NASA’s Artemis 1 flight vehicle remains in the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) in Florida while work to investigate and fix problems found in April at the launch pad continues. A series of issues were discovered during three attempts to perform the Wet Dress Rehearsal (WDR) while the Orion spacecraft and Space Launch System (SLS) rocket were out at Launch Pad 39B.
While the Exploration Ground Systems (EGS) program and prime launch processing contractor Jacobs are troubleshooting issues with connections from the Mobile Launcher to the vehicle in the VAB, they are also working with gaseous nitrogen (GN2) contractor Air Liquide to verify that the purge gas supply can meet the flow rate and duration requirements to support an SLS launch attempt. The GN2 purge supply necessary to allow the vehicle to be loaded with propellant was lost on both tanking attempts in April and a 32-hour long test at the high SLS flow rates was planned to begin on May 16 to demonstrate the effectiveness of repairs and upgrades at the Air Liquide plant.
Tentative plans to roll back out to the pad for the next WDR attempt late in May will depend on how much longer the rework and retesting take.
Engineers troubleshooting SLS second stage issues while GN2 plant tests repairs
Crawler Transporter 2 returned the Orion/SLS vehicle and Mobile Launcher-1 to High Bay 3 of the VAB early on the morning of April 26. Rollback of the vehicle from Pad 39B to the VAB was always planned for Artemis 1 before launch; however, it had been hoped only one pre-launch rollback would be necessary. Now an additional rollback will be necessary after fully completing the Wet Dress Rehearsal countdown demonstration test.
The vehicle and Mobile Launcher were rolled back to the VAB to work their issues in parallel with Air Liquide’s repairs and upgrades, which are now required before the SLS rocket can be completed fueled. The VAB serves as the primary service structure for SLS launch operations, and so rolling back also offered the opportunity to troubleshoot other issues found at the pad in March and April.
Troubleshooting on an issue with the umbilical for the SLS Interim Cryogenic Propulsion Stage (ICPS) was continuing and could factor into extending the stay in the VAB deeper into May. Air intrusion was detected into the purge line on the ICPS umbilical (ICPSU) while the vehicle was at the pad.
“On the ICPS purge boot, the teams are still meeting as to exactly what is going on with that particular item,” Cliff Lanham, senior vehicle operations manager for NASA’s EGS Program, said in a May 12 interview with NASASpaceflight. “We are anticipating some design [modifications].”
The purge boot is a part on the aft plate of the ICPSU, which has a forward and an aft plate connection from the Mobile Launcher to the stage. “We’ll go implement the final outcome of the engineering boards and the review boards in terms of exactly what we’re going to do we’re waiting for now and then we’re hoping to pick that work up early next week (week of May 16).”
A check valve in the gaseous helium system on the ICPS had also stopped functioning correctly between the second attempt on April 4 and the third on April 14. The ICPS serves as an in-space second stage for SLS and the helium system is used for multiple functions on the stage on the ground and in-flight, including purging lines and tanks and actuating Main Propulsion System (MPS) valves.
The issue with the ICPS helium check valve turned out to be a symptom of a problem elsewhere in the ground to vehicle helium connection. Following some maintenance on the ground side helium systems at the launch pad in between the second and third WDR attempts, the check valve would no longer close.
The check valve is only accessible when the vehicle is in the VAB and when workers were able to inspect it a piece of rubber not associated with the valve was found stuck there, preventing the check valve from operating correctly. “They found particulate in the check valve; that was what was holding the check valve open,” Lanham said.
“The failure analysis is still ongoing as to what exactly happened. The leading candidate for the source of the contamination is an O-ring on the flight-side quick disconnect and again the team is off and running that down.”
Parts of the rubber seal that was part of the quick disconnect were found downstream in a couple of places, including the check valve. “There was [also] some particulate [found] in the manifold, but all those parts have either been replaced or cleaned at this point,” Lanham noted.
Troubleshooting on that issue is now focused on why the seal failed and how to prevent future failures. “The failure mode of that seal is what is being looked at,” Lanham said.
“We’re hoping to have that out-briefed tomorrow (May 13), so we know the path forward as far as getting back into the final installation of the system, which is mostly installed but we’ll be doing the final torquing of the interfaces once we get the go-ahead.”
In addition to the issues encountered with the ICPS second stage, a hydrogen leak on a tail service mast umbilical (TSMU) for the Core Stage was discovered on the third WDR attempt, resulting in the scrub of that attempt on April 14. The leak was detected inside a “purge can” that enclosed the main hydrogen fluid lines that run into and out of the Core Stage.
An eight-inch diameter fill and drain line provides the main pathway for LH2 to flow into and out of the stage and a four-inch diameter bleed line provides an exit path for liquid hydrogen that helps chill down Main Propulsion System (MPS) and RS-25 engine lines inside the Core Stage engine section.
(Photo Caption: The American flag is seen on the ICPS second stage of the Artemis 1 SLS vehicle while out at Pad 39B on April 21. Issues with connections from ICPS Umbilical on the Mobile Launcher (to the right of the stage) are being reviewed by engineering boards to determine corrective actions. A helium check valve on the stage was contaminated with parts of a rubber O-ring that came apart upstream of the valve and prevented the valve from fully closing. Engineers are also troubleshooting outside air that is leaking into one of the connections from the umbilical to the ICPS.)
After the two-piece, clamshell purge can was disconnected and removed back inside the VAB, the bolts on a flange for the fill and drain line were found not as tightly torqued as expected. “That’s why as far as a potential cause, this is certainly a potential cause,” Lanham said.
“You’re dealing with hydrogen, [so] if you have any kind of leak path, it’s going to find it. [And] they did find some backing off [of the torques on the bolts].”
The bolted flange is around a debris plate, with gaskets on either side. “We think we’ve done what we can do as far as retorquing the flange bolts, and then they do a 30-hour retorque after that just to see if there’s been any relaxation if you will,” Lanham said.
“They went through that on a couple different cycles trying to get to the point where they didn’t see any more of that. Basically, they would go back in [after 30 hours] and see if they could turn the bolts further.”
Future plans are to verify the torque on the bolts more frequently, but Lanham noted “we won’t know if we fixed the problem until we get out there,” when the team repeats the LH2 propellant loading sequence next time out at the pad. In addition to retorquing the flange bolts on similar connections on the liquid oxygen tail service mast and the Core Stage Inter-Tank Umbilical, a May 13 NASA blog post also noted the relocation of filters on both tail service mast umbilicals.
“As a precaution, teams also moved the location of a heavy cantilevered filter on the tail service mast umbilical, which filters out any contaminants in the gaseous helium — a purge gas — that travels through the drain assist purge line. Engineers did not identify any leaks at its previous location, but relocating the filter will ensure it does not contribute to future leaks,” the blog post said.
The tail service masts are one of the few areas that can be serviced at the pad, so it’s possible that the bolts could have been retightened out at Pad 39B for another Wet Dress Rehearsal attempt instead of rolling back to the VAB first. Initial plans following the scrub on April 14 were to do just that, stay at the pad and troubleshoot the hydrogen leak; however, the gaseous nitrogen purge supply outages that occurred on April 4 and April 14 called into question the ability to run hours of testing with cryogenic propellants to find and/or fix the leak.
A continuous flow of gaseous nitrogen is required to keep the areas of the SLS vehicle inerted before, during, and after hazardous propellant operations, and the repairs and upgrades at the Air Liquide plant weren’t expected to be completed for a few weeks. Due to the busy launch schedule at Cape Canaveral Space Force Station (CCSFS) and KSC, the maintenance work at the GN2 plant just outside the KSC gates didn’t start until the end of April.
At the time of the May 12 interview, Lanham said that the repair and upgrade work was complete, and a multi-day series of verification tests were underway. “With the Air Liquide plant right now they’re actually into their portion of the testing,” he said. “We’re hoping they can wrap that up in the next day or so.”
Following the repairs and upgrades, plans were for Air Liquide to first perform high flow verification tests at the plant and then out to launch pads at CCSFS and KSC. Assuming those tests were completed successfully, an SLS stress test would follow.
The 32-hour “demand and endurance” test for SLS will flow GN2 “end to end,” from the off-site plant all the way to the 39B pad surface, requiring the area to be cleared. “Our technical management team has worked with Air Liquide and our facility management director here to develop test procedures that will allow us to exercise the system in a way that will basically stress it more than we would expect during our WDR and launch campaign,” Lanham said during a May 5 media teleconference.
“They’ve added margin to ensure the flow rates can be met. The test will actually run for 32 hours and that’s about a 10 percent margin over what we would expect to need during the actual launch campaign.”
“We’ll basically put dampers out at the interface to the Mobile Launcher and be able to adjust and regulate to ensure we’re getting the back pressures that the Mobile Launcher and vehicle would put on the system, again in an effort to make sure we’re stressing the system to meet our needs,” he added.
(Photo Caption: Ground test instrumentation can be seen fastened to the outside of the Orion Launch Abort System during the first March 17 rollout from the VAB to Pad 39B. Some rainwater leaked through temporary seals around the rectangular opening on a LAS fillet panel above its hatch (seen with circular window) but the intrusion was minor, and no damage was observed inside.)
During the May 12 interview Lanham noted, “we’re getting into our pre-test briefing tomorrow [May 13] with the full anticipation of starting our testing on Monday (May 16); it’s a 32-hour test.”
Although the GN2 plant repairs could be validated during the week of May 16, there is more uncertainty about when the vehicle and Mobile Launcher issues will be resolved. Sources have reported a range of possible rollout dates during the week of May 23, but EGS and Jacobs are also looking for additional work they could do if engineering discussions and reviews about the ICPS and ICPS umbilical issues run longer.
There was some anticipation that the VAB platforms extended around the vehicle would begin to be retracted this week, but for now, it’s been decided to leave them in place in case other work is added during this current stay in the VAB. “We decided today (May 12) we’ll wait until next week before we contemplate any platform retractions, because again our whole goal will be to do whatever additional work we can do in the time-frame needed to do any changes to the ICPSU,” Lanham said.
In early May, the tentative plan had been to roll back out to Pad 39B towards the end of May for another WDR attempt in early to mid-June. If the WDR was completed satisfactorily then, it could be possible to have the vehicle ready to fly during Artemis 1 lunar launch opportunities in or after August.
Fitting other work into the VAB schedule
EGS and Jacobs have already completed other tasks in parallel with the main issues found during the WDR attempts in April, but instead of comprehensive pre-launch preparations this extra rollback has been called a “pit stop,” and the other work is a mixture of secondary issues found out at the pad and some planned for pre-launch tasks.
One of the tasks that the Integrated Operations team in the VAB completed in parallel with troubleshooting the hydrogen leak and check valve issues was removing test instrumentation on the outer mold line of the vehicle and parts of the Mobile Launcher as a part of the Dynamic Rollout Test (DRT). As planned, two sets of data were collected during the rollout in mid-March and the rollback in late April.
“From an instrumentation standpoint, we’re fully expecting to wrap up removing all the ground instrumentation from the vehicle and the Mobile Launcher this week, we’re nearly done [with] that work,” Lanham said during the May 12 interview. “So we’re anticipating wrapping that up this week.”
The return to the VAB also allowed a couple of other issues noted at the pad to be addressed. One was water intrusion around some of the ground test instrumentation deployed on Orion’s Launch Abort System (LAS) fairing for the rollout tests.
(Photo Caption: Red tape can be seen on the visible Core Stage engine blankets in this April 1 image. The blankets have an outer plastic covering to keep water out, but the red tape was used to hold down the plastic covering in high winds outside.)
“We definitely try to environmentally protect as much as possible but while we were out there for WDR we had some significant rain events that drove some water intrusion,” Lanham said. The LAS has two sets of aerodynamic fairings, a four-panel, ogive-shaped part that covers the Orion Crew Module (CM), and two fillet panels that encapsulate the abort motor tower above it.
Some water got into the ground access doors on the fillet panels during heavy rain while the vehicle was on the pad. “We pulled off the GSE (Ground Support Equipment) panels and did some inspections to ensure we didn’t have any kind of water damage, which we did not,” Lanham said. “We’ve opened up the LAS hatch and we’re doing some additional inspections around the CM thrusters which did not show any indications of water issues.”
Now that the rollout test data is collected and the test instrumentation is removed, the flight access doors could be installed for launch and the seams around the doors could be more thoroughly sealed with a room temperature vulcanized (RTV). “The [flight] plates get bolted in and then there’s RTV around the perimeter to close it out, multiple layers of RTV,” Lanham noted.
“Now the flight plates are up, they get RTV and all in all that work is behind us.”
Another area that got some rework was the engine-mounted heat shield (EMHS) blankets on the SLS Core Stage. The Core Stage spent over a year outdoors at Stennis Space Center for its Green Run campaign, but it was surrounded and partially shielded by the B-2 Test Stand structure there.
Out at Pad 39B, without any service structure around the vehicle, the blankets saw a lot more sea breeze winds off the nearby Atlantic Ocean. The flight blankets primarily provide a thermal barrier to protect the powerheads of the four RS-25 engines from the heat generated by the engines and two Solid Rocket Boosters (SRB) during launch, but they also have a thin, plastic outer layer to keep water off of the blanket material.
Some of the plastic ended up getting buffeted in the wind at the pad. “The wind was pretty intense out of the east blowing across there and there was extra material, so it flapped a lot and then we did get some tears,” Lanham said. While out at the pad, Lanham said the extra material was taped down.
“They did a good job, we didn’t experience any more issues but when we got back to the VAB what we did was take that tape off and they repaired the weather coverings and so next time we roll out you won’t see the red tape,” he said. In addition to the flight closeouts on the Orion LAS fillet panels, other areas could be closed out with the rollout test instrumentation removed.
“We’ve done a lot of sealant work, it’s part of the environmental systems tunnel on the Boosters,” Lanham explained. “We’ve done some of that closeout work on the Boosters with that. On Orion, we’re installing the SM (Service Module) oxidizer panel, again for flight.”
With the possibility that modifications to the ICPS purge boot may add some time in the VAB before rolling out again, the team is looking for other pre-flight work they might do. “At this point, we’re considering other work,” Lanham said. “We’re trying to do as much as we can as time allots.”
“In anticipation of additional work coming out of the boot mods, we’re looking at going into the CM and doing additional work inside the capsule as we work the other areas.”
(Lead image credit: NASA)