Could a Real-life Stillsuit Keep Us Alive on a Desert World?
It's one of the most well-known pieces of speculative technology in science fiction: the Stillsuit.
As an essential feature of Frank Herbert's Dune, the Stillsuit is the body-fluid recycling full-body suit worn by the Fremen of Arrakis, a technological adaptation to a desert world with almost no water but home to an extremely valuable resource that leads to human colonization of the barren planet.
While there isn't any of the spice melange on Mars (at least none that we know of), Dune's Arrakis has some very strong parallels to the red planet just down the way from us, and some important lessons to teach about survival in such an unforgiving environment.
Arrakis as a stand-in for Mars
When Herbert wrote Dune in the 1960s, he drew on plenty of real-life places and events to build the universe in his series of novels. The most obvious inspiration is the Arabian Peninsula, under whose deserts lie vast deposits of another natural resource that has fueled the engines of empire oil.
Mars is also another obvious analog. It has been known since the late 19th and early 20th century that Mars was, at best, an inhospitably cold, dusty planet with little evidence of water on its surface beyond its polar ice caps (Percival Lowell's fantastical Martian canals aside).
By the time Herbert was writing Dune, Mars had already been the setting for some of the most formative science fiction literature of the 19th and 20th centuries, including some of the pioneering works of Edgar Rice Burroughs.
So it shouldn't be surprising that Herbert might draw inspiration from the science fiction tropes that had been long established by the time he was writing in the 1960s.
Recreating our well-known desert neighbor as a far-away sand world full of colossal sandworms, deadly political intrigue, and Stillsuit wearing Fremen doesn't diminish its capacity to inspire solutions to the genuinely pressing challenge of our current moment in space exploration.
The challenge of water
Water is second only to oxygen as the most precious resource the human body requires to function, but it is just as evanescent, sometimes quite literally. The body uses water to filter and carry away various impurities in our body through sweat, tears, urine, and various other bodily functions, and it is surprisingly liberal with its liquid use, with adults losing around 2 to 3 liters of water a day.
As a result, the body is designed to take in freshwater regularly to replace the water it has lost, which obviously poses a problem if there isn't any freshwater to drink. With any number of bodily functions slowly draining away the body's water supply, dehydration can set in within hours in some conditions, with severe dehydration following quickly after, and death coming within around three to five days.
We know Mars has some water, but whether any exists outside of its icecaps is still an open question. However, if there is any, it will likely be very difficult for human explorers to access.
Most of the water on Mars that we know of exists in the planet’s cold polar regions as ice, but with the temperatures at the poles reaching nearly -200 °Fahrenheit (-128 °C), getting to that water would take an industrial operation that would probably involve years of effort after the first footfall of human explorers on the red planet.
The first humans on Mars will likely need to bring water with them, or at least the means to make or filter out freshwater from other sources. Enter the idea of the Stillsuit.
In Herbert's novel, Stillsuits were designed to not just cool the body to limit water loss, but more importantly, to capture any water lost through the body's natural functions and recycle it. The fictional suit consisted of various layers that absorb the moisture lost through sweating, breathing, and urination, and then filter the impurities to produce drinkable water that would be stored in the suit. The wearer could then drink the reclaimed water from a tube attached to their neck.
In Herbert's novel, it was claimed that a well-made Fremen Stillsuit was so good at recycling its wearer's water, that the wearer would lose only a thimbleful of water a day on a desert world like Arrakis. The suit is described in the book by planetologist Liet Kynes:
"It's basically a micro-sandwich — a high-efficiency filter and heat-exchange system. The skin-contact layer's porous. Perspiration passes through it, having cooled the body ... near-normal evaporation process. The next two layers . . . include heat exchange filaments and salt precipitators. Salt's reclaimed. Motions of the body, especially breathing and some osmotic action provide the pumping force. Reclaimed water circulates to catchpockets from which you draw it through this tube in the clip at your neck... Urine and feces are processed in the thigh pads. In the open desert, you wear this filter across your face, this tube in the nostrils with these plugs to ensure a tight fit. Breathe in through the mouth filter, out through the nose tube. With a Fremen suit in good working order, you won't lose more than a thimbleful of moisture a day..."
Whether we could ever engineer a suit for Martian explorers that was as efficient at water reclamation remains to be seen. But if we're being honest, any Martian explorer will likely need something about as efficient, if not more so, if they have any hope of surviving on Mars.
How feasible are actual Stillsuits for future astronauts on Mars?
Fortunately, we've been doing something similar to Dune's Stillsuits for a while now on the International Space Station.
"There is an entire closed-loop system onboard the [International Space Station] dedicated to water," NASA says. "First, Astronaut wastewater is captured, such as urine, sweat, or even the moisture from their breath. Then impurities and contaminants are filtered out of the water. The final product is potable water that can be used to rehydrate food, bathe, or drink. Repeat. The system sounds disgusting, but recycled water on the ISS is cleaner than what most Earthlings drink."
This makes a lot of sense since there isn't a whole lot of water in low Earth orbit, so in many ways, the International Space Station is an Arakis – or Mars – in miniature, minus the giant sandworms.
This gives us a sense of what future exploration of both Mars and the Moon will look like. Since both worlds lack a breathable atmosphere, any astronauts on either the Moon or Mars will effectively be existing in an enclosed, airtight environment that would be perfectly capable of capturing any liquids, moisture, or vapor produced by the astronauts within it.
From there, it really is just a matter of separating out the potable liquid water from the waste material, which is something we are already doing. By the time we put humans on Mars sometime in the 2030s or later, the technology for reclaiming human wastewater will almost certainly have advanced enough that it might even make Dune's Stillsuits look downright wasteful.