Astronauts have started boarding the space shuttle Atlantis in preparation for blast off at 11:26 am (1526 GMT) Friday, DPA reported.
The boarding process was expected to take a little more than an hour and the hatch was to be closed for flight at 9:21 am, US space agency NASA said.
While there were concerns that bad weather - lightning, thunderstorms, rain - could ground the shuttle, launch director Mike Leinbach said after the latest weather briefing: "We do have a shot at this today."
This will be the final launch of the 30-year NASA space programme.