Space toilet

A space toilet or zero-gravity toilet is a toilet that can be used in a weightless environment. In the absence of weight, the collection and retention of liquid and solid waste is directed by use of airflow. Since the air used to direct the waste is returned to the cabin, it is filtered beforehand to control odor and cleanse bacteria. In older systems, wastewater is vented into space, and any solids are compressed and stored for removal upon landing. More modern systems expose solid waste to vacuum pressures to kill bacteria, which prevents odor problems and kills pathogens.

Background Astronauts say that they are most often asked how they go to the bathroom in space. In space, weightlessness causes fluids to distribute uniformly around human bodies. Kidneys detect the fluid movement and a physiological reaction causes the humans to need to relieve themselves within two hours of departure from Earth. The space toilet was thus the first device activated on shuttle flights, after astronauts unbuckled themselves.

Mechanism In the absence of gravity, space toilets use air flow to pull urine and feces away from the body and into the proper receptacles. A new feature of the space toilet is the automatic start of air flow when the toilet lid is lifted, which also helps with odor control. By popular (astronaut) demand, it also includes a more ergonomic design requiring less clean-up and maintenance time, with corrosion-resistant, durable parts to reduce the likelihood of maintenance outside of the set schedule. Less time spent on plumbing means more time for the crew to spend on science and other high-priority exploration focused tasks. The crew use a specially shaped funnel and hose for urine (suction cup) and the seat for bowel movements. The funnel and seat can be used simultaneously, reflecting feedback from female astronauts. The space toilet seat may look uncomfortably small and pointy, but in microgravity, it is ideal. It provides ideal body contact to make sure that everything goes where it should. The space toilet includes foot restraints and handholds for astronauts to keep themselves from floating away. Everyone positions themselves differently while "going", and consistent astronaut feedback indicated that the traditional thigh straps were a hassle. Toilet paper, wipes, and gloves are disposed of in water-tight bags. Solid waste in individual water-tight bags is compacted in a removable fecal storage canister. A small number of fecal canisters are returned to Earth for evaluation, but most are loaded into a cargo ship that burns up on re-entry through Earth's atmosphere. Currently, fecal waste is not processed for water recovery, but NASA is studying this capability.

Basic parts

There are four basic parts in a space toilet: the liquid-waste vacuum tube, the vacuum chamber, the waste storage drawers, and the solid-waste collection bags. The liquid-waste vacuum tube is a 2-to-3-foot (61 to 91 cm) long rubber or plastic hose that is attached to the vacuum chamber and connected to a fan that provides suction. At the end of the tube is a detachable urine receptacle, which comes in different versions for male and female astronauts. The male urine receptacle is a plastic funnel 2 to 3 inches (5 to 8 cm) in width and about 4 inches (10 cm) deep. A male astronaut urinates directly into the funnel from a distance of 2 to 3 inches (5 to 8 cm) away. The female funnel is oval and is 2 by 4 inches (5 by 10 cm) wide at the rim. Near the funnel's rim are small holes or slits that allow air movement to prevent excessive suction. The vacuum chamber is a cylinder about 1-foot (30 cm) deep and 6 inches (15 cm) wide with clips on the rim, where waste collection bags may be attached and a fan that provides suction. Urine is pumped into and stored in waste storage drawers. Solid waste is stored in a detachable bag made of a special fabric that lets gas (but not liquid or solid) escape, a feature that allows the fan at the back of the vacuum chamber to pull the waste into the bag. When the astronaut is finished, he or she then twists the bag and places it in a waste storage drawer. Samples of urine and solid waste are frozen and taken to Earth for testing.

Designs

Space Shuttle Waste Collection System The toilet used on the Space Shuttle is called the Waste Collection System (WCS). In addition to air flow, it also uses rotating fans to distribute solid waste for in-flight storage. Solid waste is distributed in a cylindrical container, which is then exposed to vacuum to dry the waste. Liquid waste was disposed of by discharging it into space. The WCS required many hours of training. For urination, a hose was used. For defecation, with a 4 inches (100 mm) diameter for the hole in the seat—much smaller than in a conventional toilet—the user's bottom needed to be exactly centered on the seat. NASA built a simulator with a video camera in the hole; those training used a crosshair to learn how to position their bodies, while other astronauts watched and made jokes. The WCS had several malfunctions in flight. On the eight-day STS-3 test flight, the toilet had broken down, and its two-man crew (Jack Lousma and Gordon Fullerton) resorted to fecal containment devices (FCD) for waste elimination and disposal. An anomaly of the liquid disposal system on Discovery during its maiden flight resulted in a buildup of frozen excrements outside the orbiter, which was then removed by means of Canadarm. During STS-46, one of the fans malfunctioned, and crew member Claude Nicollier was required to perform in-flight maintenance (IFM).

International Space Station

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