Washington, Apr 10 (IANS): NASA has yet again delayed the final wet dress rehearsal of its Artemis 1 moon mission test to April 12, the US space agency officials said.

Wet dress rehearsal is an opportunity to refine the countdown procedures and validate critical models and software interfaces. The test, earlier scheduled for April 1-3, was stopped prior to tanking, due to loss of ability to pressurise the mobile launcher using two fans.

The agency, in a statement, said it is planning to proceed with a modified wet dress rehearsal that is "primarily focused on tanking the core stage, and minimal propellant operations on the interim cryogenic propulsion stage (ICPS) with the ground systems at Kennedy".

"Due to the changes in loading procedures required for the modified test, wet dress rehearsal testing is slated to resume with calls to stations on Tuesday, April 12 and tanking on Thursday, April 14."

Engineers have identified a helium check valve that is not functioning as expected, requiring these changes to ensure safety of the flight hardware. Helium is used for several different operations, including purging the engine, or clearing the lines, prior to loading propellants during tanking, as well as draining propellant.

A check valve is a type of valve that allows liquid or gas to flow in a particular direction and prevents backflow. The helium check valve is about three inches long and prevents the helium from flowing back out of the rocket.

The modified test will enable engineers to achieve the test objectives critical to launch success, the officials said.

Following the modified test, the Space Launch System rocket and Orion spacecraft will return to the Vehicle Assembly Building (VAB) where engineers will evaluate the valve and replace it if needed. Teams are confident in the ability to replace the valve once back in the VAB.