Making a Self-Sustaining Civilization (on Mars) — Part 1
Q:What does it take for a civilization to be fully self-sustaining?
A: We need to be able to create everything it needs from resources plentifully available in the environment and that aren’t subject to rapid depletion.
Of course, this is an extremely relevant question for Earth and one that many people are worried about as the cost of hydrocarbon extraction increases. But, I propose we zoom out from Earth and instead ask what it would take to have a self-sufficient civilization on Mars. By starting with Mars rather than Earth, we make sure we won’t be subtly relying on some processes outside of what the civilization itself produces. A good example would be fixing nitrogen for fertilizer. On Earth, half of this is done by bacteria, but now civilization needs to make up the other half. On Mars, this requirement comes to the fore. There are no bacteria to synthesize nitrates for us, or to generate oxygen, or to make an abundant extra store of hydrocarbon energy. We can’t cheat. If we can live self-sufficiently on Mars, we can live sustainably on Earth.
First and most importantly, is this a hopeless goal to even try for? Are we inevitably doomed?
It all comes down to whether there is enough energy to produce our food and power the technology we need to maintain a livable habitat. So, is there enough renewable energy to feed everyone and run all of civilization for years to come?
The sun outputs way more than enough power to sustain human needs, and the Earth’s core will be quite warm for billions more years as well. We have all the energy we’ll need (for the next few millennia at least). In fact, even though life is now powered almost entirely by the sun’s glow, it was born with the energy of the Earth’s fiery depths. Also, a good point to remember, all energy that is not nuclear, geothermal or tidal is actually solar. Wind, hydro, hydrocarbons and even food all result from solar power.
So our dream of a truly self-sustaining civilization can be real.
First though, we must set the rules of our thought experiment. We are creating a civilization from scratch on Mars. How big or small does civilization need to be? How much energy do we need to get? How much metal and plastic and glass? What is the purpose of civilization? Good questions all. When you really boil it down, civilization exists to feed us, give us clean water and give us warmth and shelter. It’s really pretty simple. If we focus on how civilization satisfies these needs, we’ll be most of the way to covering all the important tasks.
What do we need to make a sustainable civilization?
Now, what materials do we need to cover those core areas of civilization: food, water, shelter.
First, what do plants need? Our food is plants or animals that ate plants. Plants need light, water, air (CO2 to build biomass and O2 for respiration) and fertilizer (specifically nitrates and phosphates).
How about shelter? And more generally, the machines that run modern civilization. We can add a few more key materials. Metals, plastics, and concrete. If we can produce all of these ingredients on Mars, we’ll be most of the way to satisfying the core goals of civilization.
Let’s break these down into their constituent elements and then see what materials we have readily available to work with. We’ll then see what processes we’ll need to get from what we have to what we need.
Water is H20. The air we need is N2, O2 and some CO2. Fertilizer to first order is ammonia NH4 as well phosphate PO4. For metals, let’s first focus on the most common ones: iron and aluminum. They are often used in their elemental (reduced) forms. Plastics actually are compositionally quite similar to plants. Both are made from chains of carbon atoms with oxygens and hydrogens attached (sometimes with a sprinkling of other elements). And concrete is a mix of CaCO3 along with silica (SiO2) or alumina (Al2O3) mixed in.
Let’s list the elements out: H, O, N, C, P ,Fe, Al, Ca, Si, Al.
In what form are these elements available on Mars?
What ingredients do we have to start with on Mars?
Hydrogen is most readily available as H2O. It is available on Mars as permafrost throughout much of the planet, occurs in small but extractable amounts in the atmosphere and also exists as ice in the poles.
Oxygen exists bound in various forms in many compounds from CO2 in the atmosphere, H2O, and in many metal oxides which we will wish to refine.
Nitrogen exists as N2 in small but usable amounts in the atmosphere.
Carbon most readily exists as CO2 in the atmosphere, but also as dry ice in the poles and in carbonate deposits scattered around Mars.
Now, let’s look at the Martian soil and rocks and see what goodies they’re made of!
Perfect! So many more of the elements we need. Phosphorous and potassium for our fertilizer. A huge amount of iron (it’s why Mars is red!). Aluminum, calcium, silicon! And a whole bunch of other useful elements that will come in handy as catalysts (Cr, Ti, Zn, Ni) or additives (Cl, S) to open up a much wider range of alloys and plastics.
Looks like we have everything we need! This is actually why Mars is such an intriguing destination for colonization. The Moon, for example, is lacking a bunch of these necessary elements like nitrogen, and even water is rare.
The Core Metabolism of Civilization
Above, I’ve shown the chemical network for the core metabolic processes of life. It takes in CO2, water and inorganic compounds and produces all the organic molecules necessary to build biomass. And even though it looks complicated, there are only a few dozen key chemical steps to go through this cycle. Can we identify a similar pattern for civilization?
As with life, civilization needs to convert the materials we have into the chemical forms we want. This will involve breaking some chemical bonds and the reason we have names for many of these processes is that these bonds are strong and it takes some effort to break the bonds. CO2 has two double bonds. N2 has a triple bond! Metal atoms bind strongly to oxygen. When we really boil it down, civilization mainly involves breaking some common chemical bonds and forming different ones.
Let’s list out the processes we need:
(electrolysis) 2 H2O -> 2H2 + O2
This is going to be one of the important reactions as H2 is very important for several processes. And it’s a nice source of oxygen as well.
Changing Carbon Dioxide into Syngas
(water gas shift reaction) CO2 + H2 ⇔ CO + H2O with iron oxide–chromium oxide catalyst for high temperature reactions (and copper-zinc based for low temp)
(Sabatier reaction) CO2 + 4 H2 → CH4 + 2 H2O + energy with a nickel catalyst
Carbon monoxide is a good reducing agent for metal refining and both carbon monoxide and methane are good feedstocks for plastic production. The mixture of CO and H2 is known as syngas and is very versatile.
(Syngas to Methanol) CO + H2 -> CH3OH with catalyst of Cu, ZnO, Al2O3, Mg or C, N and Pt
(Methanol to Plastics) Methanol can be turned into ethylene and propylene which when strung together into polyethylene and polypropylene become some of the most commonly used plastics. This uses acidic zeolite catalysts (which are porous silica-alumina sponges also known as cat litter).
There is much more nuance to make specific plastics but we’ve now covered the broad strokes of going from CO2 and water to plastics.
Breaking Nitrogen’s Triple Bond
(Haber-Bosch process) N2 + 3 H2 → 2 NH3 with partially reduced iron catalyst + (K2O, CaO, SiO2, and Al2O3)
This requires a pure source of H2 and high temperatures and pressures. This is one of the most energy intensive processes done by civilization (producing cement may be another).
(Direct reduction of Iron) Reducing iron involves mixing the iron oxide with something that likes the oxygen even more and can donate some extra electrons to the metal which “reduces” it. We do this by passing carbon monoxide and H2 gas (our syngas from earlier) around balls of heated iron oxide. This is actually the most energy efficient form of iron refining and is perfectly suited for further refining into steel.
Making Artificial Rock
(Cement Clinker Manufacturing) Concrete which uses the active ingredient cement and an aggregate is really a type of artificial rock. (I thought that was a pretty cool way of putting it). Cement on Earth is made by breaking down limestone (CaCO3) but all that is really required is CaO along with SiO2, Al2O3, Fe2O3. All these ingredients are available in Martian soil. This mixture is then progressively heated to 1450 C to create the proper calcium silicates. This heating is done in a steel rotary kiln lined with aluminum oxide bricks that can withstand high temperatures.
We see some beautiful synergies between syngas, iron and nitrogen production where iron can catalyze nitrate production (with H2 that’s part of syngas) and the water gas shift and syngas can reduce iron. We also see that there are a few places where we may need rarer catalysts like copper, platinum or other rare elements, but even nickel is present in the Martian soil.
Most of civilization involves just a few elements and a few intertwined reactions between them!
Gleaning from the soil and air
Now that we know how to transform the raw materials we have to the ones we want, we need to purify them a bit before we transform them. This will involve separating the atmosphere into different gases and separating the martian rocks and regolith (soil) into a semi-differentiated starting state.
We’ve seen that we’re going to need pure gases as inputs for several of our core processes. How do we get pure gases? There are two main ways. The first way is to cool the air to a mixed liquid and then carefully raise the temperature. Since each element has a different boiling point, we can selectively boil one gas after another. This is called cryogenic distillation. The other way is called pressure swing absorption. In essence, we again use a zeolite rocky sponge and pack it full of gas by increasing the pressure. Then we drop the pressure and only certain gas species release from the sponge.
There are many techniques for making the rocks we dig up easy to sort into their constituent compounds. The first is making them smaller by crushing or grinding. This increases the surface area making all the compounds easier to access chemically or physically. Again, crushing and grinding is using energy to break chemical bonds, in this case bonds in the rock.
Next, come several ways of concentrating certain compounds. One is gravity concentration which is pretty much using a centrifuge to separate by mass. Another is froth flotation where bubbles with a specific surface chemistry are passed through a rocky slurry and only certain compounds stick to the bubbles and float to the surface for easy froth gathering. Electrostatic and magnetic forces can also be used.
The Big Picture is coming into view
We’ve now identified the major materials and transformations we need to have a functioning and self-sufficient civilization. Surprisingly, Mars has all the ingredients we need in readily accessible forms! Now that we know what we need and what to do, the next questions are more quantitative.
How much energy do we need to cover all these processes? How much raw materials do we need to have enough machines to perform all of civilizational core metabolism? How quickly do we need to feed in energy and material (what are the power and material fluxes)?
Part 2 of this post series will dive into these details and will try to answer two questions. What is the minimum size of a viable self-contained civilization? What are the energy, power, material and material fluxes necessary to keep civilization going?
I’m about halfway done with the next post and have calculated scaling relations for many of the subquestions involved in answering these. I’ve calculated how much energy does it take to build one square meter of solar panels. I’ve calculated how much energy and metal in the form of digging machines it takes to mine one kilogram of metal or rock. And I’m working on getting energy and material requirements for many of the core processes described in this post.
In the longer term, I’m also interested in looking into the robustness of civilization. How much damage to various parts could civilization take before it collapsed? Looking at this from an information theory perspective, what is the error correction threshold for civilization? What are the most critical parts? The more I learn, the more ideas I have and the more I’m surprised by how interrelated the ideas to understand life and civilization are. Stay tuned!
(This was first published on my Wordpress blog)