The American space agency is counting down to the lift-off of its giant new Moon rocket - the Space Launch System.
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; 13:33 BST) 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.
Going to watch the launch with the volume up LOUD
Started watching this. Exciting! I watched the Apollo launches as a kid and this brings it all back.
Not looking too promising. This is just how it was in 'old days'. Sometimes you'd wait all night for lift-off and it'd be cancelled right at the last minute.
It's crazy that we're preparing for a test flight of the actual rocket which is going to take man to the moon in a few years. It's seems that it's been billed as something we'll do in ten years time for most of our loves, but this step, even if it failed today, shows we are so close to seeing a return to humans on the moon in our life time.
Even bigger than that, the whole reason we're going back to the moon is to prepare for an eventual trip to Mars. I hope that I get to quote this post one day and declare 'It finally happened!'
Not only putting man on the moon, but building an actual base there! Having people working there for long periods! Imagine the things that we could learn!