The shuttle itself was not hit by the lightning strikes
The launch of US shuttle Endeavour has been delayed after a thunderstorm around Cape Canaveral, Nasa officials say.
Blast-off was postponed for 24 hours to allow technical teams to assess the effects of lightning strikes near the launch pad on Friday.
Two previous launch attempts in June were scrapped because of a potentially hazardous leak in a hydrogen vent line.
The craft is to take and install a last piece of Japan's space station lab.
Lift-off had been scheduled for 1939 local time (2339 GMT) on Saturday.
But on Friday evening, the area surrounding the launch pad was hit by 11 lightning strikes.
Head of mission Mike Moses said the launch would take place at 1913 local time (2313 GMT) on Sunday.
He added weather forecasts suggested there was a 60% chance of acceptable conditions for take-off.
Nasa: 'We're just being cautious'
Forecasters earlier had predicted that stormy weather could delay the launch.
The launch pad is rigged with lightning protection system designed to attract bolts away from the shuttle.
But Nasa said that while none of the strikes hit the shuttle or its external tank and rocket boosters, there were strikes to the lightning mast and water tower.
Mike Moses, chairman of the pre-launch Mission Management Team, said checks were continuing but there was no indication so far of any damage to the shuttle's systems.
"We need to be 100% confident that we have a good system across the board," he said.
Nasa officials say they are also 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.
Endeavour should have blasted off in mid-June
Endeavour is due to take a seven-strong crew into space.
The crew is made up of 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.
When it launches, Endeavour will make the 127th space shuttle flight, and the 29th to the station.
Seven further flights to the station remain before the shuttles retire in 2010.
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