- Elon Musk said he was "overcome with emotion" after SpaceX's first-ever astronaut launch on Saturday.
- Though his adrenaline was at "100%" during the first launch attempt on Wednesday, the SpaceX CEO said he didn't feel nervous at all this weekend.
- Musk got choked up talking about his responsibility to bring the astronauts, who each have young children, home safely.
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Elon Musk struggled to describe how he felt after SpaceX, the company he founded in 2002, launched its first people into Earth's orbit on Saturday.
At 3:22 p.m. ET, a Falcon 9 rocket lifted off from Cape Canaveral, Florida, carrying the Crew Dragon spaceship that SpaceX designed and NASA funded. Inside sat two NASA astronauts: Bob Behnken and Doug Hurley. 
It's the first time a commercial spacecraft has carried humans into space, and the first time astronauts have launched from the US since the end of the Space Shuttle Program nine years ago.
"I'm really quite overcome with emotion on this day. It's kind of hard to talk, frankly," Musk told reporters in a call after the launch. "I've spent 18 years working toward this goal, so it's hard to believe that it's happened."
Currently on board the Crew Dragon and orbiting Earth, Hurley and Behnken will test some of the spaceship's systems, eat, and sleep before they're scheduled to join the International Space Station on Sunday at 10:27 a.m. ET.
"It is a little hard to process. I think at this point I haven't sorted out my emotions," Musk said. "This is hopefully the first step on a journey towards civilization on Mars, of life becoming multiplanetary, a base on the moon and expanding beyond Earth."
Here's what Musk shared about his feelings leading up to the launch, his fears going forward, and his responsibility for the lives of the astronauts on his company's spaceship.
By Saturday, Musk said, 'I didn't feel nervous'
The Demo-2 launch was originally scheduled for Wednesday afternoon. Behnken and Hurley boarded the Crew Dragon, and the rocket was filled with propellant below them, but bad weather forced NASA and SpaceX to scrub the launch just 17 minutes before liftoff.
"On Wednesday during the first countdown my adrenaline was railed at 100%, and when the launch was called off it went to 0%," Musk said. "I just basically collapsed and slept for the longest time I've slept in probably a year."
The next launch preparation, on Saturday, was a different story.
"Oddly enough, today, I don't know, it felt like the fates were aligned and I didn't feel nervous," Musk said. "I felt like it was going to work."
Though weather forecasts were similar to Wednesday throughout Saturday morning, the clouds cleared about an hour before launch, making way for the Falcon 9 rocket to hurtle Behnken and Hurley into space.
'We've done everything we can to make sure your dads come back OK.'
Behnken and Hurley each have a young son. Their wives are also astronauts, and they all waved goodbye before the men climbed into a Tesla to drive to the launchpad.
NASA TV microphones picked up Behnken telling his son: "Be good for mom. Make her life easy."
When asked about his responsibility for the men's lives, both as SpaceX CEO and as a dad himself, Musk noted that the mission had just begun. The astronauts must dock to the space station, live there for up to 110 days, ride the Crew Dragon on a fiery fall through Earth's atmosphere, and splash down safely off the coast of Florida.
"The return is more dangerous in some ways than the ascent, so we don't want to declare victory yet," he said.
Then he stuttered and went silent. Finally, he said, "I'm getting choked up, I'm sorry, I'm not sure I can answer the question."
Musk has previously expressed concern about the spaceship's reentry. The asymmetric design, he has said, could cause the ship to rotate too much as it hurtles through Earth's atmosphere, catch plasma in its thrusters, overheat and lose control. He has also noted a concern about the ship's parachutes, which must deploy to slow down the Crew Dragon as it falls through thicker atmosphere.
Musk told NASA TV on Wednesday that he had spoken with the astronauts' families before they boarded the spaceship for the first launch attempt.
"I felt it most strongly when I saw their families just before coming here," he said, pausing for a few seconds and appearing to gather himself before continuing. "I said, 'We've done everything we can to make sure your dads come back OK.'"
On May 23, NASA told Business Insider that it estimated there was a 1-in-276 chance that the flight could be fatal and a 1-in-60 chance that a problem would cause the mission to fail (but not kill the crew).
Behnken and Hurley, for their part, have accepted the risk.
"I think we're really comfortable with it," Behnken told Business Insider on Friday.
Despite the uncertainty of the mission's future, the astronauts, NASA officials, and Musk all expressed pride in the achievement of launching astronauts aboard the new spacecraft.
"We haven't quite yet docked to the space station, and of course we have to bring them back safely, and we need to repeat these missions, and have this be a regular occurrence, so it's a lot of work to do. But it's just incredible," Musk added. "It's something that I think humanity should be excited about and proud of."
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