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

Read: A historic rocket launch lights up the night

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.”