The US space agency NASA was confident that the repeatedly delayed launch of the space shuttle Discovery would lift off on Sunday night for a mission to the International Space Station.
The launch was scheduled for 7.43 pm (2343 GMT) Sunday from the Kennedy Space Centre at Cape Canaveral, Florida. Discovery will have seven astronauts on board, including Japanese crew member Koichi Wakata, who is slated to join the permanent crew on the orbiting space station.
The forecast was for good weather conditions for the Sunday launch, which was postponed again Wednesday due to a hydrogen gas leak.
The shuttle was to have launched in February but was pushed back several times to allow NASA engineers to examine valves that control the flow of hydrogen between the spacecraft's engine and external fuel tank.
A valve was found to be damaged after the space shuttle Endeavour's November flight, prompting NASA to delay Discovery's mission as a precautionary measure.