A valve problem led to the cancellation of a critical test of the launch vehicle for NASA's first moon mission

April 5 - NASA's second critical test of the launch vehicle for Artemis's first mission back to the moon was canceled Monday because of a jammed valve in ground equipment.

Jeremy Parsons, NASA's associate administrator for ground systems, confirmed that the Space Launch System (SLS) rocket used to launch the Artemis 1 mission had been anchored to pad 39B at Kennedy Space Center, but a ventilation valve in its mobile launcher structure jammed as it prepared to fuel. Forcing NASA to cancel the test.

The test was NASA's second "Critical Facility Pre-Launch Condition Training" (WDR) for the SLS rocket, attempting to fill 2.6 million liters of a mixture of frozen liquid oxygen and liquid hydrogen propellant into the 98-meter-high core stage. NASA attempted a similar test on April 3, but it was called off before propellant could be filled because of pressurization problems.

It was not immediately clear whether NASA would be able to proceed with the propellant refueling attempt on Tuesday local time, or whether it would halt current work to replenish supplies of propellant and allow test crews to rest. The incident could prompt another delay in SpaceX's two manned missions.