Discovery lifted off the launching pad at Cape Canaveral, Florida at 11.59 p.m. Friday (0359 GMT Saturday) after days of postponements due to a questionable valve on the shuttle's external fuel tank and poor weather.
Weather forced a delay of a planned takeoff on Tuesday and then problems with the valve scrubbed a scheduled liftoff on Wednesday. NASA then sought to fire up Discovery early on Friday, but elected to postpone it again to review data in connection with the valve.
NASA officials said on Friday afternoon the problem with the valve was resolved and begin fuelling up, turning the primary concern to the weather off the Florida coast.
The current planned 13-day mission is designed to transport new equipment and experiments to the ISS. Astronaut Nicole Stott is expected to relieve Timothy Kopra aboard the ISS, and three spacewalks are planned for the mission.
Discovery's crew for this mission includes six Americans and Swede Christer Fuglesang, flying for the European Space Agency.
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