Part of my series on common misconceptions in space journalism.
Also, an update of sorts to my post on industrializing Mars.
Ever since SpaceX publicly announced their overarching mission to build a self-sustaining city on Mars, countless articles have been written about all sorts of related things. In many ways, this whole blog series is a reflection of this explosion of common media interest. Relatively few articles go so far as to dive into (literally) the nuts and bolts, and fewer still give any useful insights into the process.
Industrializing is really difficult. In August 2020 Starship SN5 has just hopped. It’s easier for a country to industrialize now than ever before, but even so – Mars is just a really terrible place to live. Living there, in any real sense, is utterly dependent on all kinds of advanced technology, and building it all locally is a very tall order. For more on the interactions between technology, environmental hostility, and population, check out my case study on Iceland.
What I will explore in this blog is how the Mars city will go about industrializing. Initially, a small population will make relatively few things, and later on a much larger population will support ongoing production of all kinds of stuff. What gets made first, and how much?
Let’s look at a representative sample of products consumed by the US on two axes: consumption rate per capita and price per kilogram. Consumption rate can function as a proxy of how much of a given thing is needed, while price is a good proxy for manufacturing difficulty, including labor and energy inputs. There are several big caveats here to explore in later paragraphs.
The result is the above graph. The inset lower left breaks out some of the densely clustered points in the middle.
The trend shows that, for the most part, we use more of cheap things, and less of expensive things. Or, for a given consumption rate, small things have a higher dollar value density. For example, morphine is waaay off to the left not because it costs a lot (the numerator) but because the usage rate is really low (the denominator).
How do we interpret this in the context of a future Mars city?
For the most part, cargo mass constraints will encourage local production of items in the lower right corner, gradually trending up and to the left. Over time, with more local manufacturing of mass-intensive products, a greater fraction of import cargo can be devoted to humans rather than bulk, low value commodities.
Of course, relative costs and usage rates would move quite a bit. All things being equal, I think the need to have most people working on factories inside entirely artificial environments means that, to a good first approximation, the per capita usage would be about ten times higher than on Earth.
Some high volume resources would vary on usage and cost. For example, water and various gases (particularly nitrogen) would be both harder to make and much more in demand than on Earth, moving their graph location up and to the right. On the graph, I’ve marked these products with an asterisk.
At any given time, there is a dollar import cost and desired level of self-sufficiency, giving rise to the red shaded region. In this graph, it’s set according to parameters given in a recent Mars city design competition, but its overall trend is down and to the left over time.
That is, there are two competing trends wherein increasing population enables greater specialization and cheaper labor, incentivizing local manufacturing of steadily more complex products (the diagonal axis shifts left). On the other axis, shipping costs are likely to trend downwards over time, incentivizing import of products with relatively high complexity compared to usage rates (the horizontal axis shifts downwards). This trend competes with local manufacturing cost reductions (in part dependent on shipping costs) for re-offshoring of any given production system. In practice, I think the trend will favor monotonically increasing autarky.
The blue zone at the top of the graph demarcates potential products in terms of volume of demand or cost that could be profitably exported from Mars back to Earth, given rather optimistic shipping costs. It is empty, because there are no known resources in space that could be sold profitably on Earth.
Everything in between is imported. In the given case, many drugs are used in such low volumes and are so difficult to produce that importing them makes sense. Similarly for mechanical devices such as actuators and bearings. Of all the parts of machines, these are both relatively light and relatively expensive. A local nexus of cost density.
In contrast, metals, gases, water, most food, plastics, and other bulk materials are made locally.
What this diagram does is provide a way to think logically about how an industrial stack can be built up over time, and the ways in which various components move up the value chain towards a finished product.