How do you clean a space suit?

NASA is planning another crewed flight to the Moon after 51 years. Yes, it was 1972 that the last humans set foot on the lunar surface. The Artemis Program is in full swing to build an orbiting structure called Gateway as well as a surface facility called the Artemis Base Camp. A lot has changed since 1972, but an old problem that will need to be solved is still being worked on. That is how to remove moon dust from space suits.

Apollo 12 space suit covered in moon dust (NASA)

Astronauts have a jumpsuit they wear inside the capsule, space station, or space shuttle to perform normal functions. The space suit worn outside the spacecraft faces environmental conditions  significantly harsher. Suits must protect the wearer from temperature extremes, lack of air, radiation, sunlight, and injury, as well as provide the most mobility and visibility possible, ways to carry tools and operate them most efficiently. They also need to remain as white as possible to reflect sunlight and to allow others to see the astronaut, whether in space or on the Moon.

Besides the need for such suits to be durable, tough, insulating, and properly protective, astronauts who have worked on the Moon encountered a "sticky" problem that needed to be overcome. Moon dust. Collecting rock samples, walking on the lunar surface, and riding in the lunar rover all generated small particles of moon dust that were difficult to remove from the suits, electronic equipment, solar panels, and lenses. They also made tools and ladders slippery. Clogging and potentially damaging materials are obvious problems, but since the dust holds an electrical charge, some people are concerned that it may also interfere with electronics and even pose a sparking hazard.

Lunar rover kicking up moon dust on Apollo 16 (YouTube)

These particles are 50 micrometers or smaller in diameter (about 0.00078 inches), smaller than flour particles and more like ash. In comparison, the average human is 16-50 micrometers thick. Lunar material is composed of the following:

• 50% SiO2
• 15% Al2O3
• 10% CaO
• 10% MgO
• 5% TiO2 
• 5-15% iron
• traces of sodium, potassium, chromium, and zirconium

Moon dust from Apollo 11 (NASA)

Solar radiation bombarding the Moon's surface creates a negative electrical charge on lunar dust. That's what makes it stick to surfaces. The lack of moisture or erosion on the Moon makes it extremely powdery. Because of the fine particle size and their electrostatic charge, moon dust clings to everything. Astronauts can't help but bring it inside their spacecraft, where it floats around and clogs equipment, as well as causing radiators to overheat. It also blocks the seals on the space suits where helmets and gloves attach, and in some suit designs, where the bottom section joins with the upper torso. 

Moon dust on space suit, Apollo 15 (National Air and Space Museum)

What's more, it gets into the eyes, nose, and lungs. Astronaut Harrison Schmitt experienced the first case of "lunar hay fever" aboard Apollo 17 when he inhaled the dust after removing his helmet. A flight surgeon examining suits after that flight also suffered the same congestion.

Schmitt on the moon. Note dust on legs and arms. (NASA)

In 1966, Professor Brian O'Brien from the University of Western Australia developed a moon dust detector the size of a match box for Apollo 11 (and later missions). When dust covered its solar cells, there was a decrease in voltage, and that data was beamed back to Earth every minute. To date, these are the only data we have on moon dust accumulation on the surface.

Prof. O'Brien talks about his moon dust detector (YouTube)

Moon dust may be powdery but it isn't smooth like rocks on Earth. Instead, the particles are as sharp as glass and can severely damage skin, eyes, and lungs and even cut space suits. 

Moon dust particle (space.com)

Several methods have been tried or are under development to clean up the suits.

Brushes used by Apollo astronauts to remove dust before entering the lunar module only scratched the suits and did little to remove it.

Dust brush with angle-adjustable head used after Apollo 12 mission (National Air and Space Museum)

Washing suits in space or on the Moon does not sound feasible, but scientists at Washington State University have performed tests of spraying liquid nitrogen on dolls dressed in space clothing covered in Mt. St. Helens ash, which is similar to moon dust. They achieved 95-98% removal without damage to the suits. This process does not soak the suits. It makes use of the Leidenfrost effect, where a liquid close to a surface that is much hotter than its boiling point creates a vapor layer that prevents the liquid from boiling rapidly. It's like putting drops of water on a hot fry pan; they don't evaporate immediately. Here, the liquid nitrogen removes the dust particles by trapping them in its vapor.

Washing with liquid nitrogen (YouTube)

Volcanic dust is light, and the suit fabric here is black.

Researchers at Hawai'i Pacific University are working on a different approach: a new type of fabric to combat this problem. Working with a $50,000 grant from NASA, they used LiqMEST (Liquid Metal Electrostatic Protective Textile). It would generate an electrical charge on this outerwear to the space suits and theoretically repel moon dust. Alloys of indium and gallium are hot items now for electronics, but using them as surface coatings is just getting off the ground. Japanese researchers have been working on this since 2011 in a slightly different way. They stitched wires into the suit's outer fabric and ran a pulsed charge through them to electrically "flick" off moon particles with 70-80% efficiency. By adding an ultrasonic transducer to the fabric, the added mechanical vibration increased removal to 90%.

Wires stitched into Japanese space suit fabric (Kawamoto & Noritaka, 2011)

Another method involves shooting a beam of electrons directly onto the suit. A joint effort between the NASA/Jet Propulsion Laboratory and Colorado University, Boulder is working on a tool called a “Moon duster” for equipment and space suits. Since moon dust is already negatively charged, adding more charge with an electron beam will make the particles repel each other. This has been shown to work on some surfaces in a vacuum on Earth with removal of 75-85% of the particles.

From science.nasa.gov

Removal inside the spacecraft, with liquid nitrogen or electron beam, still means the suits would have to be contained in some sort of chamber during cleaning. Otherwise, the dust that is removed would float around the spacecraft interior and defeat the whole purpose.

Here is a short video showing the results of an electron beam removing dust.

From YouTube