A hydrogen leak in the external fuel tank of the space shuttle Discovery has forced NASA to delay its final mission to the International Space Station for the fifth time. Mission managers said the next launch attempt will not take place until November 30 at the earliest, after technicians found the leak which requires major repairs. NASA had previously set the next launch window at December 1. The Discovery launch aims to be the fourth and final shuttle flight of the year, and the last scheduled for Discovery, the oldest in the three-shuttle fleet that is being retired next year. But the mission has been marred by a series of delays brought on by bad weather and equipment problems. Discovery's 11-day mission with its all-American crew of six will deliver a pressurised logistics module called Leonardo, which will be permanently attached to the space station to provide more storage space. The shuttle will also bring Robonaut 2, the first human-like robot in space and a permanent addition to the orbiting space station, as well as spare parts. Two space walks, for maintenance work and component installation, are scheduled. The Discovery has launched into space 38 times, and NASA aims to retire the shuttle after this, its 39th voyage. The final official shuttle mission for the entire programme is scheduled for Endeavour on February 27, 2011.