NASA fueled its huge moon rocket for the first time Monday and went ahead with a critical countdown test despite a fuel line leak.

This was NASA�s fourth crack at the all-important dress rehearsal, the last major milestone before the moon rocket�s long-awaited launch debut.

The previous attempts in April were thwarted by a fuel leak, as well as stuck valves and other technical issues.

Another leak � this time in an external fuel line � almost curtailed Monday�s test at Kennedy Space Center. But NASA managers decided to do the countdown test anyway.

Launch director Charlie Blackwell-Thompson said they pushed ahead to see �how the team performed, how the hardware performed, and they both performed very well.�

Engineers wanted to get all the way down to the 9-second mark � just short of engine firing � to validate all the systems and procedures. But it cut off at 29 seconds. NASA spokesman Derrol Nail said it wasn�t immediately known why the countdown stopped.

Earlier, nearly 1 million gallons of super-cold liquid hydrogen and oxygen were loaded into the 322-foot (98-meter) rocket known as the Space Launch System, or SLS.

The testing delays have pushed the actual launch � with an empty Orion capsule flying around the moon and back � to the end of August at the earliest. This test flight is crucial before astronauts climb aboard.

Blackwell-Thompson said it was too early to say what NASA�s next step might be.

The second SLS flight, planned for 2024, would send a crew around the moon and back. The third mission � no earlier than 2025 � would have astronauts actually landing on the moon.

Astronauts last walked on the moon in 1972 during NASA�s Apollo program. The new program is named Artemis, Apollo�s twin sister in Greek mythology.

(AP)