...100 MW of Space Solar Power ...per single launch!
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From: Dr J R Stockton on 19 Dec 2009 16:58 In sci.space.history message <00a54b65$0$23681$c3e8da3(a)news.astraweb.com >, Thu, 17 Dec 2009 11:06:50, Sylvia Else <sylvia(a)not.at.this.address> posted: >Dr J R Stockton wrote: >> In sci.space.history message <00851e07$0$16793$c3e8da3(a)news.astraweb.com >>> , Tue, 15 Dec 2009 11:55:56, Sylvia Else <sylvia(a)not.at.this.address> >> posted: >>> Yes, and if the transmitter could run at the temperature of the surface >>> of the sun, there'd be no problem. >> We know that a body at Earth's distance from the Sun, heated by >>solar >> radiation and cooled by its own natural radiation, has an equilibrium >> temperature of about (a little below?) the melting-point of ice. (The >> Earth is such a body, but has an atmospheric greenhouse effect making >> the surface warmer.) > >Did you overlook the fact that half the Earth is in darkness at any one >time? No. Remember that half of the satellite is also shaded by the other half. >> Such an object that is transmitting a large portion of the incident >> energy as microwaves to Earth must necessarily tend to run cooler than >> that, overall. > >Did you overlook the fact that the transmitter is not the part of the >system that's receiving the solar energy because they have different >orientation requirements? No. The transmitting metalwork will not absorb much of the energy, and can radiate passively into the Universe. The individual pieces of electronics will dissipate concentrated heat, but we know how to deal with that - transfer it to radiators on the shady side. The detailed engineering must consider how to solve such things, but the physics tells us that it is soluble. You could, of course, have read the following quoted paragraph. >> The transmitting components themselves will dissipate heat, and must >>be >> cooled; but it is only necessary to transfer that heat to the rest of >> the structure. The components will be distributed across the structure, >> so the transfer should not be unduly difficult. > >Did you overlook the fact that that imposes requirements on the area of >the structure. No. The entire back side of the absorber is available to radiate. >Did you overlook the fact that that imposes requirements on the thermal >conductivity of the structure, and therefore the materials from which >it is made? No. There will be various requirements on various parts of the structure, and all will need to be considered. The transfer of bulk heat does not inevitably need to be passive. >> Perhaps you do not have a background in the physical sciences? > >Perhaps you're not as clever as you think you are. How could you tell? -- (c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME. Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
From: jimp on 19 Dec 2009 19:15 In sci.physics Pat Flannery <flanner(a)daktel.com> wrote: > David Spain wrote: >> >>> Using the concept of "If you can't raise the bridge, lower the river" >>> rectennas built not on flat land, but rather on the south-facing sides >>> of mountains would present a more perpendicular aspect to the incoming >>> microwave beam from a SPS in the southern sky. >>> >> >> Wouldn't that work regardless of which hemisphere it's constructed in North >> or South? > > Yeah, in North America it would probably be out in the Rockies facing > south; in South America in the Andes facing north. What happens to the output when the antenna is covered with several feet of snow and ice? -- Jim Pennino Remove .spam.sux to reply.
From: Sylvia Else on 19 Dec 2009 20:59 Dr J R Stockton wrote: > In sci.space.history message <00a54b65$0$23681$c3e8da3(a)news.astraweb.com >> , Thu, 17 Dec 2009 11:06:50, Sylvia Else <sylvia(a)not.at.this.address> > posted: >> Dr J R Stockton wrote: >>> In sci.space.history message <00851e07$0$16793$c3e8da3(a)news.astraweb.com >>>> , Tue, 15 Dec 2009 11:55:56, Sylvia Else <sylvia(a)not.at.this.address> >>> posted: >>>> Yes, and if the transmitter could run at the temperature of the surface >>>> of the sun, there'd be no problem. >>> We know that a body at Earth's distance from the Sun, heated by >>> solar >>> radiation and cooled by its own natural radiation, has an equilibrium >>> temperature of about (a little below?) the melting-point of ice. (The >>> Earth is such a body, but has an atmospheric greenhouse effect making >>> the surface warmer.) >> Did you overlook the fact that half the Earth is in darkness at any one >> time? > > No. Remember that half of the satellite is also shaded by the other > half. <blink> We're not talking about achieving thermal equilibrium in sunlight. We're talking about a system that's converting power supplied from another system into microwaves with less than 100% efficiency, and having to radiate the rest away as heat. > >>> Such an object that is transmitting a large portion of the incident >>> energy as microwaves to Earth must necessarily tend to run cooler than >>> that, overall. >> Did you overlook the fact that the transmitter is not the part of the >> system that's receiving the solar energy because they have different >> orientation requirements? > > No. The transmitting metalwork will not absorb much of the energy, and > can radiate passively into the Universe. The individual pieces of > electronics will dissipate concentrated heat, but we know how to deal > with that - transfer it to radiators on the shady side. The detailed > engineering must consider how to solve such things, but the physics > tells us that it is soluble. You could, of course, have read the > following quoted paragraph. > >>> The transmitting components themselves will dissipate heat, and must >>> be >>> cooled; but it is only necessary to transfer that heat to the rest of >>> the structure. The components will be distributed across the structure, >>> so the transfer should not be unduly difficult. >> Did you overlook the fact that that imposes requirements on the area of >> the structure. > > No. The entire back side of the absorber is available to radiate. The sunlight absorber and the microwave emitter are different parts. > >> Did you overlook the fact that that imposes requirements on the thermal >> conductivity of the structure, and therefore the materials from which >> it is made? > > No. There will be various requirements on various parts of the > structure, and all will need to be considered. The transfer of bulk > heat does not inevitably need to be passive. > > >>> Perhaps you do not have a background in the physical sciences? >> Perhaps you're not as clever as you think you are. > > How could you tell? > >
From: Sylvia Else on 20 Dec 2009 00:30 Pat Flannery wrote: > David Spain wrote: >> >> Some references that might help. >> >> First, Dr. T.S. Kelso's guide on GEO satellites: >> >> http://celestrak.com/columns/v04n09/ > > As has already come up, switching to batteries during eclipse isn't > practical because of the weight that would be involved to keep microwave > power transmission levels constant. Well, you wouldn't do it that way anyway. If you have suitable batteries, there's no point in putting them in orbit. You'd put them on the ground instead, to provide power when the rectantenna isn't. Sylvia.
From: Sylvia Else on 20 Dec 2009 03:18
Pat Flannery wrote: > > Sylvia's multiple SPS constellation with the individual satellites > widely spaced certainly has simplicity on its side. If we're envisaging space antennae that can be steered just be changing the phase of the transmitting elements, then it seems sensible to use that mechanism to allow on SPS to transmit to different ground stations depending on demand. This would then not only be used to address the eclipse issue, but also make for more efficient use by changing where the power is delivered depending on loads (which are reasonably predictable over a period of a day or so). The mechanism could also be used to switch between north and south hemispheres, because the times of peak loads varies with season (afternoon with airconditioning loads in summer, evening with heating loads in winter). Shame so much of the population, and particularly the energy consuming population, is in one hemisphere. Sylvia. |