Can orbital habitats have a functional economy?

Comfortable planets are in short supply. Futurists imagine a time when trillions of people will live and work in gigantic orbital habitats. Before we attempt to build such things, it is important to ask about their sustainability. Are orbital habitats just an expensive experiment, or could they have a functional economy?


No rationally-sized orbital habitat can survive as a totally independent island, nor can it survive by relying entirely upon trade with Earth. Every kilogram launched from Earth to any reasonably high orbit comes with a $25,000 shipping fee. For a habitat to engage in relatively free trade with Earth, launch costs would need to drop by three orders of magnitude. Even a hypothetical space elevator offers only two orders of magnitude at best.

So, whether there are just two habitats, or two million of them as in a Dyson sphere (aka Dyson swarm), every kilogram of imported material comes with a massive pricetag. This is perhaps easier to see in terms of waste. On Earth, typical humans discard well over 1kg of waste per day. Supplying that habit while in space would cost $10M per person per year. Clearly this is not sustainable.

In such an environment, the incentive to reuse and recycle is extreme. Without facilities to reprocess everything, financial ruin is inevitable. To survive, either each habitat must contain its own gigantic industrial recycling facility, or, all must be able to specialize in function and exchange cargo (including waste) with the others with extreme efficiency.

The question is, how efficient can we make it?


Unlike in science fiction, in the real universe any habitat that houses human activity must rotate to provide artificial gravity for its occupants. See our survey of spinning habitat designs for two dozen of these. However, importing and exporting goods from a spinning frame of reference seems to be no easy task.

To avoid the problem of spin, futurists invariably suggest that all people and cargo pass through a hub located at or near the top or bottom of the central axis. If that hub is stationary, the immediate problem becomes how to create a gigantic, rotating air lock that permits ingress and egress from the rotating frame. This is a massive technical hurdle with no clear answer.

The other option is for the center to rotate along with the habitat. Then all people and cargo must dock at, and pass through, the central axis. While this sounds practical, it is in fact a massive bottleneck to commerce.

A typical habitat might have a population of 100,000 people, much like South Bend, Indiana. Imagine if South Bend had only two parking spaces available for all vehicles picking up or dropping off people and cargo. It would be an unsolvable logistics nightmare. An axial hub simply cannot be the only means of ingress and egress for any sizable habitat.


As unlikely as it seems, the solution is to dock at the outer rim rather than the central axis. In 1974 Gerard K. O'Neill proposed a detailed habitat arrangement consisting of two parallel counter-rotating cylinders. With this he made a passing comment about how to exchange people and cargo between the cylinders:

"engineless vehicles can unlock from the outer
surface of one cylinder at a preset time, move in
free flight with the tangential velocity... and lock
on to the other cylinder at zero relative velocity."

This pilotless, thrustless transport method is uncomplicated, and works just as smoothly for any two parallel cylinders of similar rim speed. As such it is clearly the most graceful way to transfer mass between two rotating frames of reference. We'll call it the rim-to-rim transport method, or simply the R2R method.

        O- -O- -O
       / \ / \ / \
      O- -O- -O- -O
     / \ / \ / \ / \
    O- -O- -O- -O- -O
     \ / \ / \ / \ /
      O- -O- -O- -O
       \ / \ / \ /
        O- -O- -O
Thinking much bigger, we note that R2R can be extended to an array of any number of parallel spinning habitats, whether arranged in a square grid, a honeycomb-like lattice, or a ladder-like rungworld structure. Containers can be handed off from rim to rim, and routed much like data packets in a network, until they reach the desired destination habitat.

The cost of moving a single kilogram in the network now becomes trivial, and the underlying cost of shipping from one habitat to another now scales by volume rather than mass or distance. This extended R2R method is efficient, scalable, and orders of magnitude less complicated than axial-docking based commerce.


Whatever the exact layout, the conclusion is clear. The need for extremely cheap inter-habitat shipping places dramatic constraints on the configuration of orbital habitats. As such, networks of habitats spinning in parallel may well be the only viable architecture for any future Dyson sphere economy.

Dr. Timothy P. Barber / 2AI © 18 MAY 2020