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Penumbra Station
I want to put out there an artificial mega-structure concept. Specifically, a design that would be an attractive option for civilizations between around 1.0 and 0.75 on the Kardashev scale, who get energy from solar power around a single star. My thinking for this centers around the following goals:
  • Optimization of energy production
  • Maximization of civilization density
  • lesser goal: minimization of materials to build structure

These are conflicting goals with trade-offs between them. Solar power is a diffuse energy source, and that's another reason for this fairly fundamental concept. You could say that even Earth faces that conflict, since people are pushed toward high-density cities for economic reasons, yet resources are dispersed throughout the world. Even in the extreme of an alien race that is just computronium, there is a computational penalty for greater parallelization (versus single-threaded) processing.

If you're building anything short of a Dyson Sphere (consider the satellites in a Dyson Swarm), then there's a certain natural shape that you would likely use, and that is a conical shape that is formed by the shadow of a circle facing the sun. This shape maximizes the heat rejection radiator area relative to the area receiving direct sunlight. Designs of various proposed solar probes reflect this shape. Here is a gallery of some old work of mine, along with an old NASA sketch of such a probe.

For some specifics, let's start with the heat radiator. Human technology is going to work best in the range of room temperature (an assumption you are free to relax for your own versions of this). Thus, I will peg the radiator temperature at 293 Kelvin. If the radiator is a well-designed perfect blackbody, it will radiate at a power of about 420 W/m^2. Our constraint is that our radiator can't reject heat any faster than this, so that limits the maximum incoming sunlight can be, and thus, the minimum radius we can orbit the sun at. I find this to be about 0.25 AU, slightly inside of the orbit of Mercury. In our own solar system, it might make the most sense to build the station in some stable orbital location relative to Mercury.

Let's consider the implications of this. The solar flux incident on the station would be 4^2=16 times what we get on Earth. One way to rephrase this is that you would have to build 16 times fewer solar panels to get the same energy output, compared to Earth orbit. The habitat could be logically situated near the tip of the radiator cone (facing away from the sun), and receive power through ordinary power transmission lines with ruthless efficiency. As far as I can see, this is the only way (short of fusion power) to deliver such a high throughput of power to such a small space. That could be the exact thing that an advanced civilization wants. Picture all of the sunlight energy incident on Earth, collected in an area with 1/4th the diameter. Then, the electricity produced from that sunlight is delivered to an area much smaller than that.

On to some fine tuning... since I first looked into this, I have strayed away from a dual-cone approach, to preferring a single cone. The solar panels could be on the inside surface of the cone (but still oriented toward the sun). This incurs a penalty factor of 2, which means you'll have to either build twice as many solar panels, or build their equivalent area in reflectors. My rationale for this setup is that the energy collectors can be located right next to the energy sink. This way, you could avoid any long-range heat transfer to cool the solar panels, and even conduction through normal metals may suffice. This will cause the panels to be arranged in a "stair step" pattern along the cone's inner surface, with the stairs being limited in size to around a meter or less.

The habitat, on the other hand, will have its own unique issues for heat rejection. It might make more sense for it to have its own radiator. There is a possibility to connect it by a tether to the cone (which also contains the power cables) in order to give it space for its own radiator, while also keeping the structure tidally stabilized.

Thanks for entertaining my brain-dump on this topic.

Messages In This Thread
Penumbra Station - by AlanSE - 05-25-2016, 12:43 PM
RE: Penumbra Station - by stevebowers - 05-26-2016, 07:11 AM
RE: Penumbra Station - by selden - 05-26-2016, 07:20 AM
RE: Penumbra Station - by stevebowers - 05-26-2016, 04:59 PM
RE: Penumbra Station - by selden - 05-26-2016, 07:59 PM
RE: Penumbra Station - by AlanSE - 05-27-2016, 01:22 PM
RE: Penumbra Station - by stevebowers - 05-28-2016, 01:51 AM
RE: Penumbra Station - by stevebowers - 05-28-2016, 02:07 AM
RE: Penumbra Station - by Drashner1 - 05-29-2016, 10:19 AM
RE: Penumbra Station - by AlanSE - 05-31-2016, 12:06 PM
RE: Penumbra Station - by stevebowers - 06-01-2016, 09:10 AM
RE: Penumbra Station - by iancampbell - 06-01-2016, 08:25 PM
RE: Penumbra Station - by AlanSE - 09-26-2016, 10:24 AM

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