L-118: Waste and Hygiene Compartment

Back in Star City, after returning to Europe from Houston and following a brief stopover at home on the weekend.

Time to dive back into the Soyuz world, at least for the next three weeks! But first, I’d like to talk to you about one last class I had at the Johnson Space Center last week, before leaving Houston.

It’s a non-mandatory class that crewmembers can request if they feel the need to review one of the most important pieces of equipment on-board, and likely the first one I’ll want to use after my arrival. It’s the Waste and Hygiene Compartment (WHC): for friends, the space toilet.

The WHC is contained within a standard rack, one of the tiltable elements that are installed next to each other along the four walls of any USOS module. All the components – pump, fan, pipes, tanks, filters, etc.. – are hidden behind the panels. In front of the panels, but still contained in the standard rack volume, are the user interfaces: a yellow funnel with a flexible tube for the urine and a solid waste tank with a hole in top, on which a “seat” is mounted.

In front of the rack, sticking out into the free volume of Node 3, is the WHC cabin, which provides some privacy.

The WHC has a control panel with enough switches, buttons and LEDs to make you think Japanese toilets are boring (they’re not). In fact as a user, when you step in, you want to glance over the main panel to make sure the lights reflect one of the expected configurations. It’s either three or four green LEDs, depending on where the urine is going. Most of the time the urine flows directly to the Urine Processing Assembly to be treated and then is sent on to the Water Processing Assembly to be turned into potable water. However sometimes, for example if the UPA is undergoing maintenance, the urine can be directed to a removable tank instead.

As you can imagine, the panel also has a number of red lights that can come on and indicate a malfunction or simply the need of some action: replacing a full urine tank, for example; or refilling the flush water tank.

The whole system is based on airflow carrying liquid and solid waste away from the body and into respective collection tanks. Therefore, the first thing we do to use the toilet is to turn on the fan that creates that directional airflow. Urine is collected via a funnel and is mixed with flushing water and a chemical agent before being sent to the UPA or the tank. Solid waste is collected in single-use bags installed in the solid waste receptacle – after every use, a new clean bag is prepared for the next user, while the expended one needs to go into the tank just below the “seat”. On Earth, it would just fall down. In space, it takes some guiding: granted, as I hear, not the most glamorous part of living in space.

You probably guessed that the one malfunction that could potentially create a real mess is a power loss during use, since the airflow would stop and there would be nothing pulling the waste in the right direction. The immediate action: close the “seat” cover and cap the liquid waste receptacle! Then you can worry about the rest of the troubleshooting.