Eight minutes after launch the massive Core stage will separate from the second stage, called the Interim Cryogenic Propulsion System (ICPS), and the Orion crew capsule. Orion’s solar arrays will unfurl and begin charging the spacecraft’s batteries to provide power when it is not in direct sunlight.
Ninety minutes later ICPS fires its engines to raise the vehicle to a higher Earth orbit, and for the next 25 hours there will be a full systems check.
If everything is in order, Orion will separate from ICPS and there will be a form of “space ballet” between the two vehicles, more prosaically called the Proximity Operations Demonstration.
Astronauts will manually control Orion’s manoeuvring thruster to dance toward and away from ICPS. This will be to rehearse docking procedures in order to link up with a landing vehicle for the eventual Moon landing.
Twenty-three hours later Orion’s service module carries out a Translunar Injection (TLI) burn – a blast of thrust aiming it at the Moon – before Orion makes its four-day journey, taking the astronauts more than 230,000 miles from Earth.
During the journey the astronauts will be continue to carry out systems checks.
The crew will in some ways be human guinea pigs.
Experiments will monitor how their bodies are affected by space. Scientists will grow tissue samples from the astronauts’ blood called organoids both before and after their journey.
The two sets of organoids will be compared to see how the astronauts’ bodies have been affected by space, according to Dr Nicky Fox, Nasa’s head of science.
“You may be wondering why we are doing all that when we have the actual astronauts, she told BBC News.
“We want to be able to study in depth the effect of the microgravity and the radiation on these samples. I’m certainly not going to dissect an astronaut! But I can dissect these little organoid samples and really look at the difference.”
After the spacecraft slingshots past the Moon, the astronauts begin their four-day journey home, drawn back with the help of the Earth’s gravity.
On arrival, the service module, which has the spacecraft’s primary propulsion system, separates from the crew module. The astronauts will then begin a dangerous part of the mission as they re-enter the Earth’s atmosphere, and parachute back to the surface off the coast of California.
The success of the mission will determine how soon Nasa can launch Artemis III, to actually land on the Moon. But even if the mission goes to perfection, the space agency’s stated aim of “no earlier than mid-2027” is unrealistic, according to Dr Simeon Barber of the Open University.
“‘No earlier than’ is familiar language for NASA, and it means just that. That’s the earliest possibility,” he said, adding that he deemed that optimistic due to the expense of keeping Artemis III on track.
“The Moon landing will require [Elon Musk’s] SpaceX Starship to take the astronauts to and from the surface, and we’ve seen in recent months that Starship itself still has a long way to go before it can even achieve an orbital flight around the Earth, let alone put astronauts on board.”