Florida: NASA is gearing up for the first test flight of the space launch vehicle 'Orion One', part of the mission to put humans on the moon. 

The 322-foot- (98-metre)-tall rocket is scheduled to embark on its first mission to space, without any people, on August 29.

It will be a crucial, long-delayed demonstration trip to the moon for NASA's Artemis program, the United States' multi-billion-dollar effort to return humans to the lunar surface as practice for future missions to Mars.

The Space Launch System, the development of which during the past decade has been led by Boeing, emerged from its assembly building at NASA's Kennedy Space Centre in Florida about midday Wednesday (AEST) and began a six-kilometre trek to its launch pad.

Sitting atop the rocket is NASA's Orion astronaut capsule, built by Lockheed Martin Corp.

The capsule was designed to separate from the rocket in space, ferry humans toward the moon and rendezvous with a separate spacecraft that would take the astronauts to the lunar surface.

For the August 29 mission, called Artemis 1, the Orion capsule will sit empty on the Space Launch System while it orbits the moon.

The rocket is scheduled to return to Earth for an ocean splashdown 42 days later.

If bad launch weather or a minor technical issue triggers a delay, NASA has backup launch dates of September 2 and September 5.