Updated: Apr 5, 2022
It's unclear when NASA will resume the crucial test.

NASA's second attempt to fuel its Artemis 1 moon mission megarocket hit another snag on Monday (April 4) due to a valve issue on ground equipment.
A stuck vent valve high up on the mobile launcher structure supporting the Artemis 1's Space Launch System rocket at Launch Pad 39B of NASA's Kennedy Space Center forced NASA to scrub the Artemis 1 test after fueling began on Monday, agency officials said. The valve is use to relieve pressure from the rocket's core stage during fueling.
"Due [to] the vent valve issue, the launch director has called off the test for the day," Jeremy Parsons, NASA's deputy director for ground systems, wrote in a Twitter update after the scrub. "The team is preparing to offload LOX (liquid oxygen) and will begin discussing how quickly the vehicle can be turned around for the next attempt."
The vent valve was on the 160-foot (49 meters) level of the mobile launcher, which serves as both a gantry and launch platform for the SLS, according to Parsons. NASA officials said the problem occurred in a panel that controls the valve, leaving technicians unable to open the valve.
"Given the time to resolve the issue as teams were nearing the end of their shifts, the launch director made the call to stop the test for the day," NASA wrote in a statement Monday. "A crew will investigate the issue at the pad, and the team will review range availability and the time needed to turn systems around before making a determination on the path forward."
Monday's fueling attempt was NASA's second try to fill the core stage of Artemis 1's 322-foot-tall (98 m) SLS rocket with 700,000 gallons (2.6 million liters) of super-chilled liquid oxygen and liquid hydrogen propellant in what the agency calls a "wet dress rehearsal." The test, which began April 1, features a full launch countdown rehearsal, including the fueling process.