NASA's Space Launch System (SLS) rocket, topped with its Orion crew capsule, roared to life just before sunset at 6.35pm on Wednesday at the agency's Kennedy Space Center to lift its first crew of three US astronauts and a Canadian astronaut off Earth. Its thunderous ascent left behind a towering column of thick white vapor.
The Artemis II crew of NASA astronauts Reid Wiseman, Victor Glover and Christina Koch, and Canadian Space Agency astronaut Jeremy Hansen are poised for a nearly 10-day expedition around the moon and back, taking them deeper into space than humans have ever gone.
"This is Jeremy, we are going for all humanity," Hansen, strapped inside Orion, told launch control minutes before liftoff.
"Reid, Victor, Christina and Jeremy, 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 through a communications line from launch control.
"Good luck, godspeed, Artemis II. Let's go," she said.
After nearly three years of training, the crew is the first to fly in NASA's Artemis program, a multibillion-dollar series of missions created in 2017 to build up a long-term US presence on the moon over the next decade and beyond.
The launch was a major milestone more than a decade in the making for the US space agency's SLS rocket, handing its core contractors Boeing and Northrop Grumman long-sought validation that the 30-storey-tall system can safely loft humans into space, as NASA increasingly relies on newer, cheaper rockets from Elon Musk's SpaceX and others.
The crew's gumdrop-shaped Orion capsule, built for NASA by Lockheed Martin, will separate from the SLS upper stage three-and-a-half hours into flight in Earth's orbit. The crew will then take manual control of Orion to test its steering and manoeuvrability around the detached upper stage, attempting the first of dozens of test objectives planned throughout the mission.
The Artemis II mission is a key early step in the flagship US moon program, which is targeting its first crewed landing on the lunar surface in 2028 in the Artemis IV mission.
NASA is pressed to achieve that lunar landing - its first since the final Apollo mission in 1972 - as China expands its own lunar program with a planned astronaut landing as soon as 2030.
The Artemis II mission will send the crew some 406,000km into space - the farthest humans have ever travelled.
The current record for the farthest spaceflight at around 399,000km is held by the three-man crew of the Apollo 13 lunar mission in 1970, which was beset by technical problems after an oxygen tank exploded and was unable to land on the moon as planned.
NASA launched its first Artemis mission without crew in 2022, sending the Orion spacecraft on a similar path around the moon and back.
Artemis II will pose a greater test of Orion and the SLS rocket. Boeing and Northrop Grumman have led the development of SLS since 2010, a program partly known for its ballooning costs at an estimated $US2 billion ($A2.9 billion) to $US4 billion ($A5.8 billion) per launch.
Elon Musk's SpaceX and Jeff Bezos' Blue Origin are racing to develop the landers that NASA will use to put its astronauts on the lunar surface.
Artemis III had been set to be the agency's first astronaut moon landing, but new NASA Administrator Jared Isaacman in February added an extra test mission before the landing.
