(CNN) -- The launch of space shuttle Discovery scheduled for Wednesday has been scrubbed.
Space shuttle Discovery readies for launch, which was scheduled for Wednesday night.
After weeks of delay, the space shuttle Discovery was supposed to take off Wednesday evening for a two-week mission to the international space station.
The launch previously had been delayed by a month while teams of engineers worked through concerns over hydrogen valves in the engine compartment. Problems with one of the three valves on the last shuttle flight had raised the launch team's anxiety level.
NASA spent the past four weeks investigating paper-thin cracks in the valves and whether flying with those cracks would be too risky. In the end, all three of Discovery's valves were replaced, said space shuttle program manager John Shannon.
"We had sensed that we would get to this point. It's just one of those problems you just have to keep working at, and you have to keep doing the research, the analysis, the real hardware tests. And finally we got to that point," he said.
Wednesday's launch would have been the 125th shuttle flight and the 36th for Discovery. The two-week mission was to include four spacewalks to install the 31,000-pound final truss segment with two solar array wings. The final segment completes the backbone of the station, and the set of solar arrays will convert solar energy to electrical power, providing the capacity to generate enough power to maintain a full crew of six and increase scientific research on the station.
Japanese astronaut Koichi Wakata will be on STS-119's seven-member shuttle crew. He was going to spend the next couple of months on the space station, replacing American astronaut Sandra Magnus, who was expected to return to Earth when Discovery returned. A stuffed duck will be accompanying Wakata to space as a memento of his hometown of Saitama, Japan.
The crew was going to bring up a couple of flags, including a green one representing the Andretti Racing Team. Pilot Tony Antonelli was expected to serve as the starter for a race after the shuttle's flight. Eight chocolate bars were going up, too, but are unlikely to come back.
For the nation's educators, this was supposed to be an important flight. Two of the mission specialists, Joseph Acaba and Richard Arnold, are former middle school and high school teachers. Both were scheduled to make their first space flights. and both would have made spacewalks. Both men joined the astronaut corps in 2004.
Shuttle Cmdr. Lee Archambault has flown once before, as has Mission Specialist Steve Swanson. It's would have been the first flight for Pilot Tony Antonelli and the third for Mission Specialist John Phillips.
The weather for the 9:20 p.m. launch was expected to be nearly perfect. The Air Force meteorology team had been forecasting a 90 percent chance of excellent launch conditions. Emergency landing sites at three overseas locations were also forecasting good weather.
There are nine shuttle flights scheduled before NASA retires the three space shuttles in 2010. Eight missions are slated to complete the construction of the international space station, and one is dedicated to maintenance and upgrades to the Hubble Space Telescope.