Helium flow problems in the SLS rocket’s upper stage have forced NASA to return Artemis 2 to the VAB, eliminating the mission’s March window and pushing the launch to April.
NASA’s SLS rocket and Orion spacecraft at Launch Pad 39B on February 1, 2026. The vehicle will be flown back to the Vehicle Assembly Building after engineers discovered a helium problem in the rocket’s upper stage. Credit: NASA/Sam Lott
In the latest delay for the Artemis 2 mission, NASA announced Saturday that it will move the Space Launch System (SLS) rocket and Orion spacecraft back to the Vehicle Assembly Building (VAB) by Feb. 24, pushing the first crewed lunar mission since Apollo 17 to April at the earliest.
Just a day earlier, NASA had announced that it was set to launch Artemis 2 as early as March 6; The upbeat assessment came after the agency completed a second wet dress rehearsal — a fuel test and simulated launch countdown — on Feb. 19. But on February 21, engineers discovered a blockage in the flow of helium to the rocket’s upper stage. Helium is used to pressurize the stage’s liquid hydrogen and liquid oxygen tanks; Without it, propellant cannot be injected into the engine responsible for sending Orion toward the Moon.
Notably, the helium system performed normally only during wet dress rehearsals. The blockage was later discovered during routine monitoring – meaning the problem escaped a test that was designed for final verification before flight. Engineers are working to determine whether the problem is in the helium delivery lines, a valve in the upper stage, or a filter connecting the ground lines to the rocket. In the meantime, operators are using backup methods to maintain safe conditions for the upper stage and rocket.
The issue echoes a problem encountered during the Artemis 1 mission in 2022, when a malfunctioning helium check valve in a similar type of upper stage forced a rollback to the VAB. However, in that case, the problem was caught during a wet dress rehearsal.
return to base
Regardless of where the current problem originated, the rocket will have to return to the VAB before engineers can fully troubleshoot it. The 525-foot-tall building – one of the largest structures in the world by volume and the only building used to assemble rockets that carry humans to other worlds – provides engineers with crane access and the controlled environment needed to service the vehicle’s upper stage.
To get there, the rocket will be moved down a 4.2-mile road at about 1 mph by NASA’s moving platform, called a crawler. The crawler weighs about 6.65 million pounds and can tow up to 18 million pounds – burning about 165 gallons of diesel per mile.
The pad access platforms installed on February 20 in preparation for the launch first had to be removed – to protect them from predicted high winds and to clear the way for a possible rollback. That work has been completed, clearing the way for the return trip to the VAB on February 24.
Due to trajectory requirements, Artemis 2’s launch window is only open for a few days, approximately every four weeks. The helium leak and related work means the mission will miss the March 6-11 window. The next opportunity will run from April 1-6, which NASA is working on — but if teams can’t solve the problem and get the vehicle ready in time, the mission will be pushed back. The agency plans to hold a media briefing in the coming days.
The Artemis 2 crew – commander Reed Wiseman, pilot Victor Glover, and NASA mission specialist Christina Koch, along with Canadian Space Agency mission specialist Jeremy Hansen – were released from quarantine and returned to Houston for the second time. The crew first entered the standard 14-day pre-launch quarantine on January 23, but were released in early February when the launch slipped from its original February window to March.
