NASA officials have canceled a launch of Space Shuttle Endeavour planned for today because of hydrogen leak.
The problem is similar to one the space agency faced in March during the launch countdown of Discovery.
The leak was discovered while the space shuttle was being fueled.
The astronauts had not yet suited up for the planned morning launch.
Endeavour and its crew are scheduled to spend 11 1/2 days at the international space station. Five spacewalks are planned.