By MARCIA DUNN
AP Aerospace Writer
CAPE CANAVERAL, Fla. (AP) -- NASA began another countdown Wednesday for space shuttle Endeavour, but stormy weather could stall the weekend launch.
The space agency 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, launch controllers 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.
The seven astronauts assigned to the 16-day mission returned to Kennedy Space Center on Tuesday. They will deliver and install the final piece of Japan's lab at the international space station.
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.
The countdown clocks began ticking late Wednesday night.