11:15 a.m.
NASA teams have transitioned the interim cryogenic propulsion stage liquid hydrogen tank to replenish mode during the Artemis II countdown. This phase follows the successful topping process and ensures the tank remains at flight-ready levels all the way to launch.
11:09 a.m.
NASA teams have begun the topping phase for the interim cryogenic propulsion stage liquid hydrogen (LH2) tank. This critical step occurs after successful chilldown and vent-and-relief checks, ensuring the tank reaches full capacity with super-cold liquid hydrogen.
Live coverage of tanking operations continues on NASA’s YouTube channel.
10:35 a.m.
The Artemis II launch team began liquid hydrogen (LH2) replenish for the SLS (Space Launch System) rocket core stage.
Replenish is the final step in the fueling process, designed to maintain the correct LH2 levels as the super-cold propellant naturally boils off over time. This continuous, low-rate flow keeps the tanks topped off and thermally stable, ensuring the rocket remains fully fueled and ready for liftoff.
From chilldown to replenish, every phase of fueling is carefully managed to protect hardware and guarantee mission success. With replenish underway, Artemis II is in its final stretch toward launch and humanity’s next giant leap.
10:24 a.m.
The Artemis II launch team initiated liquid hydrogen (LH2) topping for the SLS (Space Launch System) rocket core stage.
Topping is the process of adding small amounts of LH2 to the tanks after fast fill is complete, ensuring they remain at full capacity as the super-cold propellant naturally boils off. This step is critical for maintaining the precise levels needed for launch while keeping the system thermally stable.
Watch continuing live coverage of tanking operations on NASA’s YouTube channel.
9:52 a.m.
The Artemis II launch team transitioned to the fast fill of liquid hydrogen (LH2) for the interim cryogenic propulsion stage, or SLS (Space Launch System) rocket upper stage.
After completing the chilldown phase, this step rapidly loads super-cold LH2 into the SLS upper stage tanks, ensuring the upper stage is fueled and ready to perform its fundamental role of raising the Orion spacecraft into a high Earth orbit ahead of a proximity operations demonstration test and Orion’s translunar injection burn.
Fast fill accelerates the fueling process while maintaining safety, marking another major milestone in the countdown as Artemis II moves closer to liftoff.
9:36 a.m.
The Artemis II launch team has begun the liquid hydrogen chilldown for the interim cryogenic propulsion stage, or SLS (Space Launch System) rocket upper stage.
This process gradually cools the interim cryogenic propulsion stage fuel lines and components to cryogenic temperatures using super-cold liquid hydrogen. The chilldown step is essential to prevent thermal shock and ensure the stage is properly conditioned for full propellant loading. By stabilizing the system at these extreme temperatures, engineers guarantee safe and efficient fueling for the upper stage that will help position Orion into high Earth orbit for its journey toward the Moon.
9:25 a.m.
NASA astronauts Reid Wiseman, Victor Glover, and Christina Koch, along with CSA (Canadian Space Agency) astronaut Jeremy Hansen have officially begun their launch day with a scheduled wake-up call at 9:25 a.m., marking the start of their final preparations for the historic Artemis II mission around the Moon.
9:04 a.m.
The Artemis II launch team transitioned to the fast fill of liquid hydrogen (LH2) into the SLS (Space Launch System) rocket core stage.
After completing the slow fill phase, this step rapidly loads super-cold LH2 into the rocket’s massive tanks, bringing them closer to full capacity. LH2 flows at a much higher rate, reducing overall fueling time while maintaining safety since the system is already thermally conditioned.
Watch live coverage of tanking operations on NASA’s YouTube channel.
8:45 a.m.
During tanking operations, teams transitioned the SLS (Space Launch System) rocket’s core stage liquid oxygen (LOX) system from slow fill to fast fill, rapidly loading super-cold oxidizer into the tank while monitoring for leaks and maintaining proper thermal conditioning.
LOX fast fill safely loads the bulk of the super-cold oxidizer needed for launch, allowing teams to rapidly bring the SLS rocket to flight-ready levels while closely monitoring the vehicle’s health.
8:35 a.m.
The Artemis II launch team initiated the slow fill of liquid hydrogen (LH2) and liquid oxygen (LOX) into the SLS (Space Launch System) rocket core stage.
This phase introduces the super-cold propellants at a controlled rate, allowing the rocket’s plumbing and tanks to gradually adjust to cryogenic temperatures. Slow fill minimizes thermal stress on hardware and ensures a smooth transition before moving to faster fueling stages.
It’s a vital step in the countdown, setting the stage for full tanking operations. Following completion of the slow-fill process for both propellants, teams will transition operations to the fast-fill phase.
Watch continuing live coverage of tanking operations on NASA’s YouTube channel.
7:58 a.m.
The Artemis II launch team is now performing the liquid oxygen main propulsion system chilldown on the SLS (Space Launch System) rocket core stage.
Follow along with live coverage of tanking operations ahead of the Artemis II test flight.
7:44 a.m.
The Artemis II launch team initiated liquid oxygen (LOX) and liquid hydrogen (LH2) transfer line chilldown for the SLS (Space Launch System) rocket core stage.
Chilldown is a critical step in preparing the rocket for safe and efficient fueling, reducing risks and maintaining system integrity. The process gradually cools the rocket’s plumbing and engine systems to cryogenic temperatures using super-cold liquid hydrogen, helping to prevent thermal shock and ensuring the hardware is conditioned for the full flow of propellant during tanking.
Once chilldown is complete, teams will initiate slow fill followed by fast fill tanking operations as they load 700,000 gallons of super-cold liquid oxygen and liquid hydrogen in the SLS core stage.
Below are the as scheduled times for core stage slow and fast fill operations:
- L-9H55M – L-9H25M: Core stage LH2 slow fill start
- L-9H40M – L-9H30M: Core stage LOX slow fill
- L-9H30M – L-6H40M: Core stage LOX fast fill
- L-9H25M – L-8H: Core stage LH2 fast fill
Live coverage of tanking operations is now airing on NASA’s YouTube channel.
7:33 a.m.
Artemis Launch Director Charlie Blackwell-Thompson has given the official “go” for tanking, and NASA teams are ready to start loading propellants into the SLS (Space Launch System) rocket. This essential step kicks off with the chilldown of the core stage liquid oxygen and liquid hydrogen transfer lines, preparing the rocket for its historic mission.
Earlier this morning, engineers at NASA’s Kennedy Space Center in Florida performed the air-to-gaseous nitrogen changeover and cavity inerting, a critical step to ensure crew safety and vehicle integrity. During this phase, atmospheric air inside the rocket’s cavities is replaced with gaseous nitrogen, an inert gas that reduces the risk of combustion and contamination, creating a safe environment for subsequent fueling operations. By displacing oxygen and moisture, engineers maintain the purity and stability of the rocket’s internal systems before cryogenic propellant loading begins.
The launch countdown, which started Monday at 4:44 p.m. EDT, is currently in a built-in hold. This planned pause is a critical checkpoint in the countdown sequence, allowing teams to complete essential tasks and verify system readiness before moving forward.
During this hold, engineers perform final configuration checks, review system health, and ensure all launch criteria are met. It’s also a window for resolving any minor issues without impacting the overall timeline. These holds are standard in complex missions like Artemis II, providing flexibility and confidence as we prepare to send astronauts on a journey around the Moon.
NASA’s launch day coverage begins with live views and audio commentary of tanking operations, as teams load propellant into the SLS rocket, at 7:45 a.m. on NASA’s YouTube channel. Full launch coverage begins at 12:50 p.m. on NASA+, Amazon Prime, and YouTube. Updates during the launch countdown and throughout the mission will be posted here on the Artemis blog.
Below are the countdown milestones as planned for tanking:
- L-10H50M: Launch team decides “go” or “no-go” to begin tanking the rocket
- L-10H40M – L-10H35M: Core stage LOX transfer line chilldown
- L-10H40M – L-9H55M: Core stage LH2 chilldown
- L-10H25M – L-9H40M: Core stage LOX main propulsion system chilldown
- L-9H55M – L-9H25M: Core stage LH2 slow fill start
- L-9H40M – L-9H30M: Core stage LOX slow fill
- L-9H30M – L-6H40M: Core stage LOX fast fill
- L-9H25M – L-8H: Core stage LH2 fast fill
- L-9H05M – L-8H30M: ICPS LH2 chilldown
- L-8H30M – L-7H45M: ICPS LH2 fast fill start
- L-8H – L-7H55M: Core stage LH2 topping
- L-7H55M – terminal count: Core stage LH2 replenish
- L-7H45M – L-7H20M: ICPS LH2 vent and relief test
- L-7H20M – L-7H10M: ICPS LH2 tank topping start
- L-7H05M – terminal count: ICPS LH2 replenish
- L-6H40M – L-6H05M: Core stage LOX topping
- L-6H40M – L-6H30M: ICPS LOX main propulsion system chilldown
- L-6H30M – L-5H45M: ICPS LOX fast fill
- L-6H05M – terminal count: Core stage LOX replenish
- L-5H45M – L-5H30M: ICPS LOX vent and relief test
- L-5H30M – L-5H10M: ICPS LOX topping
- L-5H10M – terminal count: ICPS LOX replenish
- L-5H10M: All stages replenish
- T-6M: GLS go for core stage tank pressurization
- T-5M57S: Core stage LH2 terminate replenish
- T-4M40S: GLS is go for LH2 high flow bleed check
- T-4M: Core stage LOX terminate replenish
- T-3M30S: ICPS LOX terminate replenish
- T-50S: ICPS LH2 terminate replenish
- T-33S: GLS sends “go for automated launch sequencer” command
- T-30S: Core stage flight computer to automated launching sequencer
- T-12S: Hydrogen burn off igniters initiated
- T-10S: GLS sends the command for core stage engine start
- T-6.36S: RS-25 engines startup
- T-0: Booster ignition, umbilical separation, and liftoff
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