The efficient frontier

I’m in London this week for the Summit for Space Sustainability, where I’m supposed to say something about “orbital carrying capacity”. I wanted to reflect and write a bit on how I’m thinking about the term and this question before the event, where I’ll likely reconsider many of these notions.

I think the question behind the term “orbital carrying capacity” is something like “what’s the biggest number of satellites that can be in an orbit together?” Maybe there are modifiers like “safely” thrown in there somewhere.

(Edited to add) Why does this matter? Over the next decade or so, folks are planning to launch a lot of satellites — tens to hundreds of thousands, depending on which plans materialize, and maybe more. If we don’t want to end up accidentally overfilling (and maybe trashing) valuable regions of orbital space, we should get a sense of the limits to how much we can put up there. ( Thanks @patwater for suggesting this edit! )

I think there are two ways to think about this question with analogy to terrestrial resources: a mechanical sense of “packing” objects into a box, and a biological sense of “sustaining” a population in a region. Both, I think, have serious limitations for thinking about orbits. Instead, I want to point to a third way to think about the concept: an economic sense of choosing the number of satellites that’s worth keeping in orbit. I’ll explain the first two ways of thinking about the term, then why I think they’re lacking, then explain the economic way of thinking about it. Buckle up, this one’s a bit long.

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