Living on Mars - The Water We Drink
Another chapter in our Living on Mars series -- a collection of articles on what technology and systems will be needed to survive - and thrive - on Mars.
Other articles in this series include:
There's something missing here...
NASA has recently announced evidence of liquid water on Mars. Sounds great! That just makes it easier to live there, right?
Not so fast...
There may be flowing water, at least during the warmer seasons, but could you actually drink it?
Unfortunately - no.
The water on Mars is so full of salts, called perchlorates, that it wold be highly toxic to humans and plants. Perchlorates are so toxic, in fact, that several states in the U.S., including California and Massachusetts, limit the amount of perchlorates that can be in your water.
Think of it this way:
The water on Mars is saltier than the saltiest water on Earth: Don Juan Pond -- in the heart of Antarctica's Wright Valley. As NASA planetologist Chris Mckay stated:
Nothing can live in the brine of Don Juan Pond.
So what does that mean for those who want to settle Mars? How can we possibly live on Mars if we can't drink the water?
How Much Water Do We Need?
On Earth, a person typically needs to drink about half a gallon (2 liters) of water per day- the equivalent of 8 8-oz glasses of water. Active people need even more. Perhaps as much as a gallon a day.
That's just what we need to drink. In addition, we also need water for other things like washing and farming. In fact, according to Data360.org, the typical American uses about 150 gallons (575 liters) of water per day. In the UK, the average person uses much less but still uses almost 40 gallons (149 liters) each day.
That's a lot of water -- and if you were to bring it with you all the way from Earth (at 8.34 pounds, or 3.79 kilos , per gallon), a lot of weight.
It's so much, in fact, that NASA doesn't even come close to using this much water on the International Space Station. They limit the water usage on the ISS to just 3 gallons or 11 liters per day. Through recycling (yes - they drink their own pee) the ISS can maintain sufficient water supplies for a time, but still needs to be periodically resupplied.
But for Mars? How would you resupply a settlement on Mars?
The fact is - you wouldn't.
Too far away. Too long to get there. And way too expensive!
Settlers on Mars will need more than just 11 liters per day. Physical activity, washing, farming - the demands for clean water on Mars are plenty. Even if we take two-thirds of, say, the amount a typical person in the UK uses and plan on a 80% recycle rate (more on that later), that still means 20 liters of water per day would be lost and have to be replenished. Per person.
(149 liters * 2/3 = 100 liters. 20% lost = 20 liters)
So, for a settlement the size we envision, 1000 people, 20 liters per day means the colony would need 20,000 liters of new water each and every day.
So the question becomes: If we can't ship it there, how do we get the water we will need to survive? How will we be making water on Mars?
There are basically three things we can do...
1. Bring the Water With Us
Although bringing enough water from Earth to Mars for 1,000 settlers is not feasible, what if we were to bring just one of the elements of water -- like the hydrogen? Combine that with with CO2 from Mars itself, and it should be easy enough to convert the hydrogen into water, right?
This is exactly what Robert Zubrin proposed in his book The Case for Mars. A slightly different approach for making clean water on Mars was shown in the movie (and book) The Martian by Andy Weir.
The Martian first...
Making Clean Water on Mars from Hydrazine
In the movie The Martian, Mark Watney made water by taking the excess hydrazine from the lander and using chemistry to convert it into water. Could that actually work?
In theory - yes.
But not quite like the movie showed.
Hydrazine has been used as rocket fuel for Mars landers for a long time. Viking, Phoenix, and, most recently, Curiosity, all used hydrazine powered rockets to land. It's a fairly low power, low efficiency fuel for a rocket but it's attractive because it's a monopropellant -- meaning you don't need an oxidizer to burn it.
In fact, it doesn't burn at all.
NOTE: Watney didn't burn the hydrazine - he burned the hydrogen that came out of the hydrazine.
Here's how it works...
For a rocket engine, hydrazine (N2H4) is passed through a catalyst which causes it to decompose into ammonia, nitrogen gas, and hydrogen gas according to the following reaction:
N2H4 → N2 + 2 H2
In the movie The Martian, Mark Watney used that same reaction to produce the hydrogen gas and then, in combination with the oxygen in the hab, he burned the hydrogen and made water.
2H2 + O2→ 2 H2O
He didn't actually capture or store the water - he just let it accumulate and be absorbed directly into his farm soil for the potatoes.
In reality, it wouldn't be quite that easy.
First, hydrazine is incredibly toxic. Just wearing a mask, like the movie showed, would still leave your skin exposed and would be incredibly dangerous. On Earth, technicians who handle hydrazine wear full body safety suits, like this image shows.
Second, decomposing the hydrazine into nitrogen and hydrogen is highly exothermic. It gives off a lot of heat. A lot of heat.
800 degrees Celsius in a matter of milliseconds.
Never mind an explosion - Mark Watney would have been cooked long before that...
And with that heat comes a massive expansion of the gases. It's very hot and very fast -- which is why it is so good for a rocket engine.
Which is why it so difficult -- and dangerous -- to use this process for making clean water on Mars.
Finally, if you were able to contain the gases and the heat, you would still be limited by the amount of water that could be produced. You would need a constant supply of hydrazine from Earth to support a settlement of thousands.
It's just not feasible.
So if hydrazine is not the answer, what about Zubrin's method?
Making Water on Mars from CO2
In The Case for Mars, Zubrin laid out a simple chemical process for producing methane from the martian atmosphere. His intent was to show that by bringing along additional hydrogen on the trip from Earth, it would be a simple, and frankly, quite elegant, way of producing fuel for the trip back to Earth.
The process was a breakthrough at the time and led to the Mars Direct mission profile. NASA adopted parts of the process, some of which you can see today in their Journey to Mars program.
For the purposes of this discussion, however, the beauty of combining hydrogen with carbon dioxide is that it produces water as a byproduct.
Clean, clear drinking water.
Basically it goes like this: take carbon dioxide from the atmosphere of Mars, combine it with hydrogen, and you get methane (CH4) and water, according to the reaction:
CO2 +4 H2 → CH4 + 2 H2O
Zubrin went on to show how the water could be dissociated into its parts, hydrogen and oxygen. The hydrogen would be pushed back through the system to produce more methane, and the oxygen would be stored for the methane-oxygen rocket engines.
What Zubrin essentially showed is that with just a little extra hydrogen brought from Earth, you could produce plenty of methane and water. Enough to get back to Earth at least, but would it be enough to sustain a colony?
Water is, by weight, about 11% Hydrogen and 89% Oxygen. What that means is that 1 kilo of water, which is the same as 1 liter, would have about 111 grams of hydrogen. If we took NASA's estimate of 11 liters of water needed per person per day, that's the same as 11 kilos of water, or 1.221 kg of hydrogen -- without any recycling.
I'll spare you the math, but even if you brought an extra 8 metric tonnes extra of hydrogen (8,000 kilos) from Earth, that would only produce about 72,000 liters of water.
With recycling, the water could stretch for a while, but for a settlement of 1,000 people, it would still only last a few days.
Bringing water from Earth , then, might work for a short time -- for a few people. For longer stays -- like, say, forever -- we need something different.
We need to use that water that is already on Mars.
But how do we we get it? And how do we make it safe enough to drink?
Although there have been a few ideas on making clean water from Mars, there are really only two options:
- Extract it from the soil, or
- Extract from the polar ice caps
2. Water from Mars
Extracting the Water on Mars from Soil
Martain soil has trace amount of water in it. We've known that since the days of Viking.
The Viking landers tested surface soil samples by heating them to 500oC and found they emitted about 1% of their weight in water. Many believe these tests were inaccurate, though, and that the amount of water, on average, in soil is around 4%.
It may even be as high as 20% or more in some areas.
And those super-saturate flows NASA recently discovered? Their moisture content hasn't been measured, but they may be entirely liquid!
The question, then, is -- how do you get it out?
There are a couple of ways that have been proposed. One method uses the most abundant element in the Martian atmosphere - carbon dioxide.
First you compress carbon dioxide gas and pass it over martian rocks and soil. The gas dissolves some of the water locked up in the soil. Then, as the gas is allowed to expand, it releases nice, clean water which can be collected and stored.
It's not a very efficient process, but there is a lot of carbon dioxide and a lot of soil.
Another method would be to simply collect saturated soils and then heat them to 500oC, at which point the water would dissociate from the soil and escape as steam. The steam could be collected and condensed into pure, desalinated water.
Higher outputs could be attained if you used more saturated soils . Drilling into possible permafrost layers or, better yet, collecting highly saturated soils around the newly discovered flows NASA recently announced, are two ways we could get those more super-saturated soils.
This is actually one of the ways desalination works on Earth today. Instead of heating hydrated soil, though, we heat seawater. The steam, once condensed, is free from salt (perchlorates).
If that doesn't work, there are other ways to desalinate water besides ion exchange (which is really what the heating process does) -- reverse osmosis and biological treatment.
Biologics may not be a good choice for Mars simply because it would require using bacteria to basically 'eat up' the perchlorates. Introducing bacteria to Mars doesn't sit well with scientists who want to keep the Red Planet as pristine as possible, so let's just toss that one out for now.
Which leaves Reverse Osmosis.
This is a very common method of desalination here on Earth. Basically, it involves pushing seawater through a thin plastic membrane to make fresh water. The membrane has holes in it -- small enough to not let salt or dirt through, but large enough to let water through.
The nasty stuff collects on one side one of the membrane while clean, clear water passes through.
There are a couple of problems with this process, though.
First, although it is very good for filtering out salt, it only yields a trickle of fresh water. That might be fine for a small settlement on Mars, but it would be better to have a way that produces more clean water. Studies are working to improve this process, including some newly announced nanotech research.
Second, reverse osmosis a uses a thin membrane in its process. That membrane will need to be replaced periodically. And getting replacement parts on Mars will be an issue. It's not like we can just call a repairmen or have a new part sent out.
As NASA spokesperson Stephanie Schierholz said when asked about this:
The big challenge is getting the equipment necessary to Mars and ensuring the technology is reliable for a mission to Mars because if something breaks it would take at least another six months to get a replacement there.
So, even though reverse osmosis will work, the simplest way of making clean water on Mars may be to just collect those briny flows and heat them to remove the salts.
Those flows aren't everywhere, though. They have only been discovered in a few locations, typically around the warmer regions near the equator.
And that means any settlement that is established on Mars would need to be located fairly close by.
that is, unless we want to get our water from another source...
The Martian Ice Caps
On Mars, there are tons of water in the polar ice caps. The northern ice cap alone is 1,000 km across (621 miles) and contains about 1.6 million cubic km of ice. Compare that to the Greenland Ice Sheet which has about 2.85 million cubic km of ice.
The southern ice cap is estimated to have about the same volume of water, but the ice cap here is covered by 3-4 times as much dry ice (frozen carbon dioxide) as the northern ice cap and is much harder to reach.
Plus, the dry ice in the north completely disappears (sublimates) in the summer, leaving pure fresh water ice - ready for harvest. This part of the cap is called the north residual cap and is believed to be as much as three kilometers thick.
That's a lot of water. But how to retrieve it?
One solution would be to simply locate settlements close enough that the ice could be mined and shipped to the colony for processing. In the book Red Mars, by Kim Stanley Robinson, the settlers set up automated, self-driving vehicles (hey - aren't we making those now?) that transported blocks of polar ice from the ice cap back along a pre-determined path to the colony for processing.
That may very well be what happens.
And even though analysis of the caps shows a large amount of water, that water may still need to be desalinated just like with the soil extraction processes.
So -- getting the water shouldn't be too much of a problem. At least once we've had a chance to explore and find the best spot for a settlement.
That means the first people on Mars, then, will have one primary function.
Not to look for life.
And not to just collect rocks.
Their mission will be to find a source of water sufficient for a settlement. And that means that they won't have be making their own water on Mars at first. They will have to bring their water with them, and stretch its use as far as possible.
And that means ...
3. Recycling Water with Closed-Loop Life Support
For over twenty years, NASA has been researching life support technologies in space.
The ultimate goal is to create a completely 'closed-loop' system - one of our 10 'Must-Have' technologies for settling Mars.
What that means is basically creating a system that can completely recycle the air, water and human waste in a closed environment.
A Mars settlement will definitely be a closed environment,
No system has ever been developed that is 100% efficient, but that doesn't mean it hasn't been tried. The most famous (or infamous) example was Biosphere 2.
Biosphere 2 was originally meant to research how different life functions interacted with each other and how to combine those functions into a self-contained 'biome' that could even potentially be used for space colonization.
In the early 1990's, construction of a 3.14 acre facility was built to test the concepts. The basic idea was to build a series of different earth biomes -- a farm, a rain forest, a desert, even a coral reef -- and study how they interacted with each other.
But it wasn't just about the interaction -- it was also an attempt to show how such interactions could be used to develop a completely closed-loop life support system.
Well -- needless to say -- it failed.
Two attempts were made to enclose a few scientists inside the biosphere and seal it up completely to study the environmental and biological interactions. On both attempts, some items had to be brought in (like food) and, after the second attempt, the project folded.
Eventually, Biosphere2 was taken over by the the University of Arizona, which continues to run the facility today as a research station.
NASA's plans have never been quite that big.
Their goals have been to create a more mechanical -- and smaller -- solution. They call it Environment Control and Life Support System (ECLSS).
The ECLSS is a comprehensive recycling system that recycles those things we all consume or give off as waste - oxygen, carbon dioxide, water, heat, humidity -- even urine and... Well, you get it.
The system is currently deployed in the ISS.
It's not a completely closed-loop life support system. In fact, it's only about 80% efficient, which means that items like oxygen, food and water need to be replaced periodically. Cargo mission are sent to the ISS every 6 months or so, like clockwork, just for that reason.
That's still pretty good!
We're not looking at the whole system right now, though. For our purposes, let's just look at the part that recycles the water.
The system is called the Water Regeneration System. It reclaims all the potable and 'gray' water that is produced -- even the water from the toilet.
That's right. 80% of the water that is used in the ISS has been recycled and includes the astronauts own urine.
It might not sound very appealing, but it keeps the need for water resupply to a minimum -- a crucial piece for settling Mars.
And as a martian -- you'll get used to it.
What does all this mean for living on Mars?
The recent discovery of liquid water flows are exciting, and hold promise as a way to supply Martian settlements with they water they will need. But Martian water is highly toxic to humans and will require a bit of processing before it will be safe to drink.
And, although the polar ice caps contain a lot of water ice, we need to develop -- and test -- ways to collect the water and to purify it and make it safe.
Until then, artificial life support systems will have to suffice.
Previously on 'Living on Mars' - The Mars Oxygenator
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