In a countdown rehearsal, NASA fuels the moon rocket for the first time.

Despite a fuel line leak, NASA fueled its massive moon rocket for the first time Monday and proceeded with a vital countdown test.

This was NASA’s fourth attempt at the crucial dress rehearsal, the final significant step before the long-awaited launch debut of the moon rocket.

A fuel leak, as well as clogged valves and other technical concerns, prevented prior attempts in April.

Another leak, this time in an external fuel line, threatened to put the test at Kennedy Space Center on hold on Monday. Nonetheless, NASA officials opted to conduct the countdown test.

They pushed forward to see ‘how the crew performed, how the hardware performed, and they both performed very well,’ according to launch director Charlie Blackwell-Thompson.

Engineers wanted to check all of the systems and procedures down to the 9-second mark, just short of engine ignition. However, it was cut off at 29 seconds. The reason for the countdown’s halt, according to NASA spokesman Derrol Nail, is unknown.

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

The actual launch — with an empty Orion capsule flying around the moon and back — has been pushed out to the end of August at the earliest due to testing difficulties. Before astronauts join, this test flight is critical.

It’s too early to determine what NASA’s next step will be, according to Blackwell-Thompson.

A crew would be sent around the moon and back on the second SLS voyage, which is scheduled for 2024. Astronauts would arrive on the moon on the third mission, which would take place no later than 2025.

The last time astronauts stepped on the moon was in 1972, as part of NASA’s Apollo mission. Artemis, Apollo’s twin sister in Greek mythology, is the name of the new programme.