ARTEMIS LAUNCH COVERAGE: See the Rocket Live on the Launch Pad at Kennedy Space Center

Artemis 1 launch countdown begins about two days before liftoff at KSC

WATCH THE ROCKET LIVE ON THE LAUNCH PAD AT KENNEDY SPACE CENTER: The much anticipated Artemis 1 moon mission blastoff is set for Monday from Kennedy Space Center Launch Pad 39B, with a two-hour launch window that will open at 8:33 a.m. local time.

BREVARD COUNTY • KENNEDY SPACE CENTER, FLORIDA (NASA) – Before the Artemis I mission launches on its way around the Moon, the launch team at Kennedy Space Center and supporting teams across the country will begin the launch countdown about two days before liftoff.

The much anticipated Artemis 1 moon mission blastoff is set for Monday from Kennedy Space Center Launch Pad 39B, with a two-hour launch window that will open at 8:33 a.m. local time.

Teams have and incorporated lessons learned from the wet dress rehearsal testing and have refined the launch timeline accordingly.

The launch countdown contains “L Minus” and “T Minus” times. “L minus” indicates how far away we are from liftoff in hours and minutes. “T minus” time is a sequence of events that are built into the launch countdown.

Pauses in the countdown, or “holds,” are built into the countdown to allow the launch team to target a precise launch window and to provide a cushion of time for certain tasks and procedures without impacting the overall schedule. During planned holds in the countdown process, the countdown clock is intentionally stopped and the T- time also stops. The L- time, however, continues to advance.

Below are some of the key events that take place at each milestone after the countdown begins.

L-46 hours 40 minutes and counting

■ The launch team arrives on their stations and the countdown begins (L-46, 40 minutes hours)
■ Fill the water tank for the sound suppression system (L-46H – L-41H)
■ Liquid Oxygen (LO2)/Liquid Hydrogen (LH2) System Preparations for Vehicle Loading (L-46H – L-37H)
■ The Orion spacecraft is powered up if not already powered at Call to Stations (CTS) (L-42H – L-41H30M)
■ The interim cryogenic propulsion stage (ICPS) is Powered-up (L-38H30M – L-35H30M)
■ The core stage is powered up (L-34H – L-33H20M))
■ Final preparations of the four RS-25 engines (L-36H20M – L-31H)

L-32 hours and counting

■ Core stage composite overwrapped pressure vessel (COPV) Pressurization to Flight Pressure (L-31M – L-22H)
■ Charge Orion Flight Batteries to 100% (L-30H – L-26H)
■ Charge core stage Flight Batteries (L-27H – L-21H)
■ The ICPS is Powered-up for launch (L-18H30M – L-15H30M)

L-15 hours and counting

■ All non-essential personnel leave Launch Complex 39B (L-12H – L-10H)
■ Ground Launch Sequencer (GLS) Activation (L-11H15M – 9H15M)
■ Air-to-gaseous nitrogen (GN2) Changeover for vehicle cavity inerting (L-10H45M – Launch)

L-9 hours, 40 minutes and counting

■ Built in countdown hold begins (L-9H40M – L-7H10M)
■ Launch team conducts a weather and tanking briefing (L-9H40M – L-8H50M)
■ Launch team decides if they are “go” or “no-go” to begin tanking the rocket (L-8H40M)
■ Core Stage LO2 transfer line chilldown (L-8H15M – L-8H)

L-8 hours and counting

■ Core stage LO2 main propulsion system (MPS) chilldown (L-8H – L-7H20M)
■ Core stage LO2 slow fill (L-7H20M – L-7H5M)
■ Core Stage LO2 fast fill (L-7H5M – L-4H15M)
■ Core Stage LH2 chilldown (L-7H15M – L-7H5M)
■ Core Stage LH2 slow fill start (L-7H5M – L-6H15M)
■ Core Stage LH2 fast fill (L-6H15M – L-5H5M)
■ Core Stage LH2 topping (L-5H5M – L-5H)

L-5 hours and counting

■ Core Stage LH2 replenish (L-5H – Launch)
■ ICPS LH2 ground support equipment (GSE) and tank chilldown (L-4H45M – L-4H30M)
■ ICPS LH2 fast fill start (L-4H30M – L-3H30M)
■ Orion communications system activated (RF to Mission Control) (L-4H20M – L-3H45M)
■ Core stage LO2 topping (L-4H15M– L-3H55M)
■ Core Stage LO2 replenish (L-3H55M – Launch)
■ ICPS L02 MPS chilldown (L-3H55M– L-3H45M)
■ ICPS L02 fast fill (L-3H45M– L-2H55M)
■ ICPS LH2 validation and leak test (L-3H30M – L-3H15M)
■ ICPS LH2 tank topping start (L-3H15M – L-2H55M)

L-3 hours and counting

■ ICPS/Space Launch System (SLS) telemetry data verified with Mission Control and SLS Engineering Support Center (L-2H55M – L-2H45M)
■ ICPS LO2 validation and leak test (L-2H55M – L-2H30M)
■ ICPS LH2 replenish (L-2H50M – Launch)
■ ICPS LO2 topping (L-2H30M – L-2H10M)
■ ICPS LO2 replenish (L-2H10M – Launch)

L-50 minutes and counting

■ Final NASA Test Director briefing is held (L-50M)

L-40 minutes and holding

■ Built in 30-minute countdown hold begins (L-40M)

L-15 minutes and holding

■ The launch director polls the team to ensure they are “go” for launch

T-10 minutes and counting

■ Ground Launch Sequencer (GLS) initiates terminal count (T-10M)
■ Orion ascent pyros are armed (T-6M)
■ Orion set to internal power (T-6M)
■ Core Stage LH2 terminate replenish (T-5M57S)
■ Core Stage auxiliary power unit starts (T-4M)
■ Core stage L02 terminate replenish (T-4M)
■ ICPS LO2 terminate replenish (T-3M30S)
■ ICPS switches to internal battery power (T-1M56S)
■ Core stage switches to internal power (T-1M30S)
■ ICPS enters terminal countdown mode (T-1M20S)
■ ICPS LH2 terminate replenish (T-50S)
■ GLS sends “Go for automated launch sequencer” command (T-33S)
■ Core stage flight computer to automated launching sequencer (T-30S)
■ Hydrogen burn off igniters initiated (T-12S)
■ GLS sends the command for core stage engine start (T-10S)
■ RS-25 engines startup (T-6.36S)

T-0

■ Booster ignition, umbilical separation, and liftoff

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