crew on,” he added.
(Photo Caption: Rollout of the first SLS Core Stage flight article, Core Stage-1, at MAF on January 8. The self-propelled modular transporters (SPMT) moving the stage and its carrier hardware are under wireless control by operators moving with the equipment.)
The development test campaign also includes some testing not directly related to the WDR and hot-fire later in the year. After the stage is initially bolted down in the stand preparations will be made for one of those tests. “Once we get on the stand we’ll do what’s called a modal test to understand the resonant frequency of the vehicle,” Shannon said.
“So NASA actually has the ownership of the stage right now, we did what’s called a DD 1149 which is a form that you sign that transfers the ownership of it, it happened yesterday,” he noted on rollout day. “That’s the first one and then when it is nine inches from the holddown posts (in the test stand) they hand it back to Boeing, so we get it then and we do that final nine inches and put it into the holddowns and do some work setting up instrumentation for the modal test.”
The stage is covered with development flight and ground test instrumentation; for the modal test, wiring that runs to instrumentation installed on the surface of the vehicle’s TPS and underneath it directly to its metallic structure will be connected into the data acquisition system of the test stand.
As with many tests, much more work time is consumed preparing for a test compared to executing the test procedure. “We’ll take about two or three weeks [for the modal test], 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,” Mark Nappi, Boeing Green Run Test Manager, said in December.
Once the sensors are connected, verified to be working and integrated with test stand infrastructure, the structural frequency response of the Core Stage will be recorded in three separate test runs. The derrick crane will be reattached to the lift spider and the stage will be 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,” Nappi noted. “Do some data analysis, come back again pick it up, do modal, put it back in the stand. Same thing, three times.”
“[They’re] like mechanical hammers that will actually ring the structure so that you can get the resonant frequency of the vehicle and understand it unloaded,” Shannon noted. “All the modal stuff comes off after we do the modal test because it wouldn’t survive the [hot-fire] itself.”
“Once we do that then we go through a very rigorous, well-thought out period of activation of the developmental flight instrumentation, we connect umbilicals, we drag on instrumentation all while we’re doing the finishing work on things like the hydrogen lines and then we’ll activate the vehicle with the hydraulics and all the different control systems,” he explained. “We’ve had teams for the last seven months that have been in the control center at Stennis working with an emulator and all the screens and command systems and telemetry, practicing all the first avionics power up, vehicle power up, hydraulics activation, modal test, so they’ve kind of run through all that before.”
“So when the vehicle shows up then we’ll make sure that the vehicle actually looks like what the emulator looked like. It should, but you have to make sure that your system is going to work with the real vehicle just like it worked with the emulator.”
Wet Dress Rehearsal is first-ever propellant load
The Wet Dress Rehearsal is a big milestone at Green Run and one for the SLS Program, being the first cryogenic propellant loading (or “tanking”) of a Core Stage. This will be the first opportunity to load the large liquid oxygen (LOX) and liquid hydrogen (LH2) propellant tanks that make up most of the length of the stage and to run through final countdown procedures which typically begin with tanking.
“The first fun thing is going to be to thermally condition the tank, where you put a little bit of cryos in and you start to chill the tank down before you go into what you call the ‘fast fill’ time-frame and then it’s going to be a lot of looking at stable replenish and make sure we can keep pressure on the tank,” Shannon said. “Primarily we’re looking at the haz gas (hazardous gas detection) system to make sure that we don’t have any leaks once we get down to cryogenic temperatures.”
Much of the vehicle testing completed at Michoud and to be conducted at Stennis prior to the WDR builds up to its first tanking.
(Photo Caption: Final outfitting of Core Stage-1 at MAF is in progress as seen in this image taken on December 30. Final integrated functional testing (FIFT) at MAF was completed just before Christmas Day allowing the stage to be rolled to provide better access for adding final thermal protection system (TPS) elements to the stage for Green Run.)
“We did a very comprehensive set of functional testing on the vehicle before it got on the barge today and that included pressure tests, seal checks, all the electrical tests in the world you could think of, software checks, things like that and the vehicle came through really with flying colors,” Shannon, who was NASA’s Space Shuttle Program Manager for its final fourteen flights, noted. “We found no real issues with the design or the way that it was produced, but things change when you get down to cryogenic temperatures and as we saw after our experience with the Shuttle that you can end up having systems perform differently.”
“The next big unknown for the program is when we put the cryogenic liquids in the oxygen tank and the hydrogen tank and we look at the plumbing and all the systems and make sure that they remain tight and that they perform as expected. Through our qualification tests we have high confidence that they will but until you see it in an integrated fashion you don’t really know, so we have prepared the team with contingency procedures — if they see anything unexpected to be able to handle that expeditiously.”
“So I think that’s the next big milestone for us that we’re going to be learning a lot about the vehicle and that’s when we put the cryos into the tanks.”
Serving as both a test article and first flight article for the SLS Program, this will be the first of multiple cryogenic tankings and detankings of this Core Stage. While other engineers are monitoring performance of the vehicle’s avionics, software, mechanical systems, and main propulsion system, TPS engineers will be monitoring the performance of the spray-on foam insulation (SOFI) that covers most of the stage.
“The first thing we’re going to be looking for is do we see cracks in the foam, do we see cracks with liberation especially in critical areas like the hydrogen tank flange, similar to what we had on ET (External Tank),” Michael Alldredge, NASA SLS TPS Subsystem Manager, said. “You get a lot of dynamic motion in that area.”
“We’re going to be looking at ice buildup, if we get ice buildup like in the feedline yokes, anywhere we may have mechanical problems due to ice buildup, those kind of things,” he added. As with Shuttle, the foam still insulates the cryogenic propellant inside the tanks from outside ambient conditions before launch and ascent heating during it, but the situation is also different.
(Photo Caption: Dozens of brackets can be seen in this image holding LOX feedlines and gaseous oxygen and hydrogen pressurization lines in place on the outside of the rocket stage. These are some of the areas that TPS engineers will be monitoring during propellant loading and hot-fire tests during the Green Run campaign.)
“We don’t have a debris requirement per se similar to what we had on Shuttle, because at the end of the program we had the NSTS 60559 and NSTS 8303 [requirements] which dictated this is how much you can lose and this is your probability curve you have to meet and you have to go show your engineering that says you won’t lose it unless it’s later in flight or not in critical times,” Alldredge explained.
“We don’t have that same scenario with this vehicle because the crew vehicle is forward of all the insulation; however, we do have critical things below us, the engine bells for both the booster and the main engines and those folks obviously don’t want us raining down foam on their stuff and also we wouldn’t want to lose it because we start impeding our propellant quality which is what we’re there for so we have that delicate balance.”
“We typically saw on External Tank some level of cracking of the TPS during that first cryocycle,” Honeycutt said. “History shows that that’s about as bad as it gets once you hit it with that first cycle. I’m not expecting anything to get worse after that first Wet Dress Rehearsal for the Green Run.”
“There will probably be some thermal protection system fixes that we’ll need to do just because the tank will contract fairly significantly when the very cold cryogenics are loaded in it and then it expands as it warms back up,” Shannon noted. “We have experience with that from the Shuttle Program so none of that work is daunting to us, it’s just understanding what it is and being able to fix it.”
In addition to loading the vehicle with propellant, the WDR will take the Core Stage through its part of a terminal countdown sequence stopping short of igniting the engines. “It is called ‘wet dress,’ the dress is dress rehearsal, it’s the rehearsal for how we’re going to do things on hot-fire day so we will count and we will cut off [the countdown] and we will drain,” Shannon said.
Most eyes will be on the hot-fire
The most attention will be on the hot-fire test, which will repeat the terminal countdown sequence for the stage and proceed through ignition and into the stage firing. “We’ve scrubbed the Green Run schedule very hard and by and large I think you’re sitting on a June-ish time-frame for hot-fire, so getting to the June date will be driven by how many non-conformances we have to deal with in doing the work at Stennis,” Honeycutt said.
NASA and Boeing have considered how much of the planned 500 second long firing would be acceptable if the test ends early. Earlier assessments were that reaching four minutes of run time on the stage would be enough, but that minimum duration is now a little shorter.
“We looked at it from an engineering standpoint and said if we have just over two minutes of run-time on the vehicle that will satisfy all of our engineering requirements to button up and go to the Cape and so we’ll be happy,” Shannon said. If the test were to end early, one of the factors to be weighed is whether the cause was from a problem with the vehicle or the facility; Honeycutt noted that the facility test team at Stennis recently conducted a stress test to compile additional data to help make that judgment should it be necessary.
(Photo Caption: Core Stage-1 is rolled onto the Pegasus barge at MAF on January 8. The reflective foil tape covering the boattail on the aft end of the stage is seen here in the foreground. The RS-25 engines have their own TPS in the nozzles for elements that are not actively cooled, but the engine design incorporates over a thousand tubes that actively cool the nozzle while they are running.)
“All these commodities that we’ve got to have the day of launch, the high-pressure water, the nitrogen, the helium, the oxygen, the hydrogen, all those commodities, we went off and did a stress test on the entire integrated system to make sure that we had ample commodity and capability to handle the hot-fire, because you’re talking about a significant amount of water and nitrogen and helium in order to pull this test off and granted once we have the cryos onboard the vehicle will take care of itself there,” he said. “But Stennis is in good shape.”
“If the vehicle has a problem, we may have to repeat [the hot-fire], we’d have to go fix something and repeat,” Shannon said. “If the facility has a problem where we go do a cut, we wanted to know where we were good to be able to say ‘we’re done’ and so that’s just over the two-minute time-frame.”
With the discussion about how much run time was necessary, one question that came up was why continue firing the stage past minimums, why not just stop there? “We talked about do we want to cutoff at that point and then drain the tank and everybody’s assessment of that was ‘no,'” Shannon noted.
“If things are going well, the facility is going all right it’s the faster way to drain, keep it going and let it cut off on the low-level sensors. You’ll get some additional data on the ullage pressure going back into the tanks, but it added so much risk to try and do a cut at some arbitrary time and then go drain the tank, just let it keep running.”
The engineering data can largely be collected while the stage is firing by following a normal flight profile with the engines typically throttled at 109 percent of their original 1970s rated power level (RPL), but there are other tests planned. The four engines will be gimbaled by the hydraulically-powered thrust vector control (TVC) system while they are firing to gain data in a couple of areas.
“We take a bleed off of the hydrogen exhaust to be able to drive the auxiliary power units for hydraulic pressure; we also take that same bleed coming off the engine to fill the hydrogen tank pressure to keep it up and pressurized,” Shannon explained. “When the hydrogen tank is at a level of about two-thirds down we’re going to really aggressively gimbal all four of the engines and it’s going to put a lot of pressure on the ability to continue to feed those hydraulic units and provide sufficient pressure to the LH2 tank.”
(Photo Caption: A view of the January 8 Core Stage-1 rollout at MAF from a NASA drone as the move team drive was approaching Pegasus with the stage and transportation system.)
The engine gimbaling will also provide data for a frequency response test (FRT). “The FRT stuff is to see how much the tail wags the dog,” Shannon explained. “As the gimbals and the big engines are moving around how much is the forces on the Core Stage going to be.”
A final test during the firing that would come right at the end is still under discussion. If the stage behaves largely as predicted, the engines can be shutdown at the end of a 500-second, full-duration timer or they could test running the stage to depletion by continuing until the low-level cut off sensors were uncovered, which would trigger a shutdown before completely running out of propellant.
“It is being discussed,” Shannon said. “I’m a fan of going to the low-level cutoff sensors which should be on the LOX side if we did all our mixture ratio calculations correctly.”
“We had a couple of instances on the Shuttle where we hit the low-level cut sensors due to issues during [launch]. Typically you’d have a guided cutoff where you hit the velocity and point in the sky where you wanted to be, that should be whatever your mass reserve is above the low-level sensors.”
Refurbishment work schedule uncertainty
Most of the changes to the Green Run schedule are for the refurbishment work that would be performed after the hot-fire test. The stage will be inspected inside and out and the four RS-25 engines will go through standard post-firing drying, inspections, and refurbishment to get them ready for their next firing, which would be the Artemis 1 launch.
“We had about three months of refurb at the end of [the schedule] and that was just a guess on what we might want to do,” Shannon said. “We looked at that and thought as long as it’s safe to take out of the stand and put it on the barge we’re better off doing most of that work at Kennedy where you’re inside the VAB (Vehicle Assembly Building) and don’t have weather constraints to do it, so we cut down the refurb piece quite a bit, but from a test stand point we didn’t cut out anything.”
“We went off and worked with EGS (Exploration Ground Systems) on transferring the refurb work to them, so we got all that planning laid out,” Honeycutt added.
(Photo Caption: The top half of Core Stage-1 at MAF as it rolled by on January 8 headed out to the Pegasus barge for its trip to Stennis. The wiring bundles seen in the foreground clipped onto the surface of the LH2 tank acreage foam will be used to capture sensor data during the modal test that will be performed at the beginning of the Green Run campaign. Below them the checkboard of cover plates on the systems tunnel that runs essentially the length of the stage on the -Z side; the red cover plates are temporary ones; to minimize repair work, they will be used for the Green Run campaign at Stennis and then will be replaced at KSC with foam-covered flight covers for launch.)
“The question for why would you do it at the Cape as opposed to Stennis and the answer is a roof,” Shannon explained. “If you can get inside the VAB and do any kind of foam repair or any kind of other inspection that you might want to do at Stennis it’s a lot nicer to do it in the VAB where it’s not potentially raining or you don’t have lightning or anything else.”
“We have great platforms inside the VAB as well, so we’ll make a list after the hot-fire and sit down and determine which things are better and safer to do at Kennedy Space Center for our team and we’ll carry that work to Kennedy. Those things that we can do at Stennis fairly easily we’ll probably do at Stennis.”
Part of the challenge in figuring out how long refurbishment will take is the uncertainty about what might need work. “I wish I could speak about the refurbishment because we don’t really know,” Shannon said.
“We’ve made some estimates based on what we saw from loadings and detankings of the Space Shuttle External Tank. I think primarily it’s going to be inspections to make sure that in this high-vibration, high-acoustic environment that we did not break anything, so we’ll do a lot of inspections there.”
From the TPS standpoint in addition to the SOFI in prominence on the outside of the propellant tanks, all of the unseen propellant lines inside the engine section are also insulated and will be inspected after hot-fire.
“We’ll have a lot of inspections for the external stuff, because once you get to Kennedy and you get ready to fly obviously you have aero loads that you want to make sure you’re cleared for as well, so we’ve got to make sure the outside meets our requirements and then we’ll do inspections on the inside,” Alldredge said. “If we see anything, then we’ll go back and talk with our design team and our thermal team and say ‘hey we saw this particular situation, can we live with it?’ And we’ll go from there.”
NASA is trying to mitigate some TPS refurbishment by adding a layer of thermal protection just for the hot-fire test. “You may have noticed if you saw the rollout pictures it looks like we chromed the bottom of the rocket but that’s actually a silver, reflective tape that has been placed over the cork insulator on the bottom of the rocket,” Shannon said. “That cork we were estimating would char fairly significantly during the Green Run due to thermal reflection from the flame trench so we put that silver tape on there.”
(Photo Caption: In addition to covering the boattail at the bottom of the stage, any low, aft-facing surfaces on hardware that protrudes or sticks out from the outer mold line also have the extra thermal protection applied for the Stage Green Run hot-fire test. The aft reaction structure (ARS) beams on the +Z side of the stage are highlighted in this composite image showing where the foil is applied. The view on the left was taken above the stage when it was rolled into Building 110 at MAF on New Year’s Day. The view on the right, taken during the rollout on January 8, shows how the foil application covers the aft-facing parts of the ARS beams and LOX downcomer when “looking up.”)
“We showed in testing that if we put the tape on that the cork should absolutely have no problems being used for the flight, we wouldn’t have to do any changes to it so that’s just one example of the things we did to minimize the amount of refurbishment that we would have to do.”
“The heat loads that we’re going to see in the B-2 test stand are much higher than what we’re going to see in flight so that’s what that tape is on there for which is to help absorb and to reflect and keep from damaging any of the underlying TPS,” Alldredge added. So what we have there is you have that on the boattail, but you have it on every aft-facing surface as well because you get radiative energy as well.”
“It’s the boattail, it’s the boattail fairings, it’s that base heatshield, and then it’s any of the aft-facing surfaces so the ARS beams and the cameras,” he noted. The ARS or aft reaction structure beams support the LOX feedlines as they enter the engine section. The faces of the ARS in the aft direction have foil tape, in addition to the aft-facing surfaces of the LOX feedlines themselves.
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