Saturday, October 28, 2017

Principles of Mars urban planning (first pass)

Autarky Complete and indefinite self sufficiency, or breakout capability to reach such with trivial effort.

Regular readers will know that I occasionally discuss aspects of Mars settlement. This blog is inspired by some slides presented by SpaceX at IAC2017, which showed a SimCity base growing on Mars. Since Mars cities won't look like this, what will they look like?


The first city on Mars is oriented toward rapidly developing autarky, to minimize exposure to the period of time when the base is dependent on shipments from Earth. This differs a lot from a mostly static Antarctic station outpost, and thus determines a lot about how the city must be planned. No one knows for sure how many people are needed for autarky, but is likely at least a million and will thus require decades of blistering growth. The primary role of fixed infrastructure on Mars then, besides keeping death out, is enabling growth.

In Estimating Mars Settlement Rates, I attempt to estimate growth rates using ship construction and utilization estimates, combined with a population/self sufficiency relation. The Earth Mars launch window occurs every 2.2 years, and initial population growth targets are a factor of 4 per window, later dropping to a factor of 2 depending on ship production, capacity, and reuse.

No city in history has needed or managed to sustain growth this fast. On Mars, the primary task is building more city for impending arrivals, and the primary constraint is labor availability. To maximize production efficiency, construction will need to use mechanization, automation, and wherever possible, a shirtsleeves environment.

All this is fairly obvious. Can we now draw a map? Not really. I don't know what a self sustaining Mars city looks like and I probably will not live long enough to find out. Indeed, attempting to learn from experience that doesn't yet exist is a pointless endeavor. But I will wave my hands a bit about the first decade of growth.

In addition to enabling its own maximal growth, the Mars city will perform every other kind of function from life support, transport, recycling, and entertainment to privacy, education, mining, manufacturing, communication, and emergency management. Some of these functions will be distributed, others more centralized. To maximize the utility of limited living space, for instance, compact apartment geometries can be imported from Earth, while landing and launch operations, and other especially hazardous activities, will have to be separated from more vulnerable or less defensible areas. Practically speaking, all functions span a continuum from local to centralized. Somewhere in the middle of this continuum is a point of mandatory separation, and it is here around which individual pressure vessels, habs, vaults, arcades, tunnels, small domes, and vehicles will be divided from each other.

All of the more local functions (health, education, libraries, sport, food, recreation, spirituality, music, common space, food distribution, non-transformative recycling, life support, temperature control, atmospheric processing, grid stabilization, communications, data storage, residential, non-hazardous industrial live-work spaces, etc) are ideally collocated. Since these all take place in a climate controlled pressure vessel, each pod is self-contained and resilient enough to withstand substantial extrinsic challenges, while nominally meshing and sharing capacity with adjacent systems. Vacuum ops are required only for initial construction and exterior maintenance. Everything else is done in shirtsleeves at minimal marginal labor cost.

Opinions vary on ideal structure design and material, and methods will no doubt continue to evolve drastically during deployment. My personal preference is for hangar-like structures. A cylindrical roof spreads pressure, requires no internal support, can be shielded with dirt, and unlike spherical domes, has simple curvature and decouples ideal volume from geotechnical concerns in the foundation. With few or no windows, the interior could be somewhere between a modern submarine or a Vegas casino - both structures quite comfortable despite uninhabitable exterior environments. I envision structures ranging in size from Quonset huts to Hangar One at Moffett field and larger.

Arched structures of various scales (lrtb). Quonset huts, Project Iceworm, South Pole logistics archways, some building in Hawthorne, Hangar One, Atlantic City Convention Hall.

They may be connected by sealable bulkhead doors, while the roof can support solar panels or farms, especially the equatorward face of east-west oriented pods. They also have good volume to material/labor ratios. Building materials can range from curved prefab panels to locally produced concrete or brick. Brick vaults may be assembled robotically without formwork using a variety of techniques. Brick and concrete structures are compressional so need preloading before pressurization with several meters of dirt. Numerous other materials and methods are possible, including inflatables.

A growing Mars base, then, could be a densely packed crosscutting network of arched pods, with outskirts being built out at ever more ambitious scale. Manufacturing, chemical work and other non residential activities can be confined to dedicated pods, which can be repurposed (loft conversion!) over time as demand shifts.

Primary demand for water, (nuclear or solar) power, fuel synthesis and storage is associated with launch, so it makes sense to collocate much of this capacity outside the city. Pads with retractable hoses and robot arms can handle ship surface operations at each pad. If the city outgrows the spaceport, construction of new pads and pipes is much less labor intensive than demolishing and/or rebuilding pressurized pods. Spaceports will ideally be located 5-10km north and/or south of the city to keep east-west approach/departure paths clear. On Mars this is well over the horizon!

While it may be possible to house a million people under a square km of high rise roofs, and contain industrial processes under 10sqkm, farming on Mars, while not an immediate priority, will eventually require the bulk of covered land, perhaps 100sqkm. It makes sense to operate at the same pressure as the base, rovers, and suits (perhaps 340mbar) but with enriched CO2 for plant growth, and every other trick worked out by decades of dedicated research that hasn't happened yet! The primary difference between farming and habitation structures is that farms need transparent roofs, though ideally still with a layer of water, ice, or glass to mitigate radiation. I like the idea of transparent inflatables sealed to the ground at the periphery and anchored with cables at regular intervals to spread the pressure load into the ground. There's no reason why residential pods couldn't be interspersed between greenhouses. These structures, similar in concept to an air mattress, would look a bit like this.

One final consideration is scaling and congestion. Pod bulkhead doors are natural choke points. While clever neighbourhood designs will keep the base walkable for most activities (food, hygiene, schooling, training, recreation), movement of large equipment or lots of people may require progressively larger thoroughfares. This is a great problem to have, since that many people on Mars implies many other problems have already been solved! I think use of tunnel boring machines for subgrade roads and repurposing of legacy structures will prevent problematic congestion.

This is my first pass at Mars urban planning. I have no doubt overlooked many details and obvious issues. I'm interested in developing sensible system design axioms from which any given city plan can be more-or-less trivially derived. I don't know of much other work done with such an aggressive focus on growth, and I'm curious to get a better understanding.

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