SpaceX and NASA aim for historic launch

NASA and SpaceX will do this all over again in three days.

The next launch attempt is slated for Saturday, May 30, at 3:22 p.m. ET.

Until then, astronauts Bob Behnken and Doug Hurley will head back to quarantine.

The astronauts were just informed that this launch is scrubbed for today.

The weather just wouldn't clear up enough to permit liftoff.

NASA and SpaceX will try again on May 30.

Now begins the "scrub sequence" — they'll unload the rocket's propellant. After that, the crew access arm will swing back around and the astronauts will be able to disembark.

Watch:

We're less than a hour away from liftoff. And that means it's time to load the rocket up with fuel.

SpaceX's Falcon 9 rocket will be loaded with RP-1, or "Rocket Propellant 1," and "LOX" — or "liquid oxygen."

The oxygen is made so cold that it turns liquid, and after LOX loading, viewers will be able to see what looks like steam or smoke emanating from the rocket. That's just the super-chilled oxygen boiling off the side of the rocket as the surrounding air heats some of the excess LOX.

Launch officials are still keeping a close eye on the weather. Right now, it's not looking great. But NASA Administrator Jim Bridenstine shared an optimistic tweet as fueling began:

Earlier this week, a group of NASA personnel gathered to take a picture with the Crew Dragon spacecraft and rocket on the launch pad. And it wasn't just for the memories: It's something they do before every mission and there's definitely some superstition around it.

And after launch, they'll dig in to bowls of chili. In the Space Shuttle days, they used to eat just beans. But, as one NASA official told CNN Business, some traditions are being tweaked for this new era of human spaceflight.

Over at the weather squadron, which is part of the military's 45th Space Wing, no one is allowed to wear red socks — the color code for inclement weather.

Food is also involved: "For every launch, about 30 minutes prior, we will bring out a big box of popcorn, and everyone will have a handful."

The reason? The weather group liked their popcorn. But before the fatal destruction of Space Shuttle Columbia in 2003, no one made a batch. So they resolved never to skip the popcorn again.

SpaceX began what's called the "Go/No-go poll" now that we're about 45 minutes away from liftoff.

Right now, the weather is still a bit rough, and it's not clear if conditions will ultimately look good enough to light the engine when the countdown clock runs out.

SpaceX decided to move forward with fueling the rocket. More than 1 million pounds of propellant will be funneled into the Falcon 9 over the next half hour. Meanwhile, the astronauts are still sitting tight inside the Crew Dragon capsule, which sits atop the rocket.

SpaceX's John Insprucker said the latest update on weather from the 45th Space Wing is "red." That's the code for weather too severe to permit liftoff.

It's still possible things will clear up before the liftoff time of 4:33 pm ET.

SpaceX put a couple pieces of special cargo on board with the astronauts for today's launch.

First, a piece of art made of gold, brass and aluminum — meant to signify how far the space program has come and how far humanity has to go in exploring the cosmos.

Second is a mosaic of more than 100,000 photographs of 2020 graduates from all over the world. The composite image makes up an image of planet Earth.

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.