NASA Releases Artemis II Moon Mission Launch Countdown
Before NASA sends its astronauts Reid Wiseman, Victor Glover, Christina Koch and CSA (Canadian Space Agency) astronaut Jeremy Hansen on their Artemis II mission around the Moon, the launch team from NASA’s Kennedy Space Center in Florida and teams across the country will begin the countdown approximately two days before liftoff.
A launch countdown contains the times “L Minus” and “T Minus”. The “L minus” indicates the takeoff distance in hours and minutes. “T minus” time is a sequence of events built into the launch countdown. Breaks in the countdown, or “waits,” are built in to allow the launch team to target a specific launch window and provide a deadline for certain tasks and procedures without impacting the overall schedule. During scheduled holds of the countdown process, the countdown clock is intentionally stopped and time T also stops. However, L- time continues to advance.
Below are some of the key events that take place at each stage after the countdown begins.
All times are approximate for when these steps occur.
L-49 hours 50 minutes and counting
- L-49H50M – Launch team arrives at stations
- L-49H40M – The countdown begins
- L-49H40M – L-42H30M: Liquid oxygen (LOX)/liquid hydrogen (LH2) system
preparations for loading the vehicle - L-45H30M – L-44H: Orion spacecraft powered on
- L-42H20M – L-41H: Central stage under voltage
- L-42H10M – L-40H30M: Intermediate cryogenic propulsion stage (ICPS) energized
- L-39H45M – L-35H30M: final preparations for the four RS-25 engines
L-35 hours and counting
- L-34H45M – L-34H10M: ICPS is powered off
- L-33H30M – L-29H30M: Charge Orion flight batteries to 100%
- L-31H30M – L-24H30M: Charge the main stage flight batteries
- L-20H15M – L-18H45M: ICPS powered on for launch
L-4 p.m. and counting
- L-3:30M – L-2P: All non-essential personnel leave Launch Complex 39B
- L-14H15M – L-12H05M: Air-nitrogen gas (GN2) change and rocket
cavity inerting - L-13H15M – L-11H45M: activation of the ground launch sequencer (GLS)
L-1 p.m. and counting
- L-12H35M – L-9H50M: the built-in countdown of 2 hours and 45 minutes begins
- L-10H50M – Launch team decides “Go” or “No-Go” to begin tanking
- L-10H50M – L-9H35M: Orion cold soak
- L-10H40M – L-10H35M: Central stage LOX transfer line cooling
- L-10H40M – L-9H55M: LH2 main stage cooling
- L-10H25M – L-9H40M: cooling of the main stage LOX main propulsion system
L-10 hours and counting
- L-9H55M – L-9H25M: Slow start of LH2 main stage filling
- L-9H50M – Take back the T-Clock from the T-8H10M
- L-9H40M – L-9H30M: slow filling LOX central stage
- L-9H30M – L-6H40M: LOX rapid filling of the central stage
- L-9H25M – L-8H: LH2 central stage, rapid filling
- L-9H05M – L-8H30M: ICPS LH2 cooling
- L-8H30M – L-7H45M: ICPS LH2 rapid filling start
- L-8H – L-7H55M: Center stage LH2 trim
- L-7H55M – number of terminals: LH2 main stage resupply
- L-7H45M – L-7H20M: ICPS LH2 ventilation and discharge test
- L-7H20M – L-7H10M: start of filling of the ICPS LH2 tank
- L-7H05M – number of terminals: ICPS LH2 replenishment
- L-6H40M – L-6H10M: Orion communications system activated (radio frequency to mission control)
- L-6H40M – L-6H05M: Center stage LOX trim
- L-6H40M – L-6H30M: ICPS LOX main propulsion system cooling
- L-6H30M – L-5H45M: ICPS LOX rapid filling
- L-6H10M – Stage rescue
- L-6H10M: – The closing team assembles
- L-6H05M – number of terminals: LOX reconstruction of the main stage
L-6 hours and counting
- L-6H – Flight crew weather note
- L-5H45M – L-5H30M: ICPS LOX ventilation and discharge test
- L-5H30M – L-5H10M: ICPS LOX trim
- L-5H10M – number of terminals: ICPS LOX replenishment
- L-5H10M – Replenishment of all stages
- L-5H10M – Startup 1 hour 10 minutes built-in hold
- L-5H10M – L-4H55M: Clean room closing team
- L-4H40M – L-4H10M: Deployment of the flight crew on the platform
- L-4H: Flight crew boards Orion
- L-3H40M – L-3H10M: preparation and closing of the crew module hatches
- L-3H10M – L-2H45M: Deterioration of the counterweight mechanism hatch seal
checks - L-2H20M – L-1H40M: Installation/closing of crew module hatch service panel
- L-1H40M – L1H30M: launch abort system (LAS) hatches closed for flight
- L-1H10M – Launch Director’s Brief – Results of Rocket and Thermal Protection System Analysis with the Imaging Console
- L-50M – L-40M: closing crew leaves Launch Complex 39B
- L-50M – Final briefing from NASA test director takes place
L-40 minutes and maintenance
- L-40M – Built-in 30 minute countdown begins
L-25 minutes and now
- L-25M – Team transitioning to Orion-Earth communications loop after final NTD briefing
- L-17M – Launch Director interviews team to ensure they are ready for launch
- L-15M – Flight crew visors down
- L-14M – Flight Crew Short Purge Check
T-10 minutes and counting
- T-10M – GLS launches terminal count
- T-8M – Crew Access Arm Retraction
- T-6M – GLS opts for pressurization of main stage tanks
- T-6M – Orion ascension pyros are armed
- T-6M – Orion set to internal power
- T-5M57S – LH2 main stage final replenishment
- T-5M20S – LAS capability is available
- T-5M20S – NTD informs Commander that LAS capability is available
- T-4M40S – GLS opts for LH2 high flow purge control
- T-4M30S – Armed Flight Termination System
- T-4M – GLS is ready for main stage auxiliary power unit (APU) start-up
- T-4M – APU Core Stage Starts
- T-4M – End of Main Stage LOX Resupply
- T-3M30S – ICPS LOX completes replenishment
- T-3M10S – GLS opts for purge sequence 4
- T-2M02S – ICPS switches to internal battery power
- T-2M – Booster switches to internal battery power
- T-1M30S – Main stage switches to internal power
- T-1M20S – ICPS enters terminal countdown mode
- T-50S – ICPS LH2 completes replenishment
- T-33S – GLS sends “go to automated launch sequencer” command
- T-30S – Core Stage Flight Computer to Automated Launch Sequencer
- T-12S – Hydrogen Combustion Igniters Launched
- T-10S – GLS sends main stage motor start command
- T-6.36S – Starting RS-25 engines
T-0
- Booster ignition, umbilical separation and takeoff
During the terminal countdown, teams have a few options to maintain the countdown if necessary.
- The launch team can wait 6 minutes for the duration of the launch window, minus the 6 minutes needed to launch, without having to recycle up to 10 minutes.
- If teams need to stop the clock between T-6 minutes and T-1 minute 30 seconds, they can wait up to 3 minutes and restart the clock to throw. If they require more than 3 minutes of wait time, the countdown will return to T-10.
- If the clock stops after T-1 minute and 30 seconds, but before the automated launch sequencer takes over, teams may return to T-10 to try again, provided there is an adequate launch window remaining.
- After transfer to the automated launch sequencer, any issues that could stop the countdown would result in the launch attempt being concluded for that day.
The launch of the Artemis II Moon rocket will launch the agency’s first crewed mission under the Artemis program, testing the systems that will return astronauts to the Moon for a lasting presence and paving the way for human exploration of Mars.
To learn more about the Artemis program, visit:
https://www.nasa.gov/artemis
