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Statite Dynamic Shell, aka, Stapledon Dyson Shell

1. The Standard Story

The continued increase of the human population, expanding into the solar system and later to other star systems, is a common assumption in 20th century science fiction. People move into orbiting space habitats at the L4 and L5, terraform Mars, etc. When planetary systems are exhausted, the expansion continues into more space habitats orbiting the sun, perhaps manufactured from the asteroids, Mercury, and Venus. Some propose dismantling the Earth to build more habitats, eventually capturing most of the energy from the Sun.

Nikolai Kardashev characterized future supercivilizations by the energy they capture and use.

  • A type I supercivilization captures all the power reaching their planet from their star for artificial uses. For the Earth, that is 174 petawatts, 1.74e17 watts incoming, of which perhaps 120 petawatts reaches the surface - the rest is reflected into space. Plants intercept about 20 petawatts (2e16 W), and convert 200 terawatts (2e14 W) into material animals (and now biofuel-guzzling machinery) can eat. Current global artificial power production is about 15 terawatts (1.5e13 W).

    A type II supercivilization captures all the power emitted by their star. Our sun emits 380 yottawatts (3.8e26 W) visible light, UV, and infrared, 2 billion times more power than the earth intercepts, and 25 trillion times more power than human artificial power production.

    A type III supercivilization captures all the power emitted by all the stars in their galaxy. Our galaxy emits perhaps 40 trillion yottawatts, (4e37 W), more than two heptillion (2e24) times more power than human artificial power production.

So, a supercivilization capturing all the power emitted by the Sun with a shell of habitats would be a Type II supercivilization.

Olaf Stapledon wrote about type II and type III supercivilizations in his 1937 space fantasy novel Starmaker. Freeman Dyson wrote about how such supercivilizations might appear as highly luminous, compact infrared sources in 1960, Search for Artificial Stellar Sources of Infrared Radiation. He described them as shells, an assembly surrounding a star - he did not claim they would be solid or spherical.

Because of this paper in Science, a journalist misleadingly named these sources Dyson Spheres, a source of confusion ever since. Dr. Dyson wishes they were named something else, as I will do below.

What do Type II Humans Need?

Intelligent life resembling us is probably very rare. There may be many possible substrates for many kinds of intelligence, though, and we may invent other forms that are more compatible with long-term goals for intelligence.

Earth life needed more than a billion years to invent oxygen-producing photosynthesis, and RevolutionEarth. This involved the development of more than 100 proteins in a complex configuration with two coupled photosynthesis systems; it took a long time for nature to develop and combine all the elements out of anaerobic predecessors. The conditions that produced us are mostly those that sustain us. What do unmodified humans need?

Breathable Air

> 150 KPa oxygen, moisture, nonreactive gas filler, N₂ (He?)

CO₂ collection

< 1000 ppm, plants can recycle


Carbs, proteins, trace elements

Gut Bacteria

From food


15 to 27 °C, heating and cooling as necessary

Visible Light

diurnal cycle


medicines, surgery


"A few minutes a day", NOT UVA, UVC and shorter

Low Radiation

< 100 mREM/yr Ionizing Radiation


Poisons, pathogens, accidents, many hazards in space


Situational, cultural, written, programmed, communication


don't do damaging stuff

Resources and tools

Many humans make stuff. Homo Faber defines most of us.


Says Maslow


Says Maslow


Says Maslow


Personal, Cultural, Species: 1 billion years for observability

The last is the reason to build a Type II civilization in the first place. A billion years of resources may be impossible to provide, if we are limited to the earth, with imperfect recycling and our ore-derived materials slowly eroding into the sea. The sun is heating up, and the earth may be unlivable within a few hundred million years. We will need to be active in space to protect our planet, and restore it after a major catastrophe.


The "Dyson" "Sphere"

The scare quotes are intentional - the attribution is wrong, as is the noun. I will describe the idea the label has come to describe, before disposing of it.

For many science fiction readers, this is a large solid sphere, inhabited on the inner surface with the sun overhead. Details intentionally vague ... because a solid sphere doesn't work, for numerous reasons.

A Miscellany of Physical Pathologies

First pass - light from above

The area of a sphere is 4πR² - the area facing in one direction (like the sun) is πR², so the average surface illumination is ¼ of the total. Add in atmospheric reflection, and the average illumination (visible light and near IR < 2 μm wavelength) reaching the Earth's surface is about 240 W, averaged over 24 hours. If this was somehow duplicated across the inner surface of a huge sphere, and radiated into deep space on the outer surface with an emissivity ε of 1, the black body temperature would be T = 255 K = /sqrt(4){240 / \epsilon \sigma} where σ = 3.567e-8 W/m²K⁴ $. A temperature of 13℃ (55℉) is considered optimal - a black body temperature of 286 K. We can achieve that with an emissivity of ε = 0.63. Except - if we want to preserve the diurnal and annual cycles of nature, we will want to modulate the light on a 24 hour and an 8766 hour cycle. Easy; we put reflective shutters on a region and the sun, and turn the shutters open to closed on a 24 hour cycle. The light not used by one area will be reflected into the sphere, and used elsewhere, perhaps creating a daily cycle ranging from zero light to 750W at "noon", more in some regions ("the tropics"), less in others ("the poles"), with these regions interspersed in such a way as to create winds, migrations, etc.

The surface of the sphere must be ( 3.8e26 W / 240 W/m² ) = 1.6e24 m² = 4πR² so R = 3.5e11 m = 2.4 AU (Astonomical Units = 1.492e11m), around the middle of the asteroid belt.

But what about gravity? The sun's gravitational parameter is 1.327e20 m³/s², so the gravitational force at that distance is 1e-3 m/s². And it is inward, in the same direction as the sun. That won't work.

Second pass - mirrors and centrifuges

This will look more like a vast array of cylindrical space colonies, with light injected through conical mirrors on the central axis.


StaDyShell (last edited 2021-03-20 21:20:20 by KeithLofstrom)