Let's Talk Space Toilets

Let's talk space toilets!

You should have gone before you left Earth

The traditional astronaut’s ‘low residue’ breakfast of steak and eggs pays tribute to the oldest and wisest strategy for going to the bathroom in space, which is to do everything possible to avoid it.

While capsules like Soyuz and the Crew Dragon are equipped with a rudimentary toilet kit, astronauts use a mix of drugs, diet, and occult knowledge passed down the generations to keep from having to use it. It can take more than two days for a Crew Dragon capsule to reach the space station, but the crew in the cramped spacecraft is expected to save the real fireworks for the relative comfort of the space station toilet.

The longest anyone has attempted to hold it in space is Frank Borman, on Gemini 7. Stuck in a two-man capsule the size of a phone booth, Borman was determined to get through his two-week mission without releasing the hounds. His crewmate Jim Lovell describes the outcome:

*STONE: Can you give me some idea how you spent 14 days in that little, cramped quarters with somebody else without going absolutely mad? *

LOVELL: It’s not easy. But you have to remember that you work so long—I was there 3 years—for a spaceflight, so I’d go up with just about anybody. And Frank and I were, you know, just this close together. And you get to know each other quite well.

STONE: Yes!

*LOVELL: I mean it was something. As a matter of fact, Frank went, I think, 9 days without having to go to the bathroom. And he said, “Jim, this is it.” *

LOVELL: “I said, “Frank, you only have 5 more days left to go here.”

Borman would go on to suffer miserably from spacesickness on Apollo 8, giving his fellow astronauts (including poor Lovell again) an unwitting but convincing demonstration of the inadequacies of the Apollo waste collection system, from both ends.

Everyone agrees that the sanitary conditions aboard Apollo were barbarous. Going to the Moon in the tiny capsule was like living in a three-man port-a-potty, made worse by the fact that doing the deed took the best part of an hour, with much of that time spent kneading antimicrobial powder through the contents of the collection bag.

But astronauts back then were hardy, they wanted to go to the Moon, and so they dealt with ‘escapees’ and the continual stench aboard their capsule without kvetching. And so it took twelve years to get from the first manned spaceflight to the first halfway-usable toilet.

Space Toilet Theory

The next time you find yourself in the bathroom, take a minute to consider the three ways gravity helps to make the process hygienic and easy on Earth:

It presses you down against the toilet with enough force that you can position your body comfortably, and maintain that position.

It pulls waste away from the body with vigor, easily overcoming contact forces like surface tension.

It sequesters body waste, first under a layer of water, then ultimately in a gravity-fed sewer pipe or septic tank. The water barrier in the toilet bowl minimizes the time waste is exposed to air and prevents odors from downstream parts of the system from reaching your nose.

In a zero-gravity environment, you have to find alternatives for all three jobs.

The first task, body positioning, turns out to vary a lot across people. Over the years NASA tried a lot of methods that didn’t work, including thigh straps and special rubber shoes with suction-cup soles. They came to realize that the best approach was to provide options (handholds, thigh bars, foot rests) and let astronauts figure the details out for themselves.

The second task, separating waste from the body, has to be done with air suction. The need to maintain a strong air stream means toilet seats can’t be too wide (four to six inches is the norm), making correct body positioning even more important. The various fans also make space toilets noisy, even by the cacophonous standards of space flight.

The third task, sequestering waste and controlling odor, is tricky. Urine can be collected in a funnel, where it gets mixed with an antimicrobial agent before being sucked into a storage tank. The state of the art for fecal collection is single-use porous bags that allow airflow but retain solids and water. These are tied off after use and placed in a collection cylinder, along with any gloves and wipes that the astronaut used for cleanup.

Each collection cylinder is designed to hold about ten bags, with astronauts adding compression plates between deposits as needed to squash things down. The fecal bags are not sterilized, so the lid of the collection cylinder has a permeable filter meant to trap odors while letting evolved gases escape to the cabin.

The process works but is imperfect. Odor control in particular remains a problem, and chronic sewer smell is one theory for why astronauts tend to chronically undereat on the space station.

The Rise of the Space Toilet

The original design for Apollo waste handling was too much for even the steeliest-eyed space man. Fred Hughes describes it in an oral history:

There was a toilet design that you sat on this—the idea with the designers—that you sat on the wall and you put all your apparatus inside this ‘device’ and then you would crack this valve, and it went to vacuum. [The astronauts] said, “Nobody’s going to do that. Pull a vacuum?” You can imagine just turning your whole body inside out in it. That was a big laugh, but they said, “Take it out, we’re not going to fly it, we’re not going to use that.”

And so the Apollo program got by with a mixture of condom-like penis sleeves and plastic bags.

When Skylab launched in 1973, it was clear it would need a proper toilet. The orbital laboratory had ambitious medical goals around collecting astronaut waste, in particular a desire to freeze individual urine samples from the three-man crew over the course of the mission. And at 84 days, the longest Skylab mission would exceed the ability of even the most iron-sphinctered astronaut to hold out. So a lot of effort went into designing a toilet and urine freezer the crew wouldn’t hate.

The final design was bold, with the toilet seat mounted vertically on one of the walls of the spacecraft, so an astronaut could defecate like Spider-Man. But it needed testing, and that meant finding people who could do their business in twenty seconds aboard an aircraft flying a zero-G parabola.

Here I will cite the official Skylab history:

Urination could be successfully simulated by mechanical devices, and a urine-collecting device was easy to test; but defecation could not be simulated. Test subjects who could perform on cue were needed. The Huntsville program office was able to find a few people with this talent, and in November 1969 two days of aircraft testing produced nine good “data points” for the fecal collector.

The Skylab toilet was a hit with the astronauts and helped inform the design of the next chapter in orbital elimination, the Space Shuttle toilet.

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.

The Shuttle stored urine in storage in tanks that were periodically vented through space through a heated port in the hull. But On STS-41-D, a malfunctioning heater caused the material to freeze, creating a large yellow urinecicle outside the spacecraft. Astronaut Mike Mullane describes the aftermath:

*[Mission control] called us. The heater on the outside of the dump nozzle failed, so this blob of frozen urine froze on the side of the vehicle, and what they were worried about was on reentry this blob of ice would