NASA’s giant Space Launch System will start its first journey into space with a slow crawl along the ground. The first window for the rocket’s highly anticipated launch will open on August 29th, and for once in its extremely long development history, everything is running ahead of schedule.

The original plan was to roll out the Space Launch System (SLS) this Thursday, but earlier this week, NASA decided to accelerate that schedule and announced it would start moving on August 16th. Tonight, the SLS will begin its trip by leaving the massive building where it has been carefully assembled and examined and head out to its launchpad. It’s roughly a four-mile trip but could take about 11 hours to complete.

SLS is NASA’s next big rocket, designed to carry people and cargo to deep space destinations like the Moon. It’s more powerful than the rockets that currently ferry astronauts back and forth from the International Space Station, which circles the planet in low Earth orbit. SLS has been in development for more than a decade, suffering from multiple delays and facing a rapidly ballooning budget.

The rocket could get its big debut as early as August 29th, the first opportunity for the launch of the Artemis I mission. Artemis I will see the SLS loft NASA’s Orion capsule into space and around the Moon on a trip that will take between 39 and 42 days, depending on the launch time. No people will be on board during this mission, which is a test run for future planned missions to the Moon.

NASA says that the SLS could start rolling out to the launch pad as early as 9PM ET on Tuesday, August 16th. Progress will be incredibly slow, but if you are interested in watching, NASA will be streaming footage of the rollout on its Kennedy Space Center YouTube channel, and we’ll also embed it here.