For the first time in more than 50 years, astronauts are on their way to the moon.

NASA’s colossal Space Launch System rocket lifted off at 3:35 p.m. Pacific time from the Kennedy Space Center in Florida, marking the start of the 10-day Artemis II mission.

In the hours and minutes leading up to launch, as the astronauts waited aboard, NASA engineers troubleshooted minor issues with the 30-story-tall rocket. First, the teams identified an issue with the hardware that communicates with a system designed to detonate the rocket to protect public safety if the rocket veers off course. Next, there was a fluke temperature reading on the Launch Abort System, designed to pull the crew to safety during such an event. Finally, they managed a brief telemetry issue with the capsule.

All were ultimately resolved, and the agency proceeded.

“On this historic mission, you take with you the heart of this Artemis team, the daring spirit of the American people and our partners across the globe, and the hopes and dreams of a new generation,” Artemis II launch director Charlie Blackwell-Thompson said to the crew minutes before launch. “Good luck. Godspeed, Artemis II. Let’s go.”

In a few days’ time, the four astronauts aboard will perform a flyby of the moon — they will not land on the surface nor will they enter the moon’s orbit. Instead, the flyby is designed as an essential stepping-stone mission to test the rocket, human life support systems and flight procedures ahead of a lunar landing, which NASA hopes to pull off in 2028.

This includes studies on the astronauts’ sleep and mental health, as well as how deep-space radiation and microgravity affect organs and immune system. The crew will also practice manually piloting the spacecraft while still close to Earth.

NASA expects the crew to reach the moon Monday morning, around 10 a.m. Pacific time. As the astronauts pass the far side of the moon, NASA expects to temporarily lose communication with the crew, who will focus on documenting and analyzing the rugged lunar surface. Around this point, NASA anticipates the crew will break the Apollo 13 crew’s record for the farthest distance any human has traveled from Earth.

The crew will then begin their four-day return. The crew capsule is set to slam into the Earth’s atmosphere at roughly 30 times the speed of sound — potentially making it the fastest reentry of a crewed capsule in history — on April 10. NASA anticipates the crew will splash down off the coast of San Diego around 5 p.m. Pacific time.

The mission, made possible by scientists, engineers and support crews across the country and world, has a touch of Southern California, too.

Victor Glover, the astronaut piloting the mission, was once a kid in the Pomona Valley, watching the space shuttle launch on TV and dreaming of driving the thing. He cut his teeth as a test pilot out in the Mojave, attending test pilot school at Edwards Air Force Base and serving on a Navy test pilot squadron in China Lake, Calif.

If the mission is successful, Glover will become the first Black person to travel to the moon. With him will be the first woman to do so, NASA astronaut Christina Koch, and the first non-American to do so, Jeremy Hansen of the Canadian Space Agency. Not to be outdone by his crewmates, mission commander Reid Wiseman, at 50, will be the oldest to do so.

NASA’s Armstrong Flight Research Center inside Edwards Air Force Base is also conducting critical research and testing for the mission. They supported two tests of the rocket’s Launch Abort System — designed to accelerate from 0 to 500 mph in just two seconds to literally outrun the debris of an exploding rocket — in the 2010s. (The rocket discarded the abort system after the crew safely escaped the majority of Earth’s atmosphere.)

During reentry, the center will participate in a high-speed relay of military and civilian planes to chase the capsule and measure how the heat shield performs with high-tech telescopes and sensors. Artemis II is testing out a new reentry trajectory after an uncrewed test mission in 2022 resulted in unexpected damage to the heat shield.

Finally, once the capsule safely splashes down off San Diego, NASA and U.S. Navy divers will secure the capsule, with medical staff from both on standby. A Navy ship will then bring the capsule back to Naval Base San Diego, right next to the city’s downtown.

The Artemis program ultimately aims to land humans back on the moon, help the space agency establish a lunar base and serve as the testing grounds for future missions to Mars.

NASA plans to launch Artemis III, a mission in Earth’s orbit to test docking the NASA spacecraft with SpaceX’s and Blue Origin’s lunar landers, in 2027. It aspires to launch Artemis IV, which would put humans on the surface of the moon, in 2028.

“Artemis II is the opening act,” said NASA Administrator Jared Isaacman shortly before launch. “We’re going into the golden age of science and discovery right now.”