Stormy weather could stall this weekend's launch of space shuttle Endeavour.
NASA will try to launch Endeavour on Saturday night, following a pair of delays last month caused by a hydrogen gas leak. The leak has since been plugged; a fueling test validated the repairs last week. But now, NASA will have to deal with thunderstorms.
Forecasters on Wednesday put the odds of acceptable weather at just 40 percent for a Saturday evening launch. Conditions improve only slightly on Sunday.
Five spacewalks are planned, more than usual, to complete work on the Japanese lab, replace space station batteries and unload spare parts carried up on Endeavour.
The linked shuttle-station will be home to 13 people for nearly two weeks, a record crowd.
"This promises to be a very exciting mission, and we're certainly eager to get it under way," said NASA test director Charlie Blackwell-Thompson.
NASA's countdown clocks were set to begin ticking late Wednesday.