NASA’s massive US moon rocket is ready for its first launch.

NASA’s massive Space Launch System moon rocket, topped with an uncrewed astronaut capsule, began an hours-long journey to its launchpad Tuesday night, in preparation for the behemoth’s first test flight later this month.

The 322-foot-tall rocket is set to launch into orbit for the first time – without humans — on August 29. It will be a critical, long-delayed demonstration mission to the moon for NASA’s Artemis programme, the US’ multibillion-dollar endeavour to return humans to the lunar surface as practise for future Mars missions.

The Space Launch System, whose development has been led by Boeing over the last decade, emerged from its assembly building at NASA’s Kennedy Space Center in Florida at 10 p.m. EDT (0200 GMT) on Tuesday and began a four-mile (6-kilometer) journey to its launchpad. The rollout will take approximately 11 hours if the speed is less than 1mph (1.6kph).

NASA’s Orion astronaut capsule, constructed by Lockheed Martin, is perched atop the rocket. It is intended to break away from the rocket in space, ferry humans to the moon, and rendezvous with a separate spacecraft that will transport astronauts to the lunar surface.

The Orion spacecraft will launch atop the Space Launch System without any astronauts on August 29 and orbit the moon before returning to Earth for a 42-day ocean splashdown.

If the launch is delayed on August 29 due to inclement weather or a minor technical difficulty, the National Aeronautics and Space Administration has backup launch dates on September 2 and September 5.