NASA will try again to get its new 30-storey rocket off the ground and send its unmanned test capsule towards the Moon
The launch is scheduled for 2:17pm from Kennedy Space Center in Florida.
The purpose of the Artemis 1 mission is to verify that the Orion capsule, which sits atop the SLS rocket, is safe to carry astronauts in the future.
Mannequins equipped with sensors are standing in for astronauts on the mission and will record acceleration, vibration and radiation levels.
The capsule will fire its engines to get to a distant retrograde orbit of 64,000km (40,000 miles) beyond the Moon, a record for a spacecraft rated to carry humans.
Artemis is named after the twin sister of the Greek god Apollo, after whom the first Moon missions were named.
The crew of Artemis 3 is to land on the Moon in 2025 at the earliest, with later missions envisaging a lunar space station and a sustainable presence on the lunar surface.
According to NASA chief Bill Nelson, a crewed trip to Mars on board Orion, which would last several years, could be attempted by the end of the 2030s.