SpaceX and NASA aim for historic launch

To make sure this rocket makes it safely into Earth's orbit, SpaceX and NASA will need a bit of luck when it comes to Mother Nature.

The 45th Space Wing, an arm of the US military, is constantly monitoring the weather — both at the launch pad and across a broad stretch of the Atlantic Ocean.

The team uses all sorts of instruments, including radars and weather balloons, to ensure that the rocket will have a smooth ride all the way through the upper atmosphere. And conditions are monitored at sea as well: If the rocket misfires and SpaceX's Crew Dragon capsule needs to use its emergency abort system to jettison the astronauts to safety, they'll land in the ocean. And that means officials must ensure that landing won't be made more dangerous by a severe storm or rough waves, so they scan a massive stretch of the Atlantic Ocean all the way to the coast of Ireland.

The 45th Space Wing's weather squadron keeps in constant contact with SpaceX officials, and together they make the final call on whether to move forward or hold off on launch.

President Donald Trump just arrived at Kennedy Space Center aboard Air Force One, and the plane took a quick detour over the launch pad to get a good view of the SpaceX rocket and Crew Dragon capsule.

The aircraft will land at the Shuttle Landing Facility — the same site where Space Shuttle orbiters used to land when they returned from space.

After taking a brief moment to keep an eye on the weather, the hatch was closed on the SpaceX Crew Dragon capsule holding astronauts Bob Behnken and Doug Hurley.

They'll stay locked inside the capsule, waiting for liftoff, while launch officials continue to monitor for storms and technical issues leading up the 4:33 pm ET liftoff time.

Just now, SpaceX carried out a series of communications checks to make sure the astronauts have contact with mission controllers at NASA's Johnson Space Center in Houston and SpaceX's mission control in Hawthorne, California.

On acronym you may hear flying around on the livestream during checks is "GNC" — which stands for "Guidance, Navigation and Control."

NASA has paid SpaceX a total of more than $3 billion via a fixed-price to build and test Crew Dragon. And one new analysis from the nonprofit Planetary Society suggests that, compared to previous NASA programs, the deal is a bargain.

As for the Russian Soyuz spacecraft, which has been the only vehicle capable of carrying humans to the International Space Station for a decade, there isn't really a straightforward comparison.

Soyuz seats have cost NASA up to about $86 million each and around $55 million on average over the past decade, according to a 2019 report from NASA's Office of the Inspector General.

That same report estimates that Crew Dragon seats will cost NASA about $55 million each. But those are estimates based on a contract that doesn't clearly define the per-seat cost.

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.

Speaking on NASA's livestream, SpaceX CEO Elon Musk reflected on today's launch:

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.

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.

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

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.

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.