On Earth, we often take for granted the convenience of household plumbing. Dedicated experts keep water flowing in, and waste flowing out – the obvious normalcy of this is testament to centuries of skilled people. In space, aboard the International Space Station (ISS), it was important to transfer as much of this same comfort as possible. Astronauts should be able to drink and clean in a safe, sustainable environment, as familiar to Earth life as they could make it.
But in free fall around the Earth, it’s easier said than done.
Which Way is Down?
Here on Terra Firma, ‘down’ is a concept we all naturally understand. It’s the direction Newton’s apple falls. It’s where you go if you take a seat. It’s that feeling of resistance you get from that chair, or the soles of your feet, or palms of your hands during a handstand.
‘Down’ exists because Earth pulls you toward itself via gravity (and you pull back on it in return). When you flush a toilet, that waste-water passes through the U-bend because water presses it down and through – and it continues flowing downward into the sewers.
In orbit around Earth, the ISS is constantly falling ‘down’. But it’s travelling so fast horizontally that it doesn’t reach the ground. This is called ‘free fall’. Aboard the ISS, this creates a ‘zero-g’ environment. That is, nothing on board falls towards the Earth – not a single drop of water.
In Earth pipes, liquid flows along the bottom, while any gas within them – since it is less dense – rises to the top. In free fall, there’s nothing to pull that liquid to the bottom. Instead, it clings to the walls of the pipe, while the gas travels through the centre core.
To move this liquid, it needs to be pressurised slightly. Dozens of pumps and fans circulate water and air around the various modules. So, toilets in space need to function fundamentally differently. In a word: suction.
Ecosystem Contained
Water is a vital requirement for Human life. The Earth is a giant ecosystem of water – in many ways, life itself is built on the natural plumbing of the planet. And to a more controlled degree, we’ve created a similar system for ourselves through fresh water plumbing and waste water treatment.
In an aluminium can, zooming around that planet 16 times a day, you’re no longer a part of either system. The solution is to create an entirely contained ecosystem within it.
What this means in practice is making the most of the resources available. Waste water is recycled into potable (safely drinkable) water.
• Sweat
• Shower water
• Water vapour in the air
• Urine (both from humans and lab animals!)
The idea was to squeeze as much mileage out of every drop of water as possible. The water treatment system onboard the ISS brings the daily consumption per person down from 1 gallon to just a third of a gallon.
Material Comforts
On Earth, copper and PVC serves as ideal materials in plumbing. They resist the corrosive effects of water, are durable, and are relatively cheap. The vacuum of space introduces quite a few extra requirements though.
Firstly, it still needs to fulfil the basic requirements of durability and corrosion resistance. Cost is always a factor, but we’re working with a much much higher budget up here.
Next, leak resistance becomes a much higher priority. A burst pipe on the ISS is a catastrophic event. The astronauts would find themselves losing the life-giving elixir rapidly – especially if the pipe is somehow exposed to the vacuum. But that could be the least of their problems. The ISS has a multitude of complex systems to prevent water getting into the electronics for good reason.
It also needs to be lightweight to reduce the cost of launching it into orbit, and compact enough to save as much space as possible: in weightless space, space and weight are a high commodities.
And the last of the most significant requirements is microbial resistance. Getting sick on the ISS isn’t an easy problem to resolve, so making sure the poop pipes are just as clean as the drinking pipes is a high priority.
Even on the most technologically complex creation of humankind, Plumbing lays at the absolute heart of it.
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