One option considered by NASA engineers is to add “active heating” elements to the shoes to provide additional warmth. Boot heaters come with a trade-off, Pbister says. “If you’re actively heating, you’ve got to get the power from somewhere.” That means batteries and cables that can add weight to the shoes and the overall load the astronauts carry.

Astronauts are expected to explore the lunar surface for long periods of time and build a permanent lunar base on future missions, as even a small addition would make the journey inefficient. Engineers had to make sure the shoes fit as closely as possible, but they faced another challenge that their Apollo counterparts didn’t — the astronauts’ body sizes. It will see Artemis, the first woman to set foot on the moon. That means launch may have required a much larger size limit than the Apollo missions, where all astronauts were male. They are all about the same height, age and weight.

“We’re looking at ways to get a shoe that works for individuals,” says Pfister, who spends hours on model shoes and suits to test how they feel. But instead of having multiple custom sizes, the shoes come in specific sizes that can be adjusted with padded inserts and external tightening mechanisms.

“The AxEMU lunar launcher will be more convenient and mobile than the one used on the Apollo missions,” adds Ralston.

Astronauts spend a lot of time on the moon training in their boots to ensure they perform as planned. “They train in these shoes and try different options until they get the right fit,” Pfister says. “Breaking in moon shoes is as important as breaking in a new pair of shoes.”

For those who want more convenience, there are always less technical solutions. “Personally, I wear two socks on each leg—I feel much better after six hours,” Pister says.