Article Posted on : - Jan 12, 2011

Discovery may embark on its final space mission on February 24. A file photo

WASHINGTON (AFP):NASA has said it will aim to launch space shuttle Discovery on February 24, after engineers found a way to shore up cracks on its external fuel tank that have delayed its final liftoff.

"We think we can support a launch date for the 24th of February," International Space Station Programme manager Mike Suffredini said Tuesday.

NASA engineers have been working since November to figure out why cracks were emerging on the 22-foot-long U-shaped aluminum brackets, called stringers, on the shuttle's external fuel tank.

According to shuttle programme manager John Shannon, engineers performed exhaustive tests and found that the complex problem was not solely a result of material quality or flaws that took root during assembly.

Shannon described the dilemma as "low risk" but at the same time, "hard to quantify."

In the end, engineers agreed that installing small metal strips, called radius blocks, on to the stringers would reinforce their strength.

"It is very hard to tell where your assembly stresses are, you can't really tell that by X-ray, so what we decided to was we could get rid of the whole discussion by putting in these things called radius blocks," Shannon said.

"It is a very simple, elegant fix to the problem," he said. "We are going to fly with a lot of confidence in this tank," Shannon told reporters.

The work that is currently being done to fix the stringers should be complete by January 23, Shannon said.

"I'm very confident that we finally got it figured out," said Shannon. "We are on the road to bringing this tank to 100 percent."

Discovery has been plagued by setbacks since its latest attempt to launch was scratched on November 5 when technicians found a hydrogen leak and later a series of long cracks on the shuttle's external fuel tank.

Another shuttle, Endeavour, is set to take off in April in what will be the last shuttle launch scheduled for the US programme, though a final launch could take place in the summer before the entire fleet is retired for good.

NASA officials declined to answer questions about the Endeavour launch, which is to be led by astronaut Mark Kelly.

Kelly's wife, US lawmaker Gabrielle Giffords, is recovering from a gunshot to the brain after a political meeting in Tucson, Arizona.

The Discovery has launched into space 38 times, and NASA aims to retire the shuttle after its final and 39th voyage.

Discovery is the oldest in the remaining three-shuttle fleet. The three US shuttles – the other two are Atlantis and Endeavour – are due to become museum pieces once the final shuttle mission takes place.

Then, the Russian Soyuz spacecraft – a modernised version of which recently dropped off three fresh crew members to the ISS, doubling the crew to six – will for several years be the only vehicle for transporting humans into space.