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#1
April 8th 04, 02:22 PM
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Starpower?
The ultimate in solar collectors must be the deposition of solar
collectors onto the solar surface. The sun puts out 3.86x10^26 watts of power. Distributed over a sphere whose radius is equal to the radius of Earth's orbit this falls to a little less than 1,400 watts per square meter. But on the solar surface this energy density exceeds 60 megawatts per square meter! Clearly, if we could figure out how to build useful devices that operate under the extreme conditions of the solar surface, we could collect solar energy 40,000x more efficiently than we can on Earth! Any ideas? The business model would be as follows; (1) build a factory that makes the equipment that operates on the solar surface. (2) Launch the equipment in a rocket to Jupiter. (3) Execute a gravity assist from Jupiter to cancel all orbital motion, allowing the equipment to fall toward the sun. (4) Somehow slow the equipment to survive its 'landing' on the solar surface - perhaps using solar sails. (5) Unfold the equipment on the solar surface, and beam 60 megawatts per square meter to anyplace in the solar system (or beyond) you need it. Interesting things to keep in mind; About the sun; http://blueox.uoregon.edu/~jimbrau/a...r16.html#facts About optics; http://www.licha.de/AstroWeb/article...php3?iHowTo=16 http://www.astro.ufl.edu/~oliver/ast...copeoptics.htm About astrodynamics; http://www.go.ednet.ns.ca/~larry/orb.../gravasst.html (you can cancel orbital speed as well as add to it!) A thin film system capable of operating on the solar surface could process quite a bit of power. A square kilometer for instance has a million square meters and could process over 60 trillion watts of power. At a few grams per meter a 'sheet' this size could weigh only a few tons. Something people could build today. Using conjugate optics http://www.futureworld.dk/tech/ether...n/phasecon.htm It is possible to energize a thin film laser medium and then interrogate that system with another laser, extracting a large portion of the energy contained in that medium and delivering it to where its required. The accuracy which things can be delivered large distances are limited by Rayleigh's limit; Theta = 1.22 Lambda / Diameter GREEN LANTERN OPTICS: So, if lambda is 500 nm and diameter is 1 km then theta is; Theta = 1.22 * 500e-9 / 1e3 = 5e-10 radians Multiply this angle by 150 million km (1.5e9 m) and we can see that a 1 km diameter optically active film producing laser beams efficiently on the surface of the sun could create a spot that's 0.75 meters across on the surface of the Earth (capable of putting over 60 trillion watts into that space too - depending on laser and optical efficiencies! But even an overall efficiency of 1% yeilds 600 billion watts per square kilometer) This is more energy than humanity currently uses. With the ability to produce multiple beams we can deliver this energy to billions of users simultaneously and power any manner of industrial or transportation processes. Including space transportation systems. A quadrillion watts - 1e15 watts - enough to power a starship -requires 16 square kilometers. A circle 4.5 kilometers across on the solar surface processes this much power. Stretching our beam out to 1,000 AU from 1 AU, and noting the increase in diameter, we can see that we can deliver this beam to a 'spot' 250 meters across 1000 AU from the sun. At this point, we can reflect the beam around the sun and use the sun's own gravity to focus it reliably any distance we like from the sun, to be used by owners of laser light sails anywhere in the galaxy. But of course, we need to figure out how to make something work reliably on the solar surface. Which I haven't done. Again, any suggestions? 
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#2
April 9th 04, 08:44 AM
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Starpower?
"william mook" wrote in message
om... The ultimate in solar collectors must be the deposition of solar collectors onto the solar surface. The sun puts out 3.86x10^26 watts of power. Distributed over a sphere whose radius is equal to the radius of Earth's orbit this falls to a little less than 1,400 watts per square meter. But on the solar surface this energy density exceeds 60 megawatts per square meter! Clearly, if we could figure out how to build useful devices that operate under the extreme conditions of the solar surface, we could collect solar energy 40,000x more efficiently than we can on Earth! Any ideas? The business model would be as follows; (1) build a factory that makes the equipment that operates on the solar surface. (2) Launch the equipment in a rocket to Jupiter. (3) Execute a gravity assist from Jupiter to cancel all orbital motion, allowing the equipment to fall toward the sun. (4) Somehow slow the equipment to survive its 'landing' on the solar surface - perhaps using solar sails. (5) Unfold the equipment on the solar surface, and beam 60 megawatts per square meter to anyplace in the solar system (or beyond) you need it. Interesting things to keep in mind; About the sun; http://blueox.uoregon.edu/~jimbrau/a...r16.html#facts About optics; http://www.licha.de/AstroWeb/article...php3?iHowTo=16 http://www.astro.ufl.edu/~oliver/ast...copeoptics.htm About astrodynamics; http://www.go.ednet.ns.ca/~larry/orb.../gravasst.html (you can cancel orbital speed as well as add to it!) A thin film system capable of operating on the solar surface could process quite a bit of power. A square kilometer for instance has a million square meters and could process over 60 trillion watts of power. At a few grams per meter a 'sheet' this size could weigh only a few tons. Something people could build today. Using conjugate optics http://www.futureworld.dk/tech/ether...n/phasecon.htm It is possible to energize a thin film laser medium and then interrogate that system with another laser, extracting a large portion of the energy contained in that medium and delivering it to where its required. The accuracy which things can be delivered large distances are limited by Rayleigh's limit; Theta = 1.22 Lambda / Diameter GREEN LANTERN OPTICS: So, if lambda is 500 nm and diameter is 1 km then theta is; Theta = 1.22 * 500e-9 / 1e3 = 5e-10 radians Multiply this angle by 150 million km (1.5e9 m) and we can see that a 1 km diameter optically active film producing laser beams efficiently on the surface of the sun could create a spot that's 0.75 meters across on the surface of the Earth (capable of putting over 60 trillion watts into that space too - depending on laser and optical efficiencies! But even an overall efficiency of 1% yeilds 600 billion watts per square kilometer) This is more energy than humanity currently uses. With the ability to produce multiple beams we can deliver this energy to billions of users simultaneously and power any manner of industrial or transportation processes. Including space transportation systems. A quadrillion watts - 1e15 watts - enough to power a starship -requires 16 square kilometers. A circle 4.5 kilometers across on the solar surface processes this much power. Stretching our beam out to 1,000 AU from 1 AU, and noting the increase in diameter, we can see that we can deliver this beam to a 'spot' 250 meters across 1000 AU from the sun. At this point, we can reflect the beam around the sun and use the sun's own gravity to focus it reliably any distance we like from the sun, to be used by owners of laser light sails anywhere in the galaxy. But of course, we need to figure out how to make something work reliably on the solar surface. Which I haven't done. Again, any suggestions? Keep taking the pills.
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#3
April 9th 04, 04:12 PM
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Starpower?
william mook wrote:
The ultimate in solar collectors must be the deposition of solar collectors onto the solar surface. The sun puts out 3.86x10^26 watts of power. Distributed over a sphere whose radius is equal to the radius of Earth's orbit this falls to a little less than 1,400 watts per square meter. But on the solar surface this energy density exceeds 60 megawatts per square meter! Clearly, if we could figure snip But of course, we need to figure out how to make something work reliably on the solar surface. Which I haven't done. Trivial matter of engineering... 60Mw/m^2 is not a big problem. A millimeter of copper will only have about 140C across it at 60Mw/m^2. The problem is the cooling. You can only radiate to the sky, no convection is possible. It may be possible to get a hair under solar temperatures by using coatings that are more efficiant radiators than the solar atmosphere (no absorbtion bands) but you'r still looking at well over 5000K. This is a problem, as everything melts at this temperature. It's probably easier to move out a bit, as you'r not charged by the square meter for solar surface.
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#4
April 17th 04, 06:57 AM
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Starpower?
Ian Stirling wrote in message ...
william mook wrote: The ultimate in solar collectors must be the deposition of solar collectors onto the solar surface. The sun puts out 3.86x10^26 watts of power. Distributed over a sphere whose radius is equal to the radius of Earth's orbit this falls to a little less than 1,400 watts per square meter. But on the solar surface this energy density exceeds 60 megawatts per square meter! Clearly, if we could figure snip But of course, we need to figure out how to make something work reliably on the solar surface. Which I haven't done. Trivial matter of engineering... 60Mw/m^2 is not a big problem. A millimeter of copper will only have about 140C across it at 60Mw/m^2. The problem is the cooling. You can only radiate to the sky, no convection is possible. It may be possible to get a hair under solar temperatures by using coatings that are more efficiant radiators than the solar atmosphere (no absorbtion bands) but you'r still looking at well over 5000K. This is a problem, as everything melts at this temperature. It's probably easier to move out a bit, as you'r not charged by the square meter for solar surface. Well, following up on this idea. The melting point of Copper is 1,357K the melting point of W is 3695K. This translates to; Solar Surface: 5770K 64 MW/m2 - Surface (400,000 km from center) MP Carbon: 3800K 12 MW/m2 - 522,000 km (922,000 km from center) MP Tungsten: 3695K 10 MW/m2 - 610,000 km (1,010,000km from center) MP Copper: 1357K 195 KW/m2 - 6,830,000 km (7,230,000) Still 50 million miles inside of Mercury's orbit.. Peak radiation color is; Solar Surface: 5770K 502 nm Blue/Green MP Carbon: 3800K 763 nm Dark Red MP Tungsten: 3695K 785 nm Deep Red MP Copper: 1357K 2,137 nm Infrared A carbon film 1,000,000 km in radius and 1 micron thick would have a volume of 12,566,370,614,359,172,953 cubic meters and weigh 28,487,962,182,752,245,086 metric tons. A solid ball of carbon this size would have a diameter of 145 km. A fancy carbon nanotube structure composed of lots of empty space encompassing the sun might mass 1 quintillion tons which would be 48 km in diameter before deployment. Think of a wire mesh reduced to the scale of carbon tubes. Could we concievably process a ball of carbon 50 km across, and unfold it to embrace the entire output of the sun? Why not? There is sufficient resources in the asteroid belt to do this - carbonaceous chondrites would do nicely. GaAs lasers would radiate at this wavelength. Carbon nanotubes could be structured to emit laser light at any wavelength when energized. Combined with conjugate optical techniques the bulk of this energy could be made to radiate at any color or mix of colors anywhere. And we could make use of the entire output of the sun! Of course, we'd have to take care to keep the Earth and other planets illuminated as they are now. This is also a technique that could manage the increasing brightness of the sun over the aeons - by controlling the output falling on Earth and the other planets - its possible to maintain present conditions for astronomical time periods.
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#6
April 28th 04, 12:00 AM
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Starpower?
"william mook" wrote in message
om... Well, lessee, we all make mistakes... Okay, I'm talking about a hollow sphere totally encompassing the sun with a 1 million km (1e9m) radius. The area of a sphere that big is; {snip} Just a sec... If your sphere contained solar cells of some kind that absorbed even a tiny fraction of the stellar radiation, wouldn't it get kind of *dark* back here on Earth? ..Perhaps even "life as we know it would cease to exist" kind of dark?? Cameron:-)
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#7
April 28th 04, 11:19 AM
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Starpower?
Karl,
A 'structure' composed of trillions of mass produced 'cells' does have an advantage, as long as all the 'cells' operate together optically. Discrete structures separated by millions of meters can operate together optically via conjugate optics, as described here; http://ol.osa.org/abstract.cfm?id=7073 Not only can light be reflected from an array of discrete components as if the entire array of components were operating as a single optical element, but the reflected light can be amplified via laser action; http://ol.osa.org/abstract.cfm?id=8347 So, for these reasons I have assumed that the entire 'structure' - regardless of how its assembled, acts as a single optical element 2 million kilometers - or 2 billion meters - in diameter. So, the limits of resolution of a 2 billion meter diameter optical element is easily computed. http://www.mellesgriot.com/products/optics/gb_2_3.htm The diameter of the airy disk is; sin(theta-r) = 2.44 * lambda / r and r = 1e9 m lambda = 1e-6 m so sin(theta-r) = 2.44e-15 ~ 2.44e-15 radians ~1.4e-13 degrees This implies at various distances most of the energy (86.5%) will fall within a disk of a particular diameter. A light year is the distance light travels in one year. So, this is; 3e8 * 3600 * 24 * 365.25 = 9.467e15 meters A spot that is 2.44e-15*9.467e15 = 23.1 meters in diameter can be reliably illuminated by an optical element 2e9 meters in diameter at this distance by 1 micron wavelength light. Tighter resolutions can be achieved at higher wavelengths. Green light for example would have an airy spot half this size. Of course, illuminating smaller portions of the sphere reduces the effective size of the optical element you're dealing with. Anyone in the solar system requiring power would only need interrogate a small portion of this 2 million kilometer diameter optical element. A kilometer diameter sized spot could be formed to power a laser light sail or laser sustained rocket up to 40 light years from sol at 1 micron and up to 80 light years from sol in green light. Up to 160 light years in UV. Response times could be a problem. Because you must wait round trip times in one spot for the power to respond to your request for it. In these instances it may be preferable to set up automated equipment to deliver 'waves' of power - like a surf on the beach - that repeat in well defined spaces and patterns. That way to make use of the energy, all ships must do is communicate with the automated equipment as to the times dates and places of the next series of light surf. Radio telescopes could communicate information great distances allowing the coordination of deep space travel from star to star. They could also allow the collection of electronic payment for use of energy. So, fees could be collected from great distances automatically over long periods of times. The size, scope and length of time such economic entities could exist would be unprecedented in human history. Against these vast economic powerhouses even present day governments pale by comparison. Of course, controlling the output of entire stars and reliably delivering that output anywhere in a volume up to 100 light years from that star is also unprecedented in human history. Such capacity would give our species immediate access to the galaxy and would likely end poverty as we know it. Although I would suspect poverty as we don't know it now would likely continue. (Karl Hallowell) wrote in message . com... (william mook) wrote in message om... Ian Stirling wrote in message ... william mook wrote: The ultimate in solar collectors must be the deposition of solar collectors onto the solar surface. The sun puts out 3.86x10^26 watts of power. Distributed over a sphere whose radius is equal to the radius of Earth's orbit this falls to a little less than 1,400 watts per square meter. But on the solar surface this energy density exceeds 60 megawatts per square meter! Clearly, if we could figure snip But of course, we need to figure out how to make something work reliably on the solar surface. Which I haven't done. Trivial matter of engineering... 60Mw/m^2 is not a big problem. A millimeter of copper will only have about 140C across it at 60Mw/m^2. The problem is the cooling. You can only radiate to the sky, no convection is possible. It may be possible to get a hair under solar temperatures by using coatings that are more efficiant radiators than the solar atmosphere (no absorbtion bands) but you'r still looking at well over 5000K. This is a problem, as everything melts at this temperature. It's probably easier to move out a bit, as you'r not charged by the square meter for solar surface. Well, following up on this idea. The melting point of Copper is 1,357K the melting point of W is 3695K. This translates to; Solar Surface: 5770K 64 MW/m2 - Surface (400,000 km from center) MP Carbon: 3800K 12 MW/m2 - 522,000 km (922,000 km from center) MP Tungsten: 3695K 10 MW/m2 - 610,000 km (1,010,000km from center) MP Copper: 1357K 195 KW/m2 - 6,830,000 km (7,230,000) Still 50 million miles inside of Mercury's orbit.. Peak radiation color is; Solar Surface: 5770K 502 nm Blue/Green MP Carbon: 3800K 763 nm Dark Red MP Tungsten: 3695K 785 nm Deep Red MP Copper: 1357K 2,137 nm Infrared A carbon film 1,000,000 km in radius and 1 micron thick would have a volume of 12,566,370,614,359,172,953 cubic meters and weigh 28,487,962,182,752,245,086 metric tons. A solid ball of carbon this size would have a diameter of 145 km. A fancy carbon nanotube structure composed of lots of empty space encompassing the sun might mass 1 quintillion tons which would be 48 km in diameter before deployment. Think of a wire mesh reduced to the scale of carbon tubes. Could we concievably process a ball of carbon 50 km across, and unfold it to embrace the entire output of the sun? Why not? There is sufficient resources in the asteroid belt to do this - carbonaceous chondrites would do nicely. GaAs lasers would radiate at this wavelength. Carbon nanotubes could be structured to emit laser light at any wavelength when energized. Combined with conjugate optical techniques the bulk of this energy could be made to radiate at any color or mix of colors anywhere. And we could make use of the entire output of the sun! Of course, we'd have to take care to keep the Earth and other planets illuminated as they are now. This is also a technique that could manage the increasing brightness of the sun over the aeons - by controlling the output falling on Earth and the other planets - its possible to maintain present conditions for astronomical time periods. Rather than a single large structure, this is likely to be achieved by a host of small structures. It makes it easier to pass light through since one could orient the structures edgewise to the Sun whenever they pass through the plane of the Solar system. Care needs to be taken with Earth since the radiating structure would still have the heat output of the Sun. That coupled with the illumination that would be required means that the Earth gets heated in two ways. Power transportation is also a problem. Visible (or UV) light lasers should be able to illuminate efficiently throughout the inner Solar system, but it'll take significant surface area or higher frequencies to beam power out to say Uranus (IMHO). Still dissipation appears to be a problem to me particularly outside the Solar system. You will need to find a better way to transport power there. Karl Hallowell
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#8
April 28th 04, 12:24 PM
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Starpower?
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#9
May 2nd 04, 08:41 PM
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Starpower?
(Mike Miller) wrote in message . com...
(william mook) wrote in message . com... Okay, I'm talking about a hollow sphere totally encompassing the sun with a 1 million km (1e9m) radius. The area of a sphere that big is; Ah, I thought I read 2-million km diameter *disk,* not a sphere. I see what you're getting at now. Mike Miller, MatE Light pressure can be used to support stationary cellular elements above the solar surface at any distance. Since the light pressure and gravitational attraction both scale as the inverse square of distance from the sun's center, they the acceleration exerted by sunlight will be the same at any distance. A particle that absorbs perfectly all light falling on it from the Sun will feel a force equal to; f = pA = 3.56e-18 N At 1 AU. where, p = 4.53e-6 newtons/m2 at 1 AU and where, for a 1 micrometer diameter particle projected area is; A = 7.85e-13 m2 Now, the mass of a 1 micrometer diameter spherical particle with a density of 1 gram/cc is its volume times its density; m = 5.24e-16 kg So, acceleration is equal to; a= 6.79e-3 m/sec2 at 1 AU. Now the gravitational acceleration is equal to; a = f/m = GM/r^2 and at 1 AU this is equal to; a = 5.92e-3 m/sec2 And the ratio (which is independent of R from the solar center) is; 1.15 Which explains why comet tails point away from the sun. The ice particles of which they are composed are smaller than 1 um in diameter. Particles that are denser than ice, such as carbon particles, must be smaller than 1 um to be supported by light pressure alone. Structured carbon particles that interact with light to project powerful laser energy in response to being illuminated with weaker laser energy must be smaller than 386 nm in diameter in at least 1 dimension to be supported by light pressure. A 'laser flake' of structured carbon that absorbs sunlight and projects powerful laser beams in response to being illuminated by weak laser beams that is 350 nm thick and perhaps a millimeter in diameter, would have the capacity to navigate throughout the solar system if it could control its transparency and reflectiveness. With the ability to circulate a current around its edge, the 'laser flake' would have added control by affecting the passage of solar wind. These cells would make a mass at 1 million km radius that is about 1/3rd the total mass computed earlier which assumed a shell 1 um in thickness. http://www.pcimag.com/CDA/ArticleInf...,76195,00.html http://ol.osa.org/abstract.cfm?id=7877 Ceramic, rather than carbon, microspheres or micro flakes would likely make better lasers that operate more efficiently at high temperatures using less mass overall to encompass the sun. In this scenario several asteroids of the appropriate composition would be processed into microspheres and those spheres ejected from the surface of the asteorid. Once free of the asteroid's gravity, the microspheres would navigate to their operational radius and begin operation. As the 'cloud' of 'flakes' accumulated, output of the system would increase. One of the first uses of the systems output would be to beam energy to the chosen asteroids so as to increase their output by increasing the energy available to the automated manufacturing processes.
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#10
May 5th 04, 09:25 AM
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Starpower?
(william mook) wrote in message . com...
(Alex Terrell) wrote in message . com... You would also heat up the sun, which would increase the rate of the fusion, which would heat up the sun, which could go Nova. Really? Consider, two spherical surfaces one nested inside the other sharing a common center. One is 800,000 kilometers across (the surface of the sun) another 2,000,000 kilometers across (the surface of the power shell). Now, if the temperatures of each of the surfaces are such that the amount of energy radiated from a sphere 2 million kilometers across is equal to the amount of energy radiated from a sphere 800,000 kilometers across - there is no opportunity for energy to accumulate in the sun, increasing rate of fusion presumably. You are correct in the steady state. However, you are effectively increasing the insulation of the sun. Therefore, to emit the same amount of radiation, it needs to be hotter. However, if it's hotter, it will emit more radiation. This will either stabilise at a hotter sun, or be unstable and go nova. Another way of looking at it: The spehere will reflect / reemit a proportion (50%) of the energy it receives in the direction of the sun. That has the effect of increasing the heat generated by the sun by more than 50%. But this begs an interesting question. Could one increase the rate of fusion? (Nova's are something quite different see http://observe.arc.nasa.gov/nasa/spa...rdeath_4a.html ) This would brighten the star and increase total output of the sun. Which could be interesting if more energy is needed. Could this be done? I don't know. It does seem that if we have a sphere made of reflectors that return energy to the sun, then the sun would heat up. This is likely to result in an increase in the solar wind. Which could be interesting. The solar wind might be harvested for raw materials like hydrogen, helium, and other elements it contains. But since it takes on the order of 10,000 years for energy to move from deep inside the sun to the surface, it is likely to take equally long for surface changes to affect deep processes like rate of fusion (if it affects it at all!) But it would be cool to be able to control illumination levels on each of the planets while independently controlling stellar output over some range. But, I'm not smart enough to figure out right now if this will indeed happen. Maybe a solar astronomer can give us a clue. One thing is for certain. Theconditions are not right for a nova. It would shorten the life of the sun, but that life span is fantastically long to start out with.
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