Artemis II sequence of events

L-49 hours 15 minutes and counting

• L-49H15M00S: The launch team arrives on their stations and the countdown begins.
• L-48H40M00S: The countdown clock begins.
• L-47H30M00S – L-38H30M00S: Fill the water tank for the sound suppression system.
• L-48H45M00S – L-39H45M00S: Liquid Oxygen (LOX)/Liquid Hydrogen (LH2) system preparations for vehicle loading.
• L-39H30M00S – L-38H45M00S: The core stage is powered up.
• L-40H30M00S – L-39H00M00S: The interim cryogenic propulsion stage (ICPS) is powered up.
• L-38H45M00S – L-34H30M00S: Final preparations of the four RS-25 engines.

L-34 hours 30 minutes and counting

• L-33H45M00S – L-33H10M00S: The ICPS is powered down.
• L-32H30M00S – L-28H30M00S: Charge Orion flight batteries to 100%.
• L-30H30M00S – L-23H30M00S: Charge core stage flight batteries.
• L-19H15M00S – L-17H45M00S: The ICPS is powered-up for launch.
• L-19H30M00S – L-16H00M00S: Orion crew suit regulator leak checks.

L-15 hours and counting

• L-14H30M00S – L-13H00M00S: All non-essential personnel leave Launch Complex 39B.
• L-12H45M00S – L-11H15M00S: Ground Launch Sequencer (GLS) activation.
• L-13H15M00S – L-11H05M00S: Air-to-gaseous nitrogen (GN2) changeover and vehicle cavity inerting.

L-11 hours 40 minutes and counting

• L-11H35M00S – L-9H20M00S: 2-hour 15-minute built in countdown Hold begins.
• L-11H40M00S – L-10H30M00S: Launch team conducts a weather and tanking briefing.
• L-10H20M00S: Launch team decides if they are “go” or “no-go” to begin tanking the rocket.
• L-10H20M00S – L-9H00M00S: Orion cold soak.
• L-10H10M00S – L-9H50M00S: Core stage LOX transfer line chilldown.
• L-10H10M00S – L-9H25M00S: Core stage LH2 chilldown.

L-10 hours and counting

• L-9H50M00S – L-9H10M00S: Core stage LOX main propulsion system chilldown.
• L-9H25M00S – L-9H00M00S: Core stage LH2 slow fill start.
• L-9H20M00S: Resume T-Clock from T-8H10M00S.
• L-9H10M00S – L-8H55M00S: Core stage LOX slow fill.
• L-9H00M00S – L-7H40M00S: Core stage LH2 fast fill.
• L-8H55M00S – L-6H10M00S: Core stage LOX fast fill.
• L-8H45M00S – L-8H10M00S: ICPS LH2 chilldown.
• L-8H10M00S – L-7H25M00S: ICPS LH2 fast fill start.
• L-7H45M00S – L-6H00M00S: ICPS LOX main propulsion system chilldown.
• L-7H40M00S – L-7H30M00S: Core stage LH2 topping.
• L-7H30M00S: Terminal count: Core stage LH2 replenish.
• L-7H25M00S – L-7H05M00S: ICPS LH2 vent and relief test.
• L-7H05M00S – L-6H55M00S: ICPS LH2 tank topping start.
• L-6H50M00S: Terminal count: ICPS LH2 replenish.
• L-6H10M00S – L-5H40M00S: Orion communications system activated (RF to mission control)
• L-6H10M00S – L-5H40M00S: Core stage LOX topping.

L-6 hours and counting

• L-6H00M00S – L-5H15M00S: ICPS LOX fast fill.
• L-5H40M00S: Terminal count: Core stage LOX replenish.
• L-5H15M00S – L-5H00M00S: ICPS LOX vent and relief test.
• L-5H00M00S – L-4H40M00S: ICPS LOX topping.
• L-5H40M00S: Stage pad rescue.
• L-5H40M00S: Closeout crew assemble.
• L-4H40M00S: Terminal count: ICPS LOX replenish.
• L-4H40M00S: All stages replenish.
• L-4H40M00S: Start 40-minute built in Hold.
• L-4H40M00S – L-4H25M00S: Closeout crew to white room.
• L-4H30M00S – L-4H20M00S: Crew Module hatch preps and closure.
• L-4H20M00S – L-3H20M00S: Counterbalance mechanism hatch sealpress decay checks.
• L-3H20M00S – L-2H40M00S: Crew Module Hatch service panel install/closeouts.
• L-2H40M00S – L2H20M00S: Launch Abort System (LAS) Hatch closure for flight.
• L-1H10M00S: Launch Director brief – Flight vehicle/TPS Scan results with CICE.
• L-1H45M00S – L-1H40M00S: Closeout crew departs Launch Complex 39B.

L-40 minutes and holding

• L-40M00S: Built in 30-minute countdown Hold begins.

L-25 minutes and holding

• L-25M00S: Transition team to Orion to Earth communication loop following final NTD briefing.
• L-16M00S: The launch director polls the team to ensure they are “go” for launch.

T-10 minutes and counting

• T-10M00S: Ground Launch Sequencer (GLS) initiates terminal count.
• T-8M00S: Crew Access Arm retract.
• T-6M00S: GLS go for core stage tank pressurization.
• T-6M00S: Orion set to internal power.
• T-5M57S: Core stage LH2 terminate replenish.
• T-4M00S: GLS is go for core stage auxiliary power unit (APU) start.
• T-4M00S: Core Stage APU starts.
• T-4M00S: 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-2M00S: Booster switches to internal batter power.
• T-1M30S: Hold for three minutes to verify core stage certification.
• 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.