# On our way to Mars: how do we do the laundry?

A human crew of 6 has been sent on mission to Mars

The lowest energy transfer to Mars is a Hohmann transfer orbit, which would involve an approximately 9 month travel time from Earth to Mars, about five hundred days at Mars to wait for the transfer window to Earth, and a travel time of about 9 months to return to Earth.

Shorter Mars mission plans have round-trip flight times of 400 to 450 days, but would require significantly higher energy. A fast Mars mission of 245 days round trip could be possible with on-orbit staging.

On ISS the crew wears clean underwear every day and exchanges dirty for clean at every supply mission, storing the dirty until that moment. This approach sounds problematic on a mission to Mars. 245 days worth of clothing for a crew of 6 looks quite a lot.

What is a space-viable method to clean and reuse space laundry?

• assume current tech level, no handwavium
• assume a fast mission, with few days of permanence on Mars. Conceptually similar to the Apollo missions to the Moon.
• only requirement is for the garment to be hygienic and safe to wear after treatment
• the treatment shall leave the garment wearable and usable for at least the duration of the mission
• the less accessory materials needed, the better (i.e. for running a washing machine I would count water, soap and water filtering/cleaning equipment, plus power supply)
• Very much depends on the size of the ship, available energy and space. Can you please try to add some details that can offer some indication? (Are they an Apolo-there-and-back-again-everything-supplied? Or are they expected to setup an outpost, thus land an energy generator and build some enclosure on Mars? Something, anything) Mar 4 '20 at 8:45
• Nasa is building a washing machine for space, spacesafetymagazine.com/spaceflight/life-in-orbit/…
– John
Mar 4 '20 at 10:41
• You do laundry the same way I did in college: don't. And I kept that up for 4 years, not a measly 245 days. Amateurs. :) Mar 4 '20 at 16:24
• @Richie Frame "if you are not sweating or soiling them" - this is a small, but still unresolved problem with human physiology. Mar 4 '20 at 20:08
• There is a detailed article with possible solutions from NASA titled: "Will Astronauts Wash Clothes on the Way to Mars?"
– 0..
Mar 4 '20 at 20:24

Dry cleaning.

Dry cleaning is expensive on earth because water is so cheap. In space it is easily cost competitive. One could use conventional solvents (e.g. trichloroethane) and capitalize on easy access to low atmospheric pressures to recapture solvents for reuse, distilling used solvent back to fresh and leaving body oils / dirt behind. Conventional dry cleaning solvents would work fine in a low pressure environment. This is not very edgy.

One could also use supercritical CO2 which is now commercially used for "environmentally friendly" dry cleaning. Space travelers have a surfeit of CO2 anyway which must be scrubbed from the air. Supercritical CO2 dry cleaning is not edgy either, although using exhaled CO2 to do it would be kind of cool for a fiction.

• Dry cleaning uses the same tumble process that normal washing uses resulting in the same fundamental problem: no gravity. Mar 4 '20 at 19:59
• @Anketam - "The Hughes system uses liquid CO2 and special washing machines that move clothes around with jets instead of moving parts, which make it more difficult to maintain high pressure inside the machine, Chao said." latimes.com/archives/la-xpm-1997-sep-08-fi-30002-story.html Now about that downvote... Mar 4 '20 at 20:19
• @anketam you might ask yourself if you are being petty. Like you are assuming they would do dry-cleaning in space the same way they do on Earth. Heck, every activity in space has to be adapted for microgravity anyway, that's a given IMHO. Mar 5 '20 at 14:44
• @Anketam If you have a centrifuge you have gravity. If you want tumbling, just have a smaller rotating cylinder off center inside a larger rotating cylinder. Mar 6 '20 at 9:52
• The only thing i would be hesitant with about this answer is the additional risks posed by having a pressurised container with a opening on it (and all the components required to close off that opening) full of C02 on board. if your super-critical washing machine suddenly springs a leak, this could easily spell the end for your astronauts (though i can also see them being at less risk than your average washing machine user on earth due to already being in a highly regulated atmosphere with breather apparatus and space suits presumably not too far away if alarms sounded) Mar 6 '20 at 15:22

Easy, use a regular washing machine in an artificial gravity environment.

Why:

1. Washing machines on Earth are an established technology with decades of research and development attached to them
2. The craft will already have equipment for recycling gray- (showers) and wastewater (bathrooms). Pumping washing machine wastewater into that system shouldn't be a problem and nor should supplying it with fresh water be an issue either.
3. Power supply isn't really a problem for such a low-powered device and bringing enough soap/detergent for a couple years isn't that much mass
4. Traditional washing machines need gravity to work and I'm convinced that any serious Mars mission, especially early ones, will need to have some sort of artificial gravity in the form of tethered counterweights or rotating ring sections of the spacecraft. Especially for a short stay Apollo-style mission, astronauts need to be acclimated to Mars gravity before they arrive. Otherwise they will essentially be immobile cripples on arrival and unable to complete any tasks. Recovery from microgravity takes weeks, which isn't something you want when you've just landed on the red planet and only have a short stay.
• @L.Dutch-ReinstateMonica there is no artificial gravity on the ISS. Traditional washing machines only work with gravity. Mar 4 '20 at 15:59
• @Fels the momentum of a well-balanced washing machine would have little effect on a spacecraft multiple orders of magnitude more massive. Astronauts pushing off a wall imparts more momentum than spinning up a washing machine. Mar 4 '20 at 16:06
• For reaction wheels to turn a spacecraft or space station, they need to be quite massive. A single load of laundry doesn't nearly have enough mass to upset the spacecraft, particularly if it's already located in a rotating section of the craft (due to the gyroscopic stabilization of the artificial gravity). Additionally, since the laundry is eventually done, the washing machine effectively recuperates any induced momentum. Again, astronauts moving around the ship would have a bigger effect on it's attitude than a single washing machine. Mar 4 '20 at 17:41
• @L.Dutch - Reinstate Monica♦ There's a couple comments attempting to answer why the ISS doesn't have a washing machine but I have a counter question: Do you really think washing clothes is a good usage of time for highly trained scientists in a one-of-a-kind laboratory that takes millions to run and maintain? Mar 4 '20 at 22:22
• @L.Dutch-ReinstateMonica most importantly, ISS is constantly supplied from Earth with food, water and other stuff. It's trivial to throw in a few undies, and the extra mass is almost negligible. And while it certainly would have been possible to create a zero-g washing machine, the real issue is maintenance. Read "Astronaut's guide to life on earth": each astronaut has to know how, and most of them have to, repair the space toilet. Would you like to add washing machine repairs to their tasks?
– IMil
Mar 5 '20 at 6:58

Print new clothes every day

I propose an alternative : Create new clothes regularly, and toss old ones in the recycler.

Clothes are already made of polyester, made from forcing melted polymer feedstock through spinnerets, then weaving the resulting thread into cloth. This is exactly how a 3D printer works, and can be done with minimal human intervention.

The mission will already be bringing at least one 3D printer, due to the obvious mass benefits of not having to bring every single spare part needed to maintain the mission, but only an excess of polymer feedstock.

I am not a materials scientist. I don't know which polymers would be appropriate, but let us consider polyester. Polyester is among the most common fabrics in use on Earth today. https://www.commonobjective.co/article/what-are-our-clothes-made-from

Polyester is extruded using a spinneret, which is exactly how a 3D printer works. http://schwartz.eng.auburn.edu/polyester/manufacturing.html

The astronauts get the advantage of precisely-sized personalized jumpsuits, important when they gain several centimeters of height over months in low gravity.

Neither 3D printing nor recycling is handwavium - they're just expensive as of 2020. You can completely automate the creation of a jumpsuit from tiny spray nozzles and perhaps some manipulator arms. There are other methods of 3D polymer crafting available as well : immersion in liquid, UV light exposure, etc.

The initial commentors challenged me on solving the recycling problem. I'll make an amateur attempt here : First, mulch the old jumpsuit, aerate violently and filter out hairs and skin (like a cyclonic vacuum). Dissolve the results in appropriate chemicals to dissolve the polymer but leave behind sweat and salt. Push the polymer goop through a spinneret again, using whatever chemical steps are necessary to render it fiber, and then you have 3D printer stock again. I lack the chemistry knowledge to be more precise, but I know that it can be done, due to this link regarding polyester : https://www.eco-business.com/news/a-way-to-repeatedly-recycle-polyester-has-just-been-discovered/

• This answer spends most of it's content talking about something the question didn't ask about and skirts around the real question: How do you clean the materials in the recycler? Mar 4 '20 at 22:17
• I expect a printer capable of this, and the raw materials, would cost (and weigh) more than the washer options already given, making it an impractical choice. Plus the crew would need additional training and specialty spare parts to repair it, whereas traditional-style washers aren't that complex. Mar 5 '20 at 4:58
• This is brilliant. They don't even have to do it every day. Their outer wear can probably go a while. Mar 5 '20 at 8:36
• ...And you can make new clothes in case of any new crew members/passengers. Mar 5 '20 at 23:15
• Polyester underwear? I foresee mutiny. Maybe that will be useful in the narrative. Mar 6 '20 at 19:09

There seems several ways viable to me.

If you have a full water recycling system for the crew's shower and toilet, dumping water from a washing machine into it is probably the easiest solution, with some suitable detergent the recycling system can handle. The clothes should probably be vacuum dried inside the machine after washing, to prevent water escaping.

I'd imagine steam cleaning can substitute heat for water consumption, reducing your water needs, but this will require fabric that survives high temperatures.

Alternatively Russia is developing a washing machine that should run on liquid CO2. Of course, this then involves high-pressure vessels, which increases weight by themselves. Source: https://phys.org/news/2019-03-frontier-russia-machine-space.html

• I'm sure even if heavy, the CO2 washer will be loved by the crew Mar 4 '20 at 12:46

I was about to elaborate a tongue-in-cheek answer about g-strings underwear that one can wash into a teaspoon of water, then I suddenly remembered two possible solutions in the 'disposable' category.

1. spray-on clothing style - instead of pressurized spray cans, have a canister that you connect to the ship's air recycling/supply. Disadvantage - in zero-g sprays are messy.

2. those Wysi compressed towellets - just make them using a longer cellulose fiber to have them stronger. Then you put it into a little water to expand, vacuum dry them (to recover the water) and there you have a good-for-a-day pamper style underwear that's as biodegradable as your poop. BTW, before discarding them, you should be able to use them as toilet paper;

In any case, I believe both solutions are technologically simpler than a washing machine, will take less space than the washing machine and definitely will consume less energy.

You would just use a normal washing machine, with some minor modifications

I don't know why so many people here are saying a washing machine needs gravity. When the barrel spins it will agitate the water and soap and clothes mixing them together and cleaning them.

Modifications would be to stop water pooling in place so you would want the barrel to have some "spokes" that stick in toward the center of the barrel acting as paddles. You may also want to block the center of the barrel to stop everything gathering there. And finally you could also make sure the machine changes spin direction regularly.

To dry, most water can be pressed out of the clothes so they are only damp. Then a regular dryer can be used to finish off the drying process. All water can be captured, filtered, and re-used for the next wash. In a system designed for efficiency there would be very little water loss so 10's of litres could last the entire trip.

• Another modification: bolt it to the ship so an un-balanced load doesn't go flying off somewhere accidentally. Mar 5 '20 at 5:07
• Well, a top loader is not usually sealed on top, so you'd have to fix that or go with a side loader to avoid water escaping. The problem with gravity is not the washing, but draining after the wash is done. I imagine they'd have to use some kind of suction to get all the water out of the drum, while a standard washer just drains via gravity. (Also, standard washers and dryers are kind of heavy, so you'd probably want to design something lighter just because weight = money in terms of getting things into space.) Mar 5 '20 at 17:29
• Uh... it should drain just fine simply from spinning. Salad spinners already work on this principle. (Okay, gravity helps a little, but it's hard to imagine this being an insurmountable problem.) Mar 5 '20 at 20:35
• @Matthew - The water spins out of the salad spinner, yes, but it then goes down. Without gravity, there's nothing stopping the water from simply drifting back in after it stops spinning. Hence you'd need some sort of suction to collect the water that drains out of the drum. Not insurmountable, sure, but definitely not a feature of a standard Earth-bound washing machine. Mar 5 '20 at 23:38
• Actually, a cleverly placed slot on the outer cylinder should allow it "out", but at some point, you do need to pump the water elsewhere. I could further imagine a sort of paddle-wheel pump, almost like a squirrel-cage fan, to keep the water from feeding back into the washer, but at some point, the difference between "pump" and "suction" does start to blur... Mar 6 '20 at 3:04

# DON'T

Over on Space Exploration, the question was asked Nudism in Space: Why Wear Clothes Anyway?

Laundering clothing is energy intensive, takes up time and critical space and even Maytags break down from time to time. When that happens, you've just got a useless piece of junk in your very limited living space.

Getting long-haul astronauts used being naked for the duration of the mission might end up being the best solution. They'd only need to suit up when leaving the vessel.

• Totally agree. AFAIK clothes were invented not for modesty but for protection from the environment as we migrated from Africa to Europe, especially its cold north, and for decoration/ceremony. There are still plenty of tribes that don't wear them. We are all aware of our physiology, what's the big deal with it being visible. Just go without clothes. Within a couple of weeks you would forget you would stop noticing you weren't wearing clothes, although you would probably notice, and be thankful for, the convenience of not having to put them on or wash them. Mar 6 '20 at 2:48
• That brings some problems in zero gravity, as the contaminants you'd usually have to wash out of the clothing - namely, shed skin cells, shed body hair and sweat - would now be floating around the station instead of being contained in the clothing. Mar 6 '20 at 13:32
• And even if you wear (some minimal) clothes, they need not be washed or changed often. The only goal is to prevent diseases. You certainly don't want to use lots of resources or haul washing machines to Mars and back; what an absurd idea. I envision kneadable plastic bags with a reusable mild disinfectant. Crew is selected by tolerance to body odor (I'm not joking): If you can't bear it easily you don't go. A semi autonomous space ship will be a stinking barrel no matter what anyway; deal with it. Mar 6 '20 at 14:50
• @Peteris - All that stuff is floating around aplenty clothing or no clothing. Just look at some pictures of the crew of the ISS -- they're all wearing short sleeve shirts, often short pants, no hair nets, no gloves, no surgical gowns. They breathe and gleek and sneeze and cough and sweat and who knows what else all the time they're in space and no one bats an eyelash over all those "contaminants". I think the solution to the trivially increased amount of shed skin cells is simply the vessel's air handling system. Couple hepa filters and Bob's you uncle.. Mar 7 '20 at 1:49

One of the issues that gets raised a lot, is the problems of extended periods is zero G. One solution proposed for the Mars trips would be to split the load in two masses connected by a cable. This is spun, giving artificial gravity, probably at the strength of Mars surface gravity.

Coriolus effects are uncomfortable with rotation periods under 1-2 minutes.

$$a=v^2/R$$ but this is an awkward form

$$C=2\pi R$$ where C = circumference of the circle.

So the period, $$T=C/v = 2\pi R/v$$

Solving for $$v$$ we get $$v=2\pi R/T$$

so $$R=v^2/a$$

substituting $$R=4\pi^2R^2/aT^2$$

divide by $$4\pi^2R/aT^2$$

$$R=aT^2/4\pi^2$$

To get $$3 m/s^2$$ and a 2 minute period $$R= 3*120^2/4*3.14^3 = 1094m$$

This would allow an ordinary washing machine with possible reprogramming for different timing to be used.

Solution 2: Freeze drying.

I saw this originally in Heinlein's short story "Misfit" Garments soiled by space sick individuals were secured to pegs in the airlock, allowed to freeze/dry for a while, then were brushed hard in front of an air return duct.

This sort of happens with my nylon wind pants. I come in from tramping outside, and I've got mud from shoe top to mid calf. Let the mud dry, whip the pants against something solid, and most of the dirt is gone. Wear for a few hours in dry conditions and the rest falls of.

Couple this with leaving it out in the sun for a few minutes, and UV will sterilize anything, or put it in a black metal container and bake for a while.

Brushing hard by an air duct is tedious. Perhaps a rotating drum with fins, and a mix of clothes and superballs. Drum changes direction freqently. Superballs carom off the fins beating on the clothes. Air is continuously injected at the center and withdrawn from the drum surface pulling dust with it.

Artificial gravity/Exercise/Washing machine

Build a flywheel into the ship that is operated by astronaut's muscle power. This can rotate fast enough to provide partial gravity to the rest of the ship's crew, and the center can be used for doing laundry.

Or they could just go naked. Spacecraft are climate controlled so what's the big deal?

• Compare the momentum of inertia of a spaceship with the torque which a human can exert, and with the angular velocity needed to have a sensible apparent gravity.
– L.Dutch
Mar 4 '20 at 19:14
• Well they could certainly wash clothes in the center anyway Mar 4 '20 at 19:16
• look at other answers. Without gravity a wash machine is useless
– L.Dutch
Mar 4 '20 at 19:17
• I see your point and the laundry-as-exercise is a good idea, but as far as being naked... something as simple as farting in close/closed quarters without anything between your hole and my mouth doesn't sound to appealing. I'm sure there's some eproctophiles out there that might disagree, but I'm not convinced there's significant overlap of astronauts and eproctophiles in the population. Mar 5 '20 at 2:40
• Nakedness isn't a big deal for the astronauts, most likely. However any space mission has cameras everywhere. It's essentially a 24/7 surveillance culture, because if they do something wrong then the whole crew can die. NASA also has a commitment to release all pictures to the world. NASA therefore has to clothe the astronauts, not for their benefit, but for the benefit of people back on Earth who'll be watching those cameras, because creating space porn is not on the mission agenda. Mar 5 '20 at 8:48

First you need to have the following:

1.) Soap 2.) Water 3.) Downy bango 4.) Llaundry

1st step is to hold the laundry using 2 hands then meet each other and repeatedly use force so that the friction would clean the dirty party.

do the 1st step

remove soap rinse water and do the 1st step

then put the laundry in the stone to make it dry.

Put the dirty clothing outside.

Vacuum + radiation = clean (ie., sterile) clothing...but it won't be visible clean (ie. stain-free).

Picture the spacecraft exterior covered with clotheslines, with dirty laundry flapping in the breeze. :)

• What breeze will the dirty laundry flap in? Mar 6 '20 at 16:27
• @Thymine, obviously the solar wind...
– L.Dutch
Mar 6 '20 at 19:46

Some of the existing answers are very unrealistic. For example, the 3D printing one doesn't consider that 3D printers don't print fabrics and assumes that the technology for recycling fabric into plastic will be lightweight and extremely reliable. If you had the magic recycling tech - which would need to be magic and I'll explain why - then you wouldn't want to use a 3D printer at all. You'd make thread and then just weave it.

3D-printed clothes are currently nothing more than unwearable junk, and there is no reason to think this will change. 3D printing just isn't a relevant technology to making clothes, because it produces rigid things and clothes are made from flexible meshes.

As for the recycling magic: the problem isn't hairs, it's fat. Fat from sweat bonds with clothes and acts as a home for bacteria. The same fat would drive a 3D printer crazy. Removing the fat from recycling fabric is no easier than removing it from intact clothes - unless you assume magic, which appears to be the case above.

In fact there are two simple solutions:

1. Take spare clothes. Compared to other consumables, a new singlet and pair of shorts every couple of months weighs nothing at all. You make them of a hybrid merino polyester impregnated with silver - that will actually be reasonably non-smelly after two months of low-exertion use.

2. Put the clothes in hot water, shake them around, filter the dirt out of water. The same few litres can be used for months.

Boring, but realistic.

Nudism would be a technical solution, but probably not a politically acceptable one.

Also, the question is even more flawed than the answers. If you're getting to and from Mars using Hohmann transfers - which is what seems to be the case from the 245 day reference - you have to wait for the next return window when you get to Mars. You can't just spend a few days there because you want to. Assuming the transfer windows are symmetrical you're looking at a 17-month stopover - they occur every 26 months and a transfer takes 9 months.

• Hey, I think you're getting downvoted because your post reads as written by someone with a pretty arrogant attitude, the things you say would be better received with less snark. Mar 6 '20 at 16:25
• No, they're being downvoted because people who post and vote on threads like this want to feel smart and resent anything that interferes with this. People want to think they're potentially the hero in a hard SF novel. But if you're posting - or even voting - about Mars missions on Hohman transfer orbits without knowing what one is, or about 3D printing without knowing what a 3D printer does, then you're the loser background character instead. Check facts, people. (And also: what sort of loser even cares about up or down votes??) Mar 8 '20 at 14:45

The garments replicator is like a CAT scan machine. You lay in naked, spread your legs and it weaves a a web all around you from head to toe. This web protects you from cuts,cold and radiation. it hates microbes with a passion. When you need a shower, you simply disposed of it and it is recycled in the replication system where it is cleansed, turned into raw material and spun again into a web that will be re-used.

• "assume current tech level, no handwavium" Mar 6 '20 at 13:33