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    Missile Defense

Technology has always found its greatest consumer in a nation's war and defense efforts. Since the last attempts at a "Star Wars" defense system, has technology changed considerably enough to make the latest Missile Defense initiatives more successful? Can such an application of science be successful? Is a militarized space inevitable, necessary or impossible?

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rshow55 - 06:36pm May 11, 2002 EST (#2166 of 2169) Delete Message

John Perlin has written From Space to Earth: The Story of Solar Electricity (Aatic Publications 1999) , setting out the enormous amount of work that's been done to harnass solar energy since the first photocell in 1883. He summarizes much of that information in Solar Power: The Slow Revolution in Invention and Technology , Summer 2002.

The overwhelming problem with photoelectricity (something Exxon and other oil companies know a lot about) is cost . Because costs remain very high, after more than a century of work, photocells provide less than a hundredth of a percent of the world's power.

Gisterme points out in questions in MD2137-2138 gisterme 5/10/02 3:44am that a hydrogen based solar energy system would have major difficulties even if the photocells were free. Gisterme raises other questions, too. I have some workups on those questions, but the issue Perlin emphasizes needs treating first.

" Is it possible to make a breakthrough reduction - a several order of magnitude reduction - in the cost of photocells that can actually be used?"

I still think so, but inventors are often wrong. Here was my reasoning, from MD1131 rshow55 4/5/02 9:40pm

"People can now print photovoltaic layers on flexible plastic sheets. For very large areas, in large scale production, the marginal cost per unit area would approach 0 -- and metal conductive layers with small conductive losses for tens of meters are also workable.

" The key technical problem is floating thin assemblies of sheet plastic (perhaps 30 microns thick in all, including top sheet, bottom sheet, and bubble floatation) with very extensive areas -- and having the assemblies stand up to wind, rain, wave, and whale problems, on the equatorial seas.

Now, to say that's "the key problem" is too simple, and I'm embarassed to have used those words without qualification. It doesn't adress any of the other problems gisterme points out. But let's look at the logic, just that far, in isolation first.

The "photocell assembly" I'm positing, if it could be developed, would use 1 cubic meter of material for 33,000 square meters of photocell area. On glassy or very calm seas, with equatorial levels of sunlight (if you could find such seas) - there might be a lot of electrical energy generated on that basis. The calm sea would provide a near-ideal supporting structure for the assembly. That's much less material than any terrestrial photocell assembly would involve. And a structure that would lend itself to very large scale automation.

Proof of principle at the "simple" level of such a photocell-sheet (assuming a calm enough sea) would involve demonstration of a few tens (at most a few hundreds) of square kilometers. A large area, but not the hundreds of thousands of square kilometers that would be required (along with much else) to take over the current world's energy needs.

Could a calm enough sea be found? I believe so. Before the age of steam, equatorial seas were much feared by sailors, because there was so little wind -- there are really terrible stories of ships caught for weeks becalmed. Seas at latitudes close to the center of convection for the earth (latitudes that vary with season) are comparitively calm, and although thunder storms are common - large circular storms would be extraordinarily rare insurable risks.

From quick calculations, I also believe that the "thirty micron thick photo-assembly" could withstand significant wave action - conform to the wave with only small bending strains or shears -- but I was calculating curvatures short of the kind of wave severity that causes extensive whitecaps.

rshow55 - 06:38pm May 11, 2002 EST (#2167 of 2169) Delete Message

The plastic sheet assemblies have water between the layers, and sloshing would provide considerable damping of wind waves - a damping that would increase rapidly with wave severity. For very large arrays, that damping might be convenient.

To get this far (proof of principle for a sheet of a few square miles) would involve major hurdles. If you could make this breakthrough in photocell cost -- reducing photocell cost several orders of magnitude from what it is now - the other issues gisterme raises in MD2137-2138 gisterme 5/10/02 3:44am would remain.

If this breakthrough in photocell cost were made - those other issues, I believe, would be well worth adressing, and feasible to address.

Having looked some at Perlin's material, I'm not going to consider land-based photocells further - after a century of development, they remain much too expensive.

lchic - 06:54pm May 11, 2002 EST (#2168 of 2169)


Perlin, John (1989) A Forest Journal;the role of wood in the developement of civilization W.W. Norton & Company, New York.

Golden Thread : Twentyfive Hundred Years of Solar Architecture and Technology by Ken Butti, John Perlin (Hardcover - June 1980)

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