Discovery is scheduled to take off from Kennedy Space Center at Cape Canaveral at 5:38 pm (2138 GMT) on Thursday with a five-minute launch window.

"Weather conditions look promising," said Ed Priselac, the shuttle programme's weather officer, a day after a weakening Tropical Storm Barry blew itself out over northern Florida.

Pete Nickolenko, NASA's test director, said preparations were progressing well.

"We are right where we want to be -- on schedule," he said.

During its 12-day mission, the shuttle will bring the Italian-made Leonardo Multi-Purpose Logistics Module -- carrying scientific equipment and experiments -- to the station. Leonardo, on its second journey to the space station, is also chock-full of food and water supplies.

After delivering its payload, Leonardo will return to earth with Discovery on August 21.

Also arriving on Discovery is the space station's third resident crew -- US Commander Frank Culbertson and Russians Vladimir Dezhurov and Mikhail Tyurin.

They will relieve Russian Commander Yury Usachev and US astronauts James Voss and Susan Helms, who have been on the station since March.

The new crew's arrival represents a turning point for the space station, whose first phase of construction was completed with the installation of the Quest airlock in July.

The 164-million-dollar (187-million-euro) aluminum airlock serves as the portal to the space station, allowing resident astronauts to perform spacewalks without having to wait for a visit from a shuttle.

With the addition of the airlock, the station is now 424 cubic metres (15,000 cubic feet) in size -- equivalent to a four-room apartment.

Twenty Russian experiments and 18 US experiments, primarily examining the effects of weightlessness on humans, will be carried out during the trio's mission.

In order to measure the effects of space exposure on objects, four containers will be attached to the station's exterior. An attempt will also be made to grow ovarian cancer cells in the zero-gravity environment.

Space shuttle astronauts Daniel Barry and Patrick Forrester will perform two space walks, one to supply coolant to the station and install the experiment containers, the second to install cables for a planned extension of the Destiny Laboratory.

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