The crew, Reid Wiseman, Christina Koch, Victor Glover, and Jeremy Hansen, are now at Kennedy Space Center getting ready for launch.
They'll ride the Orion spacecraft on NASA's massive Space Launch System rocket.
The 20-day journey kicks off (if all goes to plan) on April 1 from Launch Pad 39B and will check out navigation and heat shield tech needed for long-term moon missions.
There are backup launch dates until April 6 if needed.