NASA announced the delay with just nine hours to go before liftoff, citing 11 lightning strikes near the Cape Canaveral launch site during a powerful electrical storm Friday evening.

"The launch is scrubbed for at least 24 hours," NASA spokesman George Diller said.

"This delay will give technical teams additional time to evaluate lightning strikes at Launch Pad 39A that occurred during Friday's thunderstorm.

There was "no damage found on the shuttle or on the pad systems," Diller said, although scientists are now examining whether the inclement weather could have caused other problems.

NASA said the lightning strikes were within 0.3 nautical miles (kilometers) of the pad, with several of them striking the wiring system designed to protect the shuttle from taking direct lightning hits.

The hold-up spells more tension for Endeavour's seven-member crew and the NASA boffins who have now been forced to abandon the shuttle's launch three times.

Two previous launch attempts were scuttled by potentially hazardous fuel leaks, apparently caused by a misaligned plate linking a hydrogen gas vent line with the external fuel tank.

Saturday's delay came before NASA could begin the process of pouring two million liters (half a million gallons) of liquid hydrogen into the tanks at very low temperatures, which engineers would have eagerly monitored for more leaks.

But the bad weather had been expected.

Shuttle weather officer Kathy Winters earlier warned that showers, thunderstorms and icy clouds could interfere with the final countdown.

There had been 60 percent chance of inclement weather conditions "prohibiting" the shuttle's latest launch attempt, she said.

Despite the warnings NASA late on Friday removed the shuttle's giant scaffolding-flanked shroud, heralding the final preparations for the beginning of Endeavour's voyage to the International Space Station at 7:39 pm (2339 GMT).

Endeavour's crew -- including six Americans and one Canadian -- had been expected to leave Cape Canaveral for a 16-day voyage to the ISS.

There they were expected to install a platform for astronauts to conduct experiments in the vacuum of space, 350 kilometers (220 miles) above Earth's surface.

Among the crew Julie Payette, an electrical and information engineer, is the only woman on board.

She has been into space before, as have two other members of the crew, including shuttle commander Mark Polansky.

The crew's four other members will be on their maiden space voyage.

American aerospace engineer Tim Kopra, 46, will replace Japanese astronaut Koichi Wakata, spending several months aboard the floating space station.

He would be the latest addition to the permanent crew of the ISS, which is a joint collaboration between 16 different countries.

The rest of the crew is scheduled to head back to Earth on July 27, with a planned landing at the Kennedy Space Center and back up landing sites in case of bad weather in Edwards, California or White Sands, New Mexico.

The astronauts would also undertake repair and replacement work, including installing six new batteries in the ISS.

That mission will require two astronauts to conduct five space walks totaling 32.5 hours.

The Endeavour mission is the last of three trips being undertaken to assemble the Japanese Kibo laboratory aboard the orbiting space station.

Kibo's two pressurized modules were attached to the ISS in 2008, along with the European lab Columbus.

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