A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

How do astronauts go to the bathroom in space?

August 3, 1990

Dear Cecil:

How do astronauts perform their bodily functions in space? I've seen mentions of "collection systems," but that's about it. By the way, do you pay a reward for good questions? It would help to stimulate my thinking.

Cecil replies:

A reward? You mosquito, the search for knowledge is its own reward. Besides, we're out of T-shirts this week.

Up until Skylab, "waste management systems" aboard spacecraft were primitive. The "device that collected the feces was a plastic bag that was stuck to the posterior [with adhesive] during defecation," NASA bluntly reports. "The system used for urination was a version of the time-honored `motorman's friend,' so called because the hose-and-bag unit was worn by the streetcar motorman, whose job gave him little opportunity for a rest stop."  Cecil frankly is appalled — not that the astronauts were subjected to this indignity (there wasn't much choice), but that the motormen were. Puts a whole different spin on the idea of labor unrest.

Things improved considerably with the advent of Skylab and later the space shuttle, both of which were equipped with what was recognizably a toilet, though admittedly of the George Jetson variety. The problem is the lack of gravity, which plays such an important role in earthbound elimination. Instead we substitute what amounts to a vacuum cleaner. That may sound a little drastic, but there are times when only drastic measures will do.

Here's how it works. First you seat yourself firmly on the commode. (Bear in mind that you wear civvies aboard the space shuttle, not a space suit.) Restraining devices are provided so you don't drift off at an untoward moment. In front of you is a urine cup — essentially a funnel with a hose. Each astronaut has his or her own cup; those for women are shaped differently from those for men. The commode seat is cushioned to make a good seal with your bottom, ensuring proper suction and preventing waste from escaping.

Then you turn on a fan inside the commode and proceed with business. The fan pulls the goods into a sort of mesh bag that traps solids but allows liquids to pass through. The water is pumped to a storage tank, which is later emptied into space. When you're done, you seal up the top of the commode and open the bowl to the vacuum of space. The moisture in the solids boils away instantly, reducing their bulk. (NASA folks cheerfully refer to this process as "freeze-drying.") A special device compacts what's left and it's stored in the commode until you get back down to the ground.

Doesn't sound all that complicated in principle, but I'm skipping a lot of the fine points. (You don't really want to know about the waste water crosstie quick disconnect, do you?) Here's how astronaut Woody Spring described the experience in an interview with the Journal of the Water Pollution Control Federation:

During some of our training in the weightlessness environment, we practiced "potty training," which is unlike any seat one is accustomed to. It involves placing yourself over a special 4-inch hole seat, and sitting just right in order to maintain a vacuum seal. Naturally, this seat must accommodate people of all different sizes. To help practice placing ourselves correctly we used a closed circuit TV with a bull's-eye target from which we practiced; it wasn't easy.

I'll bet. Worse, there's always the chance that the high-tech stuff may fail, forcing you to fall back on the good old "Apollo bag," already described. Worst of all, there's the danger you could leave the seat up while flushing, as it were, thus sucking out the spacecraft's air. All in all, Cecil thinks he'd just as soon hold it till he got home.

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