Differences between revisions 7 and 8
 ⇤ ← Revision 7 as of 2015-10-23 04:20:49 → Size: 3524 Editor: KeithLofstrom Comment: ← Revision 8 as of 2015-10-23 15:07:50 → ⇥ Size: 5302 Editor: KeithLofstrom Comment: Deletions are marked like this. Additions are marked like this. Line 20: Line 20: Olaf Stapledon wrote about type II and type III supercivilizations in his 1937 space fantasy novel '''[[ StapledonDyson | Starmaker]]'''. Freeman Dyson wrote about how such supercivilizations might appear as highly luminous, compact infrared sources in 1960, [[ http://www.sciencemag.org/content/131/3414/1667.short | 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 round. Olaf Stapledon wrote about type II and type III supercivilizations in his 1937 space fantasy novel '''[[ StapledonDyson | Starmaker]]'''. Freeman Dyson wrote about how such supercivilizations might appear as highly luminous, compact infrared sources in 1960, [[ http://www.sciencemag.org/content/131/3414/1667.short | 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. Line 23: Line 23: === What do Type II Humans Need? ===Intelligent life is probably very rare. Earth life needed more than a billion years to invent oxygen-producing photosynthesis, and [[ RevolutionEarth || did so only once ]]. Line 28: Line 37: For many science fiction readers, this is a large solid sphere, inhabited on the inner surface with the sun overhead. Details intentionally vague ... because that doesn't work. The 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. Line 30: Line 39: === A Miscellany of Physical Pathologies === Line 32: Line 40: 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 250 W. If this was somehow duplicated across the inner surface of a huge sphere, and radiated into deep space on the outer surface, == 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 ### 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 is probably very rare. Earth life needed more than a billion years to invent oxygen-producing photosynthesis, and RevolutionEarth. ### 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)