NASA canceled Saturday's launch attempt of space shuttle Endeavour on a construction mission to the International Space Station to assess possible damage from nearby lightning strikes, officials said, Reuters reported.
Launch was reset for 7:13 p.m. EDT (2313 GMT) on Sunday. 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 11 lightning strikes less than a half-mile (three-quarters of a km) from the launch pad.
"We need to be 100 percent confident that we have a good system across the board," said Mike Moses, the shuttle program manager at the Kennedy Space Center in Florida.
The shuttle is protected from direct strikes by lightning masts and wires that divert currents to the ground. The concern is that related electromagnetic fields could trigger currents in the shuttle's electrical systems.
"We see nothing so far that indicates anything was actually affected by the lighting strikes, so I fully expect this to be a positive story, but we have a lot of equipment that has to be checked and that's what takes time," Moses said.
The delay is the third for Endeavour, which is scheduled to spend 16 days in orbit.
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.
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 $100 billion project of 16 nations.
Including Endeavour's mission, the agency plans eight more flights to the station.
After the shuttles are retired, U.S. astronauts will fly on Russian Soyuz capsules and cargo will be delivered by Russian, European and Japanese vehicles.
The station has been under construction 225 miles (360 km) above Earth for more than a decade. It consists of nearly 26,000 cubic feet (735 cubic metres) of pressurized 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.