The astronauts Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen are preparing to launch into space on a trajectory that will make them the first humans to travel to the Moon in over half a century.

Their 10-day mission, known as Artemis II, loops around the Moon but will not land. It will see them travel 4,700 miles (7,600 kilometres) beyond the lunar far side in Nasa’s Orion spacecraft. As such, the four astronauts will travel further from Earth than any humans before them.

The quarter-of-a-million mile Artemis II expedition is audacious, but it’s the last five minutes of the mission that might be the most cause for concern for the safety of the astronauts.

An uncrewed test of the Orion spacecraft in 2022 first highlighted problems with the heat shield. This is the part of Orion that bears the brunt of the searing heat the capsule experiences during re-entry through Earth’s atmosphere.

When engineers examined the Orion heat shield from 2022’s Artemis I mission, they found large chunks of material had been lost. The worry was that, should this happen again on the crewed Artemis II mission, it could expose the interior of the capsule to dangerously high temperatures.

Since the earliest days of human spaceflight, engineers have protected capsules from the extreme heat of re-entry with so-called “ablative” heat shields, made from material that’s designed to burn away evenly as the capsule scorches its way through the atmosphere.

To meet the demands of the reusable space shuttle, Nasa developed an incredible heat shield system made from ultra-light tiles of glass-coated........

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