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NASA technicians said they found no damage, but will need another day to check critical systems.
The launch had been scheduled for Saturday night. The next launch attempt will be at 7:13 p.m. Sunday.
Endeavour should have blasted off to the international space station in mid-June, but was grounded by potentially dangerous leaks of hydrogen gas. Repairs to a misaligned plate on the external fuel tank, which hooks up with a hydrogen vent line, solved the problem.
The shuttle and its crew are set to deliver and install the third and final piece of Japan's $1 billion space station lab, named Kibo, Japanese for hope. The first two sections flew up last year.
Seven shuttle astronauts plus six station residents will make for the biggest crowd ever in orbit.
Five spacewalks are planned during the 16-day flight.
NASA has until Tuesday or possibly Wednesday to send up Endeavour before making way for the launch of an unmanned Russian supply ship. If that happened, the shuttle flight would be off until late July.
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