Weather forces second shuttle launch delay [video report]

The launch has been postponed until 6.38am Wednesday (NZT). Picture / Reuters.

CAPE CANAVERAL - Bad weather has forced Nasa to postpone the launch of the space shuttle Discovery for the second consecutive day, with the next launch attempt set for Tuesday Florida time.

The decision to cancel liftoff came minutes after the seven crew members boarded the spaceship, even before the vessel's hatch was closed. Hours before, Nasa forecasters had estimated only a 30 per cent chance that weather would favour launch, as thunderclouds menaced the Kennedy Space Centre.

"We've concluded that we're not going to have a chance to launch today," launch director Mike Leinbach told the crew as they sat strapped into their shuttle seats.

"OK, we copy," said shuttle commander Steve Lindsey. "Looking out the window, it doesn't look good today, and we think that's a great plan."

Any rain during liftoff might damage the spaceship's heat-shielding tiles, and a lightning strike could knock out the computers that control the ship. Even some kinds of thick, high clouds make launch hazardous.

The next launch was set for 2.38pm Tuesday (6.38am Wednesday NZT).

Discovery's mission is only the second since the 2003 Columbia accident, and another disaster or serious problem likely would end the shuttle programme. Nasa is hoping to fly 16 more missions to complete the US$100 billion ($168 billion) space station before the shuttle fleet is retired in 2010.

Shuttle safety has been at the forefront of the programme since Columbia disintegrated on re-entry, killing seven astronauts. Nasa has twice redesigned the shuttle's fuel tank, which shed insulating foam that triggered the accident.

The agency's top engineer and chief of safety wanted more repairs on the tank before Discovery was launched, but Nasa administrator Michael Griffin overruled them, arguing that if foam falls again from the fuel tank and damages the shuttle, the crew could stay aboard the space station and await rescue.

Griffin said this debate over safety is a good thing.

"Nasa had been criticized in the past for adhering to groupthink, for enforcing a needless conformity in decision-making," Griffin said on CNN's Late Edition.

"We have difficult, technically complex and subtle decisions to make ... We did the best analysis we can, and we make a decision, and I'm comfortable with that."

Delaying the launch would put more pressure on the shuttles, which are the only vehicles that can deliver and install the station's remaining trusses, solar arrays and laboratories.

The agency plans two more flights this year and about four a year until the station is finished and the fleet is retired.

Nasa had hoped to resume space station construction last year, but the shuttle's fuel tank failed its first test flight. Engineers then removed two long wind deflectors from the tank, which had shed foam during Discovery's 2005 liftoff.

- REUTERS