Third attempt is shuttle record

The Cape Canaveral vegetation blows in the wind

For the first time in 19 years, Nasa will make a third attempt in three days to launch a shuttle.

High winds at the Kennedy Space Center (KSC), Florida forced postponements of the launch of Atlantis on Monday and Tuesday. But, with improved weather forecasts, the mission to repair the International Space Station will now try to launch at 2027 BST (1927 GMT) on Wednesday.

Normally after two scrubbed launch attempts, the astronauts and ground crews are given a rest day. But if that was done in this case, the next chance to launch Atlantis would be on 11 May, due to other scheduled launches of unmanned rockets.

Nasa are keen to visit the ISS because it is currently losing altitude and decided to go for three in a row this time because the afternoon launch time is convenient and because no problems have cropped up during the countdowns.

Crosswind danger

Nasa will not launch the shuttle if the crosswinds exceed 27 km/h (17 mph), as this would endanger a shuttle landing if an emergency return to Earth was required.

The winds on Tuesday afternoon were gusting to 60 km/h (37 mph).

High winds endanger emergency landings

"We knew our chances were iffy with the winds today, but it was the right thing to do to try and we appreciate everybody's efforts," Commander James Halsell said from inside Atlantis.

The weather at KSC is forecast to have a 90% chance of being acceptable, meaning conditions at emergency landing sites in Spain and Morocco are more likely to cause another postponement.

Mending mission

Atlantis is loaded with fresh batteries, smoke detectors, fire extinguishers and fans for the 18-month-old space station.

Since astronauts last visited the station last spring, two of its six main batteries have failed and another two are showing signs of deterioration.

In addition, an antenna is broken, a crane is loose and the space station's orbit is dropping over three kilometres (two miles) closer to the Earth each week because of increased solar activity.

Nasa wants Atlantis and its crew up there as soon as possible to fix all the problems.

Double delay

Atlantis was not supposed to fly until the Russians had launched a critical service module with guidance and life-support systems. But with the service module more than two years behind schedule and due to fly no earlier than July, Nasa advanced Atlantis' repair mission.

The weather at KSC is not the only thing that has kept Atlantis grounded. Mission Commander Halsell twisted an ankle during training last month, forcing a one-week postponement.

More than 100 changes have been made to the shuttle for this mission, including improved communications and air-conditioning systems and a new instrument panel.

The shuttle will be carrying more than a tonne of cargo for the ISS, but will also take the Olympic torch into space. During Atlantis' 10-day mission, the carefully packed torch will fly over virtually all the nations which are participating in the games.