"We've had a very clean countdown so far and we're currently on schedule, and we're not working on any issues," said Jeremy Graeber, NASA test director at the Kennedy Space Center.
The shuttle and its all-male crew of six was to launch at 2:20 p.m. for a 12-day mission to deliver an integrated cargo carrier and a Russian-built research module, CNN reported.
Just two shuttle flights are scheduled after Atlantis lifts off -- one flight by the shuttle Discovery and one by Endeavour. NASA plans to end the three-decade-old program by the end of this year.
The station is to remain operational until at least 2020 with NASA astronauts reaching it via Russian Soyuz spaceships until private companies develop spacecraft that can reliably ferry people into space.
Copyright 2010 United Press International.