'Endeavour's next launch attempt for its STS-127 mission is targeted for July 11 at 7.39 pm Singapore time,' the US space agency said in a statement after scrubbing the liftoff despite efforts to troubleshoot the liquid hydrogen leak.

The leak was in the same spot that halted the previous launch, in the venting system supposed to carry excess hydrogen safely away from the launch pad.

The leak's cause remains unknown. It was the same problem that forced NASA to abandon its first attempt to launch the shuttle Discovery in March.

When Endeavour eventually does head out from NASA's Kennedy Space Center in Florida, it will help finish work on the International Space Station, which orbits 350 kilometres above Earth. -- AFP