The moonboots worn by astronauts on the Artemis missions will need to protect their wearers from difficult terrain and extreme temperatures, but their most memorable role will be the prints they leave behind.
It is one of the most enduring images of the Apollo space era – a lone, shallow lozenge pressed into the grey, dusty soil of the lunar surface. Bars of compacted regolith streak horizontally across, formed by the grips on the sole of astronaut Buzz Aldrin's boot. Now unmistakable as one of the first footprints a human has ever left on another world, it is a potent symbol of human endeavour.
In reality, the print is just one of hundreds left by the 12 astronauts who set foot on the Moon between 1969 and 1972.
And, as far as we know, those prints are still there to this day. Without wind or rain to erode them away, they will remain on the surface for millions of years.
Nasa is now preparing to send a new crop of astronauts to the Moon's South Pole with its Artemis missions, there could be another set of footprints making their indelible mark on the lunar surface. But what will the first footprints on the lunar surface in 50 years look like? And how different will the boots that create them be from those worn by the original Apollo astronauts?
Nasa and its commercial partners have spent years designing and finessing the materials for the next generation of moonboots. The astronauts of Nasa's Artemis II only got to see the lunar surface from 4,067 miles (6,545km) at their closest point as they flew around the Moon, but future missions will place astronauts on the dust covered surface. Two astronauts on board Artemis IV, which is expected to launch in 2028, will need footwear that can perform in ways the Apollo boots never had to in order to keep their wearers comfortable and safe. They will need to protect the astronauts for extended periods in temperatures as low as -225 (-373°F), as well as keeping them steady on the dusty, heavily cratered terrain of the lunar South Pole.
Alongside incorporating innovative materials and technologies into the boots, engineers are also turning their attention to the prints that will mark the surface of the Moon for millenia to come. The soles of these lunar shoes will not only need to give adequate grip on the surface of the Moon, but they will be as iconic and instantly recognisable as those left by the first moonwalkers.
"There's definitely some functional characteristics that have to be built into it," says Zach Fester, a space suit engineer at the Nasa Johnson Space Center who has been leading the research and development on the new moonboot. "Traction is absolutely important – you're exposing the boot sole to a variety of surface features, so it needs good grip on harder rock and the fluffy regolith but also on harder metal surface such as vehicles, ladders and rovers. The tread also has to be robust against wear and tear. But aesthetics are certainly part of it too, because those pictures [of the footprints] are pretty iconic."
The overall design of the spacesuits that will be used in the Artemis missions has been contracted to Axiom Space, a commercial space company that earlier this year conducted its second all-private astronaut mission to the International Space Station. A key part of the new spacesuits, which were revealed in March 2023, will be the moonboot itself. However, the exact design for the boots has yet to be made public. (Find out more about what it takes to make a suit fit for the Moon.)
But research published by Nasa about the requirements the boots will need to fulfil, together with early tests on some of the designs put forward, offer some clues.
Perhaps the biggest challenge will be the temperatures the astronauts will face compared to the Apollo missions, which were mainly conducted in relatively flat landing areas in the equatorial regions of the Moon. When Artemis IV lands on the Moon, the two members of its crew to make the trip to the surface will be touching down in a very different environment in the lunar South Pole.
"For the South Pole, we're looking at much colder temperatures," says Fester.
The region is known to have areas that remain permanently in shadow. "They haven't seen the sun for thousands of years," Fester says. "Some of them can get down to 48 degrees Kelvin (-373F/-225C ) or lower. If you are in the Sun, it can get north of 150F (65C). And a spacewalk can be anything from four to eight hours, so in that time you can encounter pretty large swings in temperature."
This means insulation is going to be key. Both Nasa and Axiom have been testing new types of insulating foams and coatings to help keep the temperature inside the boot comfortable.
