The space shuttle Discovery blasted off into the darkening Florida sky Sunday evening, several days after the launch was delayed by a potentially fatal hydrogen leak.

The seven crew members aboard are set to complete the final installation of solar wings and other construction projects on the International Space Station.

With near-perfect weather, Sunday's launch went ahead as planned after the shuttle's ground crew fixed the leak by swapping seals and valves on its massive orange fuel tank.

While the switch appeared to fix the leak, engineers kept a close watch on the fuel system ahead of the launch, which took place at 7:43 p.m. ET.

"It appears this system is tight," said NASA spokesman George Diller prior to launch.

Problems with the shuttle's hydrogen fuel system had led to delays of about a month heading into this week.

The Discovery mission is crucial because it contains essential construction materials for the space station, including the final set of solar wings and gear for a system that will recycle urine into drinking water.

In May, the space station is due to expand to a crew of six, up from its current complement of three, and it will require more electricity to support the new space station personnel and their experiments.

The STS-19 mission will also see astronauts undertake several spacewalks to help install the solar array wings.

Discovery will also drop off Japanese astronaut Koichi Wakata at the space station and pick up U.S. astronaut Sandra Magnus for a return to Earth.

The shuttle was on a tight timeline to make its way to the space station: NASA only had until Tuesday to send the shuttle on its way. Otherwise, the Russian Soyuz rocket would have bumped Discovery during a launch set for March 26.

Still, there was one perplexing development before the launch - a bat was hanging off the back of the fuel tank.

With files from The Associated Press