Countdown for shuttle mission

ISS several years behind schedule

By Richard Hollingham of BBC Science

Final preparations are being made for the scheduled 2015 GMT launch of the space shuttle Atlantis on a mission to service the International Space Station.

STS -101

Launch - 2115 BST, 24 April

ISS Docking - 1535 BST, 26 April

ISS Undocking - 0851 BST 2 May

Landing - 1742 BST, 4 May

Orbit Altitude - 300 km

"We are ready to go," said Nasa's Bob Cabana.

The International Space Station is several years behind schedule and many billions of dollars over budget.

It is currently unoccupied, awaiting a crucial Russian service module which is due to be launched later this year.

During this latest mission, the seven astronauts on board Atlantis will help prevent the space station from falling into disrepair.

Among their tasks, they will be transferring more than a tonne of cargo, replacing failed batteries and installing new equipment.

The shuttle will also be used to boost the space station's orbit.

Torch into space

Among the many items being taken into space is the torch for this year's Olympic Games in Sydney as part of the longest tour in the history of the Games.

During Atlantis' 10-day mission, the carefully packed torch will overfly virtually all the nations which are participating in the games.

In May the Olympic's organisers also plan to take the flame underwater in special casing at the Great Barrier Reef.

The launch from the Kennedy Space Center was originally scheduled for 13 April.

It was delayed after shuttle commander Jim Halsell twisted his ankle during a training exercise.

This will be Atlantis' 21st mission. More than 100 changes have been made to the shuttle, including improved communications and air-conditioning systems and a new instrument panel.

The shuttle is scheduled to return to the Kennedy Space Center on 4 May.