Artemis II astronauts in moon orbit

Four astronauts embarked on a high-stakes flight around the moon on Wednesday, humanity's first lunar voyage in more than half a century and the thrilling leadoff in NASA's push toward a landing in two years.

Carrying three Americans and one Canadian, the 32-story rocket rose from NASA's Kennedy Space Centre, where tens of thousands gathered to witness the dawn of this new era. Crowds also jammed the surrounding roads and beaches, reminiscent of the Apollo moonshots in the 1960s and '70s. It is NASA's biggest step yet toward establishing a permanent lunar presence.

"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," launch director Charlie Blackwell-Thompson told the crew right before liftoff. "Good luck, Godspeed Artemis II. Let's go."

Artemis II set sail from the same Florida launch site that sent Apollo's explorers to the moon so long ago. The handful still alive cheered this next generation's grand adventure as the Space Launch System rocket thundered into the early evening sky, a nearly full moon beckoning some 248,000 miles (400,000 km) away.

Five minutes into the flight, Commander Reid Wiseman saw the team's target: "We have a beautiful moonrise, we're headed right at it," he said from the capsule.

On board with him are pilot Victor Glover, Christina Koch and Canada's Jeremy Hansen. It is the most diverse lunar crew ever, with the first woman, person of colour and non-US citizen riding in NASA's new Orion capsule.

"NASA is back in the business of sending astronauts to the moon," NASA Administrator Jared Isaacman told reporters following liftoff, calling the half-century hiatus a brief intermission.

Tensions were high earlier in the day as hydrogen fuel started flowing into the rocket. Dangerous hydrogen leaks erupted during a countdown test earlier this year, forcing a lengthy flight delay.

To NASA's relief, no significant hydrogen leaks occurred. The launch team loaded more than 700,000 gallons of fuel (2.6 million litres) into the 32-story Space Launch System rocket on the pad, a smooth operation that set the stage for the Artemis II crew to board.

Then NASA had to overcome a flurry of last-minute technical issues — bad battery sensors and an inability to get commands through to the rocket's flight termination system. In both cases, the issues were quickly resolved, allowing the launch to proceed.

The astronauts will stick close to home for the first 25 hours of their 10-day test flight, checking out the capsule in orbit around Earth before firing the main engine that will propel them to the moon. They won't pause for a stopover or orbit the moon like Apollo 8's first lunar visitors did so famously on Christmas Eve 1968, reading from Genesis.

But they stand to become the most distant humans ever when their capsule zooms past the moon and continues another 4,000 miles (6,400 km) beyond, before making a U-turn and tearing straight home to a splashdown in the Pacific.

Once settled in a high orbit around Earth, the astronauts assumed manual control and practiced steering their capsule around the rocket's detached upper stage, venturing as close as 33 feet (10 metres). NASA wants to know how Orion handles in case the self-flying feature fails and the pilots need to take control.

During Monday's lunar flyby, the moon will appear to be the size of a basketball held at arm's length. The astronauts will take turns peering through Orion's windows with cameras.

If the lighting is right, they should see features never before viewed through human eyes. They'll also catch snippets of a total solar eclipse, donning eclipse glasses as the moon briefly blocks the sun from their perspective and the corona is revealed.

All of NASA's moon plans - a surge in launches over the next several years leading to a sustainable moon base for astronauts assisted by robotic rovers and drones - hinge on Artemis II going well.

It's been more than three years since Artemis I, the only other time NASA's SLS rocket and Orion capsule have soared. With no one aboard, the Artemis I capsule lacked life-support equipment and other crew essentials like a water dispenser and toilet.

These systems are now making their space debut on Artemis II, ratcheting up the risk. That's why NASA is waiting a full day before committing Wiseman and his crew to a four-day trip to the moon and a four-day journey back.

The capsule's toilet is already acting up. Koch informed Mission Control that it shut down seconds after she activated it. Mission Control advised her to use a handheld bag-and-funnel system for now - CCU, short for Collapsible Contingency Urinal - while engineers pondered how to deal with the so-called lunar loo.

"There's always been a lot riding on this mission," NASA's Lori Glaze said ahead of launch. But the teams are even more "energized" now that the space agency is finally accelerating the lunar launch pace and laser-focusing on surface operations - seismic changes recently announced by Isaacman.

With half the world's population not yet born when NASA's 12 moonwalkers left their boot prints in the gray lunar dust, Artemis offers a fresh beginning, NASA's science mission chief Nicky Fox said earlier this week.

"There are a lot of people who don't remember Apollo. There are generations who weren't alive when Apollo launched. This is their Apollo," said Fox, who was 4 when Apollo 17 closed out the era.

NASA is in it for the long haul this time. Unlike Apollo, which focused on fast flags and footprints in a breakneck race against the Soviet Union, Artemis is striving for a sustainable moon base elaborate enough to satisfy even the most hardcore science fiction fans.

But make no mistake: Isaacman and the Trump Administration want the next boot prints to be made by Americans, not the Chinese.

Until Isaacman's program makeover, Artemis III was crawling toward a moon landing no sooner than 2029. The billionaire spacewalker slid in a new Artemis III for 2027 so astronauts could practice docking their Orion capsule with a lunar lander in orbit around Earth.

Astronauts' momentous landing near the moon's south pole shifted to Artemis IV in 2028 - two years before an anticipated Chinese crew's arrival.

Like Apollo 13 - astronauts' only moon landing miss - Artemis II will use a free-return, lunar flyby trajectory to get home with gravity's tug and a minimum of gas. The gravity of both the moon and Earth will provide much if not most of the oomph to keep Orion on its out-and-back, figure-eight loop.

The danger is right up there for Artemis II. NASA has refused to release its risk assessment for the mission. Managers contend it's better than 50-50 - the usual odds for a new rocket - but how much more is murky.

The SLS rocket leaked flammable hydrogen fuel during ground tests, a recurring problem that engineers still do not completely understand. The hydrogen leaks and unrelated helium blockages stalled the flight for two months, coming on top of years of vexing delays and cost overruns.

Both problems also thwarted Artemis I, whose capsule returned with excessive heat shield damage. To NASA's relief, Wednesday's countdown was leak-free.

Beating the Soviet Union to the moon made the huge risks acceptable for Apollo, said Charlie Duke, one of only four surviving moonwalkers.

"I'm cheering you on," Duke said in a note to Wiseman and his crew before their flight.

During a weekend news conference, Koch stressed how humanity's path to Mars goes through the moon, the proving ground for points beyond.

"It is our strong hope that this mission is the start of an era where everyone, every person on Earth, can look at the moon and think of it as also a destination," she said.

Added Glover: "It's the story of humanity. Not Black history, not women's history, but that it becomes human history."