How Do Astronauts Go to the Bathroom in Space?

The Unspoken Challenge

It’s a question that crosses nearly everyone’s mind when they watch astronauts float weightlessly inside a spacecraft: How do they go to the bathroom? The query isn’t juvenile; it’s one of the most complex and fundamental engineering problems of human spaceflight. On Earth, gravity is the unsung hero of sanitation, pulling waste down and away from the body. In the microgravity environment of space, this entire process is inverted. Liquids and solids don’t “fall”; they float. This creates a situation that is not only unpleasant but also dangerous, as free-floating waste can contaminate the cabin, short-circuit electronics, and pose a serious health hazard.

Solving the “plumbing problem” has been an evolutionary process, moving from rudimentary, last-ditch solutions to high-tech recycling plants that turn human waste into drinking water. This article explores the unglamorous but essential history and technology of sanitation beyond Earth.

The Fundamental Problem: Gravity and the Human Body

The human body’s excretory functions are passively assisted by gravity. When a person urinates or defecates, gravity ensures the waste falls away. In space, this doesn’t happen. Any liquid released from the body will, due to surface tension, cling to the skin or break apart into a spray of floating globules. Solid waste, likewise, has no incentive to detach from the body and will simply float nearby once it does.

This reality means that every space toilet, from the simplest to the most complex, must replace the force of gravity with something else. The solution is airflow. Every “space toilet” is a specialized vacuum cleaner. A system of fans creates a steady stream of air that pulls waste away from the astronaut’s body and directs it into a collection receptacle. This principle of using differential air pressure is the one constant in space sanitation technology, from the 1960s to today.

A Crude Beginning: The Early Days of Spaceflight

The first forays into space were so short that engineers hoped to avoid the problem entirely. They were wrong.

The Project Mercury missions were designed to last only a few hours at most. For his 15-minute suborbital flight, Alan Shepard was not equipped with any kind of waste collection. When his launch was delayed for hours, he famously radioed launch control to report a biological necessity. After some deliberation, controllers gave him permission to urinate in his suit. The warm liquid shorted out some of his medical sensors, but the mission proceeded.

For longer Mercury flights, like John Glenn’s orbit, a simple urine collection device (UCD) was added. It was little more than a “roll-on” cuff connected to a hose and a collection bag inside the suit. There was no provision for defecation; astronauts were expected to hold it, often relying on low-residue diets before launch.

Project Gemini pushed missions to last days, and then weeks, making the problem unavoidable. The urine system was slightly improved: a hose vented the liquid directly out of the spacecraft into the vacuum of space, where it instantly froze into a cloud of tiny, glistening crystals.

Defecation was a far more primitive and dreaded affair. The system was a “fecal bag,” a simple plastic bag with an adhesive ring on the opening. Astronauts had to stick the bag to their posterior to create a seal, a difficult task in a cramped, zero-g capsule. After finishing, the astronaut had to use a pouch containing a germicide to manually knead the bag’s contents to stabilize them and prevent bacterial growth. The bags were then sealed and stored in an empty container in the cabin for the remainder of the mission. It was a time-consuming, unpleasant, and odorous process that astronauts universally loathed.

The Apollo Era: Reaching for the Moon

The missions to the Moon presented new challenges. The Apollo Command Module was the crew’s home for the multi-day trip, but it was still incredibly cramped. It did not have a “toilet.”

The urine system remained basic. Male astronauts used a roll-on cuff attached to a hose. This hose could either vent the urine into space (creating the famous “urine constellations” observed by astronomers) or empty it into a collection tank. The system was imperfect. A famous log from the Apollo 10 mission documents a moment of panic when a fecal bag leaked, setting a “turd” floating through the cabin, much to the crew’s dismay and disgust.

The fecal collection system was unchanged from Gemini: the adhesive bag. The process took up to 45 minutes and required intense focus and dexterity. The bags, once used, were stored and brought back to Earth. When astronauts walked on the Moon, they wore a special “maximum absorbency garment” (essentially an adult diaper) under their spacesuits, as leaving the suit to use a bag was impossible. These, along with bags of waste, were among the items left behind on the lunar surface to save weight for the return trip.

The First Space Stations: Skylab and Salyut

Living in space for months at a time, rather than just visiting, required a genuine “bathroom.” The first true space toilets appeared on the first space stations.

Skylab, America’s first space station, launched in 1973 and featured a waste management compartment that finally resembled a small room. For urination, astronauts used a hose and funnel attached to a wall, with a fan pulling the urine into a collection tank.

For defecation, Skylab had a “commode” that was essentially a hole in the wall with a seat. An airflow system pulled the waste into a collection bag. A major innovation was that this system also included a vacuum-drying unit. Solid waste was heated and exposed to a vacuum to remove all water, which killed bacteria and reduced the mass and odor. The dried, powdered waste was then stored. Astronauts had to manually bolt the waste collection unit to the vacuum-drying system, a process that still had its operational challenges.

The Soviet Salyut programme and the later Mir space station featured similar designs, all centered on airflow. The Soviet engineers were pioneers in “closing the loop.” The systems on Mir were designed not just to collect urine but to process it. The “SRV-K” system recycled condensed humidity from the air and reclaimed water from urine, filtering it to become potable water. This was a massive step forward, proving that a crew could become partially self-sufficient on a long journey.

The Space Shuttle: A New Generation of Waste Management

The Space Shuttle orbiter was designed to be a reusable workhorse, carrying large crews, including both men and women, for weeks at a time. This required a more sophisticated solution: the Waste Collection System (WCS).

The WCS was the first space toilet that truly tried to accommodate both genders in its design. It looked somewhat like a terrestrial toilet, with a commode and a separate urinal hose.

Urine Collection: The system used a personal-use “urinal funnel” that astronauts would attach to the urinal hose. There were different-shaped funnels for male and female crew members. A powerful fan pulled the urine through the hose and into a wastewater tank. On most missions, this wastewater was simply vented overboard at specific times.

Fecal Collection: This is where the Shuttle system became notoriously complex. The commode “bowl” was only about four inches in diameter – much smaller than a household toilet. To use it, an astronaut had to sit down, fastening thigh bars to hold them against the seat. They then had to align their body perfectly over the small opening.

To help with this, NASA created the “Positional Training Unit,” a mock-up toilet on Earth with a light and a camera at the bottom of the bowl. Trainee astronauts would use it to practice their alignment, watching their progress on a video monitor.

Once the astronaut was in position, they would activate the airflow. The air would pull the feces into a “slinger” motor. This rotating device would spread the waste against the walls of a collection container, where it was exposed to vacuum to dry out over time. Toilet paper was deposited in a separate “dry trash” container.

The WCS was functional but famously finicky. It was prone to clogging, and the slinger motor could fail. Astronauts spent a significant amount of their training learning how to perform in-flight maintenance on the WCS, a job that was every bit as unpleasant as it sounds.

Life on the International Space Station (ISS)

The International Space Station (ISS) is a permanent human outpost. Crews live and work there for six months or more. Launching water from Earth is prohibitively expensive; a single liter of water costs thousands of dollars to transport. For long-duration life in space, recycling isn’t just a good idea – it’s a requirement for survival.

The ISS is equipped with two primary toilet systems. The first is in the Russian-built Zvezda (ISS module), a design derived from the reliable Mir system. The second, more advanced system is in the American Tranquility (ISS module) and is called the Waste and Hygiene Compartment (WHC).

The Mechanics of the ISS Toilets

Using the WHC is a practiced skill. It consists of two separate systems: one for liquid waste (urine) and one for solid waste (feces).

Urine: Astronauts use a personal funnel (anatomically specific) attached to a long hose. When they flip a switch, a fan creates strong suction. The urine is pulled through the hose and mixed with a pre-treatment chemical (a combination of chromic acid and other compounds) to prevent microbial growth and the buildup of urea crystals (which can clog the plumbing). This urine-and-chemical mix is then sent to the station’s water recycling system.

Feces: The commode itself is a small, silver can with a seat on top. The opening is, like the Shuttle’s, only about 4 to 5 inches wide. Astronauts secure themselves to the seat using foot restraints and thigh bars. When they “flush,” a fan generates airflow to pull the waste down.

The waste is not sent to a slinger but is instead collected in a porous bag. This bag lines a metal canister. The air pulls the feces into the bag while the air itself is drawn through the bag’s pores and passed through a complex filter to remove all odor and bacteria before being returned to the cabin.

When the astronaut is finished, they seal the bag and use a tool to push it down into the canister. This canister holds about 30 individual “deposits.” When the canister is full, the crew seals it, removes it, and installs a new one. The full canister is then moved to a cargo ship, such as a Progress (spacecraft) or Cygnus (spacecraft). When that ship is full of station trash, it detaches and performs a “destructive re-entry,” burning up in Earth’s atmosphere – a fiery end for the station’s refuse.

From Urine to Drinking Water: The Environmental Control and Life Support System (ECLSS)

The most remarkable part of the ISS sanitation system is what happens after the urine is collected. The Environmental Control and Life Support System (ECLSS) is the station’s circulatory system. Its Water Processor Assembly (WPA) is arguably one of the most advanced pieces of technology on the station.

The WPA collects wastewater from every possible source:

1. Urine: Collected from the toilet’s pre-treatment tank.
2. Condensate: Moisture from the air, which includes astronaut sweat and respiration (breath).
3. Hygiene Water: “Gray water” from hand-washing and oral hygiene.

This combined wastewater is sent through a multi-stage purification process.

First, the urine is pumped into a “Urine Processor Assembly” (UPA). This is a large, rotating drum that performs low-pressure vacuum distillation. By spinning the drum, the liquid waste is spread thin against the walls. In the low pressure, the water evaporates (boils) at a much lower temperature, leaving the contaminants (salt, urea, minerals, and the pre-treat chemicals) behind as a thick “brine.”

This water vapor (steam) is then collected and condensed back into liquid. This “distillate” is still not ready to drink. It is mixed with the condensed water from the cabin air and sent to the main Water Processor Assembly.

Here, it goes through a series of filters. It passes through a particulate filter to remove any debris. Then it flows through a “catalytic reactor” that essentially “burns” any remaining volatile organic compounds, breaking them down into harmless byproducts. Finally, the water is treated with iodine to kill any surviving bacteria or viruses.

Sensors constantly check the water quality. If it’s not pure enough, it’s automatically sent back through the system for another round of cleaning. The final product is stored in bags, ready for drinking, rehydrating food, or hygiene. The result is water that is significantly cleaner than most terrestrial tap water.

This system is incredibly efficient, reclaiming over 90% of all water on the station. As astronauts are fond of saying, “Today’s coffee is tomorrow’s coffee.” This closed-loop system is fundamental for enabling long-term human presence in space and is a necessary technology for any future missions to the Moon or Mars.

Here is a comparison of the different waste management systems throughout spaceflight history:

The Next Frontier: Toilets for the Moon and Mars

As NASA plans to return to the Moon with the Artemis program and looks ahead to Mars, the toilet technology must evolve again. The next-generation spacecraft, Orion (spacecraft), will be equipped with a new system called the Universal Waste Management System (UWMS).

The Universal Waste Management System (UWMS)

The UWMS is the new standard. It’s smaller, lighter, more power-efficient, and designed with much more user feedback, particularly from female astronauts, to be more ergonomic and comfortable.

Like the ISS toilet, it uses airflow to separate urine and feces. The urine is collected via a hose and funnel, automatically mixed with a pre-treat chemical, and stored in a tank. On the Lunar Gateway station, this urine will eventually be recycled. On shorter Orion missions, it will be stored.

The fecal system is also improved. It uses a commode with airflow, but the waste is automatically compacted in a collection canister, making it more efficient for storage on long missions where it can’t be regularly thrown out. The UWMS is designed to be a “universal” system that can be used on Orion, the Gateway, and future lunar surface habitats.

Challenges for Mars

A mission to Mars will last two to three years. There is no resupply and no “throwing the trash out.” This requires a 98% (or better) closed-loop system. The ECLSS on the ISS is the model, but it must become even more efficient.

The partial gravity of Mars (about 38% of Earth’s) also presents a new problem. While it’s not zero-g, the gravity is not strong enough for a terrestrial toilet to work. Any Mars habitat will still need an airflow-assisted commode.

The biggest challenge is solid waste. On the ISS, feces are discarded. On a Mars mission, that’s lost mass and, more important, lost water. Future systems are being designed to “process” solid waste, likely through a combination of heating and chemical reactions (pyrolysis) to recover the remaining water (feces are about 75% water) and break the organic material down into sterile, inert components. This processed “biomass” could potentially be used as a component in radiation shielding or, after extensive treatment, as a fertilizer for growing plants.

The Human Element: Training and Psychology

Using a space toilet is not intuitive. Astronauts spend hours on Earth training for it. Beyond the positional trainer for the Shuttle, they learn the entire system’s mechanics. This is because, in space, the astronaut is also the plumber.

If the toilet clogs or a fan fails, it’s an “all hands on deck” emergency. Repairs are difficult, messy, and unpleasant. Astronauts must wear gloves and masks to perform maintenance, catching any floating debris or liquids with special absorbent cloths.

There is also the psychological aspect. On Earth, a bathroom is a private space. On the ISS, the WHC is a small compartment located in a busy “intersection” of the station. Privacy is limited to a curtain. The fans are also very loud, so everyone knows when the toilet is in use. It’s a part of the “expeditionary” mindset astronauts must adopt, where social norms of privacy are secondary to operational necessity.

Beyond the Toilet: Other Bodily Functions

Sanitation in space isn’t just about the toilet.

• Vomiting: Space sickness is common during the first few days of a mission. Vomiting in zero-g is hazardous, as the ejecta can scatter and be inhaled. Astronauts use “emesis bags,” which are sealable plastic bags with a highly absorbent cloth inside.
• Hygiene: Bathing is done with sponge baths, using a washcloth and a small “blob” of water that clings to the skin. Astronauts use no-rinse soap and shampoo.
• Flatulence: On Earth, gas in the digestive system separates from liquids and solids, allowing a person to burp. In space, this separation doesn’t happen. Gas, food, and liquid mix in the stomach, leading to “wet burps,” which are unpleasant. Gas passed rectally also doesn’t “disperse” but lingers in a cloud until the cabin air circulation filters it out.

Summary

The history of going to the bathroom in space is a perfect illustration of the challenges of human space exploration. It is an unglamorous field of engineering, but without it, no long-duration mission is possible. The technology has evolved from a desperate solution in a spacesuit to a complex recycling plant that provides life-giving water to the crew of the International Space Station.

The core principle remains the same: in the absence of gravity, a directed flow of air is the only way to ensure waste goes where it’s supposed to. As humanity sets its sights on returning to the Moon and pressing onward to Mars, the continued refinement of these life-support systems – the space toilet and the water recycler – is as fundamental as the rocket that will get them there.