...100 MW of Space Solar Power ...per single launch!
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From: jmfbahciv on 21 Dec 2009 07:42 Pat Flannery wrote: > jmfbahciv wrote: >>> What happens to the output when the antenna is covered with several feet >>> of snow and ice? >> >> Isn't that when the grad student gets to go outside on Mount Washington >> and discover what real wind chill feels like? > > You would have to mount the antenna elements far enough away from the > side of the mountain (on tall poles probably) so that they would stay > above the snow in winter. > Of course an avalanche wouldn't help things any. :-) > You don't know how bad things can get. Snow, sleet, and frozen rain can coat anything with inches of stuff in that region. /BAH
From: Sylvia Else on 21 Dec 2009 08:00 Pat Flannery wrote: > Sylvia Else wrote: >>> 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. > > Duh, hadn't thought of that one... > (Sheepish) > > Pat :-) Been there. Done that. I suspect the only way to avoid such blunders is not to express views in public. Not going to to happen ;) Sylvia.
From: Pat Flannery on 21 Dec 2009 17:23 jmfbahciv wrote: > Pat Flannery wrote: >> jmfbahciv wrote: >> > You don't know how bad things can get. Snow, sleet, and frozen > rain can coat anything with inches of stuff in that region. I live in North Dakota, and the same thing can happen around here, despite it being as flat as a billiard table. This could mean that the rectennas are limited to the southern parts of the continent to escape being covered in ice. In regards to satellite TV that's inconvenient, but when your power grid is relying on it it becomes critical. They are better in the south anyway, as a GEO SPS is higher in the sky from there, so the rectenna array can be more round in shape. Pat
From: Dr J R Stockton on 21 Dec 2009 14:02 In sci.space.history message <00a95a62$0$23691$c3e8da3(a)news.astraweb.com >, Sun, 20 Dec 2009 12:59:40, Sylvia Else <sylvia(a)not.at.this.address> posted: >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. That is correct. The Sun-facing half absorbs approximately the same energy as it would if it were black, but a large percentage of that energy goes away in the microwave beam. The other half will be, as near as practicable, black. Therefore the system runs, overall, cooler, than a uniformly-coloured body 1 AU from the Sun does. The Earth is such a body, but with a greenhouse effect raising the surface temperature. Some parts of the system may need active arrangements to transfer heat to the back; but with distributed absorption and transmission that should nor be necessary. Remember - to an object in GEO, a small fraction of the "sky" is Earth, at about 300K, and a much smaller fraction is Sun, at 6000K ; the rest is almost everywhere at 3K. Think of an SPS as being similar to a mirror facing the Sun. The back will be black (or as black as needed); the front is in effect a fairly good reflector of energy, except that it changes the wavelength and direction. -- (c) John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME. Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links. Proper <= 4-line sig. separator as above, a line exactly "-- " (RFCs 5536/7) Do not Mail News to me. Before a reply, quote with ">" or "> " (RFCs 5536/7)
From: Sylvia Else on 21 Dec 2009 19:19
Dr J R Stockton wrote: > In sci.space.history message <00a95a62$0$23691$c3e8da3(a)news.astraweb.com >> , Sun, 20 Dec 2009 12:59:40, Sylvia Else <sylvia(a)not.at.this.address> > posted: >> 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. > > > That is correct. > > The Sun-facing half absorbs approximately the same energy as it would if > it were black, but a large percentage of that energy goes away in the > microwave beam. The other half will be, as near as practicable, black. > > Therefore the system runs, overall, cooler, than a uniformly-coloured > body 1 AU from the Sun does. The Earth is such a body, but with a > greenhouse effect raising the surface temperature. > > Some parts of the system may need active arrangements to transfer heat > to the back; but with distributed absorption and transmission that > should nor be necessary. > > Remember - to an object in GEO, a small fraction of the "sky" is Earth, > at about 300K, and a much smaller fraction is Sun, at 6000K ; the rest > is almost everywhere at 3K. > > Think of an SPS as being similar to a mirror facing the Sun. The back > will be black (or as black as needed); the front is in effect a fairly > good reflector of energy, except that it changes the wavelength and > direction. > What you seem determined to ignore is that the microwave part is a separate assembly. It is not an integral part of the solar absorber. Its thermal requirements have to be addressed separately. Sylvia. |