The Discovery shuttle has successfully blasted into orbit from America's Kennedy Space Center.
Its crew of seven astronauts are heading to the International Space Station(ISS) to deliver a huge cylinder for Japan's Kibo science lab.
They're also taking a new pump to fix the station's toilet, which broke last week leaving astronauts having to spend 10 minutes flushing it manually!
The mission is expected to take about two weeks, including three spacewalks.
Buzz Lightyear has finally got his dream of going to infinity and beyond
Nasa say it's one of the most complicated they've ever tried.
But the astronauts won't be on their own as they've got a special passenger on board - space ranger Buzz Lightyear!
The Toy Story action figure will be taking part in different experiments, including soaring about in zero gravity, to try to get more kids interested in science.