On Monday, NASA fueled its huge lunar rocket for the first time and, despite a fuel line leak, embarked on a critical countdown test, according to AP NEWS..

It was NASA's fourth attempt at an important dress rehearsal, the last major milestone before the long-awaited debut of a rocket for a manned mission to the Moon..

Previous attempts in April were thwarted by fuel leaks, as well as stuck valves and other technical problems..

Another leak - this time in an external fuel line - nearly derailed Monday's tests at Kennedy Space Center. But NASA executives decided to run a countdown test anyway..

Launch director Charlie Blackwell-Thompson said they went into it to see "

The engineers wanted to go all the way to the 9-second mark - just short of starting the engine - to test all systems and procedures.. But it was interrupted at 29 seconds. NASA spokesman Derrol Neil said it is not yet known why the countdown stopped..

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The 322-foot (98-meter) rocket, known as the Space Launch System, or SLS, was previously loaded with about 1 million gallons of ultra-cold liquid hydrogen and oxygen..

Delays in testing have meant that a real launch - with an empty Orion capsule flying around the moon and back - will not take place until the end of August.. This test flight is critical before the astronauts get on board..

The first unmanned test flight of the Space Launch System (SLS) launch vehicle and the Orion spacecraft to orbit the Moon as part of the Artemis program was scheduled for February 2022.

Project Artemis is NASA's US government-funded manned space program to send humans to the moon.. The project will involve American private companies, the European Space Agency (ESA), Japan, Canada, Australia, the UK, Italy, the UAE, Luxembourg and Ukraine.

On July 20, at 20:17:42 GMT, the lunar module of the US Apollo 11 mission landed in the Sea of \u200b\u200bTranquility.. Astronaut Neil Armstrong stepped onto the Moon on July 21, 1969 at 02:56:20 GMT.. There have been 6 successful NASA missions to the Moon. The last - "