NASA delays launch of space shuttle Endeavour due to hydrogen leak

NASA halted the countdown clock less than seven hours before the scheduled 7.17am lift-off from Kennedy Space Centre at Cape Canaveral, Florida, after highly volatile hydrogen gas was found to be escaping from the external tank during the final stages of the fuelling process.

The delay is critical for Nasa, which had been set to launch Endeavour on a 6.6 million-mile mission to continue construction of the International Space Station.

Shuttle managers will assess the leak and meet Saturday morning to discuss what steps to take next, including setting a new launch date, the space agency said.

Endeavour, carrying seven astronauts and a key component for Japan's Kibo science laboratory, is scheduled for a mission to the International Space Station. 

Five spacewalks are planned for the crew after the shuttle docks with the station for a planned 16-day mission. 

On arrival at the $100 billion International Space Station, the crew will be welcomed aboard by the six-strong team already living there, creating the biggest gathering ever held in space.

They will work together on a gruelling series of tasks that will include installing the final segment of the station's Japanese laboratory module – known as Kibo – to create an external platform on which scientific experiments can be conducted in the vacuum of space.