High winds will keep Atlantis on the launch pad another night. Photo: NASA/KSC

For the second day running, NASA was forced to call off the launch of space shuttle Atlantis due to gusty winds at its Florida launch site. Liftoff has been tentatively rescheduled for Wednesday, an unprecedented third consecutive launch attempt for the shuttle program.

With winds whipping at more than 24 knots across the shuttle's emergency landing strip and no hope of improvement, NASA managers gave up their countdown at 2:17 p.m. EDT (1817 GMT).

"It looks like the winds ... are pretty far out of limits and not going to come back in today," launch director Dave King informed the crew. "So in light of that, we're going to call a scrub for the day. We'll try again tomorrow."

"We knew our chances were iffy with the winds today but it was the right thing to do to try," replied shuttle commander Jim Halsell. "We appreciate everybody's efforts and we'll be ready to support tomorrow."

At the launch pad today winds were also out of limits, peaking at about 32 knots. A U.S. flag flying next to the countdown clock at the press site was torn by the strong breeze. A second flag carrying an Atlantis logo was blown away.

The weather for Wednesday is expected to be near-perfect, with a less than 10 percent chance of a weather-related delay. The only potential weather problem lies across the Atlantis at the emergency landing sites in Spain and Africa. The Spanish runways are expected to be affect by rain showers. Low cloud could be a problem for the runway at Ben Guerir in Morocco. The five-minute launch window opens at 3:26:50 p.m. (1926:50 GMT).

The crew of space shuttle Atlantis leave for the launch pad. Photo: NASA/KSC

Traditionally NASA has only ever made two back-to-back launch attempts before giving ground crews a day's rest. Agency managers decided to try a third consecutive launch attempt because if the shuttle does not get off the ground on Wednesday a packed launch schedule at Cape Canaveral could delay the mission until around May 11.

If all goes according to plan, Atlantis will dock with the fledgling International Space Station on Friday at 9:48 a.m. EDT (1348 GMT).

The crew of seven astronauts will patch up the station's faltering power system, installing four new batteries, replacing three current converters and two current converter controllers. Russia will meet the $1.3 million cost of the replacement components.

The astronauts will also make a spacewalk to secure a loose crane and deliver more than one ton of supplies to the station.

Atlantis is due back at the Kennedy Space Center on May 6 at 12:03 p.m. EDT (1603 GMT).