The launch of the mission that aims to put humans back on the moon is finally on course for lift-off today after it was postponed at the last minute on Tuesday.
Artemis 1 was ready to take off from Cape Canaveral earlier this week, but a hydrogen leak saw its maiden voyage pulled with just 40 minutes to go.
With the new date falling on the US’ Labor Day weekend, even more people are expected to turn out to watch in Florida, with crowds of up to 40,000 people expected.
As the launch gets the all-clear for the second time, here’s what you need to know about the historic space endeavour.
What does Artemis hope to achieve?
The mission is made up of three stages.
The first is a 42-day uncrewed flight around the moon. It will test the huge rocket and the Orion spacecraft that astronauts will eventually travel in.
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While in space it will deploy 10 CubeSats (a type of miniaturised satellite), which will perform a variety of work in deep space, from studying how radiation affects yeast DNA to hunting for water ice on the moon.
Weather is a big focus of the test mission, with galactic cosmic rays presenting the biggest risk to future crews.
Newly built space weather centres will research solar wind – charged particles released from the Sun – and solar fluxes (concentrated sunlight), as well as coronal mass ejections (large expulsions of plasma and magnetic field from the top layer of the Sun).
A new lunar vehicle will also combine the best from the Apollo moon buggies and Mars rovers, allowing astronauts to pilot them in person and remotely.
Orion will fly 60 miles above the moon at its closest, and during re-entry weeks later will emerge into the Earth’s atmosphere at 25,000mph before splashing down off the California coast on 10 October.
Cameras inside and outside of Orion will share images and video throughout the mission.
If all goes to plan, it will have been in space longer than any human craft in history without docking to a station.
A crew will strap in and blast off for the first time for more testing during Artemis 2. The four astronauts have so far not been named, but this stage is pencilled in for 2024.
Lasting about eight to 10 days, they will do a lunar flyby before returning to Earth.
Humans will finally land on the moon again during Artemis 3, with NASA saying the crew will include the first woman and person of colour.
The timeline depends on how well the previous missions go, but it’s currently slated for 2025.
NASA hopes to build a base camp and conduct annual missions and use it as a test bed for even more ambitious missions, starting with getting a human to Mars.
Most fun fact about the mission?
The Orion capsule will have just mannequins and a soft toy on board.
The mannequin captain is called Commander Moonikin Campos, who will sit in the commander’s seat throughout (see more below).
A Snoopy soft toy will also float around the Orion capsule as a zero gravity indicator.
Mannequins on a mission to go ‘where no man (or woman) has gone before’
David Blevins, Sky correspondent, at Cape Canaveral, Florida
They are three mannequins on a mission to the moon and beyond – Commander Moonikin Campos, Helga and Zohar.
The phantoms, as they are described, will play a critical role in Artemis 1, the maiden voyage of NASA’s plan to put humans back on the lunar surface.
Commander Moonikin Campos, a name chosen by public vote, honours Arturo Campos, an engineer who helped bring Apollo 13 safely back to earth.
He will occupy the commander’s seat and wear an Orion Crew Survival System suit and be equipped with radiation, acceleration, and vibration sensors.
In due course, real-life astronauts will experience two and a half times the force of gravity during ascent and four times its force at two points during re-entry.
Before Artemis 2, engineers plan to compare flight data from Artemis 1 with previous ground-based vibration tests already carried out on the same mannequin.
The two female-bodied mannequins, Helga named by the German Aerospace Centre and Zohar by the Israeli Space Agency, will chart a course for history.
In 2025, NASA plans to land the first woman on the moon, alongside the first person of colour.
Charlie Blackwell-Thompson, the female Launch Commander for Artemis 1, said: “The next set of boot prints that are left on the moon by our astronauts will belong to a woman.”
“There are no boundaries, there are no limits,” she added.
Both female-bodied phantoms are made of materials that mimic the soft tissue, organs, bones, lung, and brain tissue of a woman to test how radiation passes through the body.
The torsos have more than 5,600 sensors and 34 radiation detectors to measure radiation exposure within different organs during the mission.
Zohar will wear AstroRad, a radiation protection vest, while Helga will be unprotected.
Orion, the command capsule, will come within 60 miles of the moon, before travelling another 40,000 miles beyond it, further than any spacecraft has gone before.
With the aim of establishing a permanent moon base, from which humans might one day land on Mars, it signals the dawn of a new era in space exploration.
If all goes to plan, it really will be one small step for three mannequins, one giant leap for humans.
How powerful is the Artemis 1 rocket?
The 98-metre Space Launch System (SLS) is the most powerful rocket NASA has ever built and in this crucial testing phase it will fly further than any spacecraft built for humans: 40,000 miles past the far side of the moon and 280,000 miles from Earth.
The megarocket’s 8.8 million pounds of thrust at launch is 13% more than the Space Shuttle, and 15% greater than the Saturn V rocket used on the Apollo missions.
Each of the two boosters generates more thrust than 14 four-engine commercial airliners, according to NASA, and will fire for 126 seconds, providing more than 75% of the vehicle’s thrust before they break off.
It’s also powered by four RS-25 engines, with the outbound trip to the moon taking several days.
When’s launch day, and how can I watch?
The first Artemis mission is set to blast off from Kennedy Space Center today, with a two-hour launch window that opens at 2.17pm local time (7.17pm UK time).
Streaming of the launch will start on NASA’s website at 12.15pm local time (5.15pm UK time) – but there’s also a stream available of the rocket on the launchpad.
Hollywood stars Jack Black, Keke Palmer and Chris Evans will feature in a live broadcast of the launch.
When was the last time a human was on the moon?
More than 50 years ago: it was Apollo 17 in December 1972 – about three and a half years after Neil Armstrong made history with the first moon walk.
With President Kennedy’s big goal achieved, the final three Apollo missions were cancelled and NASA’s funding cut.
The new missions are named after Greek goddess Artemis, the twin sister of Apollo. She was the goddess of the hunt, the moon, and chastity.