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?
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.
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.
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?
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.
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.
- 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.
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.
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.
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.
> 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.
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.
That was an oddly interesting article.. I never thought about doing your business in space.
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.
My degree is chemical engineering and thats pretty close to a degree in plumbing
this feels like a chute diameter issue, many older (cheaper?) ones are 2in, but high flow are 3in I believe
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.
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?
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.
Is it simpler to build a better space toilet, or to build a ship with centrifugal gravity and use a regular toilet?
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/
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.
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.
You can try it with small capsules and tethers, but it's still a pain.
Ah a fellow Hail Mary fan :)
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.
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.
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.
The roasting process is both hypermodern and curiously antique. Burning dung is a tradition passed down across the millenia!
> 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
Not a great lunch read.
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.