The seven-member crew is to deliver an outside porch to be installed on the International Space Station's Japanese Kibo module to expose scientific experiments to the extremities of space.

The mission has suffered a slew of delays that kept the craft on the ground for weeks longer than planned. A planned Sunday launch was cancelled due to storms and a Saturday launch was also scrubbed due to lightening the night before that struck the launch pad, but sparred the shuttle itself.

NASA was forced to postponed the launch twice in just four days last month, after technicians detected hydrogen gas leaks during fuelling, just hours before scheduled liftoff.