SpaceX and NASA are keeping a close eye on the weather ahead of their second attempt at a historic crewed launch from Florida. The launch will see astronauts travel to space from U.S. soil for the first time since 2011.

NASA astronauts Doug Hurley and Bob Behnken are scheduled to launch from Kennedy Space Center’s launch pad 39A, at 3:22 p.m. EDT on Saturday. The launch pad was also used for the Apollo and space shuttle missions.

The first attempt to launch SpaceX’s Falcon 9 rocket and the Crew Dragon spacecraft was scrubbed just 16 minutes and 54 seconds before launch on Wednesday as a result of unfavorable weather in the flight path.

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Dolphins swim in a lagoon near Launch Complex 39A at sunrise at Kennedy Space Center in Florida on May 30, 2020.

Dolphins swim in a lagoon near Launch Complex 39A at sunrise at Kennedy Space Center in Florida on May 30, 2020. (Photo by GREGG NEWTON/Gregg Newton/AFP via Getty Images)

“We are moving forward with launch today. Weather challenges remain with a 50% chance of cancellation,” tweeted NASA Administrator Jim Bridenstine early on Saturday.

The launch of the Demo-2 mission will be the first time a private company, rather than a national government, sends astronauts into orbit.

In a blog post late on Friday, NASA’s Commercial Crew program explained that the space agency and its SpaceX partner are closely monitoring the weather. “Although the weather models for Saturday show an improvement in conditions around Launch Complex 39A at NASA’s Kennedy Space Center in Florida, teams continue to monitor launch and down range weather,” it said.

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SpaceX and NASA are monitoring the weather not just at Kennedy Space Center, but all the way up the Eastern Seaboard and across the North Atlantic to Ireland. Waves and wind need to be within limits in case the SpaceX Dragon crew capsule, carry Hurley Behnken, needs to make an emergency splashdown on the way to orbit.

“The primary concerns remain flight through precipitation, anvil clouds and cumulus clouds. However, outside of the launch site are some areas of concern with a potential for lightning storms and high winds and waves along the flight path,” NASA said, in its blog post late Friday.

“All systems go for Crew Dragon’s test flight with @NASA astronauts @AstroBehnken and @Astro_Doug . Teams are keeping an eye on weather,” tweeted SpaceX.

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“Proceeding with countdown today, weather cancellation risk ~50%,” tweeted SpaceX CEO Elon Musk.

“Launch Day. In America. Again,” tweeted Behnken on Saturday morning.

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The Demo-2 mission has an instantaneous launch window, which means that the flight is scheduled to launch at exactly at 3:22 p.m. EDT with no potential to extend the window.

Launched atop the Falcon 9 rocket, Crew Dragon will accelerate to approximately 17,000 mph, according to NASA, placing the capsule on course for the International Space Station. The duration of the astronauts’ stay on the orbiting space lab is yet to be determined.

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If Saturday’s launch is scrubbed, another launch attempt could take place on Sunday, according to NASA.

The Associated Press contributed to this article.

Follow James Rogers on Twitter @jamesjrogers