NASA’s first crewed return to the vicinity of the Moon in more than half a century has slipped again, this time from an early February target to a no-earlier-than March launch window, after a hydrogen leak disrupted a critical fueling test. The scrubbed countdown underscores how unforgiving the Space Launch System and its cryogenic propellants can be, even after years of design work and one successful uncrewed lunar flight. It also raises fresh questions about how tightly NASA can run the schedule for a mission that will carry four astronauts around the Moon and back.
The agency is now racing to understand what went wrong in the test, how to fix it without introducing new risks, and what that means for the broader Artemis program that is supposed to lead to sustained lunar exploration. The delay is a reminder that in human spaceflight, technical margins and safety culture matter more than calendar promises, even when political and public expectations are high.
From flagship mission to moving target
Artemis II is designed as a 10 day crewed flight that will send astronauts on a loop around the Moon and return them to Earth, a crucial shakedown of the Orion spacecraft and the Space Launch System before any attempt to land on the lunar surface. NASA describes the mission as the first time the agency will send a crew aboard the integrated Artemis II stack, using the same core architecture that eventually is meant to support a sustained presence in lunar orbit and on the ground. It is the successor to the uncrewed Artemis I flight that proved the basic performance of the rocket and capsule but did not have to meet the same safety thresholds required for human passengers.
The mission has already lived several lives on paper. In earlier planning, it was known as Exploration Mission 2 and was tied to a single launch of a Space Launch System Block 1B configuration, part of a broader History of shifting concepts for how to use the SLS and Orion hardware. That evolution reflects both technical realities and budget constraints, and it helps explain why the current crewed flyby has become such a focal point: it is the bridge between a demonstration program and a long promised era of regular deep space operations.
The hydrogen leak that halted the countdown
The latest schedule slip traces directly to a problem that has haunted NASA’s big rockets for decades, the behavior of liquid hydrogen in complex plumbing at cryogenic temperatures. During a recent wet dress rehearsal, when teams fully fuel the Space Launch System and run through a simulated countdown, sensors detected that hydrogen leaking from the tail service mast umbilical interface into the core stage exceeded allowable limits. NASA reported that the Artemis II SLS fueling sequence had to be halted once that threshold was crossed, a conservative move that reflects how seriously the agency treats any sign of hydrogen escaping where it should not.
Hydrogen is attractive as a rocket fuel because it delivers high performance, but it is also notoriously difficult to contain, with tiny molecules that can slip through seals and joints and create flammability hazards. Earlier in the Artemis program, hydrogen leaks kept the first SLS vehicle on the pad for extended periods, and managers acknowledged that those issues had to be resolved before a crew could fly. Reporting on the latest test noted that Hydrogen leaks had already been a factor in 2022, and that history loomed over the decision to stop the flow again once the latest anomaly appeared. In the most recent rehearsal, NASA said Teams stopped the flow of liquid hydrogen through the tail service mast umbilical interface into the core stage after leak checks showed values outside the acceptable range, a step described in detail in coverage of the Teams response.
How the launch date slid from February to March
Before the leak, NASA had been working toward an early February launch, with internal targets clustered around the first week of the month. The agency had already signaled some flexibility, indicating that the mission to the Moon would start Feb. 8 or later after it delayed a previous wet dress rehearsal, a shift described when NASA delays to the test were announced. That earlier adjustment already hinted at how tightly the countdown was coupled to the success of the fueling run, since any slip in the rehearsal would cascade into the launch window.
As the fueling anomaly unfolded, it became clear that the schedule would need more than a few days of padding. Coverage of the mission noted that NASA had been preparing for a Feb. 6 target for the 10 day crewed flight, describing how NASA is preparing to send the crew around the Moon and back. Once the hydrogen leak appeared, however, the agency shifted to a no-earlier-than March posture, with reports explaining that the launch was delayed till March 2026 after a hydrogen leak in key tests, a change captured in detail in coverage of Artemis II Pushed. That new timeline gives engineers room to inspect hardware, refine procedures and, if necessary, roll the vehicle back to the Vehicle Assembly Building without the pressure of an imminent launch window.
What the scrubbed test reveals about SLS and risk
The wet dress rehearsal that exposed the leak is not a mere formality, it is the closest thing to a full launch without lighting the engines, and it is designed to surface exactly the kind of issues that could threaten a crew. NASA has emphasized that during wet dress rehearsal all systems will perform as they would on launch day, a point underscored in a briefing that described why the agency delayed the event in Jan to ensure readiness. By catching the hydrogen leak in this context, the program is effectively trading schedule certainty for a deeper understanding of how the Space Launch System behaves under real propellant loads.
That trade is not new for NASA, but it is particularly visible in a program that has already faced criticism for cost and complexity. The SLS core stage, upper stage and associated ground systems rely on a web of valves, seals and umbilicals that must all function within tight tolerances, and the hydrogen leak at the tail service mast umbilical interface highlights how any weak point can ripple through the entire operation. The agency’s own mission overview notes that Artemis II will rely on the integrated SLS and Orion stack to send astronauts on a trajectory around the Moon and back, a plan laid out in detail on the official mission page. The latest setback suggests that even after the uncrewed Artemis I flight, the rocket’s ground interfaces and fueling choreography still demand careful tuning before they can be trusted with human lives.
Implications for the crew and the wider Artemis timeline
For the four astronauts assigned to Artemis II, the delay is both a frustration and a validation of NASA’s safety culture. The crew, highlighted in mission previews that describe how Artemis II will send them around the Moon and back, must now extend their training and simulations to match the new March target. That means more time in Orion mockups, more emergency drills and more coordination with flight controllers, all while their families and support teams adjust to another shift in the calendar. For astronauts who have already waited years for a chance to fly beyond low Earth orbit, the extra weeks are a small price to pay for confidence that the vehicle is ready.
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