SpaceX's landmark launch to the International Space Station -- the first crewed mission to blast off from US soil in almost a decade -- was scrubbed Wednesday due to bad weather.
With NASA astronauts Bob Behnken and Doug Hurley strapped into the Crew Dragon capsule, the launch pad platform retracted and rocket fueling underway, SpaceX made the call to abort.
"Unfortunately, we are not going to launch today," launch director Mike Taylor said, with less than 20 minutes to go until takeoff.
Officials cited the threat of lightning, among other factors.
It means a wait of at least a few more days for the first crewed launch on an American rocket since the space shuttle program ended in 2011. They will try again on Saturday.
If successful, the launch will be the first time the feat has been performed by a privately-owned company.
A live video feed showed Behnken and Hurley -- in their futuristic white uniforms adorned with the US flag and the logos of NASA and SpaceX -- waiting as propellant was unloaded from the reusable Falcon 9 rocket.
The emergency ejection system remained armed until the fuel tanks were emptied, in case of an accidental explosion.
The launch had been scheduled for 4:33 pm (2033 GMT) from the Kennedy Space Center's Launch Pad 39A. Neil Armstrong and his Apollo 11 crewmates lifted off from the same spot on their historic journey to the Moon.
The mission comes despite shutdowns caused by the coronavirus pandemic, with the crew in quarantine for the past two weeks.
President Donald Trump and First Lady Melania Trump had arrived in Florida to watch, but headed back to the White House once the launch was called off.
Highlights of SpaceX Rocket Launch
🌩️ No launch for today - safety for our crew members @Astro_Doug and @AstroBehnken is our top priority.- Jim Bridenstine (@JimBridenstine) May 27, 2020
We'll try, try again to #LaunchAmerica on Saturday with liftoff at 3:22pm ET. NASA TV will begin coverage at 11 am. Join us again virtually: https://t.co/LO1sJwia2G