NASA teams have transitioned all cryogenic tanks on the SLS (Space Launch System) rocket to replenish mode during the Artemis II wet dress rehearsal. This includes both liquid hydrogen and liquid oxygen tanks for the core stage and the interim cryogenic propulsion stage. Engineers continue to monitor liquid hydrogen concentration levels in the tail service mast umbilical, where a leak was previously detected. Levels are currently stable.
Teams enter replenish mode because cryogenic propellants naturally warm and evaporate over time, even in insulated tanks. Replenish counteracts this by continuously adding small amounts of liquid hydrogen and liquid oxygen to maintain proper levels and pressure. This ensures the rocket remains fully fueled and stable as the countdown progresses toward terminal count.
Following all stages replenish, teams will perform final system checks and verify valve and sensor performance before transitioning to the terminal countdown sequence, which includes simulated launch operations and final readiness verifications. The countdown clock has also entered a 40-minute hold, a new addition from Artemis I.
With all stages in replenish, the Artemis II wet dress rehearsal is now in its final fueling configuration, bringing operations closer to terminal count. NASA’s closeout crew is preparing to head to Launch Complex 39B to ensure safety and readiness during the critical fueling operations.
A 24/7 live stream of the rocket at the pad remains online, as well as a separate feed to capture wet dress activities.
