Let's talk space toilets | Hacker News Reader

Let's talk space toilets

mceglowski.substack.com

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I was surprised there were no pictures of the actual toilets. Would love more but found this.

https://en.wikipedia.org/wiki/Space_toilet

Some info on the new one: https://www.scientificamerican.com/article/artemis-iis-toile...

https://ntrs.nasa.gov/api/citations/20220005710/downloads/NA...

So... it's essentially the same thing that has been on the ISS for three or four years?

This goes into a bit more mechanical detail than the Substack post (which only gestures at "air suction"). I'm still not sure whether there are different urine hose adapters for men and women or not.

The hose is the same but there are different funnel attachments (the part looks kind of like the cup from a jock strap, and is longer and narrower for women)

Thanks! Any idea why simultaneous operation of seat and hose wasn't possible before ISS/Orion (not sure which)? And why were they able to get rid of the Space Shuttle camera?

If you like space toilets you may be interested in this [0] HN submission where you can track how full the ISS urine tank is from the comfort of your menu bar.

[0] https://news.ycombinator.com/item?id=42505454

Dude, I just looked a picture of old socks and urine stuffed together in a waste bag. I think I need some time before I can feel the delight to get interested in any kind of toilet.

But thanks for the info.

And as someone else said....the entire business would be solved if not for our cultural tabboo that requires astronauts to do the whole procedure by themselves. If you could have another crew member actively helping it would be done quicker in a much more hygenic way. But because it's "private" they have to do these crazy acrobatics to do it alone. And like, back on Earth nurses have to do much much worse stuff every day and no one considers that weird - it's just part of the job.

I've always wondered about regular toilets and now this. Someone has to test it. I'm sure they have equivalent items to run through them but, eventually, you have to try the real thing so whose job is it to do that and how do they do that?

One popular "equivalent" for flush testing is a condom full of soybean paste (yum!)

https://slate.com/technology/2025/02/toilets-low-flow-trump-...

I had a major plumbing problem once, in a rented commercial space. The toilet simply clogged constantly and I had to snake it almost every time. The landlord finally relented and had an expert plumber come out.

The guy apparently had a master's degree in plumbing somehow (I thought he was joking but he had indeed put himself all the way into a master's level engineering degree, mostly as a hobby). He first got out his scope and confirmed there was zero blockage in the sewer pipe and the septic tank itself. All good.

Then he started simulating flushing a load: wads of toilet paper, measured by number of squares. 17 squares went down just fine, but then he did 25, which he said is the max he expects a toilet to do. Instantly clogged.

He then told the landlord to stop buying $90 toilets and that he'd just advised a nursing home that had bought a bunch of the exact same model to rip them out and put in a better, $150 model.

So yeah, that's how you test it.

this feels like a chute diameter issue, many older (cheaper?) ones are 2in, but high flow are 3in I believe

Back in "the day" you could have a toilet that lazily filled up and you only really needed a mild flow rate to send everything for a ride because once that 5gal of water starts spinning it's taking everything with it no questions asked.

You need a big hole to dump the tank fast to get the maximum kick out of that federally regulated amount of water you're allowed to dump per flush.

Plumbing fixture and residential water consumption regulation in the US is a textbook example of "should be a states issue". The feds basically let the desert states dictate everything and then everywhere east of approx the Missouri river has to suffer through washers that don't wash clothes the first time, constantly clogging drain traps, sewer lines, municipal mains, reduced septic performance, etc, etc. None of this is necessary in the nearly universally surface water consuming east. They'd all be better off using more water and having to size their water treatment plants up a notch to handle it.

My degree is chemical engineering and thats pretty close to a degree in plumbing

Well regarded cardiac surgeon Barratt-Boyes supposedly had a brother who was a good plumber.

This always made me happy.

https://en.wikipedia.org/wiki/Brian_Barratt-Boyes

Oddly enough my department done work into heart replacement valves - the fluid mechanic element of blood flows as a non-newtonian fluid matched a lot of chemical plant calculations. The labs had lots of heart valves and simulators lying around

Welcome to the world of Maximum Peformance (or MAP) testing. 22 municipalities and associations came together across the US and Canada to form a consortium to develop a 'standard' test (and test media) and test toilets to determine who flushes feces the fullest.

https://map-testing.com/background/

(And really thorough history! https://map-testing.com/wp-content/uploads/2025/12/Backgroun...)

Apparently, a "MaP Premium" toilet is going to be the golden shitter.

Is it simpler to build a better space toilet, or to build a ship with centrifugal gravity and use a regular toilet?

You wouldn’t want to use a regular toilet even if you could, given how tight water margins are. Urine you can reclaim, feces not so much.

Vacuum flush toilets are common on airplanes, trains, and ships and use a lot less water than a conventional toilet.

There are two issues:

- To build a centrifuge in space of sufficient size, you need to solve the problem of delivering a large amount of materials to orbit, because it has to be hundreds of meters in diameter at least.

- Such a centrifuge will create a gyroscopic effect, and the station will quickly become very difficult to control.

You can try it with small capsules and tethers, but it's still a pain.

Couldn't you have two centrifuges next to each other spinning in opposite directions, cancelling most of the effect out? I believe some helicopters work like that, with two sets of rotors on longer troop transport helis. A few even have two sets on top of each other. And many planes have the props on opposite wings rotate in opposite directions.

Even with centrifugal "gravity" the toilets need to be designed for the worst case scenario (no "gravity"). Even if you could use a "regular" toilet the system needs to sequester and process the septic waste. That precludes even using the likes of an airplane toilet.

It's a significant amount of engineering effort, testing, feedback, and iteration to build effective life support systems for manned spaceflight. Long duration spaceflight is orders of magnitude more difficult.

Toilets are systems that can incapacitate or even kill the crew if they malfunction. In a low or microgravity environment aerosolized septic material can get in astronauts' eyes or lungs. It can also seep into electronics or other ship systems causing malfunctions. Even just clean water spraying into the cabin could be dangerous in microgravity.

The centrifugal gravity approach requires a massive structure - you need something like 200+ meter radius to keep rotation rates low enough that Coriolis effects don't make people nauseous (which would create a whole different toilet problem). Building a better space toilet is orders of magnitude cheaper and lighter than spinning up a habitat.

SpinCalc is a useful simple tool for looking at the tradeoffs of centrifugal artificial gravity: https://www.artificial-gravity.com/sw/SpinCalc/

You could just dangle the toilet on the end of a filament, and rotate the capsule and the outhouse around the centre of mass. No massive structure needed, just remember to take the farmer’s almanac with you before you head out.

If people are going to live in space for any period of time then they are going to need gravity so long term, yes.

Scale up the nautilus body plan to a 200m radius shell and contain spindrive artificial gravity for collecting pellets.

This does sound absurd at first, but how much gravity is really needed for collection? Is there any value in just a few hundredths of earth gravity?

The article mentions that on Mars, with 0.38x Earth gravity, there will still be challenges, so I expect you need a significant fraction of 1g for the problems to go away.

It's not an absurd question. The threshold value is the one that breaks surface tension and effectively pulls waste away from the body. It will be more than a few hundredths g but less than 1g.

Unfortunately we have basically no data on the effects of partial gravity, in this context or any other. We can try flying partial-gravity parabolas in aircraft and simulate a Martian toilet the same way they tested the design for Skylab; I don't think this experiment has been done.

Ah a fellow Hail Mary fan :)

It depends on the scope of the mission. If you're going to commercialize long term space travel then you're going to want some form of artificial gravity.

If you build a better toilet you need a better pooper to use it. And they need to use it correctly every time or you're going to need a really good waste cleaning and disinfecting strategy for your ship.

>Is it simpler to build a better space toilet, or to build a ship with centrifugal gravity and use a regular toilet?

!Spoilers ahead - from Daniel Suarez's dV and Critical Mass novels.

====

The second volume (critical mass) talks a lot about exactly that problem.

> One piece of feedback from Skylab was that the toilet needed stronger airflow. This meant the Shuttle toilet opening had to be narrow. To practice correctly positioning their body, astronauts on Earth sat on a special training mockup with a camera mounted in the center of the waste tube. A successful docking with the device meant precisely centering one’s nether eye in the crosshairs of a video screen while crewmates looked on and yelled their encouragement.

I knew part of the job for astronauts is being intimate with one's crewmates, but I didn't know it was that intimate.

You could’ve told me this story without the context and I would’ve assumed it was a barracks game being played with surveillance equipment. Hilarious.

"Mom, Lise, check it out - Dad's on TV!"

https://youtu.be/S5lihwyjk8w?t=30

I can totally picture one of the engineers glancing at the Apollo docking simulator and a grin coming across his face.

I've often wondered - what is the exact amount of vacuum (pressure?) that you can get away with without disemboweling someone?

A possible point of comparison might be pool drain injuries (a/k/a suction entrapment), and some of these have disemboweled people, though largely children. Vacuum toilets in cruise ships have also been implicated in such incidents (see, among others, https://www.upi.com/Archives/1987/03/06/70-year-old-womans-i... ). A more, er, pressing concern in adults might be rectal prolapse.

A commonly trotted out argument for continued investment in manned space flight is technological spillover: that all the money we give to NASA generates positive benefits in other sectors of the economy. I'm not so sure space toilets are generating that spillover. This seems like a uniquely expensive humans-in-space engineering problem. I echo the sentiments of Why Not Mars (https://idlewords.com/2023/1/why_not_mars.htm):

> The web of Rube Goldberg devices that recycles floating animal waste on the space station has already cost twice its weight in gold and there is little appetite for it here on Earth, where plants do a better job for free. [...] I would compare keeping primates alive in spacecraft to trying to build a jet engine out of raisins. Both are colossal engineering problems, possibly the hardest ever attempted, but it does not follow that they are problems worth solving. [...] Humanity does not need a billion dollar shit dehydrator that can work for three years in zero gravity, but a Mars mission can’t leave Earth without it.

Why are we doing human spaceflight again?

Not because it is easy. But because it is hard

The roasting process is both hypermodern and curiously antique. Burning dung is a tradition passed down across the millenia!

This story of space toilers clears out many questions I had about spaceflight and... uh, going number 2.

Namely: astronauts try NOT to as much as they can, and when they do go, it's a mess for both them and their crew mates. They suffer through it because being in space is a worthy achievement.

Apparently it's such a mess that NASA estimates this is why astronauts tend to undereat. Apparently Gemini 7's Frank Borman spent 9 days without going number 2 because of this, and planned to hold it in 2 full weeks (the article doesn't clarify whether he managed). Skylab seems to have done some progress, but we're still in the early eras of space toiletry!

On Apollo 13, after the accident, the margins for propellent were so low that the astronauts had to drink very little. Nasa was afraid that venting the pee would set their trajectory off course.

One of the astronauts got an infection from dehydration as a result.

Not a great lunch read.

Give it a few hours!

I found it pretty easy to digest.

Thank you for writing and sharing this. I went into a deep dive a few days ago researching waste recycling, and your write up taught me a lot!

Thanks so much! I'm delighted you enjoyed the piece.

That was an oddly interesting article.. I never thought about doing your business in space.

made me think of zizek's hermeneutics of (gravity-based) toilets https://www.youtube.com/watch?v=rzXPyCY7jbs

> frozen urine accumulates on the hull of Discovery

right click -> Save Image As

We can see how our daily lives are supported by public welfare

So liquids are recycled but solids are still bagged and stowed. I hear human excrement is high in methane content... and certain contemporary rockets use methane fuel, right? Poop-powered spacecraft, for the win!

Edit - I wrote this tongue in cheek but it turns out there really are scientists working on it: https://explore.research.ufl.edu/process-converts-human-wast...

>A successful docking with the device meant precisely centering one’s nether eye in the crosshairs of a video screen while crewmates looked on and yelled their encouragement.

Massive Interstellar vibes, I guess it is "necessary"

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