Two previous launches were postponed after hydrogen gas was found to be leaking from a vent line connected to the external tanks. NASA technicians carried out repairs realigning a fuel plate and installing new seals to rectify the problem.
"There were absolutely no leak indications whatsoever noted on the two leak detectors," said Launch Director Pete Nickolenko. "We'll continue to look at the data, and our next step is to move toward launch."
The 16-day mission will feature five spacewalks and completion of construction to the Japan Aerospace Exploration Agency's Kibo laboratory. Astronauts will attach a platform to the outside of the Japanese module that will allow experiments to be exposed to space.
The Endeavour crew comprises Commander Mark Polansky, Pilot Doug Hurley and Mission Specialists Dave Wolf, Christopher Cassidy, Tom Marshburn, Tim Kopra and Canadian Space Agency astronaut Julie Payette.
Kopra will join the space station crew and replace Japanese astronaut Koichi Wakata. Wakata will return to Earth on Endeavour concluding a three-month stay at the station.