Weather could get in the way of space shuttle launch

CAPE CANAVERAL, Fla., June 29 (Reuters) NASA faces a formidable but familiar opponent as it prepares to launch the space shuttle Discovery from Florida on Saturday -- the weather, officials have said.

As NASA prepared to start the clocks for the traditional three-day countdown, a shuttle weather officer predicted a 60 percent chance the launch would have to be postponed. Florida's frequent summer thunderstorms are the primary concern.

Discovery is scheduled to lift off at 3:49 p.m. EDT (1949 GMT) Saturday on a voyage to the International Space Station, a critical mission whose failure likely would bring a premature end to the US space shuttle program and leave the space station only half built.

NASA has until July 19 to get Discovery airborne before facing a delay until at least late August, when suitable conditions for launch re-occur.

The agency is hoping to fly three missions in 2006 and jump-start space station assembly, which has been on hold since December 2002.

Discovery's launch is going forward over the objections of some top NASA safety and engineering officials who wanted it delayed for additional work on the external fuel tank, which triggered the destruction of shuttle Columbia and the deaths of seven astronauts in 2003.

Eliminating the problems with the fuel tank was NASA's first and most critical step after the Columbia disaster and NASA's top decision makers consider the work on the tanks sufficient to resume flight.

BUSY TRIP But Discovery's 12-day flight will need to accomplish much more for station construction to resume as planned with the launch of Atlantis during the next launch period, which begins Aug. 28.

The shuttle will be toting more than 5,000 pounds (2,268 kg) of new equipment and supplies to the outpost including replacement parts for the station's broken mobile transporter.

The rail cart, which travels on tracks on the outside of the station, has been shut down since December when a set of power, data and communications cables was severed.

Spacewalkers need the transporter to install truss and solar arrays scheduled to fly aboard Atlantis, said Discovery's lead flight director Tony Ceccacci.

''We need the repair to continue the assembly sequences,'' he said.

Fixing the transporter will be up to astronauts Piers Sellers, a British-born climate scientist flying for the second time, and Michael Fossum, who will be making his first spaceflight.

Their first spacewalk is devoted to testing a new 50-foot (15-metre) extension to the shuttle's robot arm.

Shuttle crews use the boom to inspect their ship for damage after launch, but NASA would like to know if it also could be used to maneuver spacewalkers to inaccessible parts of the shuttle to make repairs.

The rail cart repair is scheduled for the second spacewalk.

If approved, a third outing would be to test a material that could be used to repair a shuttle's carbon wing panels or nosecap.

Discovery also carries a U.S.-built oxygen generator that will be needed if and when the station's crew size is increased to six residents.

One of Discovery astronauts, Europe's Thomas Reiter, will be staying aboard the outpost as a third crewmember. Since the Columbia accident, the station has been operated by two-man crews to save on supplies while the shuttle fleet was grounded for repairs.

''After years and years of training, I think this is a remarkable moment,'' Reiter said. ''I think we all are confident our launch will signify the continuation of assembly of the station, returning to a three-man crew and utilizing the station for its (intended) purpose.'' Reuters SK VP0420