CAPE CANAVERAL, FL — The clock is officially ticking for NASA’s return to the Moon. On Saturday, January 31, 2026, mission controllers at Kennedy Space Center began the 49-hour countdown for the Artemis II “wet dress rehearsal,” a final, high-stakes test before four astronauts embark on a historic lunar flyby.
The countdown clock was activated at 8:13 p.m. EST, targeting a simulated “T-0” and tanking operations for Monday, February 2. This critical rehearsal involves loading the Space Launch System (SLS) rocket with over 700,000 gallons of super-cooled propellant to ensure every system is ready for the real deal.
Key Rehearsal Milestones
Below are some of the key events that take place at each milestone after the countdown
begins. All times are approximate for when these milestones are expected to occur.
L-49 hours 15 minutes and counting
- L-49H, 15M: The launch team arrives on their stations and the countdown begins
- L-48H40M: The countdown clock begins
- L-47H30M – L-38H30M: Fill the water tank for the sound suppression system
- L-48H45M – L-39H45M: Liquid Oxygen (LOX)/Liquid Hydrogen (LH2) system
preparations for vehicle loading - L-39H30M – L-38H45M: The core stage is powered up
- L-40H30M – L-39H: The interim cryogenic propulsion stage (ICPS) is powered
up - L-38H45M – L-34H30M: Final preparations of the four RS-25 engines
L-34 hours 30 minutes and counting
- L-33H45M – L-33H10M: The ICPS is powered down
- L-32H30M – L-28H30M: Charge Orion flight batteries to 100%
- L-30H30M – L-23H30M: Charge core stage flight batteries
- L-19H15M – L-17H45M: The ICPS is powered-up for launch
- L-19H30M – L-16H: Orion crew suit regulator leak checks
L-15 hours and counting
- L-14H30M – L-13H: All non-essential personnel leave Launch Complex 39B
- L-12H45M – 11H15M: Ground Launch Sequencer (GLS) activation
- L-13H15M – L-11H05M: Air-to-gaseous nitrogen (GN2) changeover and vehicle
cavity inerting
L-11 hours, 40 minutes and counting
- L-11H35M – L-9H20M: 2-hour 15-minute built in countdown hold begins
- L-11H40M – L-10H30M: Launch team conducts a weather and tanking briefing
- L-10H20M: Launch team decides if they are “go” or “no-go” to begin tanking the
rocket - L-10H10M – L-9H50M: Core stage LOX transfer line chilldown
- L-10H10M – L-9H25M: Core stage LH2 chilldown
- L-10H20M – L-9H: Orion cold soak
L-10 hours and counting - L-9H50M – L-9H10M: Core stage LOX main propulsion system chilldown
- L-9H25M – L-9H: Core stage LH2 slow fill start
- L-9H20M: Resume T-Clock from T-8H10M
- L-9H10M – L-8H55M: Core stage LOX slow fill
- L-9H – L-7H40M: Core stage LH2 fast fill
- L-8H55M – L-6H10M: Core stage LOX fast fill
- L-8H45M – L-8H10M: ICPS LH2 chilldown
- L-8H10M – L-7H25M: ICPS LH2 fast fill start
- L-7H45M – L-6H: ICPS LOX main propulsion system chilldown
- L-7H40M – L-7H30M: Core stage LH2 topping
- L-7H30M – terminal count: Core stage LH2 replenish
- L-7H25M – L-7H05M: ICPS LH2 vent and relief test
- L-7H05M – L-6H55M: ICPS LH2 tank topping start
- L-6H50M – terminal count: ICPS LH2 replenish
- L-6H10M – L-5H40M: Orion communications system activated (RF to mission
control) - L-6H10M – L-5H40M: Core stage LOX topping
L-6 hours and counting
- L-6H – L-5H15M: ICPS LOX fast fill
- L-5H40M – terminal count: Core stage LOX replenish
- L-5H15M – L-5H: ICPS LOX vent and relief test
- L-5H – L-4H40M: ICPS LOX topping
- L-5H40M: Stage pad rescue
- L-5H40M: Closeout crew assemble
- L-4H40M – terminal count: ICPS LOX replenish
- L-4H40M: All stages replenish
- L-4H40M: Start 40-minute built in hold
- L-4H40M-L-4H25M: Closeout crew to white room
- L-4H30M – L-4H20M: Crew Module hatch preps and closure
- L-4H20M – L-3H20M: Counterbalance mechanism hatch sealpress decay
checks - L-3H20M – L-2H40M: Crew Module Hatch service panel install/closeouts
- L-2H40M – L2H20M: Launch Abort System (LAS) Hatch closure for flight
- L-1H10M: Launch Director brief – Flight vehicle/TPS Scan results with CICE
- L-1H45M – L-1H40M: Closeout crew departs Launch Complex 39B
L-40 minutes and holding
- L-40M: Built in 30-minute countdown hold begins
L-25 minutes and holding
- L-25M: Transition team to Orion to Earth communication loop following final NTD
briefing - L-16M: The launch director polls the team to ensure they are “go” for launch
T-10 minutes and counting
- T-10M: Ground Launch Sequencer (GLS) initiates terminal count
- T-8M: Crew Access Arm retract
- T-6M: GLS go for core stage tank pressurization
- T-6M: Orion set to internal power
- T-5M57S: Core stage LH2 terminate replenish
- T-4M: GLS is go for core stage auxiliary power unit (APU) start
- T-4M: Core Stage APU starts
- T-4M: Core stage LOX terminate replenish
- T-3M30S: ICPS LOX terminate replenish
- T-3M10S: GLS is go for purge sequence 4
- T-2M02S: ICPS switches to internal battery power
- T-2M: Booster switches to internal batter power
- T-1M30S: Hold for three minutes to verify core stage certification hold time
- T-1M30S: Core stage switches to internal power
- T-1M20S: ICPS enters terminal countdown mode
- T-50S: ICPS LH2 terminate replenish
- T-33S: GLS sends “go for automated launch sequencer” command
- T-33S: GLS Cutoff/Recycle
Weathering the “Arctic Outbreak”
The rehearsal, originally slated for earlier in the weekend, was pushed to February 2 due to an unusual cold snap in Florida. High winds and near-freezing temperatures forced managers to adjust the timeline to protect the hardware.
What’s Next for the Launch?
If Monday’s rehearsal is successful, NASA will review the data before setting a firm launch date. Because of the weather delay, the earliest possible launch opportunity has shifted to Sunday, February 8, 2026.
