CAPE CANAVERAL, Fla. -- The launch of a SpaceX rocket ship with two NASA astronauts on a history-making flight into orbit was called off with less than 17 minutes to go in the countdown Wednesday because of thunderclouds and the danger of lightning.
Liftoff was rescheduled for Saturday afternoon.
The spacecraff - designed, built and owned spacecraft by SpaceX - was set to blast off in the afternoon for the International Space Station, ushering in a new era in commercial spaceflight and putting NASA back in the business of launching astronauts from U.S. soil for the first time in nearly a decade.
But thunderstorms for much of the day threatened to force a postponement, and the word finally came down that the atmosphere was so electrically charged that the spacecraft with NASA astronauts Doug Hurley and Bob Behnken aboard was in danger of getting hit by a bolt of lightning.
"No launch for today - safety for our crew members @Astro_Doug and @AstroBehnken is our top priority," NASA Administrator Jim Bridenstine tweeted, using a lightning emoji.
The two men were scheduled to ride aboard the SpaceX's sleek, bullet-shaped Dragon capsule on top of a Falcon 9 rocket, taking off from the same launch pad used during the Apollo moon missions a half-century ago.
Both President Donald Trump and Vice President Mike Pence had arrived to watch.
The flight - the long-held dream of SpaceX founder Elon Musk - would have marked the first time a private company sent humans into orbit.
It would also have been the first time in nearly a decade that the United States launched astronauts into orbit from U.S. soil. Ever since the space shuttle was retired in 2011, NASA has relied on Russian spaceships launched from Kazakhstan to take U.S. astronauts to and from the space station.
There was no immediate comment from Trump and no word from the White House on whether he would return to Florida for the next launch attempt.
During the day, thunder could be heard as the astronauts made their way to the pad at NASA's Kennedy Space Center, and a tornado warning was issued moments after they climbed into their capsule.
"We could see some raindrops on the windows and just figured that whatever it was, was too close to the launch pad at the time we needed it not to be," Hurley, the spacecraft commander, said after the flight was scrubbed. "Understand that everybody's probably a little bit bummed out. That's just part of the deal. ... We'll do it again, I think, on Saturday."
"Appreciate your resilience sitting there in the vehicle," a controller replied.
Behnken responded: "Nothing better than being prime crew on a new spaceship."
The astronauts had to remain strapped in their seats until all the fuel in their rocket was unloaded and the emergency escape system was disarmed.
The launch preparations took place in the shadow of the coronavirus outbreak that has killed an estimated 100,000 Americans.
"We're launching American astronauts on American rockets from American soil. We haven't done this really since 2011, so this is a unique moment in time," Bridenstine said.
With this launch, he said, "everybody can look up and say, 'Look, the future is so much brighter than the present. And I really hope that this is an inspiration to the world."
The mission would put Musk and SpaceX in the same league as only three spacefaring countries - Russia, the U.S. and China, all of which have sent astronauts into orbit.
"What today is about is reigniting the dream of space and getting people fired up about the future," Musk said in a NASA interview before the postponement.
A solemn-sounding Musk said he felt his responsibilities most strongly when he saw the astronauts' wives and sons just before the launch attempt. He said he told them: "We've done everything we can to make sure your dads come back OK."
NASA pushed ahead with the launch preparations despite the viral outbreak but kept the guest list at Kennedy extremely limited and asked spectators to stay at home. Still, cars and RVs lined the roads around Cape Canaveral, with people staking out viewing spots.
The space agency also estimated 1.7 million people were watching the launch preparations online.
Among the spectators was Erin Gatz, who came prepared for both rain and pandemic. Accompanied by her 14-year-old daughter and 12-year-old son, she brought face masks and a small tent.
She said the children had faint memories of watching in person one of the last shuttle launches almost a decade ago when they were preschoolers.
"I wanted them to see the flip side and get to see the next era of space travel," said Gatz, who lives in Deltona, Florida. "It's exciting and hopeful."
NASA hired SpaceX and Boeing in 2014 to design and build spaceships to carry astronauts to the space station in a new kind of public-private partnership. Boeing's capsule, called the Starliner, is not expected to fly astronauts into space until early 2021.
"We're doing it differently than we've ever done it before," Bridenstine said. "We're transforming how we do spaceflight in the future."