It feels a hell of a lot like the multimillion dollar pen vs the pencil myth - it costs them maybe $20K to send six months worth of clothes to the ISS per astronaut on a Dragon 2. The ISS-rated dry cleaning machine would cost at the very least a million dollars to develop, would still require sending ten grand of fresh solvent every so often (maybe once a year?) and would add new fire/explosion safety concerns, which they can and do put a price tag on. It would probably take longer than the life of the station for the ISS dry cleaning machine to pay itself off.

It's just too easy to not bother. For a moon colony or a Mars base, the economics change, but for near earth orbit it just doesn't make sense.

> it costs them maybe $20K to send six months worth of clothes to the ISS per astronaut on a Dragon 2

Maybe true now, but this wasn't the case when this 2003 NASA article was written. It quotes >$5k/lbs for the Shuttle. Six months of clothes for a single person wearing each article for a week is still going to run, what, at least 40lbs, or >$200k. With six people on the ISS, that's at least few million bucks per year, and likely more. The ISS must have been planned to last minimum 10 years (without anything cheap like Dragon on the horizon), so I think it's still a valid question why they didn't design a small washing machine.

One has to wonder at what point the utility of clothes doesn’t make sense, and astronauts should just get used to working naked.

Not actually advocating for that—beyond cultural difficulties, I’m pretty sure clothes are useful enough to maintain—but it’s an interesting thought exercise to zoom out from “how to wash clothes better” to “how to do the job clothes do better with minimal cost.”

The first thing I'd miss is pockets. Working with your hands, e.g. conducting experiments, usually requires a number of items to be close at hand, and you can't put anything on a workbench at zero g.

The second thing is individual thermal comfort. Say, 20°C is usually "fine for everyone", but some people would feel that it's quite warm to wear a T-shirt, while other people would find it barely warm enough to not wear a coat.

I can't comment too much on the zero-G washing part (but I tend to agree), and I think the comment about solvent is actually very interesting.

It's likely that weight is probably not the biggest concern if such a washing system were to be implemented, as they would probably design a system to recycle the washing liquid. I think most solvents that are candidates as washing liquids post either additional health and/or fire hazards in space. In addition, and particularly for water-based washing, I think the error tolerance in engineering either (1) additional infrastructure to the existing water-recycling system and/or (2) a part that can confidently remove unwanted chemicals are challenging problems. the latter is probably the bigger concern because tolerance for error there would probably be substantially lower than urine recycling.

Just a guess because I thought it's an interesting comment, and it's quite possible that one can already design (if it doesn't already exist) a washing liquid that is safe for consumption at small quantities.

ISS has a circulating ammonia system for its active cooling loops. Maybe there's a way to leverage that system if you can filter the laundry contaminants before returning to the loop.

Also nobody's mentioned UV light. Odors are often due to bacteria and simply killing that stuff would go a long way to reusing garments without gagging on the odor.

Also, I know people have done experiments where instead of washing, they have been freezing their clothes and that gets rid of the odour. And surely, freezing things on ISS should be trivial.

So... Clotheslines between antennas?

My home washing machine is far from 1g. It’s something like 100g or more based on how fast the thing spins.

Having 1 less g would probably mess with the drainage, but not the rest.

But then I wonder how much such a machine would spin/unbalance the space station.

It's bad enough when they go into an unbalanced spin cycle here on Earth, but it does seem that could seriously affect the stability of a space station's orbit. I was surprised this wasn't mentioned even in passing in the article.

That's not how orbits work. Shaking something inside the station won't change its orbit a bit. It's because to change orbit you need to change the speed you are going with. And that's just not something you can do by vibrating a mass.

That doesn't mean that vibrations are all safe. They can break stuff on-board, or mess up experiments. If you do it exactly right (wrong?) it can even change the attitude of the station. (after all the reaction wheels and Control moment gyroscopes look kind of like washing machine's drum if you squint enough.)

Ah, thanks for the information. Interesting that such vibrations can only affect the attitude and not the orbit itself. Keen to hear from anyone who cares to share more of the science involved here!

Maybe you don't need to spin at all because reducing air pressure would allow evaporating all the water at low enough temperatures?

Unfortunately the pressure has nothing to do with the energy cost of evaporating water.