Image caption Mark Kelly flies into KSC ahead of the launch

The weather is looking excellent for the final launch of the US space shuttle Endeavour on Friday.

Forecasters say there is only a 20% chance of poor conditions holding the orbiter on the ground.

The youngest of America's shuttles is set to deliver a $2bn (£1.2bn) particle physics experiment to the International Space Station (ISS).

After the mission, the vehicle will be exhibited at the California Science Center in Los Angeles.

For its final voyage into space, Endeavour will be commanded by Mark Kelly, who flew into the Kennedy Space Center on Tuesday with his crew.

US Navy Captain Kelly's wife, Arizona Congresswoman Gabrielle Giffords, currently recovering from a gunshot wound to the head, is expected to be in the viewing stands for the launch.

"It's something she's been looking forward to for a long time," Endeavour's commander told reporters here on his arrival at KSC.

Image caption Nasa reports no technical issues of concern as it moves towards launch day

"She's been working really hard to make sure that her doctors would permit her to come, and she's more than medically ready to be here and she's excited about making this trip."

It is understood that US President Barack Obama and his family will also come to Florida's Space Coast to see the ascent.

Local police estimate that several hundred thousand people lined roads and beaches in the area to see Discovery's last lift-off in February.

That number may be eclipsed at the end of the week.

While Nasa is very pleased to see such interest in America's space programme, the agency does have some concerns over how the crowds could impact its preparations.

Staff took several hours to get off site after Discovery's lift-off because of congested roads. So, if Endeavour has a launch delay, it may be necessary for the second attempt to be put back 48 hours to allow workers to get home, have some rest time and then return to the spaceport.

Nasa managers say they are keeping that option in mind, but will be hopeful such a contingency is not necessary.

"Our going-in philosophy is that we will look at what the conditions give us - if a scrub occurs, when it occurs," explained Nasa test director Jeremy Graeber. "We'll make a smart decision when we understand whether it makes sense to do 24 hours or 48 hours."

Image caption Endeavour will become a permanent exhibit at the California Science Center in Los Angeles

A weather front is due to sweep through the Space Coast on Thursday, leaving fine conditions for launch day.

The one issue that may crop up will be the potential for gusting winds that would make it difficult for the shuttle to land back at Kennedy were it to have an abort during the ascent to orbit.

"Our main concern for launch day will be crosswinds, and there's just a 20% chance of KSC weather prohibiting launch," said shuttle weather officer Kathy Winters. "The main thing will be that we will want to see that frontal system [go] through us on Thursday evening and still be able to complete all of our pre-launch preparations."

Shuttle Endeavour was built to replace the Challenger ship which was lost, along with her crew of seven, in a catastrophic accident in 1986. All of the orbiters are being retired to make way for astronaut "taxis" to be provided by the private sector sometime this decade.

Jonathan.Amos-INTERNET@bbc.co.uk