L-12H35M – L-9H50M: 2-hour 45-minute built in countdown hold begins
L-10H50M – Launch team decides “go” or “no-go” to begin tanking
L-10H50M – L-9H35M: Orion cold soak
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-10 hours and counting
L-9H55M – L-9H25M: Core stage LH2 slow fill start
L-9H50M – Resume T-Clock from T-8H10M
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-6H10M: Orion communications system activated (radio frequency to mission control)
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-6H10M – Stage pad rescue
L-6H10M: – Closeout crew assemble
L-6H05M – terminal count: Core stage LOX replenish
L-6 hours and counting
L-6H – Flight crew weather brief
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
L-5H10M – Start 1-hour 10-minute built in hold
L-5H10M – L-4H55M: Closeout crew to white room
L-4H40M – L-4H10M: Flight crew deployment to pad
L-4H: Flight crew board Orion
L-3H40M – L-3H10M: Crew module hatch preps and closure
L-3H10M – L-2H45M: Counterbalance mechanism hatch sealpress decay
checks
L-2H20M – L-1H40M: Crew module hatch service panel install/closeouts
L-1H40M – L1H30M: Launch abort system (LAS) hatch closure for flight
L-1H10M – Launch director brief – rocket & thermal protection system scan results with the imagery console
L-50M – L-40M: Closeout crew departs Launch Complex 39B
L-50M – Final NASA test director briefing is held
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-17M – Launch director polls team to ensure they are “go” for launch
L-15M – Flight crew visors down
L-14M – Flight crew short purge verification
T-10 minutes and counting
T-10M – GLS initiates terminal count
T-8M – Crew Access Arm retract
T-6M – GLS go for core stage tank pressurization
T-6M – Orion ascent pyros are armed
T-6M – Orion set to internal power
T-5M57S – Core stage LH2 terminate replenish
T-5M20S – LAS capability is available
T-5M20S – NTD lets commander knows LAS capability is available
T-4M40S – GLS go for LH2 high flow bleed check
T-4M30S – Flight termination system armed
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 go for purge sequence 4
T-2M02S – ICPS switches to internal battery power
T-2M – Booster switches to internal batter power
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-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