Just like the Starliner, the SLS was somewhat plagued by issues, only sooner in its development cycle. NASA rolled the thing out on the launch pad of the Launch Complex 39B back in March, for a wet dress rehearsal test, only to find the rocket was leaking. It removed it from the pad after it became obvious fixing could not be done on-site, and the thing returned to the Vehicle Assembly Building (VAB), where it has been under the watchful eye of literal rocket scientists since the end of April.
For what it’s worth, NASA kept us up to date with what went on inside the VAB, but was cautious in advancing a date for the second rollout to the pad, as it seeks to resume the test. That changed over the weekend, when the agency announced the Artemis program rocket would be back out there early next month.
We’re told the liquid hydrogen system leak was fixed, some components replaced, others modified, and tons upon tons of other checks performed. Presently, engineers are “completing some of the forward work originally scheduled to take place in the Vehicle Assembly Building (VAB) after wet dress rehearsal,” including opening the Orion spaceship and installing payloads (like the Callisto) that will fly on Artemis I.
Once on the pad, the rocket will spend a couple of weeks being checked some more, before the test is allowed to proceed.
There still is no tentative date set for when Artemis I will launch, but NASA did make public the launch window calendar.