From CNN Business' Jackie Wattles
It's still more than two hours until liftoff time, but conditions aren't looking great.
Brevard County, home to the Kennedy Space Center launch site, was briefly under a tornado warning. That warning ended at 2:15 pm ET without any visible twisters coming near the launch site.
Flashes of lightning and thunder claps are a common occurrence, but weather officials are hoping it will pass before takeoff at 4:33 pm ET.
From CNN Business' Elana Zak
Speaking on NASA's livestream, SpaceX CEO Elon Musk reflected on today's launch:
This is a dream come true, I think for me and everyone at SpaceX. This is not something I ever thought would happen. When starting SpaceX in 2002, I really did not think this day would occur.
From CNN Business' Jackie Wattles
NASA astronauts Bob Behnken and Doug Hurley are at the launch pad and boarding the Crew Dragon spacecraft.
Crew Dragon is currently sitting on top of the 230-foot SpaceX Falcon 9 rocket.
To access their capsule, Hurley and Behnken climb up to an aerial "crew access arm."
Meanwhile, an alarm rang out at the press site, warning of severe weather conditions. It's possible heavy thunderstorms will roll through Kennedy Space Center.
But if they clear before liftoff, Behnken and Hurley could still take off today.
If not, NASA and SpaceX will plan to try again on May 30.
From CNN Business' Jackie Wattles
Robert "Bob" Behnken, 49, and his crewmate, Douglas Hurley, were both military test pilots before they joined NASA in 2000. The space agency has a long history of selecting test pilots, who spend hundreds of hours flying around in experimental supersonic aircraft, to be astronauts.
It's probably a dream of every test pilot school student to have the opportunity to fly on a brand new spaceship.
Hometown: St. Ann, Missouri.
Role in this mission: Joint operations commander. He will be responsible for some of the SpaceX Crew Dragon spacecraft's major milestones, including docking with the International Space Station and undocking.
Total hours previously logged in space: 708
Last spaceflight: STS-130 in February 2010
From CNN Business' Jackie Wattles
One half of the duo that will pilot this historic spaceflight is Douglas "Doug" Hurley, 53. Both Hurley and his crewmate, Robert Behnken, were selected to be NASA astronauts in 2000 and are veterans of Space Shuttle missions. They're also longtime friends who attended each others' weddings.
It has been such a long road, and it's kind of been a personal journey...to transition from the Space Shuttle era to this next era of spaceflight.
Hometown: Apalachin, New York
Role in this mission: Spacecraft commander. He's responsible for keeping things on track during launch and for landing and recovery when the astronauts return from space.
Total hours previously logged in space: 680
Last spaceflight: Hurley piloted the final space shuttle mission, STS-135, in July 2011.
From CNN Business' Jackie Wattles
Reporters lined the street as astronauts Bob Behnken and Doug Hurley passed by on the Saturn Causeway — the road that will take them to the launch pad.
Behnken and Hurley are now preparing to board SpaceX's Crew Dragon capsule, where they'll sit for the next three hours as NASA and SpaceX prepare for liftoff.
If the weather looks ok in the hours ahead, liftoff is slated to occur at 4:33 pm ET.
Officials said at about 1:45 pm ET that the odds of favorable weather stand at about 50-50.
From CNN Business' Jackie Wattles
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Astronauts Bob Behnken and Doug Hurley left their quarantine area around 1:15 pm ET on Wednesday.
Vice President Mike Pence, SpaceX CEO Elon Musk and NASA Administrator Jim Bridenstine will see the astronauts off — along with the astronauts' families. Behnken and Hurley are both married to fellow NASA astronauts and have small children.
To say farewell, the men, suited up in the SpaceX spacesuits, offered air hugs to their kids.
From CNN Business' Jackie Wattles
This mission will mark a triple crown of historic landmarks:
WATCH:
From CNN Business' Jackie Wattles
Singer Kelly Clarkson briefly joined NASA's livestream — remotely, of course — to sing the national anthem.
The NASA astronauts are expected to begin making their way to the launch pad shortly. Their mode of transportation? Two Tesla Model X's emblazoned with NASA logos.
Vice President Mike Pence, SpaceX CEO Elon Musk and NASA Administrator Jim Bridenstine will see the astronauts off.
