If you have ever shared a room with multiple people for days on end, you may know how clothes and living conditions can rapidly turn rather smelly. Imagine that happening in a confined spacecraft.
Even worse, since water on a space mission is in short supply, space travelers can’t easily do their laundry. This is more than a body odor problem — unclean clothes and linens are ripe feeding grounds for infectious bacteria. Astronauts might wear the same clothes for days or even weeks, seal away used clothes in airtight bags, then return them to Earth for cleaning or cast them away to burn up in Earth’s atmosphere.
This is fine for short trips near Earth, but what about a months-long odyssey to Mars? Engineers have devised a new way for astronauts to dry-clean their dirty laundry. They’ve crafted a prototype “laundry gun” that sterilizes fabric by shooting violet-colored plasma into it.
“This will reduce the microbial load and keep clothes and other soft surfaces clean, at least microbially, for astronaut health,” says Gabe Xu, a professor at the University of Alabama in Huntsville and one of the laundry gun’s creators, in a statement. “It could also be used to sterilize space suits and tools before they leave the habitat and step foot on Mars.”
A plasma is an energized soup of charged particles, ions and electrons. While many plasmas like that in the sun are very hot, the laundry gun’s plasma is “cold,” closer to room temperature.
Its electrons are key to killing bacteria. As the laundry gun shoots plasma into fabric, the electrons collide with gas molecules in the surrounding air, such as oxygen (O2) and water vapor (H2O). These collisions create other molecules like ozone (O3), which chemists call “oxidizing species”. These oxidizing species can chemically react with the membrane that surrounds a bacterium, damaging and destroying it.
In collaboration with NASA’s Marshall Space Flight Center, Xu and colleagues have created a prototype plasma gun, about the size of a pen, which can sanitize about a square centimeter at a time. In their tests, the prototype reduced spore colonies on a scrap of fabric by more than 75%.
Earthly disinfectants like peroxide and bleach also attack bacteria by oxidizing them in this way. The laundry gun’s creators could allow astronauts to travel without such cleaning chemicals. Instead, the apparatus creates its cleaning plasma from the spacecraft’s own air and water vapor. In space travel, where every gram of mass matters, this is a major advantage.
“The use of plasma treatment could significantly reduce the mass of goods needed for a human mission, especially one to Mars where resupply is difficult,” Xu wrote in the statement.
That said, the “laundry gun” is not a perfect replacement for the standard washing machine — not yet, at any rate. “This won’t remove coffee or grass stains (though we haven’t tried that),” Xu wrote in the statement.
Moreover, a pen-sized laundry gun is too small to be practical. Xu and colleagues are planning to build larger, but still handheld, devices. They’ll also need to deal with their plasma gun’s ozone, which can be harmful in large quantities — they’re working on a filtration system to remove this.
Space laundry is a rather active area of research today — astronauts on the International Space Station (ISS) recently tested a space detergent, and the Chinese space program has developed a washing machine suitable for low-water use.
