Weather delays space shuttle launch

The Space Shuttle Discovery is exposed and prepared for liftoff at the Kennedy Space Centre. Picture / Reuters.

CAPE CANAVERAL, Florida - Nasa postponed the launch of space shuttle Discovery until Monday morning (NZT) at the earliest, due to possible lightning and thunderstorms near the Florida launch pad.

"It's not a good day to launch the shuttle so we're going to try again tomorrow," launch director Mike Leinbach said, with the countdown clock stopped at nine minutes.

Weather was a persistent worry leading up to Saturday's scheduled launch, with storm clouds hovering over Kennedy Space Center. The forecast for Sunday local time is no better, with a 60 per cent chance that storms could force a delay of that launch too.

The preferred launch time is 3.26pm Sunday local time (7.26am Monday NZT).

This is only the second shuttle mission since the fatal Columbia accident in 2003, and is a critical turning point for Nasa.

If Discovery is critically damaged on launch or afterward, and astronauts cannot fix the problem in orbit, the seven crew members would stay on the Space Station and wait for rescue, but Nasa chief Mike Griffin has said it could be the end of the shuttle program.

That would leave the US$100 billion ($164 billion) International Space Station incomplete and would also mean the United States has no way to carry humans to space.

Griffin decided to launch the shuttle over the objections of the US space agency's head of safety and its top engineer, who wanted the mission delayed to allow more work on the fuel tank and its insulating foam.

The space shuttles began flying in 1981 and is scheduled for retirement in 2010 as Nasa develops a new manned spaceship that can travel to the moon and beyond.

The shuttle is the only spacecraft able to lift the heavy components needed to finish the space station.

Nasa has spent US$1.3 billion on repairs and safety upgrades to the shuttle fleet since Columbia disintegrated over Texas in February 2003, killing all seven crew. But the work failed to fully fix a problem with insulating foam on the fuel tank breaking off during launch.

The foam prevents the buildup of potentially damaging ice when the tank is filled with super-cold fuel.

Falling foam damaged Columbia's wing on launch, letting superheated gases rip the shuttle apart on re-entry 16 days later. The foam problem cropped up again when Discovery was launched a year ago, sending Nasa engineers back to the drawing board.

Griffin acknowledged that foam was a problem but said he felt it did not put the crew at risk in this case.

In addition to testing the redesigned fuel tank, Discovery will tote more than 5000 pounds (2200 kg) of equipment and supplies to the orbiting outpost.

Astronauts will make two spacewalks during the mission, one to test a new 50-foot (15-meter) extension to the shuttle's robot arm. Crews use the boom to inspect the ship for damage but Nasa wants to know if it could be used to maneuver spacewalkers to inaccessible parts of the shuttle for repairs.

During the second spacewalk, astronauts Piers Sellers, a British-born climate scientist, and Michael Fossum, an American making his first spaceflight, will try to fix the space station's broken mobile transporter.

- REUTERS