NASA's towering next-generation and most powerful moon rocket ever built finally blasted off from Florida on Wednesday for its debut flight on a crewless voyage to the moon in a spectacular blaze of light and sound that marked the start of the space agency's new flagship exploration program, Artemis, 50 years after the final Apollo moon mission.

The 32-story Space Launch System (SLS) rocket surged off the launch pad from the Kennedy Space Center in Cape Canaveral at 1:47 a.m. EST, to send its Orion capsule on a three-week test journey.

About 90 minutes after launch, the rocket's upper stage fired thrusters for a "trans-lunar injection" burn propelling Orion out of Earth orbit on course for the moon. That put the capsule on track for a 25-day flight that will bring it to within 97 kilometers (60 miles) of the lunar surface before sailing 64,374 kilometers (40,000 miles) beyond the moon and back to Earth.

Liftoff came on the third attempt at launching the long-delayed, multibillion-dollar rocket, after 10 weeks beset by numerous technical mishaps, back-to-back hurricanes, and two excursions trundling the spacecraft out of its hangar to the launch pad.

Wednesday's launch was not without its own drama. A three-man "red team" was scrambled out to the launch pad in the final hours of the countdown to tighten bolts on a loose connection identified as the source of a potentially flight-thwarting fuel leak.

Although specially trained to venture into the "blast zone" around a fully fueled rocket, the three were later hailed as heroes who may well have saved the mission.

"It's a great day," a beaming NASA chief Bill Nelson later said in a brief post-launch webcast interview.

Dubbed Artemis I, the mission marked the first flight for the combined SLS rocket and Orion capsule, built by Boeing Co and Lockheed Martin Corp, respectively, under contract with NASA.

It also signals a major change in direction for NASA's post-Apollo human spaceflight program after decades focused on low-Earth orbit with space shuttles and the International Space Station.

Named for the ancient Greek goddess of the hunt – and Apollo's twin sister – Artemis aims to return astronauts to the moon's surface as early as 2025.

Twelve astronauts walked on the moon during six Apollo missions from 1969 to 1972, the only spaceflights yet to place humans on the lunar surface. But Apollo, born of the Cold War-era U.S.-Soviet space race, was less science-driven than Artemis.

The new moon program has enlisted commercial partners such as Elon Musk's SpaceX and the space agencies of Europe, Canada, and Japan to eventually establish a long-term lunar base as a stepping stone to even more ambitious human voyages to Mars.

'You could feel it'

The Artemis I countdown climaxed with the rocket's four main R-25 engines and its twin solid-rocket boosters roaring to life, producing 8.8 million pounds of thrust that sent the spacecraft streaking skyward and lighting up the night sky over Florida's central Atlantic space coast.

The rocket's thunder shook the space center as a throng of spectators cheered and screamed with excitement.

"It was just incredible to see. It was so bright, so loud, you could feel it," said NASA astronaut Jessica Meir, among those who could be selected for a future Artemis crew.

Addressing mission control moments after liftoff, Artemis launch director Charlie Blackwell-Thompson saluted the hard work of her colleagues.

"We are all part of something incredibly special, the first launch of Artemis, the first step in returning our country to the moon and onto Mars," she said to applause.

The capsule is expected to splash down at sea on Dec. 11.

Spaceflight stress test

Getting the SLS-Orion spacecraft off the ground was a key hurdle for the ambitious Artemis program. Its first voyage is intended to put the vehicle through its paces in a rigorous test flight, pushing its design limits to prove the spacecraft is suitable to fly astronauts.

If the mission succeeds, a crewed Artemis II flight around the moon and back could come as early as 2024, followed within a few more years by the program's first lunar landing of astronauts, one of them a woman, with Artemis III.

Billed as the most powerful, complex rocket in the world, the SLS represents the biggest new vertical launch system NASA has built since the Saturn V of the Apollo era.

Although no people were aboard, Orion carried a simulated crew of three – one male and two female mannequins – fitted with sensors to measure radiation levels and other stresses that astronauts would experience.

The major aim is to test the durability of Orion's heat shield during re-entry as it hits Earth's atmosphere at 39,429 kilometers (24,500 miles) per hour, or 32 times the speed of sound, on its return from lunar orbit – much faster than re-entries from the space station.

The heat shield is designed to withstand re-entry friction expected to raise temperatures outside the capsule to nearly 2,760 degrees Celsius (5,000 degrees Fahrenheit).

The spacecraft also is set to release a payload of 10 miniaturized science satellites, called CubeSats, including one designed to map the abundance of ice deposits on the moon's south pole, where Artemis seeks to eventually land astronauts.

Sending astronauts to Mars, an order of magnitude more challenging than lunar landings is expected to take at least another decade and a half to achieve.

More than a decade in development with years of delays and budget overruns, the SLS-Orion spacecraft has so far cost NASA at least $37 billion, including design, construction, testing, and ground facilities. NASA's Office of Inspector General has projected total Artemis costs at $93 billion by 2025.

NASA calls the program a boon to space exploration that has generated tens of thousands of jobs and billions of dollars in commerce.