NASA’s Artemis 1 flight vehicle is headed back to the Vehicle Assembly Building (VAB) at the Kennedy Space Center (KSC) after a month at Launch Pad 39B attempting to complete the final test before its first launch.
The Wet Dress Rehearsal (WDR), a countdown demonstration test with the integrated Orion spacecraft and Space Launch System (SLS) rocket for Artemis 1 loaded with propellant, was attempted three times in April, but a hydrogen leak on the Mobile Launcher and unreliable gaseous nitrogen (GN2) service finally pulled the plug on staying at the launch pad.
The service structures for Orion and SLS are located in the VAB, and personnel with Exploration Ground Systems (EGS) and prime launch processing contractor Jacobs will also address an anomaly with a gaseous helium check valve on the SLS second stage while troubleshooting the hydrogen leak on the ground-side umbilical plate that supplies liquid hydrogen (LH2) to the launch vehicle’s Core Stage.
While EGS and Jacobs troubleshoot the vehicle and ground systems issues in the VAB and the commercial nitrogen vendor attempts to complete upgrades necessary to fully fuel the SLS vehicle, the space agency’s Exploration division management will discuss what they want to do the next time the vehicle rolls out to Pad 39B.
EGS, Jacobs will work on the vehicle in the VAB while waiting for multi-week GN2 plant maintenance
First motion of Crawler Transporter-2 (CT-2) carrying the Mobile Launcher and Artemis 1 flight vehicle from Pad 39B to the VAB was scheduled for some time around 5:30 pm Eastern time on April 25, with the journey to High Bay 3 of the assembly building expected to take at least eight hours. After initially setting up to stay at the launch pad to find and fix the hydrogen leak that scrubbed run number three of the Wet Dress Rehearsal on April 14, NASA decided only about a day and a half later on April 16 to roll the vehicle back to the VAB.
Following a closer look at the series of gaseous nitrogen service disruptions that plagued both the second and third WDR attempts, the agency concluded that the current quality of service was not robust enough to support SLS tanking operations and planned upgrades would not be completed until May at the earliest.
“The current equipment had sufficient capacity to be able to support the test as we understood it; however, we didn’t see the robustness we wanted to see with the current equipment,” Tom Whitmeyer, NASA’s deputy associate administrator for common exploration systems development, said in an April 18 media teleconference. “The planned upgrade has been in place for a while, in fact it was delayed a couple of times … because we’ve had a lot of launch activity here at the Cape, so they were looking for the right time to tie it in and make the final connections.”
(Photo Caption: The Air Liquide plant that supplies KSC with gaseous nitrogen as seen during an April 18 Cape Canaveral flyover by NSF. After multiple nitrogen outages delayed Wet Dress Rehearsal operations, NASA decided to roll the Artemis 1 vehicle back to the VAB to wait for upgrades to integrate the 14 ambient air vaporizers seen in two rows in the background. Fully tying in the new vaporizers is expected to take at least two weeks and an additional outage is also planned afterwards, which could take another week and consume most of the month of May.)
“I remember during the Shuttle program we didn’t run into too many problems,” Whitmeyer said, “and so it was a little bit of a surprise to see that we needed to bring in this system to get the robustness that we wanted. ” The commercial vendor, Air Liquide, has two types of systems providing GN2 to KSC from a facility outside the grounds of the site.
“One is an air separation system that runs and provides daily flows,” Artemis 1 Launch Director Charlie Blackwell-Thompson said in the April 18 teleconference. “That’s [for] your daily use on the pipeline.”
“Then there is a launch support system that is a series of vaporizers and pumps that provides that increased capability for when you’re in launch [operations] and some of your higher demand flows, and there’s been a plan to upgrade and bring on some new equipment which adds some ambient air vaporizers. Those are already at the plant, they’re already installed, it’s just a matter of tying them in, it gives them a better capability and so that’s part of the work that will be done.”
Gaseous nitrogen (GN2) is used extensively to purge and inert enclosed volumes of the SLS rocket before, during, and after propellant loading of the vehicle. “Nitrogen is used for umbilical purges as well as it’s used in other parts of the vehicle operations. It’s very important for the work we do,” Whitmeyer said.
Prior to beginning the hazardous propellant loading operations, the purge is switched from air to GN2. During the second WDR attempt conducted on April 4, it took several hours to resume the test when the flow of GN2 was lost after the switchover but prior to tanking.
“When we realized we lost the plant providing the gaseous nitrogen, we [switched] back to air because we have to keep those volumes purged to keep them dry,” NASA EGS Chief Engineer Greg Horvath explained in an April 20 interview with NASASpaceflight. “Once they isolated the problem, [the launch team] went back and went through a switchover of their system.”
“I think the first time it took them a little over an hour to get back up on nitrogen, and then the second time was a little bit quicker, it took about 40, 45 minutes or so. And then we’ve got some thermal conditioning that we’ve got to go check for, so it’s probably on the order of between an hour to two hours once we get back into our GN2 flow to get it all conditioned and ready for cryogenic loading .”
With a maximum launch window of two hours on a given launch day, service disruptions that occurred on April 4 and again prior to tanking in the third attempt on April 14 would have either scrubbed a launch attempt or effectively eliminated most of the workable launch window. But another, more severe GN2 outage occurred late on April 14 while the launch team was draining propellant from the vehicle, complicating post-scrub draining operations.
“It took several hours for them to come back up, much more than it took for the two issues we had prior to cryogenic loading, but we were able to get through with the reduced supply of GN2 they were actually providing through another means,” Horvath said.
(Photo Caption: Members of the Artemis 1 launch team are seen in Firing Room 1 of the Launch Control Center at KSC Launch Complex 39 early on the morning of April 14. At the time, the team was preparing to begin propellant loading during the third Wet Dress Rehearsal attempt; however, operations were again delayed for a few hours by another gaseous nitrogen outage. A third GN2 outage also occurred during detanking at the end of the day.)
It was after that second outage of the day on April 14, which extended for several hours during detanking, that NASA decided to take a closer look at the GN2 supply situation. “We had this GN2 issue at the beginning of tanking, and then maybe a little less known we also had an issue during the drain operations, a very similar failure. And so we’d had two plant issues during the same operation,” Blackwell-Thompson said.
“So we had asked the team to go take a look at that to help us understand our confidence going into Wet Dress run number four, and when we got the data back after they’d had a chance to troubleshoot it and really look at the system, their recommendation was that we tie in this additional equipment [first].”
If the upgrade work goes according to plan, it is expected to take a couple of weeks; however, the upgrade still has to be scheduled around the busy launch schedule at Cape Canaveral Space Force Station (CCSFS) and KSC. The work was only expected to begin after launch of the SpaceX Crew-4 mission to the International Space Station (ISS) from nearby Launch Pad 39A at KSC, which is now scheduled for April 27.
A second outage period for an additional week of maintenance associated with the GN2 plant was also planned sometime in May after the upgrades; between finding a few weeks of time around the launch schedule at the Cape, the additional week worth of maintenance, and the possibility of delays, a robust enough GN2 supply to conduct a full SLS countdown will not be available until June per an internal KSC email on April 25.
NASA decided to roll back to the VAB in the intervening time. “Talking to Charlie and her team [on April 16]we knew we had some other work that we needed to do… and so the combined decision was to bring the vehicle back in the VAB so we can start that work,” Whitmeyer said on April 18. “This also allows an opportunity for the nitrogen supplier to upgrade its facility.”
Due to its size, the SLS Core Stage requires a lot of nitrogen gas to purge the internal compartments that surround its propellant tanks. The nitrogen demand was similar in scale at Stennis Space Center during the Green Run design verification campaign there and prior to the arrival of the Core Stage in early 2020, the high-pressure gas facility at Stennis was “stress tested” at least two times.
The facility was stress tested on its own in October 2018, operating for a 24-hour period to meet the Core Stage’s nitrogen purge requirements. A site-wide stress test was conducted across two days in December 2019 running all the Stennis ground systems necessary to support the many hours of propellant loading and unloading operations.
Cryogenic fueling tests were conducted at KSC with the Mobile Launcher and Pad 39B in the late 2019 timeframe, which required flows of purge gases like nitrogen and helium, but it’s unknown whether a similar stress test was conducted at KSC.