The American space agency is counting down to the lift-off of its giant new Moon rocket – the Space Launch System. the BBC reports.
SLS is the most powerful vehicle ever developed by Nasa, and will be the foundation of its Artemis project which aims to put people back on the lunar surface after a 50-year absence.
The rocket is timed to go up from the Kennedy Space Centre at 08:33 local time (12:33 GMT) on Monday.
Its job will be to propel a test capsule, called Orion, far from Earth.
This spacecraft will loop around the Moon on a big arc before returning home to a splashdown in the Pacific Ocean in six weeks’ time.
Orion is uncrewed for this demonstration but assuming all the hardware works as it should, astronauts will climb aboard for a future series of ever more complex missions, starting in 2024.
“Everything we’re doing with this Artemis I flight, we’re looking at through the lens of what can we prove out and what can we demonstrate that will buy down risk for the Artemis II crewed mission,” explained Nasa astronaut Randy Bresnik.