NASA has decided to roll its Artemis 1 moon rocket off the launch pad and back to a processing facility to fix some issues revealed by a recent "wet dress rehearsal" test.

The wet dress rehearsal — a series of key trials designed to show that Artemis 1's huge Space Launch System (SLS) rocket, Orion spacecraft and their associated ground infrastructure are ready to go — began on April 1 at Pad 39B at NASA's Kennedy Space Center (KSC) in Florida.

Things were supposed to wrap up about 48 hours later, with the loading of liquid hydrogen and liquid oxygen propellants into the SLS and the execution of several simulated launch countdowns. Artemis 1 team members ran into several problems that delayed those steps, however, and they ultimately stood down to accommodate the private Ax-1 astronaut mission, which launched atop a SpaceX Falcon 9 rocket on April 8 from KSC's Pad 39A.

The wet dress got going again on April 12, in a modified format: After discovering a faulty valve on the mobile launch lower supporting the Artemis 1 stack, the team decided to fuel up just the SLS core stage, not its upper stage as well.

Technicians began fueling the core stage on April 14 as planned, but they stopped after noticing that liquid hydrogen was leaking from one of the "umbilical" lines running from the mobile launch tower to the SLS. 

After ending that fueling effort — the third of the wet dress campaign following abortive tries on April 3 and April 4 — Artemis 1 team members took some time to analyze their data and their options. They initially left the door open to resuming the wet dress next week, with another tanking try perhaps as early as Thursday (April 21).