CAPE CANAVERAL (Florida) - NASA has cancelled Saturday's launch attempt of space shuttle Endeavour on a construction mission to the International Space Station to assess possible damage from overnight lightning strikes, officials said.

Launch was reset for 7.13pm EDT on Sunday (7.13am on Monday Singapore time). The shuttle is carrying a porch for Japan's Kibo laboratory that will be used to expose experiments to the open environment of space. Nasa reported nine lightning strikes less than three-quarters km from the launch pad.

'Any time we have lighting within one mile of the pad we have to go look at the effects if there were any,' said Nasa spokesman George Diller.

Nasa tried twice last month to launch Endeavour, but was stymied by potentially dangerous hydrogen fuel leaks. Engineers discovered a misalignment in a line that vents hydrogen from the fuel tank as it is being filled. Technicians made repairs and tested the work last week.

'I have extremely high confidence' in the repair, said Mike Moses, who oversees the shuttle program at the Kennedy Space Center.

Nasa is running out of time to finish the station and retire the shuttle fleet by Sept 30, 2010, as directed by Congress. Managers say they will not compromise safety for the schedule and will ask for an extension and more funding if necessary to complete the outpost, a US$100 billion (S$146 billion) project of 16 nations.

Including Endeavour's mission, the agency plans eight more flights to the station. After the shuttles are retired, US astronauts will fly on Russian Soyuz capsules and cargo will be delivered by Russian, European and Japanese vehicles.

The station has been under construction 360 km above Earth for more than a decade. It consists of nearly 735 cubic metres of pressurised space, about as much room as a typical four-bedroom house.

Endeavour carries the last parts for Japan's elaborate three-part Kibo laboratory, including an open porch to expose science experiments to the space environment. The platform will be attached to the front of Japan's $2.4 billion Kibo complex during the first of five spacewalks planned during Endeavour's 12-day stay at the station.

One of the Endeavour astronauts, Timothy Kopra, will remain aboard the station, taking over the flight engineer's post from Japan's Koichi Wakata, who has been in orbit since March. -- REUTERS