The American space agency says it is ready to launch its giant New Moon rocket next Monday.
Nasa officials conducted a flight readiness review late Monday and concluded that no significant technical issues stood in the way.
The rocket, known as the Space Launch System, will send a capsule called Orion on an excursion around the moon.
Unmanned this time, astronauts will be on board for subsequent missions, assuming all goes according to plan.
The SLS will ascend from Kennedy Space Center (KSC) in Florida.
The vehicle was given a two-hour window to leave Earth on Monday, beginning at 08:33 local time (12:33 GMT; 13:33 BST).
“We actually had no actions from the review and we had no dissenting opinions,” said Jim Free, NASA’s deputy administrator for exploration systems development.
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The launch will be a pivotal moment for Nasa, which in December will celebrate the 50th anniversary of the last human landing on the Moon – Apollo 17.
The agency has vowed to return with its new “Artemis Program,” which uses technology befitting the modern era (Artemis was the twin sister of the Greek god Apollo and goddess of the moon).
Nasa sees a return to the moon as a way to prepare to fly to Mars with astronauts sometime in the 2030s or shortly thereafter.
“You know, right now, more than half of the world’s population has never seen anyone walk on another world, so in many ways it will be their first moonwalk,” said Keith Cowing, the editor of the Nasa Watch website, which features the Nasa reports news.
“We’re doing things differently, everything is instant, everything will be in HD… It’s going to be exciting and loud, but at the end of the day we’re going to keep sending people to another world, so hopefully this time it’ll be a global effort, not maybe.” two countries competing with each other,” he told BBC News.
SLS and Orion have been in development for over a decade and have each cost more than $20bn (£17bn) to get to this point.
Orion actually flew once before on a low-Earth test flight in 2014. But for this, an existing commercial rocket was used to go into space. This upcoming flight is therefore the first full end-to-end investigation of Artemis exploration hardware.
SLS and Orion were introduced on the launch pad last week. Engineers and technicians have spent the past few days installing fuel, electrical and communications lines in preparation for the grand countdown.
This was scheduled to begin Saturday at 9:53 a.m. EDT with a “call to the stations” for the Artemis I launch team, with the operation to load SLS with 2.7 million liters of propellants (liquid hydrogen and oxygen) just after midnight should begin on Monday.
“We’ve completed 30 Sims, so our team is certified and ready to go,” said Launch Director Charlie Blackwell-Thompson.
Nasa expects hundreds of thousands of spectators to line the beaches along the Space Coast.
This will be the most powerful rocket ever to lift off from Kennedy, generating 39.1 meganewtons (8.8 million pounds) of thrust from the platform. That’s almost 15% more than Apollo’s Saturn V rockets and over 20% more than the old space shuttle system.
Put another way, the engines on the SLS could power the equivalent of nearly 60 Concorde supersonic jets on takeoff.
“I can tell you that there is an energy and excitement surrounding Kennedy Space Center; I would say across the agency and across the Space Coast as we get closer to that launch,” commented Janet Petro, Director at KSC.
Orion is sent on a 42-day mission to the moon and beyond.
It is expected to return to Earth on October 10 for a splashdown in the Pacific Ocean near San Diego, California.
Artemis II, the first manned mission with SLS-Orion, is aimed for the year 2024. Artemis III, the first landing on the lunar surface since 1972, will not take place until late 2025 at the earliest.
Nasa has yet to name astronauts for these missions, but it has released the locations on the lunar surface where future crews could be sent in recent days.
It identified 13 candidate targets. They are all within six degrees of latitude of the lunar south pole (Apollo was largely restricted to equatorial or equatorial landing sites).
The goal is to get close to permanently shadowed areas where water ice likely accumulated over billions of years.
This ice could be used for drinking water or to make rocket fuel.
Shortly after Monday’s review concluded, Bob Cabana, a former shuttle astronaut and now NASA’s deputy administrator, said, “I’m a product of the Apollo generation and look what it did for us. I can’t wait to see what will become of the Artemis generation because I think they will inspire even more than Apollo. She will be absolutely outstanding.”