NASA’s Space Launch System has finally reached the pad — although an actual launch is still some ways off. The SLS rocket and the Orion spacecraft it carries arrived at Kennedy Space Center’s Launch Pad 39B for the first time at 4:15AM Eastern today (March 18th) for one last test before the uncrewed (and delayed) Artemis I mission to the Moon. The team will conduct a “wet dress rehearsal” that replicates the mission short of liftoff, including the propellant load, countdown procedures and draining tanks.

The test will help NASA set an exact target launch date for Artemis I. The SLS won’t stay out for very long., though, as the agency plans to roll it back to the Vehicle Assembly Building several days after the test. There, crews will remove rehearsal sensors , top up batteries, add “late-load” cargo and conduct final checks. The rocket will return to the launch pad about a week before the real launch, tentatively slated for May or later.

The preliminary deployment still marks a few important milestones. NASA officially began development of the SLS in 2011, and spent over $23 billion (in 2021 dollars) on the project in roughly a decade — the launch pad rollout shows the investment is finally bearing fruit. It’s also an important moment for Orion, which is edging closer to crewed flights.

More importantly, the arrival indicates that the next chapter of NASA’s exploratory missions is about to begin. The SLS will not only be used for Artemis missions, but is expected to serve as NASA’s primary deep space exploration launcher throughout the 2020s. As important as private rockets like SpaceX’s Starship may be, it’s likely the SLS that will carry the most historic missions in the years ahead.