Mark Shuttleworth - February 09, 2002: Toilet training - So what's the number one question people have been asking about life in space? It's "How do you go to the bathroom?". And it's a darn good question too, especially for people who will be up there for more than a day or two.

I've been struggling to find a way to answer it completely without getting too graphic, so here's a draft cut at a high-level view of the ultimate high-level loo. I could write a more detailed spec later if there are a lot of requests for it. And I'm going to try and get the relevant pages of the ISS Flight Data File (also known as the operations manual, as in: “When all else fails, read the...”) onto the site for you to read.

First, some context as to where this fits in on the training programme. We have finished the Soyuz systems training. All Soyuz training now is simulator time, running through flight segments (launch, rendezvous and docking, undocking and re-entry, etc.). But we only have one or two sim-runs a week. The rest of the time, we focus on ISS systems in the Russian segment. This is where Roberto and I will do most of our work, so we have to be able to interact with the module intensively. We’re being given a fair amount of detail on the user-visible systems in the service module (or the “base block”) and the cargo module, which make up the Russian segment, to minimise the amount of time we take from the station crew.

The Russian systems include temperature control (SOTR), life support (SOSH), radio, television, lighting, electrical supply and computing infrastructure. We are currently working through the life-support system, which includes waste management. Hence the toilet. Incidentally, there is a little loo on the Soyuz too. But it's unlikely that we will use that one for solid waste.

’Shit really can fly in space’

Before launch, we'll have our digestive systems purged (not much fun) so we shouldn't need the loo for a good few days. On the way back, we’re only supposed to be in the Soyuz a few hours after undocking, and we'll be pretty busy then. There's only one story of the Soyuz toilet being used on a station flight, and that was on a return voyage from the Mir Space Station after a very ill-advised prune binge. None of us is likely to make that mistake this time around.

Anyhow, the principles of the loo operation on the Soyuz and the ISS are identical, even if the tech is greatly improved on the ISS because it has to support up to seven crew members for long-duration flights, where waste management is an important part of the equation.

As a further aside, I should say that the Russian interpreters have a difficult time with this stuff. Russians are extremely polite, and very proper, and quite formal about what is appropriate to say and when. So getting down to the nuts and bolts of physiology is difficult for some of the interpreters. I should thank both Anna and Helena for dealing with the subject so professionally.

First of all, the principles. Liquid and solid wastes (#1 and #2, as they generally get interpreted) are trapped separately and processed separately. Air pressure (suction) is used to encourage waste to move in the right direction. Shit really can fly in space.

On both the Soyuz and the ISS, solid waste is simply isolated and discarded as soon as possible. On the Soyuz, urine is stored in a chemical tank. Nothing further is done because the Soyuz is only rated for short-term flights. On the ISS, urine is processed because it needs to fit in with the station’s long-term water-management plan. At the moment, the urine is preserved and then discarded along with the solid waste. But that might not be the case forever, and it wasn't the case on Mir.

Second time around

Water conservation used to be very important on Mir, so the Russians recycled urine into drinking water. That was because there is no ready source of water in space. Fresh water supplies had to be shipped in on Progress cargo vessels – an expensive task that was not often undertaken.

Water-recycling technology has not been installed on the ISS because the shuttle visits the ISS regularly. The shuttle creates water during flight because it uses fuel cells that "burn" hydrogen and oxygen to produce electricity.

Fuel cells are a very cool technology that’s just starting to reach the point where it’s feasible to think about having one in the basement to provide clean and reliable electricity for your house without an electricity network. They have been used on the shuttle for nearly 20 years.

Anyhow, as a result, when the shuttle docks it has bags and bags of pure water. This is water is de-ionised and taken to the ISS, where it is stored in great big balloons. I think there can be several tons of water in the station at any given time. As a result, the ISS isn't yet as aggressive about recycling urine as Mir was. I think the plan calls for urine recycling to come on stream at a future date, when the crew will be expanded and the shuttle visits might not bring enough water. Also, if we are going to get to Mars and beyond, we need to be able to recycle 100% of the food and water, which means both solid and liquid waste, and the ISS may well get to test drive some of those systems in the future.

Now the mechanics. The loo is in a cabin about 1m x 1m x 1.7m. It's unfortunately just next to two of the sleeping cabins as well as the dining-room table. Sadly, there is no window. What a loo view that would be. To power it up, one has to check a series of distribution panels (oh hell, it's 1am again and there's a test tomorrow on the electrical system!) and also check to see that there are no alerts or warnings from any of the toilet sensors.

The primary rule of operation is always to prepare the loo after use, so that it's ready for the next guy. Assuming all is well, it should be possible to fire it up in just a couple of minutes. It's an awkward process in the mockup, where gravity keeps everything in place. I don't know if it would be easier or more difficult in zero-G.

One at a time

There is a little seat in a wood finish, not sure if that is true on station too, but Yuri seemed to think it was the only real wood on station - a nice touch indeed from the Russians! Below the seat is a disposable tank for solid waste. The hole in the seat should be pre-lined with a single-use packet. Assume the position. Then there is a receptacle with a funnel and hose that will grab liquid waste. It's very important to aim at the funnel from a distance away, rather than trying to get too intimate with it once the suction is under way. This point was stressed repeatedly - in a way that suggests either it will be in the exam, or it comes from direct experience from one of the cosmonauts. Ouch.

The first thing that spins up is the urine/air separator motor. This is because we don't want any urine to get sucked into the fan, which would be a mess. So first we have to be sure we can separate urine from the air stream that pulls it along. This is done in a centrifuge. If you spin a mixture of heavy and light fluids together, the heavier stuff goes to the outside. In weightlessness, this is how they separate urine from air.

Once that device is spinning fast enough, a dose of urine preservative (mostly sulphuric acid and chrome trioxide) is flushed into the separator. This is to prevent crystals of urea or other contaminants forming in the plumbing, or in the tanks. This is another complication - we don't want nasty stuff like sulphuric acid to leak into the ISS. Horrible things could happen (far worse than if urine leaked into the compartment). So the tank that stores the preservative has to be triply redundant and extremely robust, and all the pipes have to have double layers and be resistant to acid corrosion.

Manual mode

At this stage, we are ready for action, so the sensors that measure the separator efficiency turn on the main fan. This is like a vacuum cleaner, and it creates air flow both into the solid-waste container (through the packet, which has holes in the bottom) and into the funnel. Steady, aim, fire. Whistle, whistle, whistle. Yuri, pass the magazines!

Now a lot of magic happens. The urine stream goes to the separator, and is mixed with the preservative. Then it goes down a dedicated pipe to a tank with a bag for urine storage. When that is full it is simply put into the next available Progress and will be burned up on the way back down. Same goes for the solid-waste tank. The air flow goes through another filter to remove any droplets of liquid, then through the fan, then through yet another filter to remove odours and to reduce noise (apparently it can get pretty loud).

There are a bunch of different sensors that give a warning if one of the tanks becomes full or empty, or if pressure in one of the sub-systems is too high or too low. There are also a series of buttons that allow one to override the sensors and drive the process manually. So if one of the sensors fails and you know that there is flush liquid or available space in the urine bag, it is possible to use the loo in manual mode.

After use everything needs to be cleaned. The system is very simple and should trap all waste in a safe and hygienic way. Then the seat liner packet is unhooked. It automatically seals itself and drops into the solid waste container, and a clean one is installed so the next person isn't caught out in a moment of urgency.

What's really amazing is how accessible all of these components are. Simply lift up the floor panels around the loo, or open up the wall panel, and you can replace any pump, fan, device or tank. It has to be that way... this is a mission critical system!