Mike Blake / Reuters

CAPE CANAVERAL, Fla.—About a year ago, when SpaceX made history with the successful launch of one of the most powerful rockets ever made, Elon Musk was ebullient. It had seemed possible, even to him, that on its first flight the Falcon Heavy could fail and go up in flames. So when the rocket sailed into the sky and deposited a shiny red Tesla in space, he floated into a room packed with reporters, ready to celebrate, a big grin on his face.

“It seems surreal to me,” Musk, the company’s CEO and lead designer, said then. “I had this image of just a giant explosion on the pad.”

This was not the same Elon Musk who appeared at a press conference early Saturday morning, after another historic launch at Kennedy Space Center. SpaceX had just sent a brand-new spacecraft toward the International Space Station. The spectacle was stunning: A Falcon 9 rocket rose into the dark night sky like a flame ascending a candlewick. If the mission continues to go well, NASA will use SpaceX’s spacecraft to fly astronauts to the ISS, as soon as this year. And yet Musk appeared serious, subdued.

It was 4 o’clock in the morning and, like everyone else in the room, Musk probably hadn’t slept in hours, which might have contributed to his stolid demeanor. But the pressure of the launch seemed to weigh heaviest. Instead of giddy disbelief, Musk exuded plain relief.

“To be frank, I’m a little emotionally exhausted,” Musk told reporters. “Because that was super stressful. But it worked—so far.”

While the launch went splendidly, the mission is far from over. This is the first test of the spacecraft, known as Dragon, which is designed to carry humans. Dragon will spend Saturday catching up to the ISS and dock to the station Sunday morning. The spacecraft will detach, head back to Earth, and parachute down to the Atlantic Ocean on Friday.

The schedule sounds straightforward, but each step is risky, Musk said, and engineers have imagined what could go wrong. Other, cargo-only versions of Dragon are lassoed by the station’s robotic arm, operated by an astronaut; the crew version uses autonomous software to guide itself to a port. During this maneuver, the spacecraft could fail to attach to the ISS. If it goes well, Dragon could still tumble as it reenters Earth’s atmosphere. Or, on the way down, its parachutes could fail to deploy correctly.

The complicated mission is part of a NASA program to use commercially built launch systems to ferry astronauts to and from the ISS. NASA lost that ability in 2011, when the venerable Space Shuttle program folded under the weight of cost, politics, and safety concerns. The same year, the space agency asked the private sector to come up with ideas for the future of space transportation. By 2014, two front-runners had emerged, SpaceX and Boeing, and NASA gave them billion-dollar contracts to help develop their concepts.

Over the next week, SpaceX must prove its launch system can safely carry astronauts to and from the ISS. “Unless something goes wrong, I would think that we’ll be flying hopefully this year, this summer,” Musk said. The NASA administrator, Jim Bridenstine, sitting alongside Musk, concurred.

SpaceX would make history with a crewed flight. But the company is already steeped in the stories of American spaceflight. It leases and launches from Kennedy Space Center’s launchpad 39A, the site of launches for the Apollo and Space Shuttle programs. Musk and his fellow engineers watched Saturday’s launch from inside a firing room at Kennedy Space Center, where mission control once gathered for the launches of space shuttles, glued to their headsets and computer screens. The NASA astronauts assigned to SpaceX’s first crewed flight, Doug Hurley and Bob Behnken, joined them.

A reporter asked Musk at the press conference how he felt about conducting his missions in these storied places.

“It’s hard to believe; I would never have believed that this would ever happen,” Musk said. He paused and shifted his gaze beyond the microphone in front of him, as if to focus on a scene playing out in his mind.

“Yeah, I just think, you know—humanity landing on the moon, man, that was maybe the greatest thing ever,” he continued, choking up. “So I can’t believe we’re launching from that pad.”

The emotion seemed to pass, and then Musk took on an urgent tone. “I hope we go back to the moon soon,” he said. “We should have a base on the moon, like a permanently occupied human base on the moon. And send people to Mars, and build a city on Mars. That’s what we should do.”

The remarks seemed a little off script given the subject at hand—getting humans to low-Earth orbit. But Musk is a well-known multitasker, in cosmic daydreams and real-life situations, and his past few months have been filled with tumult, both professional and personal. The unexpected display of emotion, on what could been a morning of easy triumph, hinted at the intensity of trying to live out the billionaire inventor’s version of having it all.

The Air Force, a SpaceX customer, is currently evaluating the launch-certification process for the company’s Falcon 9 and Falcon Heavy rockets, but hasn’t publicly given a reason why. SpaceX has questioned the U.S. government’s decision to use the United Launch Alliance, a Boeing and Lockheed Martin venture, to launch a NASA mission to Jupiter; SpaceX has argued that it can offer a better, cheaper deal.

NASA is also in the midst of interviewing hundreds of employees at both SpaceX and Boeing as part of a review of workplace culture. Bridenstine said he ordered the assessment because he wants to detect warning signs that could contribute to dangerous or potentially deadly errors. The review was announced not long after Musk smoked marijuana and drank whiskey on a popular podcast, which drew a rebuke from Bridenstine.

This week, the administrator sounded optimistic. “I’m highly confident that our contractors are complying with the terms of their contracts, and I expect that we will find that their culture is very safe,” he said.

And that’s just SpaceX. Musk is still dealing with the fallout from being sued by the Securities and Exchange Commission over a tweet about Tesla that officials said violated federal regulations. The parties reached a settlement in September that forced Musk to step down from his role as chairman of Tesla’s board for three years (but allowed him to still stay on as CEO) and pay $20 million in fines. It also required Tesla to establish stricter control over Musk’s communications, including on Twitter.

But the oversight doesn’t appear to have stuck. Last week, the SEC requested that a federal court hold Musk in contempt for tweeting about Tesla production goals. Less than an hour before the pivotal SpaceX launch, Musk was still conversing with other users on Twitter about the electric-car company.

The launch eventually shifted Musk’s gaze from the screen to the sky. “Need to get back to SpaceX launch control,” he tweeted. In the firing room, as the Dragon spacecraft hurtled into space, Musk said he asked his future passengers, Hurley and Behnken, for their reactions on the launch system. They told him they felt good about flying on it.

If Musk seems stone-faced now, imagine him on the day Hurley and Behnken are inside the Dragon spacecraft, perched atop the Falcon 9.

“I suspect it will be extremely stressful,” he said.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.