The countdown has begun toward the first space shuttle flight of the year.
Engineers report no major technical problems and the weather forecast looks favorable for a Friday launch of Atlantis.
The shuttle will carry seven astronauts on an 11-day mission to the international space station. They'll deliver a third pair of solar wings which help power the station and will also take three spacewalks to continue construction of the orbiting outpost.
The launch originally was set for mid-March but was postponed after a freak hail storm caused thousands of dings in the insulating foam on Atlantis' external tank.
Technicians spent more than two months making painstaking repairs to the tank.