**There is a strong chance the US shuttle Endeavour will have to wait even longer before getting its latest mission to the space station under way.**A forecast for stormy weather around Cape Canaveral on Saturday may force Nasa to hold the orbiter on the ground.
Two previous launch attempts in June were scrapped because of a potentially hazardous leak in a hydrogen vent line.
Endeavour and its crew are set to deliver and install the third and final piece of Japan’s space station lab.
Lift-off is timed for 1939 local time (2339 GMT) - if the weather does not intervene.
“We are forecasting 60% (chance of) weather prohibiting launch - which is of course, 40% chances for ‘go’ weather,” said shuttle weather officer Kathy Winters.
Nasa officials say they are now satisfied that the leak caused by a misaligned plate linking a hydrogen gas vent line with the external fuel tank has now been fixed.
If the flight gets away, Endeavour will carry into space a seven-strong crew, including six Americans and one Canadian - Julie Payette, who will operate the shuttle’s robotic arm during the mission.
During five spacewalks, an external platform will be added to the lab which will enable those experiments to be performed that require materials to be exposed to the harsh environment of space.
Endeavour astronauts also have to fit equipment to the exterior of the platform such as batteries and a spare space-to-ground antenna.
In addition, Endeavour will deliver a new long-stay crew member (Tim Kopra) to the ISS and bring back another (Koichi Wakata) who has lived aboard the platform for more than three months.
The shuttle’s visit will make it extremely crowded on the station. The platform’s residential crew complement was recently raised from three to six. The addition of Endeavour’s seven astronauts will bring the total on the outpost to 13 - a record for the ISS.
Endeavour is making the 127th space shuttle flight, and the 29th to the station.
Seven further flights to the station remain before the shuttles retire in 2010.