Here’s what to expect in the hours leading up to Artemis I launch off Florida’s Space Coast

Artemis I set to launch Monday, Aug. 29

Crews are targeting as early as 9 p.m. Tuesday to start the rollout of the Space Launch Systems rocket with the Orion spacecraft on top.

KENNEDY SPACE CENTER, Fla. – NASA is preparing to send its Space Launch System rocket as part of its Artemis I mission from the Kennedy Space Center next Monday.

Artemis I — the first launch in this mission — will be an uncrewed flight to orbit the moon with three manikins on board, including one named “Commander Moonikin Campos.”

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Monday’s launch will test the spacecraft systems, including the heat shield, which can not be properly tested on Earth. The Artemis program is the long-awaited NASA program to take Americans back to the moon and beyond, possibly to Mars.

NASA is preparing to send its Space Launch System rocket as part of its Artemis I mission from the Kennedy Space Center next Monday.

If successful, the next mission — Artemis II — will take two astronauts to the moon’s orbit in two years. NASA said Artemis III will see the first woman land on the moon as early as 2025.

The Space Launch System rocket with an Orion spacecraft on top for NASA’s Artemis I mission stands at 322 feet tall and with two heavy rocket boosters, it weighs in at 18 million pounds.

Here is what will take place leading up to launch time on Monday, Aug. 29, at 8:33 a.m.

46 hours, 40 minutes and counting

  • The launch team arrives on their stations and the countdown begins
  • Fill the water tank for the sound suppression system
  • Liquid Oxygen (LO2)/Liquid Hydrogen (LH2) System preparations for vehicle loading
  • The Orion spacecraft is powered up if not already powered at Call to Stations (CTS)
  • The interim cryogenic propulsion stage (ICPS) is powered up
  • The core stage is powered up
  • Final preparations of the four RS-25 engines

32 hours and counting

  • Core stage composite overwrapped pressure vessel (COPV) pressurization to flight pressure
  • Charge Orion flight batteries to 100%
  • Charge core stage flight batteries
  • The ICPS is powered up for launch

15 hours and counting

  • All non-essential personnel leave Launch Complex 39B
  • Ground Launch Sequencer (GLS) activation
  • Air-to-gaseous nitrogen (GN2) changeover for vehicle cavity inerting

9 hours, 40 minutes and counting

  • Built-in countdown hold begins
  • Launch team conducts a weather and tanking briefing
  • Launch team decides if they are “go” or “no-go” to begin tanking the rocket
  • Core Stage LO2 transfer line chilldown

8 hours and counting

  • Core stage LO2 main propulsion system (MPS) chilldown
  • Core stage LO2 slow fill
  • Core Stage LO2 fast fill
  • Core Stage LH2 chilldown
  • Core Stage LH2 slow fill start
  • Core Stage LH2 fast fill
  • Core Stage LH2 topping

5 hours and counting

  • Core Stage LH2 replenish
  • ICPS LH2 ground support equipment (GSE) and tank chilldown
  • ICPS LH2 fast fill start
  • Orion communications system activated (RF to Mission Control)
  • Core stage LO2 topping
  • Core Stage LO2 replenish
  • ICPS L02 MPS chilldown
  • ICPS L02 fast fill
  • ICPS LH2 validation and leak test
  • ICPS LH2 tank topping start

3 hours and counting

  • ICPS/Space Launch System (SLS) telemetry data verified with Mission Control and SLS Engineering Support Center
  • ICPS LO2 validation and leak test
  • ICPS LH2 replenish
  • ICPS LO2 topping
  • ICPS LO2 replenish

50 minutes and counting

  • Final NASA Test Director briefing is held

40 minutes and holding

  • Built-in 30-minute countdown hold begins

15 minutes and holding

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

10 minutes and counting

  • Ground Launch Sequencer (GLS) initiates terminal count
  • Orion ascent pyros are armed
  • Orion set to internal power
  • Core Stage LH2 terminate replenish
  • Core Stage auxiliary power unit starts
  • Core stage L02 terminate replenish
  • ICPS LO2 terminate replenish
  • ICPS switches to internal battery power
  • Core stage switches to internal power
  • ICPS enters terminal countdown mode
  • ICPS LH2 terminate replenish
  • GLS sends “Go for automated launch sequencer” command
  • Core stage flight computer to automated launching sequencer
  • Hydrogen burn off igniters initiated
  • GLS sends the command for core stage engine start
  • RS-25 engines startup


  • Booster ignition, umbilical separation, and liftoff

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About the Author:

Brenda Argueta is a digital journalist who joined in March 2021. She graduated from UCF and returned to Central Florida after working in Colorado.