Shuttle set for landmark mission

Discovery is waiting on the weather

American space agency officials are hoping the rain will stop and the sky will clear to allow the space shuttle Discovery to lift off as scheduled on Friday.

The launch, timed for 0138 GMT, will mark the 100th flight for the space shuttle programme.

100 flights

Days in space: 857

Distance in space: About 560m km or 350m miles

Orbits of Earth: About 13,500

Spacewalks conducted: 50

Discovery's seven astronauts are heading for the International Space Station (ISS).

They will add two new segments to the orbiting platform and practise some emergency procedures.

The crew includes the first Japanese astronaut to visit the ISS. Koichi Wakata will operate the shuttle's 15-metre (50-foot) robotic arm, lifting the two new segments from the orbiter's payload bay and positioning them on the station.

"We feel very confident we will be able to accomplish all the tasks on this flight, and I'm very much looking forward to it," Wakata said in a preflight interview.

The crew includes Japanese astronaut Koichi Wakata

One segment is called the Z-1 Truss. This will support new solar panel "wings" to be delivered on a mission in November.

The Z-1 also houses four large gyroscopes that will be used to stabilise the ISS, conserving on-board fuel supplies.

The second segment is a new docking port for space shuttles. The port currently in use will eventually be filled by the US laboratory unit called Destiny.

Two teams of astronauts must work outside the shuttle for four days to secure the new segments and attach cables.

The astronauts will also practise rescue procedures. One of these will require an astronaut to try to return to the safety of the shuttle after simulating an accident that could leave a spacewalker untethered and slowly floating away from both the orbiter and the space station.

Discovery's mission is the last shuttle flight to the ISS before the station's first permanent crew join the ship.

Astronaut Bill Shepherd and his two-cosmonaut team will arrive for a four-month tour of duty at the beginning of November.