Leaden skies, lightning and rain delayed last-minute preparations for the launch of the shuttle Atlantis on the final mission of the 30-year shuttle program.
The orbiter is scheduled to lift off at 1126 local Florida time (1526 GMT) but bad weather forced a delay in final inspections and mission control says there is only a 30 percent chance of everything running on time.
The final mission of the shuttle program is to ferry crucial supplies to the International Space Station.
NASA said the shuttle launch team was evaluating the impact of a possible lightning strike near the launch pad at Kennedy Space Center on Thursday, according to AFP.
"Engineers will review data to determine if the lightning affected space shuttle Atlantis or any of the pad's ground support equipment," NASA said.
"A continuing band of thunderstorms has prevented teams from conducting a detailed pad inspection, which must be performed before the rotating service structure can be rolled back from the shuttle."
If the launch has to be canceled on Friday NASA said there were launch windows on Saturday and Sunday.
"The weather is the weather," Mike Moses, the chair of the mission management team, told the BBC.
"It could be pouring with rain everywhere else in the county but if we get that hole in the right spot at the right time, we can go. I'm feeling pretty good about trying Friday."
Police said huge crowds of up to three quarters of a million people could try to get near the spaceport to view the historic launch, posing a headache for mission control.