NASA’s Artemis II mission encountered another hydrogen-related setback during a “confidence test” on Feb. 12, 2026, when a ground support equipment issue restricted the flow of liquid hydrogen into the Space Launch System (SLS) core stage. The glitch, which NASA said it suspected was tied to a filter in ground plumbing, came after technicians replaced seals damaged during an earlier wet dress rehearsal that was cut short by a hydrogen leak. Together, these events illustrate how small cryogenic plumbing issues can ripple through a program that NASA says is using these tests to reduce risk as it evaluates a potential March launch opportunity, even as the agency continues to characterize the recent issues as part of normal prelaunch work.
NASA has emphasized that the recent hydrogen issues are being treated as data-gathering opportunities rather than threats to the mission. Each test adds another layer of understanding about how the rocket, ground systems, and procedures behave under real conditions, and the agency is threading that information into its planning for a potential March launch opportunity. The sequence of leak detection, seal replacement, and filter troubleshooting shows how Artemis II is progressing through a methodical test-fix-test rhythm that must converge before NASA can commit to putting a crew on top of the SLS.
Wet Dress Rehearsal Halted by Hydrogen Leak
The trouble started during tanking operations in early February, when engineers loading the SLS core stage with super-cooled liquid hydrogen detected concentrations that exceeded allowable limits at the tail service mast umbilical interface. Teams paused hydrogen flow to troubleshoot while liquid oxygen continued loading into the core stage, applying procedures that NASA had refined after similar issues during Artemis I testing. Those real-time fixes, which included stopping flow and warming the interface to try to reseat the seals, were not enough to bring leak rates within acceptable bounds, even after controllers cycled valves and adjusted temperatures to see whether the hardware would respond.
The wet dress rehearsal countdown was ultimately terminated at T-5:15 because of the persistent liquid hydrogen leak at the tail service mast umbilical. Elevated hydrogen concentrations had appeared earlier in the count, signaling that the seal problem was not a momentary spike but a sustained failure that would have violated launch commit criteria. Teams moved to safe and drain the vehicle, and a separate post-test summary confirmed that full tanking had been achieved before the auto-stop, while also flagging additional anomalies including Orion hatch pressurization behavior that will need further review. Engineers closely monitored how cold weather at Kennedy Space Center affected the systems throughout the operation, adding another variable to an already complex diagnostic picture as they parsed sensor data, vent rates, and structural temperatures.
Seal Replacements and the Confidence Test
After draining the rocket, technicians zeroed in on the tail service mast umbilical area where higher-than-allowable hydrogen concentrations had been recorded. The repair involved detaching interface plates to access and replace two seals located around separate fueling lines, a task that required careful work to avoid introducing new contamination or damage. The fact that these repairs could be performed at the pad was significant; rolling the SLS stack back to the Vehicle Assembly Building would have added weeks to an already tight schedule and disrupted other operations on the range. While hardware teams conducted the physical swap, analysts reviewed leak trends from the earlier test to confirm that the identified seals were consistent with the measured hydrogen signatures.
Verification of the seal work came on February 12 in the form of a confidence test. Operators partially filled the SLS core stage liquid hydrogen tank specifically to assess the newly replaced components under cryogenic conditions, focusing their instrumentation on the repaired umbilical area. During the exercise, a ground support equipment issue reduced the flow of liquid hydrogen, and NASA suspected a filter in the ground plumbing as the cause of the restriction. Because the confidence test was intentionally limited in scope, controllers were able to halt operations without stressing the vehicle, and teams planned a purge and inspection of the suspect filter to confirm the diagnosis while they pored over data to verify that the new seals themselves were behaving as expected.
Why Hydrogen Keeps Causing Problems
Liquid hydrogen is the lightest and coldest propellant NASA uses, stored at roughly minus 423 degrees Fahrenheit, which makes it both powerful and unforgiving. Its molecules are small enough to slip through gaps that would easily contain other fluids, and the extreme cold causes metal components to contract in ways that can unseat seals, embrittle materials, or stress joints that appear tight at room temperature. The SLS holds a massive quantity of liquid hydrogen in its core stage, and NASA has previously highlighted the challenges of managing such cryogenic capacity across the rocket and its support systems. Moving that volume from storage spheres through ground lines, across umbilical interfaces, and into the vehicle creates dozens of potential leak points, each sensitive to temperature swings, pressure changes, and mechanical wear from repeated test cycles.
Much of the current coverage treats these hydrogen issues as unexpected setbacks, but the pattern is actually well established across multiple Artemis campaigns. Artemis I faced repeated wet dress rehearsal scrubs tied to hydrogen leaks before its successful launch, leading NASA to develop targeted troubleshooting procedures that are now baked into the playbook for Artemis II. The real question is not whether hydrogen will leak during ground testing but whether the engineering response can resolve each leak quickly enough to hold a launch window, a point underscored in NASA’s own discussion of using the latest fuel test results to evaluate a March opportunity for liftoff. That distinction reframes the February problems as anticipated friction in a known-difficult process rather than evidence of a deeper design flaw in the SLS or its ground infrastructure.
Filter Swap and the Path to a Second Rehearsal
Following the confidence test, NASA moved quickly to address the suspected filter issue in the ground support equipment. Teams replaced the filter that had appeared to restrict liquid hydrogen flow during the February 12 exercise, then planned additional checks to confirm that the updated configuration restored nominal rates. With both the seals and the filter now swapped, engineers set February 19 as the target date for a second wet dress rehearsal tanking day, giving them a narrow but workable window to demonstrate stable loading operations before range schedules and orbital mechanics begin to squeeze March launch options. The upcoming test is expected to repeat the full sequence of core stage fueling, including close monitoring of the previously problematic umbilical and the refurbished ground plumbing.
The second rehearsal will also include a terminal-count recycle, meaning teams plan to run the countdown deep into the final minutes, drain the tanks, and then refill them to practice scrub turnaround procedures that might be needed on an actual launch day. This addition signals that NASA wants to validate not just the hardware fixes but also the flight control team’s ability to manage complex timelines, respond to evolving data, and reconfigure the vehicle quickly after a late hold. If the seals remain tight, the filter performs as intended, and the recycle demonstration unfolds smoothly, Artemis II will be better positioned to move from rehearsal to reality, using the hydrogen troubleshooting as a final proving ground before astronauts fly the mission around the Moon.
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*This article was researched with the help of AI, with human editors creating the final content.
