Socks, The Final Frontier

What is the greatest challenge facing humans as we prepare for the first crewed missions to Mars? Solar and cosmic radiation? Atrophying bone and muscle? Growing food? How about laundry? It’s strange but true, right now we don’t have a way to clean laundry in space.

In the microgravity environment of space, just about every single aspect of how we do our laundry here on Earth becomes a deadly hazard with a single point of failure. All that sudsy water, heat cycling, spinning mass, and even the buildup of static electricity, lint, or fumes could compromise a mission or even cost lives. But surely it’s just a matter of engineering, right? If other hygiene activities like showering have been successfully adapted for life in space, why not laundry?

Making Do Without

For shorter missions it’s just not needed. The longest Apollo and Shuttle missions were generally about two weeks long, which you may know from experience you can pack for. Lugging all that laundry around is still lighter and cheaper than bringing a washer and dryer with you, especially if you’d be shipping them to space at a cost of roughly $50,000 per kilogram.

Every space station we’ve built so far has orbited just a few hundred miles above the Earth, so while missions can last up to a year, laundry is just part of the resupply process. Fresh new clothes and linens, rigorously washed many times on Earth to remove lint, are launched aboard a resupply mission. Used clothes and linens are later packed into the resupply vessel which then undocks, de-orbits, and burns up as it re-enters Earth’s atmosphere. While this sanitizes the clothing with unparalleled effectiveness, it also makes them impossible to wear again.

But for the journey to Mars, which takes six or seven months in microgravity with no chance for resupply, with current methods every astronaut would require at least 35 kilos (75 pounds) of laundry per transit. Certainly to go beyond Mars, we reach a point where cleaning laundry in microgravity, and reclaiming used air and water, becomes more mass- and power-efficient than bringing hundreds of pounds of limited-use garments per person on every mission.

Non-Liquid Solutions

One key strategy is to somehow make clothes soil slower. Simple things like wearing the same clothes on alternating days helps. Spacecraft environments are engineered to maintain a comfortable temperature and humidity, which reduces sweating. Also in microgravity clothes tend to float away from the skin, slowing their absorption of sweat and oils.

Pushing the envelope starts with experiments like NASA’s Intravehicular Activity Clothing Study and Advanced Clothing System (ACS), and JAXA’s J-Wear, which have effectively demonstrated that antimicrobial materials and treatments can make clothing last for weeks instead of days. The two main strategies are including copper oxide or silver in the fabric, or dousing the fabric in antimicrobial compounds.

Another way to save mass is to find ways to use soiled laundry. During the Mir program Russian scientists designed a bacteria farm that could digest cosmonauts’ undergarments and produce methane for power or propulsion. More recently ISS Expedition 6 Science Officer Don Pettit used folded dirty underwear in lieu of actual soil to fashion planters for tomato and basil seeds. Expedition 6 also saw Commander Ken Bowersox wash his shorts in a plastic bag. This never became a common practice on the ISS.

Counterintuitively, fluid-less options like vacuum exposure, ultraviolet, and microwaves have been found to only half work. While they kill many bacteria, they can have trouble penetrating biofilms and do not remove the bacteria’s waste products or physical remains – which is what causes the malodor of used clothing.

Weightless Washing

Perhaps the earliest practical attempt at a microgravity washing machine is the Advanced Microgravity Compatible Integrated Laundry System (AMCILS), conceptualized by UMPQUA Research Company in the 1980s. This washer-dryer combo notably relied on water jets to agitate the clothes and microwaves to dry them. As of 2017 a prototype completed parabolic zero-G testing.

In 2021 six teams of summer interns at NASA’s Glenn Research Center each spent a week designing a space washing machine. The overall Best Design award went to a team that used a central corkscrew rather than a drum, to soak and agitate the laundry. NASA has hinted that the program may grow in the coming years, taking on the scale of programs like the Human Exploration Rover Challenge.

In August of 2020 parties from NASA and Tide’s parent company Proctor and Gamble jointly signed a Space Act Agreement to develop low-toxicity detergent use in microgravity, compatible with the water reclamation system on the ISS. The result of the Agreement is P&G Telescience Investigation of Detergent Experiments (PGTIDE), to-date the most rigorously flight-tested space laundry experiment. 

The PGTIDE experiment consists of three distinct efforts. Launching in December of 2021, Objective 1’s payload is a sample of Tide Infinity, the experimental detergent. In the O-1 experiment Astronauts on the ISS produced a variety of stains on a variety of fabrics and tested the effectiveness of Tide Infinity at removing them. The experiment was repeated on the ground to control for the effect of microgravity on the detergent. Throughout this phase scientists monitored the stability of Infinity during months of microgravity and the higher ambient radiation levels of space.

Objective 2 payloads, including Tide To Go Pens and Wipes and Tide Rescue Spray, launched to the ISS in July of this year. The main O-2 experiment will have astronauts treat a sample group of pre-stained fabrics from Earth and a group of fabrics they stain in flight. The dependent variable will be the stain removal efficacy of unmodified To Go products in space over the course of several months.

Lastly, NASA and Tide researchers may design a combo washer-dryer that uses the Infinity detergent with as little power and water as possible. The washer-dryer would be intended for use in the low-gravity environment of a Moon or Mars colony, so unfortunately we may still be years away from true deep space washing.

Tide Infinity And Beyond

Picture your favorite science fiction scene. Maybe it’s a great battle. Maybe it’s an impassioned speech that has stuck with you for years. Maybe it’s a moment where you realize just how deep a friendship runs between two characters. Now ask yourself, in that scene, are their socks clean?

Doing laundry in space is not as flashy as, for example, a full-flow staged combustion engine. But it may prove equally important for going to Mars and beyond. Both technologies are essentially ways to get more performance for less mass. And in space, dropping mass is the only way forward.

For More Information

• PGTIDE summary on NASA’s Space Station Research Explorer
• IVA Clothing Study summary on NASA’s Space Station Research Explorer
• ISS National Lab article on PGTIDE
• P&G Press Release: announcement of Space Act Agreement
• P&G Press Release: Objective 1 experiment launched
• P&G Press Release: Objective 2 experiment launched