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In a few hours, four people will complete their 10-day road trip to the moon and back.
The Artemis II crew are inside a minivan-sized spacecraft hurtling towards Earth after their record-breaking lap around our cosmic neighbour.
Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen travelled further from Earth than any human has on Monday.
The Earth’s gravity is now tugging the crew back home as they strap themselves – and anything that floats – down in the Orion capsule.
But as tense as the launch was last week, experts tell Metro that Orion’s homecoming, called re-entry, tonight will be even more nail-biting.
‘For 13 minutes, we won’t know if they’re okay’
The Orion consists of two parts: the crew module, where the astronauts have spent the last 10 days and a lower service module, which houses the propulsion, power and life-support systems.
By ‘propulsion’, we don’t mean the kind that towering rockets have. Instead, the capsule, christened Integrity by the crew, is being flung back to Earth.
The moon’s gravity acted like a slingshot as the craft looped around it, called a ‘free return’ trajectory, meaning that even if the propulsion system failed, the Earthlings could still return home.
They’ll then smash into Earth’s atmosphere, reaching speeds of up to 23,839 miles per hour, the fastest any human has ever travelled.
When a spacecraft re-enters the atmosphere, the air beneath it gets hot – so hot that it turns into a different state of matter called plasma.
‘The air molecules hitting the capsule at 24,000mph will create a lot of friction and form a plasma shield around the capsule,’ explains Matthew Cook, head of space exploration at the UK Space Agency.
This blob of plasma is why spacecraft become glowing fireballs when they re-enter Earth, as they experience high heat and crushing pressure.
Radio signals barely make a dent through this plasma shield, making communication between mission control and the crew next to impossible, Cooks adds.
‘In this unprecedented level of access that we’ve had to the Artemis II crew during the entire 10-day mission, we’ll now have this 13-minute-long blackout, where we just won’t know whether they’re okay, whether everything’s going to plan.
‘We’ll just have to wait.’
Orion’s heat shield is only thing between it and 2,700°C
As this happens, the Orion’s heat shield will kick in.
The heat shield is the layer at the bottom of a spacecraft that transfers heat away from the capsule – the Orion can withstand temperatures of nearly 2,700°C, half as hot as the surface of the sun.
If the shield fails – as it nearly did during the last Artemis mission, which was unmanned – the metal could melt and break apart.
No one knows more that things could go wrong than mission control, says Libby Jackson, the head of space at the London Science Museum, who once worked in mission control for the International Space Station.
‘The team will be very focused, very quiet, very concentrated,’ she says. ‘There’s nothing mission control can do at this point.
‘We are not going to say this is “mission complete,” that this has been a great success, until the crew safely lands on Earth.’
What will it be like inside the Orion?
Pretty toasty, says Jackson. The crew will be lying on their backs to manage the mind-bending speed they’re zooming at.
‘They will see plasma out the window, a big ball of gas,’ she adds. ‘Anything not strapped down will fall. No one wants a falling piece of anything knocking them on the head.
‘The crew will feel the heat – it’s getting up to 2,700°C outside – and they will also start feeling gravity after floating for 10 days.’
The four Artemis II astronauts are expected to splash down somewhere in the Pacific Ocean, just off the coast of San Diego, California, at about 1am.
Where exactly the capsule will fall is hard to say – the Pacific Ocean is one third of the blue marble we call home, after all.
‘We can track their trajectory within millimetres of accuracy,’ adds Cook, pointing to British space officials’ own radar stations that help do this.
‘We know that even if they entered an unexpected, uncontrolled tumble, because of the dynamics of the atmosphere, it’ll still be within the safety margin.
‘I’d be very surprised if it didn’t end up in the Pacific Ocean,’ Cook says, adding: ‘They’re not going to end up in Antarctica.’
Jackson adds that the capsule will be pulling 3.9Gs, or four times the gravity that keeps our feet on the ground, as this ‘roller coaster ride’ ends with them skipping on the ocean like a stone.
Nasa officials are confident that the crew will remain alive and comfortable as they splash down, with inspections using cameras on the craft showing nothing to worry about.
As the capsule bobs about in the ocean, the final phase of the mission will begin: the recovery.
The USS John P. Murtha, a dock ship, will bring the crew to land. Once they have their feet on the ground for the first time in 10 days, they will be flown by helicopter to Naval Air Station North Island before being flown to Houston.
A big health worry will be the radiation constantly being spat out by the sun. On Earth, the planet’s magnetic field keeps us safe from it.
Up in the stars, astronauts have no such force field. Knowing how this changes their bodies could help protect nuclear power workers or provide better radiological cancer treatments, adds Cook.
Nasa aims to launch Artemis III next year, acting as a test flight to see how well astronauts can rendezvous with lunar lands in low Earth Orbit.
If this goes to plan, Artemis IV and V will happen in 2028 and send astronauts to the surface of the moon for the first time in half a century.
Until then, Cook hopes that Artemis II will help bring humanity together.
‘In a world of such division, space exploration is that unifying function that lights a beacon of hope for humanity’s future,’ he adds, ‘showing exactly what we’re capable of.’
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