It looks like a March launch is no longer in the cards for Artemis II, NASA’s first crewed trip to the moon’s vicinity since the final Apollo mission over 50 years ago. While preparations were underway at the Kennedy Space Center for a launch as soon as March 6, the space agency says it ran into an issue with the flow of helium to its SLS rocket’s upper stage this weekend and it now has to roll the rocket from the launch pad back to the Vehicle Assembly Building (VAB) to figure out what’s wrong and fix it. A media briefing is planned for sometime this week to discuss the problem and what’s next.

But in a post on X, NASA Administrator Jared Isaacman confirmed the rollback will “take the March launch window out of consideration.” NASA noted on its blog that the current effort “potentially preserves the April launch window, pending the outcome of data findings, repair efforts, and how the schedule comes to fruition in the coming days and weeks.” It’s a four-mile trip back to the VAB that will take hours to carefully transport the massive rocket and the Orion spacecraft. NASA says it’s eyeing February 24 for this trek.

The issue occurred overnight in the early hours of February 21, when NASA says it observed “interrupted flow of helium to the SLS (Space Launch System) rocket’s interim cryogenic propulsion stage.” The space agency explained:

The upper stage uses helium to maintain the proper environmental conditions for the stage’s engine and to pressurize liquid hydrogen and liquid oxygen propellant tanks. The systems worked during NASA’s Artemis II wet dress rehearsals, but teams were not able to properly flow helium during normal operations and reconfigurations following the wet dress rehearsal that concluded Feb. 19. Operators are using a backup method to maintain the environmental conditions for the upper stage engines and the rocket, which remains in a safe configuration.

The Artemis II crew — Commander Reid Wiseman, Pilot Victor Glover, Mission Specialist Christina Koch and Canadian Space Agency astronaut Jeremy Hansen, Mission Specialist — had just entered quarantine a day before the issue arose. NASA says the astronauts have since come out of quarantine.

At the start of this year, NASA announced an accelerated timeline for Artemis II, which was previously set for April 2026 after experiencing delays in 2024. For this 10-day mission, which will be the first crewed flight of the SLS rocket, the Artemis II astronauts will take a trip around the moon in the Orion spacecraft. While it initially targeted early February, the launch was pushed to March due to issues that popped up during the wet dress rehearsal. Now, we’re back to the beginning with a possible April launch, but that’ll depend on the fix being a quick one.