A technical team has drawn up a plan to repair what is known as the ground umbilical carrier plate interface from which hydrogen gas leaked on Wednesday as Discovery's external tank was being filled with fuel for the launch.

Engineers plan to replace a quick disconnect tube and two seals, one on the shuttle's external tank side and one on the ground equipment side, Nasa said in a statement on its website.

The equipment will then be re-tested and the leak checked.

The repair work has delayed the launch of the Discovery to the International Space Station (ISS) until Sunday at the earliest.

Nasa has until Tuesday to launch the shuttle in order not to hamper a Russian Soyuz mission to the ISS that is due to lift off on March 26, as two spacecraft cannot dock at the space station at once.

If Discovery is unable to launch by Tuesday, then its mission will be delayed until April, which will also put back other shuttle flights due in May to repair and maintain the Hubble telescope. -- AFP