NASA terminated the Artemis II wet dress rehearsal countdown at the T-5:15 minute mark after teams detected a liquid hydrogen leak during the final phase of the test. The issue appeared at the interface between the Space Launch System rocket and the tail service mast umbilical, an area that had already shown elevated hydrogen levels earlier in the countdown. The halt occurred shortly after the mission entered terminal count, when automated systems take control and the rocket transitions to internal power ahead of a simulated engine start. Following the stop, launch controllers began securing the vehicle and preparing to drain propellants from the tanks. The rehearsal is intended to validate systems and procedures ahead of Artemis II, which will be the first crewed mission of NASA’s Artemis lunar programme.
NASA terminates Artemis II countdown at T-5:15 during final launch rehearsal
Because liquid hydrogen is highly flammable, the launch team stopped the rehearsal immediately. The focus then shifted to placing the Space Launch System rocket in a safe condition and beginning the slow process of draining fuel from its tanks.This exercise, known as a wet dress rehearsal, is designed to mirror a real launch as closely as possible. In the final ten minutes, automated systems take control, the rocket switches to internal power, and final checks are run as if the engines are about to ignite. Halting the countdown at T-5:15 does not signal a major failure. It means the issue was caught early, allowing teams to fix it before astronauts are ever on board.
Countdown timeline includes simulated launch window
The countdown clock began at 8:13 p.m. Eastern Standard Time, which corresponds to 6:43 a.m. Indian Standard Time. This marked L-48 hours and 40 minutes ahead of a simulated launch window set to open at 9 p.m. EST on Monday, February 2, or 7:30 a.m. IST on Tuesday, February 3. The rehearsal is expected to continue until about 1 a.m. EST on February 3, which is 11:30 a.m. IST.NASA’s countdown follows a structure built around both “L minus” and “T minus” times. L-minus tracks the time remaining until the liftoff, while T-minus tracks the sequence of events leading up to launch. Teams can pause the clock to manage tasks or align with a target window. During those holds, the T-minus clock stops, while L-minus continues to run.As part of the rehearsal, teams will pause briefly at T-1 minute and 30 seconds, resume the count, then stop again at T-33 seconds. The clock will then be recycled back to T-10 minutes for a second terminal countdown, ending once more at T-33 seconds. The sequence is designed to mirror real launch conditions, including situations where a launch might be delayed or scrubbed.Once the test concludes, propellants will be drained from the rocket and engineers will review the data before setting a formal launch target.
Artemis II crew milestones practised without astronauts present
The Artemis II astronauts were not involved in the wet dress rehearsal, but several crew-related milestones were still rehearsed as part of the countdown flow. Ground teams practised tasks that would normally take place on launch day, including procedures carried out by the Artemis closeout crew. These steps include sealing the Orion crew module and closing the launch abort system hatches before terminal count begins. NASA says running through these actions during the rehearsal helps validate the overall launch timeline.
