The first integrated Orion spacecraft and Space Launch System (SLS) rocket for NASA’s Artemis 1 lunar test flight is returning to Launch Pad 39B at the Kennedy Space Center (KSC) in Florida in hopes of finishing the last major test before its inaugural launch planned for later this year. Repairs and maintenance were performed in May, both in the Vehicle Assembly Building (VAB) at KSC and outside the space center at the Air Liquide nitrogen plant.
Attempts in April to complete the Wet Dress Rehearsal (WDR) countdown demonstration test were delayed by multiple outages of gaseous nitrogen from the offsite plant and then scrubbed by issues with fueling connections from the Mobile Launcher to the two SLS liquid propellant stages. Exploration Ground Systems (EGS) and prime launch processing contractor Jacobs are looking to have the flight and ground systems ready for the next WDR attempt about two weeks after the vehicle arrives back at Pad 39B.
Back to the pad after resolving issues
First motion of Crawler Transporter-2 out of the VAB carrying Mobile Launcher-1 with the Artemis 1 vehicle is scheduled for just after midnight Eastern time on June 6, beginning the trip to Pad 39B. The approximately four-mile distance from High Bay 3 to the elevated pad surface is expected to be completed in 8-12 hours, when the Mobile Launcher is lowered to a “hard down” position on the pad pedestals.
The first lunar-capable Orion/SLS vehicle is going back to the pad six weeks after leaving to address issues uncovered during the three Wet Dress Rehearsal attempts in April. Problems were found with flight and ground systems at the pad and with gaseous nitrogen (GN2) supply systems at Air Liquide’s plant.
Without the ability to safely conduct propellant loading and unloading operations until GN2 plant maintenance and upgrade work was completed and verified, the vehicle was rolled back to the VAB late on April 25 to troubleshoot and resolve those issues in parallel. Now it will make another round trip to the pad to complete the WDR countdown demonstration test.
During the pad campaign in April, a check valve in the gaseous helium system for the Interim Cryogenic Propulsion Stage (ICPS) began malfunctioning after maintenance was carried out on a related pad system following the second WDR attempt on April 4. NASA decided to work around the partially stuck valve and conduct a WDR test that largely excluded the SLS second stage from propellant and terminal countdown operations, but that attempt on April 14 was scrubbed when hydrogen was detected leaking from a propellant line on a Core Stage umbilical.
(Photo Caption: The Artemis 1 vehicle is seen in VAB High Bay 3 on June 2. During the month-plus “pit stop” in the VAB, EGS and Jacobs workers removed the external wiring runs on the outside of the vehicle that were used to record vibrations or small movements of the vehicle during the previous rollout and rollback, one of a few “get ahead” tasks completed in parallel with repairs and modifications from issues found during the Wet Dress Rehearsal test attempts in April.)
As it turned out, work on another umbilical issue pushed the second rollout to the pad from its original late May forecast to early June. During the limited propellant operations performed with the ICPS, outside air was detected inside an enclosed area on one of the umbilical connections from the Mobile Launcher to the upper stage.
“We modified the ICPS umbilical boots, which is the area enclosed in the umbilical quick disconnect between the umbilical arm and the vehicle, adding additional leak detectors on the liquid hydrogen side of that in order to gain some visibility into any potential leaks that would occur during tanking operations,” Cliff Lanham, senior vehicle operations manager for NASA’s EGS Program, said during a May 27 media teleconference.
“We saw a little bit of air being sucked into the [hazardous gas detection system] from that boot,” Dr. John Blevins, NASA’s Chief Engineer for the SLS Program, explained during the teleconference. “We purge that [area] with warm helium with those [quick disconnects] around that boot to prevent icing as well as other situations.”
“Any contaminant, even if it’s air, shows up in our haz gas system as potential hydrogen, and we’ve got a four-percent [concentration] limit on that. We’re adding some measurements [that] we’ll take that [the launch team] can use [to] differentiate between that air and hydrogen so that we don’t falsely shutdown the tanking of the system due to [a] false alarm.”
“The ‘boot,’ as we call it, is a cover that slides up to contact a flat surface on the vehicle,” Dr. Blevins later elaborated in an email. “It doesn’t provide [a] hermetic seal since we provide [purge] gas in the boot, and that positive pressure is generally enough to prevent air from being sucked into the boot.”
“[During] the last wet dress, when we wetted the sump with cryos, we may have pulled some air in. The boot has been readjusted to ensure surface to surface contact with the flat machined surface seat it has on the vehicle, and the band clamp put in the proper place to prevent ingestion.”
“And, since a residual concern exists, and this place is hard to access on the pad, we placed additional sampling tubes to adjudicate if air does get pulled in to ensure we aren’t triggering an alarm on contaminants unless it is truly a hydrogen leak, which is what the purge in the boot is supposed to mitigate,” he added in the email. “There were no modifications to the boot, only to the tubes to provide additional sampling.”
Earlier in May, the EGS and Jacobs Integrated Operations team addressed the ICPS helium check valve and Core Stage hydrogen umbilical leak issues.
“The check valve was just fine,” Blevins said. “We did ingest a small piece of debris that held the check valve open, that’s why it didn’t pass the reverse flow check [at the pad in April].”
A broken rubber quick disconnect seal was the source of the debris, and Blevins said that engineers are continuing to investigate root cause. “We do have a fault tree; we’re working through that fault tree. There’s several suspect items,” he said.
“All of those are under mitigation, if you will, or will be under mitigation. We want to look really hard at that and not jump to conclusions on that particular one with the helium fill system.”
“I feel very confident in the system that we have today because we X-ray-ed it; we did scans to [verify] that it’s in the design configuration and it indeed is,” Blevins added. Bolts on a flange in the Core Stage liquid hydrogen tail service mast umbilical were also retightened after they were found during post-rollback inspections not to be fully torqued, but hydrogen leaks are notoriously difficult detect at ambient temperatures, so that fix will ultimately be tested during the next tanking attempt.
Meanwhile, KSC and Air Liquide carried out a long-duration, end-to-end GN2 supply test to Pad 39B to verify repairs and upgrades to the plant in mid-to-late May. “They take liquid nitrogen, and there’s different ways you can gasify the commodity,” Tom Whitmeyer, NASA’s deputy associate administrator for common exploration systems development, said.
“You can [use] steam generation. It looks like a little distiller coil; it heats up that liquid and turns it into a gas. The second thing you can do is you can use air exchangers; and air exchangers are literally what it sounds like, big cooling towers that are out there that actually heats up that liquid nitrogen and turns it into a gas.”
“They’ve added these air exchangers in addition to the steam generators that we had before, and so this is really a belts and suspender type of thing,” Whitmeyer added. “This added capacity of the air exchangers and the ability to switch back and forth really has added some incredible capacity and we’re happy to have it.”
“We asked for a long-duration test, and that was provided by the service provider,” Blevins added. “Every part of the profile [during the test] exceeded what we would do both in duration and volume of nitrogen demand with simulated resistance at the pad or dampers.”
“It is a very critical commodity, and that’s of course why we rolled back. I’m confident, but I’m also cautious because I need this commodity. [We] worked real hard to exonerate hardware if we can’t provide the purge, so I’m ready to go based on that one test.”
(Photo Caption: The Artemis 1 vehicle on the pad in April. In the right image, Jacobs technicians in Self-Contained Atmospheric Protective Ensemble (SCAPE) suits pose on the Pad 39B surface during SLS Booster hydrazine serving activities. From left to right: Molly Smith, Mark K Smith, Ryan McHenry, and David Goetz.)
During the April 14th WDR attempt, the second GN2 supply crash was more serious because the SLS Core Stage was still partially loaded with liquid hydrogen and liquid oxygen. Because propellant was still moving through the lines between the vehicle, the Mobile Launcher, and the launch pad, a backup supply of nitrogen gas provided by rechargers at KSC’s Converter Compressor Facility (CCF) was used to safely allow propellant draining operations to continue.
Wet Dress Rehearsal last major pre-launch test planned
With the repairs and upgrades in place, launch teams at Pad 39B and in the Launch Control Center adjacent to the VAB will take about two weeks to prepare Orion, SLS, the Mobile Launcher, and the pad for the “launch day” of the next Wet Dress Rehearsal attempt, which is currently forecast for June 19. “We have built in two weather days [of schedule margin] that could move that date around slightly,” Lanham said on May 27.
“It is Florida in June, so thunderstorms are expected, and we will also be working any range constraints that may come up.” Cape Canaveral Space Force Station (CCSFS) and the Eastern Test Range are busy with frequent SpaceX and other commercial launches, and the WDR is a hazardous operation that must be coordinated with launch operations at KSC and CCSFS.
With the ICPS helium system restored to full functionality, the next Wet Dress Rehearsal attempt is planned to be a full test, nearly identical to a launch countdown until the final seconds. The WDR was planned as a full countdown test of Orion, SLS, and ground systems to demonstrate that the hardware and the software are ready to fire the SLS engines and Boosters to finally launch Artemis 1.
During the two weeks from rollout to loading propellant on the two SLS stages, teams will connect the vehicle and Mobile Launcher systems to the electrical, data, fluid, and propellant transmission lines at Pad 39B. As was done in late March prior to the first WDR attempt, the launch team will once again power up Orion and SLS and verify that those connections are functioning.
Following pad verifications, the last major operation before starting the countdown is servicing the power units for the hydraulic systems in the two Solid Rocket Boosters. Those Shuttle heritage Booster hydraulic power units will be loaded with their hydrazine fuel and then the launch team should be in a position to start the two-day countdown, which is currently forecast to be late in the afternoon on June 17.
Lead image credits: NASA/Glenn Benson.