Mars is a Hellscape
Uncertainty and Consequences in Technological Development for the Red Planet
Predictions of technological futures are often very wrong. More often than not this looks like Xerox designing the future of personal computing, but missing out on actually selling it. But as people like Elon Musk (at least claim to) work to make humanity a multi-planet species, the consequences of missed predictions are much more obviously dire. If we guess wrong, and implement the wrong technical solution for a settlement on Mars, that colony is very likely to fail and all the people living there are very likely to die. Mars, it turns out, is a very harsh place. While it may be the best candidate for regular people to try to make a living off of Earth (maybe it's not and maybe we shouldn’t, I won’t even get into those questions here) that doesn’t mean it will be easy or safe to do so. In this multi-part series, I will use human settlement of Mars as a bit of a thought experiment to try to answer the question: if we can’t rely on analysis to predict and plan for technological development, then what other ways do we have to govern it?
This first entry will focus on outlining and organizing the technical challenges, with future entries discussing in more detail the political, cultural, and social systems that are designed to deal with high stakes technological development under uncertainty.
Technical Design of A Mars Settlement
Technological development is a response to barriers. And the barriers to living on Mars are many and challenging. Notably, Mars lacks oxygen, sufficient atmospheric pressure, liquid water, and food sources. Citizens will require habitats that shelter them from the harsh Martian environment. Finally, all of these systems will require power generation. Each of these barriers will require creative and functional engineering designs for denizens to overcome them.
It is impossible to know right now which of the various technical alternatives are feasible for a Martian settlement in the future. Trying to detail a specific final design is no more useful an analytical exercise than any other science fiction writing is. Instead such a settlement will require a system for assuring that the best technical possibilities are realized by the colonists as quickly and reliably as possible. Consider NASA’s brief foray in wind turbine construction in the 1980s. NASA engineers thought they understood wind power far more than they really did, quickly scaling up their designs to large megawatt prototypes that failed within a mere dozens of hours. They were outdone by small-scale Danish agricultural manufacturers, who instead learned gradually from experience, scaled-up their designs incrementally, and cooperatively shared what they learned through a widely circulated journal. A successful Mars colony can be nothing less than the product of highly organized hands-on learning by diverse groups of colonists.
But even such an exploratory system requires some structure and direction. What barriers will future Martian citizens likely face? What problems will they likely need solved? Let's take a look at some of the challenges those citizens might face and get a sense of just how difficult and complex the road of technological development for them will be.
Oxygen
A person can survive three weeks without food, three days without water, three hours in a harsh environment, and three minutes without oxygen. So the production of oxygen is the first barrier to overcome. If we assume a million people could one day live on Mars, how much oxygen would they need? Astronauts need 0.84kg (590 L) of oxygen per day, so that makes 840 thousand kg (590 million L) per day a million people. There are three different methods of getting O2 from CO2, but citizens could get it from water, or from refining Martian regolith.
Atmospheric Carbon Dioxide
Recycling oxygen from the CO2 we breathe or getting it from the Martian atmosphere both require separating carbon and oxygen from CO2. There are three main ways to do this: the Sabatier process, the Bosch process, or electrolysis.
Sabatier Process and Electrolysis
The Sabatier process, the process NASA uses to recycle oxygen on the ISS, follows the chemical reaction:
(1) CO2 + 4H2 <-> CH4 + 2H2O (2) 2H2O <-> O2 + 2H2
Assuming an 80% efficient reaction, this process would require 121.2 MW of power to meet Martian citizen breathing needs. But this process is not a closed loop system. It requires the addition of hydrogen, which will either have to be imported from Earth, or reclaimed from the CH4 produced in reaction (1) via pyrolysis. That reclamation increases the required power by 28.4 MW, totaling 149.6 MW for citizens to get their oxygen by this process.
But even if we take this process as a given, there is still a lot of uncertainty. How much oxygen should be reclaimed versus harvested from atmospheric CO2? How much, if any, hydrogen should be reclaimed vs transported from Earth? How can we even know beforehand what the right answers to those questions are? And that doesn’t even begin to weigh this process with the others like:
The Bosch Process
The Bosch process utilizes the following series of chemical reactions:
(1) CO2 + H2 <-> CO + H2O (2) CO + H2 <-> C + H2O
To give the overall reaction
(3) CO2 + 2H2 <-> C + 2H2O (4) 2H2O <-> O2 + 2H2
Assuming 80% efficiency for the reaction, this process requires 149.8 MW of power. Although this is more energy intensive than the Sabatier process, it doesn’t require importing or producing hydrogen, and the only input is iron, which is abundant on Mars, so it is pretty much identical to the Sabatier process plus pyrolysis. However, the process of reaction (2) leaves a solid film of carbon precipitate which would foul the catalyst. It would be very energy intensive to remove the carbon and, although some might be useful, the 158 metric tons/day it would produce will likely pose a serious disposal problem. Martian citizens will have to be able to decide if disposing of carbon residue is worth not having to add hydrogen. And there is still a third method to consider.
Carbon Dioxide Electrolysis
Carbon Dioxide Electrolysis directly converts CO2 to O2. By sending CO2 over a catalyzed cathode surface under an applied electric potential, Martians can split CO2 into carbon and oxygen by the reaction
(1) 2CO2 <-> 2CO + O2
This process operating at 80% efficiency will require 215.6 MW to produce the required oxygen. It is the most energy intensive, having the highest temperature requirement. But this system is still experimental. NASA intends to test it with the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) on the Mars 2020 mission. But this is only a 1% scale model of a plant that is itself only theoretically designed to produce 20 grams per hour. It would take 8750 such plants to convert enough CO2 for a million people. Will development of industrial scaling of this process be possible by the time people live on Mars? Will the simplicity of this system make up for its much higher energy requirements? Is getting oxygen from CO2 even the best method?
Oxygen from Water
Water electrolysis cuts out the first steps of the Sabatier and Bosch processes, so it is inherently more energy efficient than either. But Mars has abundant and accessible CO2 while water is not so much. We do not yet know whether citizens of Mars will struggle more with water acquisition or oxygen production. If getting water proves easy, then water electrolysis is clearly better, but if getting water proves hard, the best technology is much less clear, and the decision more complex. And there is one more alternative to explore:
Regolith Refining
A final method may be to refine oxygen from the Martian regolith itself. The Red Planet is so colored precisely because of the abundant iron oxide on the surface. How can those oxides be turned into breathable oxygen?
Regolith can be refined into metals and oxygen. The metals, such as iron, alumina, magnesia, and calcia, can be used in construction materials, structural components, and insulation, and oxygen is a byproduct. By dissolving regolith in a sulfuric acid solution, you can precipitate or crystalize out metal oxides. These oxides can then be reduced into their pure metallic form with oxygen as a byproduct.
This process is certain to be necessary for mining metals, but it is incredibly energy intensive as a way of producing oxygen. We cannot know beforehand the exact material needs on Mars, and so also cannot know what percentage of oxygen can be harnessed as a byproduct. It may even be infeasible to move enough regolith to rely on it for anything other than supplemental oxygen production. But water extraction adds another compounding variable. Regolith will have to be mined to get water, so should this material be utilized for oxygen anyway? Accurate prediction of how Martians will get oxygen is clearly off the table.
Water
Liquid water does not flow across the Martian surface as it does on Earth, but other sources of water may be able to supply Martian citizens. But it may not be plentiful or easy to access. So how much water would 1 million people require every day?
The average person requires 3.2L per day. For 1 million people, that amounts to 3.2M liters per day. But water is for more than drinking. Growing food also takes water. The most water-wise crops need about 1000mm of water per 90 day growing season. Feeding a million people requires, conservatively the equivalent of a crop area of about 46*107 m2. Food production thus requires approximately 5.2M liters of water per day. That gives us a subtotal of 8.4M liters per day. But people need to wash and many industrial processes use water as well, so we’ll double our estimate so far to get a total of 16.8 M liters of water per day. But it doesn’t all have to be fresh. The ISS reuses 93% of its water, but due to the large scale required for a Martian city, a better assumption for reuse is about 80%. Thus, the total daily production requirement of water sits at about 3.36M L/day.
But how to get it?
Mining Ice
Intuitively mining and melting subsurface ice sounds the most straightforward. But subsurface ice is only found in certain locations on Mars, and deposits of water ice are covered in 1-10m of debris and dust.
Location
Subsurface ice is more abundant at high latitudes, and less so near the equator. But it is harder to take-off and land at high latitudes, so there is an inverse relationship between ease of Terrestrial travel and ease of access to ice. High latitudes also have less solar energy for electricity. NASA has set preliminary boundaries for crewed missions at no more than 50 degrees, but we cannot know how those trade-offs will pan out until people go there.
Extraction
Another barrier to accessing ice is the layer of debris, or overburden, covering it. If the ice is too deep, it may be better to go after the water in the regolith rather than dig for the ice. How deep is too deep? The volume of overburden that must be removed depends on how the pit is dug.
Fortunately, NASA has done the math. Gypsum rich regolith yields more water than ice below 2.2m. Smectite rich regolith yields more water than ice below 3.7m, and regular regolith yields more water than ice below 5.2m. So not only does the depth of the ice matter, but so too does the type of overburden sitting on top of it.
But even if our Martians have to remove more material, melting ice still takes less energy. So it still may be better to use deeper ice. The latent heat of fusion for water is 333 J/gram. Thus, to gain the 3.36 million liters per day of water by melting ice requires 13 MW. Based on this initial estimate, ice mining presents substantial energy savings over any kind of regolith refining.
Water in the Regolith
Even if mining ice is the primary source of water for Martians, access to ice may be initially difficult. So Martian citizens may initially have to get their water from regolith. NASA currently considers centralized processing and collection of regolith from water refining to be the baseline setup for such a water collection system. But Martian regolith is an amalgamation of different minerals and is not homogeneous. So how much water you get from it, and how easily, depends on what's in the dirt.
For normal regolith, getting enough water will require heating 3.08 billion metric tons to 500C, expending 74 GW of power. But if it turns out excavating more regolith is easier than generating more power, heating the regolith to under 100C only uses 32 GW of power, but takes about 7.7 billion metric tons. And then, of course, there are multiple types of regolith.
Smectite and Gypsum rich regolith are substantially more water rich and therefore require less energy and less regolith to get the same amount of water. Smectite rich regolith is about 2.74% water by mass and only needs to be heated to 300C, which takes 27.2 GW of power and 1.73 billion metric tons of regolith. Gypsum rich regolith is 9.08% water by mass, needs only to be heated to 150C, which takes 9.88 GW and uses 618 million metric tons of regolith.
So while regolith refining takes about a factor of 10 more power than melting ice, the more substantial challenge may be moving that much material. To put it in perspective, one of the largest mines on Earth, the oil sand mine in Alberta, Canada, moves about 200 million metric tons of material per year. Regolith operations on Mars will have to move several orders of magnitude more material per day. In fact, in general the tasks that, on Mars, will need to be routine are comparable to their largest and most intensive scales ever conducted on Earth.
Food
Unlike oxygen and water, which can be refined from existing Martian material, there is no easy way to create food from what already exists on the red planet. But people still have to eat, so they’ll have to grow food. The main challenges are minimizing water and power usage and selecting food sources suitable for the challenges of Martian life.
Crops
The surface of Mars is very hazardous to crop growth. There is no soil, UV radiation is deadly to all plants, violent weather could easily destroy protective structures on the surface, and the sunlight that reaches Mars is not sufficient for growing most crops. The bright side is that all these challenges make growing crops underground in tunnels with high strength LEDs as the primary light source a competitive strategy to farming on the surface.
Connon and Britt suggest that 14,500km of 12m diameter tunnels could sustain the necessary agriculture. But this scale is unprecedented. The largest vertical farm facility in the world is in Mirai, Japan and only has about 25000m2 of growing area. They also only grow lettuce. Who knows what complications could arrise scaling that process by 100 times and diversifying crops to dozens more varieties. But since thats the best model we have, we can use Mirai’s power usage of 369 MWhr/month to estimate a power requirement of 930MW for Mars.
But even the scale of Martian agriculture may not be the thorniest problem. Mars has no soil, and so far, attempts to create soil from inert Martian regolith simulants can’t even support earthworms, much less grow crops. Plus, soilless systems require substantially less water per yield. On the other hand, hydroponic equipment can’t be made using in situ materials, so would have to be flown from Earth. Compost is easier to make than plastics. It is possible that by the time Martian citizens are growing their own food, they will have enough compost to make soil anyway. We may not know which method is best until we get there.
Protein
Animal based proteins are the most common sources on Earth, but taking animals to Mars would be both difficult, and waste valuable resources and space for relatively low caloric return. The main potential alternatives are plant protein, lab grown animal protein, and insect protein (don’t tell Florida’s or Alabama’s governors!).
Some varieties of plant based foods are both low water use and high in protein. Quinoa, black-eyed pea, chia, and tarwi are examples. The use of gene editing techniques could also increase the variety of plant based proteins available on Mars. For instance, the legume, Vetch, is protein rich and xeric, but also toxic. But gene editing could remove the toxin. Gene editing focused on plant protein BAG4 may also be able to reduce water requirements for otherwise high protein plants. The main barrier to lab grown animal protein is price and easy access to traditional meat. But prices have been going down, and there may not be other meat on Mars. Finally, insects are a far more efficient source of protein than other animals. Many cultures are not put off by eating insects, and have a variety of ways to prepare them that future Martians might find enjoyable. But processed insect protein could also supplement other foods in a way more acceptable to some palates. There are several ways to get protein, and no way of knowing which will work the best.
Habitats
Mars is cold, has an extremely thin atmosphere, and lacks a magnetic field. Wildernesses on Earth can be deadly enough, but shelter on Mars is an even more immediate concern.
Structural Challenges
Internal pressure, low gravity, thermo-elastic loads, and potential micro-meteoroid impacts all pose threats to Martian habitats. On Mars gravity is ⅓ the force of Earth, and the atmospheric pressure is very low. Keeping habitats from popping is more important than keeping them from collapsing, a far cry from terrestrial structural engineering. The pressure differential is 2090 psf on Mars, compared to 1400 psf in airplanes flying at 30,000 feet. In addition, due to Mars’s thin atmosphere, the thermal gradient due to the sun is 148F. Not only is that a lot of expanding and contracting between night and day, but it means a lot of insulation to keep the inside comfortable. Finally, micrometeorites pose the threat of puncturing habitats, which could lose valuable air or even collapse structures. Not to mention the necessity of protecting citizens from solar radiation, since Mars has no magnetic field. Combining all of these challenges makes for an extreme technical challenge when designing structures.
Structural Solutions
Simply locating habitats inside lava tubes solves many problems. First, they would protect citizens from the harsh radiation on Mars’s surface. Basalt also has a thermal conductivity an order of magnitude better than most terrestrial insulations and is 1-15 meters thick. Plenty of protection from whatever Mars could throw at it.
But it isn’t so simple. Lava tubes aren’t air tight, so Martian citizens will still need to install inflatable barriers, like a liner. The tube provides the structure, so the barrier doesn’t need to be structural or resist the harsh Martian conditions. But it still needs airlocks for ingress and egress. While an inflatable airlock would be able to fit the irregular openings, it would be more vulnerable to puncture and Martian wear and tear. On the other hand, a standard rigid airlock would be simpler and hardier, some solution, like hardening foam, would have to connect the airlock to the lava tube opening. This could present its own maintenance issues.
On the other hand, living one’s life in a tunnel is likely to be drab, confining, and depressing. How much will these psychological needs need to be balanced with the needs of structural engineering? Perhaps adding some surface habitats, where citizens can go see the stars or walk around “outside” will be necessary. If this is the case, the complexity of these structures is immeasurable compared to the already challenging cave habitats. Who knows what they will end up looking like!
Power
This is where it gets sticky. Powering a Mars settlement is going to take a lot more energy than an equivalent city on Earth. In fact, the Martian environment limits the available sources of energy production in general. Mars cannot independently support hydroelectric power, geothermal power, wind power, or fossil fuels. This leaves solar energy and nuclear energy as the two primary sources of power production to consider.
Solar Energy
Solar has some advantages. It is a well established technology in space applications. If the city is underground, panels could be placed above the city. The main drawback is the distance from the sun, which dramatically reduces the potential power from solar energy.
Design and Installation
First, because the solar intensity is so much lower on Mars than on Earth, the panels will likely require a tracking mechanism to continually optimize their angle relative to the sun. Second, dust accumulation will require a system to regularly clear dust from the surface of the panels, either permanently affixed or moved between panels. Third, solar panels will require substantial diagnostic equipment in order to indicate loss of efficiency both from dust or age related degradation. Fourth, each panel would also have to be periodically replaced as they age and efficiency gets too low. Finally, Each of these systems will need a maintenance system, as well as cleared land around each panel to provide maintenance access. All of which are harder to implement in the Martian environment than on Earth.
Power Estimates
On Mars the solar intensity averaged over the whole surface, between seasons, and the day night cycle is about 100 W/m2. Solar panels currently used by NASA are 30-40% efficient. Using a conservative 30% efficiency, the available power from solar panels will be 30 W/m2. But each panel will not always be operating at full capacity. So if we say each panel operates at 90% capacity on average, our final estimate for the available power from solar panels is 27 W/m2 or about 37000 m2/MW. So one giant square solar panel 192m on each side would net 1 MW. But it isn’t one big panel. If we include spaces between panels it becomes a square 250m on each side: 62500 m2/MW of Martian surface area.
In addition to our existing estimates for other technological systems, we have to account for domestic and industrial energy consumption . Assuming this is similar to the United States, it amounts to 13 MWhr/yr/person. Thus, 1 million people would require about 1484 MW for domestic use.
Let's put that together with all of our other power consumption in a nice visual table:
Nuclear
As this table shows, the total surface area necessary to power the Martian city is nearly 170 km2. It would take up a land area the size of Las Cruces, NM. Nuclear power of some variety is likely necessary to supplement solar. Mars has no tectonic activity and most of the planet likely lacks a water table. Thus we predict that nuclear waste storage will be substantially easier on Mars. But Nuclear power stations would still have to be away from the populated areas in case of meltdown, while solar panels could be right above.
Furthermore, from a political and legal standpoint, it seems unlikely that nuclear material will launch from Earth. Mars does have viable deposits of nuclear material, but this does mean that all of the necessary infrastructure for refining raw nuclear material into usable fuel will have to be developed in situ. In addition, the only well practiced nuclear technology on Earth, light water reactors, are extremely water intensive. In the United States, nuclear energy production uses approximately 400 gallons of water (1516 L) per megawatt hour. Liquid salt and gas cooled reactors would alleviate this problem, but such technologies have not yet been commercially implemented.
Where does that leave us?
How should Martians get their oxygen? Will there be enough water? How much regolith will they need to refine, or even be able to refine? What needs should refinement be prioritized to meet? What foods will they grow and how? Where will they live? What will their energy source be? The complexity and relative tradeoffs of different technological choices for living on Mars are mind boggling. And that doesn’t even get in to what kinds of innovations will be made in the mean time. It seems extremely unlikely that anyone will know exactly what kinds of technologies will work and which won’t for an endeavor as difficult as Mars ahead of time. But is that really all that different than on Earth? Perhaps the most substantial difference is that Mars throws a harsh light on the limits of prediction when making decisions about innovation. On Earth we can get away, to some extent, relying on venture capitalists and tech company executives to make these decisions, and the errors that come with them, for us. But on Mars, there is much less slack. So if we can’t rely on analysis and prediction, then what can we rely on? If we can’t know until we get there, then how should Martian citizens (and maybe those of us on Earth too) go about picking the direction of our technological society?
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