Sealed safely inside the International Space Station, astronauts dress for comfort and convenience. Their typical getups—short-sleeve collared shirts and long cargo pants—are regular Earth clothes, sourced from retailers that include Cabela’s and Lands’ End. But astronauts require exceptional attire when outside the ISS’s climate-controlled confines. NASA’s chunky spacesuits are, essentially, spacecraft condensed to human size. They protect wearers from an environment that swings from 250 degrees Fahrenheit in the sun to minus 250 degrees in the shade. 

Inside the suits, spacewalkers often work up a sweat, despite cooling tubes that wick away body heat. Extravehicular activities, or EVAs, may involve hours of strenuous labor. To stay warm and pressurized, astronauts also have to wear layers—including an inner form-fitting garment akin to long underwear—that they re-wear and even share. Complicating matters still: There are no laundry machines on the ISS. Because water is so valuable, washing a suit in orbit is not an option. Which is why NASA, the European Space Agency (ESA), and other organizations have asked textiles experts to investigate the problem of biocontamination in suits and develop fabrics that might solve it.

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Heavy work in heavy gear leads to filth. After mock EVAs on Earth, technicians who help peel stand-in astronauts out of their suits have learned to turn their heads away on the first unzip to avoid a stinky blast, says Gernot Grömer, director of the Austrian Space Forum, a research group that conducts simulated astronautical missions. “Everybody sees those beautiful, shiny white spacesuits. But nobody knows what it smells like at the ISS.” (It’s not particularly pleasant.)

As these suits are used again and again, worries go beyond foul odors to hygiene and health hazards. The possibility for biocontamination, which includes human debris, bacteria, and other foreign substances, may get worse as spacefarers travel past low-Earth orbit for longer trips to the moon. 

“Washing spacesuit interiors on a consistent basis may well not be practical” in lunar habitats, ESA materials and processes engineer Malgorzata Holynska says in a statement. That space agency is investing in unusual ways to keep suits clean, such as antibiotic chemicals churned out by microbes.

Sanitary death metal

During NASA’s shuttle program, which ran from 1981 to 2011, spacesuits were designed to be used on two-week trips. But as astronauts began to live on the ISS for longer periods in the late 2000s, suit lifespans had to be extended up to six years. That meant microbes became a concern in ways they hadn’t before, says Evelyne Orndoff, a textiles engineer at the NASA Johnson Space Center. 

In NASA’s first comprehensive attempt to address spacesuit contamination more than a decade ago, Orndoff and her colleagues evaluated several off-the-shelf methods to kill germs on fabric, including Cupron and SilverClear. They cut treated textiles into two-inch squares, placed them in petri dishes, and grew several species of fungi and bacteria on the samples. 

Astronauts’ typical getups are regular Earth clothes, sourced from retailers that include Cabela’s and Lands’ End.

Some of the fabrics were infused with copper, which has impressive antimicrobial properties. When bacteria touch the element, it destabilizes their cell walls and membranes, making the microbes vulnerable to damage from the metal’s ions. The NASA scientists also examined textiles treated with silver—likewise toxic to germs on contact—and silicone.

After observing the gunk that grew on the fabrics for up to 14 days, they found that only one compound kept bacteria and fungi below targets set by NASA’s Constellation program—a now-defunct plan for lunar missions in which a spacesuit would have been reused up to 90 times in six months. The winner was a solution of silver molecules used for disinfecting hospital dressings and other fabrics. But the metal ion was too good at its job. “It kills everything,” Orndoff says. Total sterility can cause even more problems than grime, given than humans need a balanced ecosystem of millions of microorganisms to keep the skin and other organs healthy.

The experiments showed that concentrations of other antimicrobial compounds were generally too low to be effective. Some microbes would initially dip in numbers, but the resistant ones would repopulate the samples. The scientists worried that, at high-enough amounts, antimicrobial particles would irritate anyone wearing the fabric or pollute the space station. “After that we never really revisited antimicrobial treatments,” Orndoff explains, for the “simple reason” that it would present complications for the ISS life-support system that provides clean air and water. 

[Related: Onboard the ISS, nothing goes to waste—including sweat and pee]

While Orndoff’s team did not pursue their idea further, NASA’s commercial contractors have. In 2022, the agency hired US companies Axiom Space and Collins Aerospace to develop the next generation of suits for spacewalks. Earlier this year, Axiom unveiled a prototype suit that Artemis III astronauts might use to explore the lunar south pole. In a statement to Popular Science, the company says: “The Axiom Space AxEMU spacesuits will use textiles that have antimicrobial properties to reduce biocontamination.” The suits’ cooling system will also use biocide in its water loops “to prevent microbial buildup.” The company did not share the exact type of the agents, citing their proprietary nature.

Biological agents at work

Future astronauts might get a helping hygienic hand from the microscopic world. Partnering with the Vienna Textile Lab, and with funding from the ESA, Austrian Space Forum researchers have been studying how to turn a bacterial cell’s own defenses against it

Specifically, Grömer and his collaborators have been investigating biological compounds called secondary metabolites that microbes sweat out as a defense against other microorganisms. The researchers bonded several of these molecules to textiles and, over the past few years, subjected those samples to hundreds of tests, including zaps of radiation from a nuclear accelerator in Austria and baths in synthetic sweat. (The nasty liquid, which reminds Grömer of the acidic blood of the monsters in Alien, ages fabrics quickly.)

Fabric fibers under magnification. In greyscale.
A scanning electron microscope view of textiles tested by the Austrian Space Forum. OeWF

One metabolite in particular, named violacein, survived every hostile attack with its antimicrobial properties intact. The purple-black substance can be found in the bacteria that live on the skin of red-backed salamanders. It’s so good at killing microbes that some biologists suspect it protects the amphibians from deadly chytrid fungus infections. The Austrian Space Forum plans to field-test violacein in a simulated Mars mission, in which six astronaut roleplayers will spend four weeks in Armenia’s rugged mountains in 2024. 

Grömer envisions a future where this pigment’s potent defenses leave the planet, not only on treated spacesuits but also towels and other gear. While dirty linens might just sound like a chore, they can be a breeding ground for microbes, which thrive in low gravity and may mutate faster in space. “When you go to Mars, you’re at the edge of what’s technologically possible, so little nuisances can transform into real disaster-prone situations,” Grömer says. “And so if there’s a risk we can control, hell, let’s do it.”