One of the back burner issues involved in the colonization of Mars is how will colonists do laundry? It seems like a rather simple question and a general task that is taken for granted, especially with the convenience of the developed world. However, on Mars heavy conservation of both energy and water will eliminate both conventional machine washing or even hand washing. So with these significant limitations how will Mars colonists clean their clothing?
Looking towards the behavior of astronauts on the International Space Station (ISS) does not provide any immediate assistance. While it is standard procedure for astronauts on the ISS to wear clothing for longer than a 24-hour period, its close proximity to Earth allows for simple clothing replacement during cargo missions with dirty laundry being burnt up during re-entry. This re-supply process is obviously not available for Martian colonists because additional clothing will add weight and cost to the initial launch and in addition to these negative elements will also take months to arrive in any supplementary launches. Another non-helpful aspect is that most conventionally worn clothing by astronauts visiting the ISS is not specialized in any real sense beyond having a reduced number of seams (or being seamless) with Cabelas and Lands End seemingly being the more prominent brands worn.
With the difficulties associated with cleaning and/or providing new clothing after the initial launch some could argue that after the habitat is established clothing may not be necessary. A well-kept habitat would have a comfortable temperature between 65 and 80 degrees F with little humidity. A lack of non-human origin microbes eliminates any direct infection issues. An air lock separates the preparation staging area for extravehicular activities (EVAs) and the remaining living area of the habitat eliminating the incursion of any negative outer environmental elements. Psychological evaluations and training can manage any potential colonist “revulsion” towards interacting with their nude crewmates. However, while the major immediate issues for accepting nudity appear manageable there are a number of smaller issues.
One of the less heralded benefits of clothing is absorption of general excretions like sweat, shed skin cells, etc. Without clothing there is a much higher probability that these excretions are deposited on various solid surfaces within the habitat, which would not be hygienic and could even damage equipment. Also clothing offers a secondary protective barrier to wards off various ailments that could breach the skin like burns or various cuts and scratches. This additional protection would also serve as a valuable psychological assurance when performing maintenance on various life support systems like waste disposal/recycling or when creating new parts in situ within a prospective machine shop. Not many individuals would be comfortable sanding/welding something with only eye protection.
Some rudimentary experiments have been conducted with some more specialized clothing options like the Japanese Space Federation’s “J-wear”, which includes underwear, shirts, pants, and socks made from cotton and polyester and purports to be anti-bacterial, water-absorbent, odor eliminating, antistatic and flame retardant. Most likely this material has these properties because it is doped with titanium oxide (titania or TiO2) and some other additives. However, the actual testing of this material is limited, especially in its publication, so the time frame for the efficacy of these claims is unknown. One “famous” study with a Japanese astronaut on the ISS created some anecdotal evidence that underwear can retain a chiefly non-offensive odor when worn for around one month.
The reason TiO2 is effective at creating the cleaning advantages is because it is a potent photocatalyst that is able to neutralize the staining of almost any organic compound when exposed to ultra violet (UV) radiation. When TiO2 is exposed to and absorbs UV it results in excited electrons on the valence band of TiO2. This excess energy promotes electrons to the conduction band creating new negative electrons and positive holes. In the presence of water the positive hole interacts with the water to form hydrogen gas and hydroxyl radicals. The free negative electron reacts with the newly formed hydroxyl radical to form a super oxide anion, which decomposes organic stains. In addition if TiO2 is doped onto a fabric it creates a protective film that provides a bio-static, super oxidative and hydrophilic barrier.
Photocatalytic effects, as described above, can also kill bacteria due to the large amounts of hydroxyl radicals produced during the reaction steps. These hydroxyl radicals also aid in eliminating odors as they breakdown the molecular bonds that comprise most volatile organic compounds (VOCs). Some have envisioned the further evolution of this process by doping the TiO2 with nitrogen and adding silver iodide to make the process applicable to visible light, but this is not necessary because a small portion of the habitat could inundated with a UV light source to act as a “laundry area” of sorts. Also it is unclear how safe the silver doping would be for excess exposure to silver iodide is toxic when ingested and repeated contact with skin can lead to argyria, which turns one’s skin blue. Therefore, it makes little sense to include silver iodide. Unfortunately efficient operation of photocatalysts, including TiO2 requires water, which will be in short supply on Mars. Therefore, testing would have to be performed to determine the length of time between UV “washes”.
With or without TiO2 doping exposure to UV light should be sufficient to eliminate any bacteria growth born from the bodies of the colonists. Therefore, the biggest issue will be odor. Another strategy to eliminate odors may be to incorporate a “Febreze” strategy. The active ingredient in the household odor eliminating product Febreze is hydroxypropyl beta-cyclodextrin. Various cyclodextrins including beta-cyclodextrin, are produced from starch via enzymatic conversion. These elements can theoretically be produced in situ on Mars, but the difficult element would be converting the beta-cyclodextrin to hydroxypropyl beta-cyclodextrin due to the lack of easily available carbon elements on Mars. Therefore, this type of solution may not be prudent.
Overall it is clear that some area of the habitat will have to be converted into a dark room of sorts with UV lights to act as an area to clean bacteria from clothing. Limiting the influence of odor on the psychological well being of the colonists is the principle question. Some could argue that individuals have a tendency to become accustomed to smells, but that desensitization demands a static element to the odors; it stands to reason that if odors are not managed then they will progressively expand in a negative manner, thus colonists will probably never generate an accustomed affinity. Therefore, an odor elimination strategy will need to be incorporated. Determining between either an “Febreze” chemical strategy versus a photocatalytic strategy will involve identifying the production capacity in situ of the desired odor eliminating chemical and the amount of water that will be required to active that phootcatalytic effect to sufficiently remove odor. This information can be easily determined in a long-term Martian colonization simulation study performed on Earth, which sadly do not yet incorporate such testing.