How Artemis II Will Return Astronauts to the Moon

NASA is preparing for the launch of Artemis II, the first mission to send humans to the moon since Apollo 17 in 1972. With launch now mere hours away, NASA and the astronauts are moving into final preparations for flight. 

The official countdown began about forty-nine hours prior to liftoff. With launch at time of writing slated for 6:24PM EDT on April 1st, countdown began at around 5:30PM EDT on Monday, March 30th. 

Countdown To Launch

The countdown phase brings the rocket from neutral on the launchpad all the way to the moment before liftoff over the course of about two days. Most of the main activity begins about ten hours prior to launch. 

• At T-10 hours, teams will begin loading propellant into the SLS rocket. Over the next several hours, over 700,000 gallons of cryogenic liquid hydrogen and liquid oxygen will be loaded into the rocket to power Artemis II to the moon. 
• Four hours and forty minutes before liftoff, the four astronauts will depart for the launch pad. They will then ascend the launch tower, don their gloves and helmets, and enter the Orion spacecraft for flight. Final closeout checks will complete and the hatch will be sealed for flight about one hour and twenty minutes before liftoff. The next time it opens, astronauts Kristina Koch, Victor Glover, Reid Wiseman, and Jeremy Hansen will have just returned from the Moon.
• Forty minutes before launch, the countdown will enter a planned hold for thirty minutes. The hold allows time to conduct final checks, and perform the famous GO/NO-GO poll, when Artemis II will officially be declared “GO” for flight. 
• The countdown will resume at T-10 minutes. The crew access arm will retract three minutes later, clearing the way for SLS to launch to the moon. 
• Over the next few minutes, the rocket and spacecraft will begin spinning up dozens of systems and transitioning to internal power in preparation for launch. 
• Twelve seconds before launch, the hydrogen burn off igniters will ignite, showering the base of the rocket in sparks to prevent buildup of hydrogen gas.
• Six seconds before launch, the four core-stage RS-25 engines will ignite. They spend the next few seconds coming up to full power in preparation for…

LAUNCH.

At the moment of liftoff, the two solid rocket boosters, the most powerful rocket motors ever flown, roar to life. The countless hoses and cables tethering SLS to the pad spring free as the rocket leaps skyward. 

• Nine seconds into flight, the SLS rocket will clear the tower and begin to rotate to the correct angle to begin flying out over the ocean and towards orbit. It will clear the sound barrier just about one minute into flight. 
• Two minutes and eight seconds into flight, the two titanic solid rocket boosters will burn out and detach. The four core stage engines will continue powering Artemis II towards a parking orbit. 
• Eight minutes and six seconds into flight, the core stage will have burned all its fuel and shut down. Twelve seconds later, it detaches from the Interim Cryogenic Propulsion Stage, or ICPS, the stage that will power Orion the rest of the way towards the Moon. The ICPS will extend the nozzle of its rocket engine, a trick to help increase performance in the vacuum of space. 
• Twenty minutes into the mission, Orion will extend its four power-generating solar arrays, providing electrical power to the spacecraft throughout the mission. Orion is NASA’s first crewed spacecraft to use solar power, as all previous NASA crew spacecraft have used hydrogen fuel cells for electricity.
• At the forty-nine minute mark, the ICPS will ignite to raise the perigee, or lowest point, of Orion’s orbit to a safe altitude. Without this maneuver, Orion would reenter the atmosphere and land. 
• Upon reaching the newly-raised perigee, the ICPS will reignite at the one hour, forty-seven minute mark, kicking the apogee, or highest point, out towards deep space. 
• At three hours and twenty five minutes into the flight, Orion will separate from the ICPS and begin a series of proximity operations. These operations use the newly-detached ICPS as a target to practice maneuvering Orion near other spacecraft, including manual piloting of Orion. These operations will prove out Orion’s ability to interact with other spacecraft, including the Starship HLS and Blue Moon Mk.2 landers that Orion will dock with on future Artemis missions. These operations will wrap up one hour later, at four hours and twenty five minutes into flight. Orion will perform a burn about twenty minutes later to move safely away from the spent ICPS, which will conduct a third and final burn to be safely disposed of in the Pacific Ocean. 

One day, one hour, and thirty-seven minutes into flight, on Flight Day 2, the four astronauts will hear words not spoken to any crewed mission in over fifty years. 

“Artemis II, you are GO for TLI.”

• The Orion spacecraft will perform the trans-lunar injection burn, placing itself on its final trajectory around the moon. A small correction burn will be performed later that day. 
• On Flight Days 3 and 4, the astronauts will conduct a number of tests of both astronaut capabilities and the Orion spacecraft as they coast towards the moon, the earth shrinking in their windows as they approach…

The Moon

• On Flight Day 5, Orion will officially enter the lunar sphere of influence, making the four crew members the first people to leave the realm of Earth’s gravity behind since 1972. 
• Flight Day 6 will see the majority of the lunar operations take place. Orion will reach its closest point to the moon five days, one hour, and twenty-three minutes into the flight. They will image the moon in two shifts, and at five days, one hour, and twenty six minutes, they will reach their maximum distance from Earth. No humans have ever traveled so far from our home planet. 
• Flight Day 7 will be something of a “weekend” for the crew as they coast back towards earth, with only a debriefing and a few minor tasks to complete as the crew rests from their busy previous days. Flight Days 8 and 9 will include a few more demonstrations, including ones of the radiation shielding on the spacecraft and a manual piloting demonstration on their way…

Back to Earth

• The final flight day, Flight Day 10, will begin with a third and final course correction burn at 8 days, 20 hours, and 33 minutes into flight. Two hours later, the crew will begin working through the reentry checklist and will don their pressure suits. At nine days, one hour, and thirteen minutes into flight, Orion will separate from the service module which provided power and propulsion throughout the mission, and perform a small burn to move itself away from the discarded stage. 
• At nine days, one hour, and thirty-three minutes, Orion will enter the outermost fringes of the atmosphere, 400,000 feet above the Pacific Ocean. Over the next few minutes, Orion will experience intense g-forces and heat near half that of the temperature of the sun as it streaks through the upper atmosphere at over 25,000 miles per hour. After the intense heat and deceleration of reentry is over, Orion will initiate a complex sequence of parachute deployments to bring the capsule to a safe splashdown off the California coast nine days, one hour, and forty six minutes after taking off from Florida. Their mission now complete, the crew will power Orion down and be scooped up by the waiting recovery ship within about two hours of splashing down.