The US 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 there were no significant technical problems 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, there will be astronauts on board for subsequent missions, assuming all goes according to plan.
SLS will lift off from the Kennedy Space Center (KSC) in Florida.
The vehicle has been given a two-hour window on Monday to get off Earth, starting at 08:33 local time (12:33 GMT; 13:33 BST).
“We actually had no actions that came out of the review and we had no dissenting opinions,” said Jim Free, NASA’s assistant administrator for exploration systems development.
Watch Return To The Moon on iPlayer (UK only).
The launch will be a key moment for Nasa, which in December will celebrate the 50th anniversary of the last human landing on the moon – Apollo 17.
The agency has promised to return with its new “Artemis program”, using technology suitable for modern times (Artemis was the twin sister of the Greek god Apollo and the goddess of the moon).
Nasa sees a return to the moon as a way to prepare to go to Mars with astronauts sometime in the 2030s or soon after.
“You know, right now more than half of the world’s population has never seen anybody walk on another world, so in many ways it’s going to be their first moon walk,” said Keith Cowing, the editor of the Nasa Watch website that covers Nasa news.
“We’re doing things differently, everything’s instant, everything’s going to be in HD… It’s going to be exciting and noisy, but at the end of the day we’re going to send people walking on another world and again hopefully maybe this time it will be a global effort, not 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 has actually flown before, once, on a near-Earth test trip in 2014. But that used an existing commercial rocket to get into space. This upcoming flight is therefore the first full end-to-end survey of the Artemis exploration hardware.
SLS and Orion were rolled out to the launch pad last week. Engineers and technicians have spent the intervening days connecting fuel, electrical and communications lines in readiness for the big countdown.
This should begin with a “call to stations” for the Artemis I launch team at 09:53 a.m. EDT on Saturday, with the operation to load the SLS with 2.7 million liters of propellant gas (liquid hydrogen and oxygen) set to begin just after midnight 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, producing 39.1 meganewtons (8.8 million pounds) of thrust from the pad. That’s close to 15% more than from Apollo’s Saturn V rockets and over 20% more than from the old Space Shuttle system.
Put another way, the SLS engines can power the equivalent of nearly 60 Concorde supersonic jets at takeoff.
“I can tell you that there is an energy and there is an excitement around the Kennedy Space Center; I would say across the agency and the entire Space Coast as we get closer and closer to this launch,” commented Janet Petro, the director at KSC.
Orion will be sent on a 42-day mission to and beyond the moon.
It is expected to return to Earth for a splashdown in the Pacific Ocean near San Diego, California, on October 10.
Artemis II, the first crewed mission using SLS-Orion, is targeted for 2024. Artemis III, the first landing on the lunar surface since 1972, will not occur until late 2025.
Nasa has not yet named any astronauts for these missions, but in recent days it has published the locations on the moon’s surface where future crews could be sent.
It has identified 13 candidate destinations. They are all within six degrees of latitude of the Moon’s south pole (Apollo was largely limited to equatorial or near-equatorial landing sites).
The goal is to get close to permanently shadowed areas where water ice is likely to have accumulated over billions of years.
These ices can be used for drinking water or to make rocket fuel.
Speaking shortly after Monday’s review was completed, Bob Cabana, a former shuttle astronaut and now NASA’s assistant administrator, said: “I’m a product of the Apollo generation, and look what it did for us. I can’t wait to see what comes from the Artemis generation because I think it’s going to inspire even more than Apollo did. It’s going to be absolutely outstanding.”