The massive core stage that will power the Artemis II mission to the moon next year was transported into Kennedy Space Center’s Vehicle Assembly Building on Wednesday.

The 212-foot-long hardware manufactured by Boeing makes up the largest part of NASA’s Space Launch System rocket. It’s powered by four RS-25 engines from Aerojet Rocketdyne that were converted from the Space Shuttle Program. Two of the engines for Artemis II flew on previous missions including one from the final flight of Space Shuttle Atlantis when it flew STS-135 in 2011.

It arrived on NASA’s Pegasus barge on Tuesday to KSC’s Turn Basin, and made the three-hour journey from ship to the VAB one day later.

The core stage when combined with two solid rocket boosters from Northrop Grumman give SLS 8.8. million pounds of thrust on liftoff, which is more powerful that the Saturn V rockets from the Apollo program.

Artemis II is slated to launch no earlier than September 2025 with SLS topped by the Orion capsule from Lockheed Martin carrying NASA astronauts Reid Wiseman, Victor Glover and Christina Koch, along with Canadian astronaut Jeremy Hansen, on what would be the first return of humans to the moon since the Apollo 17 mission in 1972.

Their flight will be the most powerful rocket ever ridden by humans.

Their flight will taken them around the moon as a test mission to ensure the Orion’s life support systems work. It would then set up the Artemis III mission as early as September 2026 that aims to return humans including the first woman to the lunar surface.

The core stage will spend several weeks in its horizontal position before NASA begins preparations to begin stacking it along with the solid rocket boosters. That vertical stacking work could begin as early as September.