DISCOVERY ROLLS OUT TO LAUNCH PAD

Discovery's orange external tank has been undergoing repairs for over a month

The US shuttle Discovery has rolled out for what should be its final mission.

The orbiter completed its slow journey to the Kennedy Space Center's Launch Pad 39A overnight, Monday into Tuesday.

Every step of the 5.4km (3.4-mile) crawl was bathed in bright xenon light.

Discovery's flight to the space station is scheduled to begin on 24 February. With its crew of six astronauts, the ship will deliver a storeroom to be attached to the 350km-high platform, along with further supplies and spares.

Stacked with its external fuel tank and solid rocket boosters, Discovery took seven hours to complete the roll from Kennedy's vast Vehicle Assembly Building to complex 39A. Many Kennedy employees, along with their families, came to witness the event.

Nasa last tried to launch the vehicle in November but technical hitches, including cracks on its giant external fuel tank, kept the ship on the ground.

The agency said engineers had now fixed those defects and carried out further work to strengthen the tank.

President Barack Obama and the US Congress have determined that the shuttle fleet should be retired this year.

Discovery is the oldest of the three surviving orbiters. First launched in 1984, it has since completed 38 missions, travelling some 230 million km in the process.

Endeavour is expected to fly to the station in April. Atlantis will go no earlier than June, if Nasa has sufficient money left in its shuttle programme budget.

Following the fleet's retirement, the plan is for US astronauts to fly to the space station on Russian Soyuz rockets until perhaps the middle of the decade.

A number of American companies then hope to be in a position to sell launch services to Nasa on a range of new vehicles.

The intention is that the agency should put its efforts into leading the development of a large rocket that can send astronauts beyond the space station to destinations such as asteroids.

Congress has set out the broad capabilities it expects to see in this rocket and has given a deadline of 2016 for its introduction. However, Nasa has said it cannot deliver such a vehicle in the time and with the budget the politicians have specified.

Discovery is targeting a 1650 EST (2150 GMT) launch on 24 February.

The mission's lead spacewalker Tim Kopra was injured in a bicycle accident last month and has had to be replaced by back-up crewman Steve Bowen.