"We have decided to roll back," Nasa spokesman Bruce Buckingham told reporters at the KSC.

Atlantis' launch had been pushed back from Sunday to Tuesday to allow engineers more time to examine the effects of a lightning strike on Friday. The investigations showed up no problems.

Launch delay

Dismantling sections of the shuttle and then moving it indoors and back out again would take at least nine days. It will now be difficult for Nasa to meet its target of launching Atlantis by 7 September.

If Nasa fails to fly Atlantis before its launch window closes on 13 September, the next opportunity to lift off during daylight is in late October. A daytime launch allows the space agency to take pictures of the shuttle to check for debris from the external fuel tank that could damage the orbiter.

Nasa's administrator Mike Griffin has said the agency may lift the launch restrictions if the Atlantis flight goes well.

Construction tasks

Atlantis' six-strong crew is taking giant new power-generating solar arrays - solar panels which convert the Sun's energy into electricity - to the International Space Station.

The mission's main objective is to fit the P3/P4 truss, a 17-ton segment of the station's truss backbone that includes a huge set of solar arrays and a giant rotary joint to allow them to track the Sun.

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The wings will provide power for three science laboratories, two living chambers and other systems onboard the ISS. They effectively double the station's current ability to generate power from sunlight.

During the 11-day mission, the crew will undertake three spacewalks to complete their construction duties.

Atlantis is the first of 15 or 16 flights planned to complete the construction of the half-built $100bn (£53bn; 78bn euros) space station by 2010, when the shuttle fleet is set to retire. Delaying this flight might have a knock-on effect on the schedule of later flights.