By Ind Job Info Team
The American space agency is counting down the days until the Space Launch System, its huge new Moon rocket, takes off.
SLS is the most powerful vehicle Nasa has ever made. It will be the base of its Artemis project, which aims to put people back on the moon's surface after 50 years.
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.
This spacecraft will make a big loop around the Moon before coming back home in six weeks. It will land in the Pacific Ocean.
The US space agency has several chances to fly SLS-Orion in the next week, but it will want to choose the one that is right in front of it.
"Basically, the beginning of the launch window, or just after 08:30 in the morning, has an 80% chance of favourable weather," said meteorologist Melody Lovin.
But if technical problems push the launch to the end of the two-hour window, the chance drops to 60% because it's likely that rain will start to fall.