...100 MW of Space Solar Power ...per single launch!
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From: Androcles on 14 Dec 2009 20:29 "Sylvia Else" <sylvia(a)not.at.this.address> wrote in message news:00851e07$0$16793$c3e8da3(a)news.astraweb.com... > Androcles wrote: >> "Sylvia Else" <sylvia(a)not.at.this.address> wrote in message >> news:016dcf9f$0$10143$c3e8da3(a)news.astraweb.com... >>> Uncle Al wrote: >>>> Sylvia Else wrote: >>>>> Uncle Al wrote: >>>>> >>>>>> 80% bullshit business plan number for RF >>>>>> conversion >>>>> At 80%, the remaining 20%, or 80MW, is heat that has to be got rid of, >>>>> by radiation alone. >>>>> >>>>> Sylvia. >>>> Given 0% carbon footprint, 80 MW continuous ground heating cannot add >>>> to Global Warming. Besides, it is add over a broad area. It's not >>>> like lighting a candle or grilling a steak - both of which are >>>> Enviro-whiner atrocities. >>>> >>> I wasn't talking about on the ground. If the space side conversion of >>> generated power to microwaves is only 80% efficient, then there's 20% >>> loss in heat. That heat has to be got rid of, or the system will melt. >>> Given that it's in a vacuum, the heat has to be got rid of entirely by >>> radiation. >>> >>> Sylvia. >> >> It had to arrive entirely by radiation. Didn't you know the Sun is hot? >> >> > > Yes, and if the transmitter could run at the temperature of the surface of > the sun, there'd be no problem. > > Sylvia. Oh, you mean an incandescent lamp. It's gonna need a mighty big solar array to power it for 100 MW. Perhaps someone is planning to orbit a nuclear reactor instead, or else they'll need a lot of coal.
From: Peter Fairbrother on 14 Dec 2009 20:41 Sylvia Else wrote: > Peter Fairbrother wrote: >> Sylvia Else wrote: >>> Uncle Al wrote: >>>> Sylvia Else wrote: >>>>> Uncle Al wrote: >>>>> >>>>>> 80% bullshit business plan number for RF >>>>>> conversion >>>>> At 80%, the remaining 20%, or 80MW, is heat that has to be got rid of, >>>>> by radiation alone. >>>>> >>>>> Sylvia. >>>> >>>> Given 0% carbon footprint, 80 MW continuous ground heating cannot add >>>> to Global Warming. Besides, it is add over a broad area. It's not >>>> like lighting a candle or grilling a steak - both of which are >>>> Enviro-whiner atrocities. >>>> >>> >>> I wasn't talking about on the ground. If the space side conversion of >>> generated power to microwaves is only 80% efficient, then there's 20% >>> loss in heat. That heat has to be got rid of, or the system will >>> melt. Given that it's in a vacuum, the heat has to be got rid of >>> entirely by radiation. >> >> For physics reasons (in order to get a small enough beam spread) the >> transmitter will need to be 0.5-1 km across, regardless of power; and >> there is no real reason why it should not be made from heat-tolerant >> materials, excepting maybe some of the electronics. > > Typically, the transmitting antenna would be a mesh to minimise the mass > - the holes merely have to be small compared with the transmitted > wavelength. But a mesh doesn't have a large surface area, which would be > required to radiate away the heat. Most designs don't use a mesh, but rather a matrix of transmitting elements in a solid plane. The individual elements are closely spaced, and even if a grid was used it would be fairly full. Think of a phased array antenna rather than a loose grid of wires >> >> Even for my proposed 100 GW systems, cooling the transmitter isn't a >> big problem. No external cooling systems are needed, just sunshades. >> Indeed if it can operate at a few hundred C even sunshades are not >> required. > > What's the blackbody radiation per square metre at a few hundred Celsius? 7348 w/m^2 at 600 K or 327 C. A 3 km^2 area transmitter at 327C would radiate over 20GW, enough for a 100 GW transmitter at 20% efficiency. -- Peter Fairbrother
From: Peter Fairbrother on 14 Dec 2009 21:55 Peter Fairbrother wrote: > Sylvia Else wrote: >> Peter Fairbrother wrote: >>> Sylvia Else wrote: >>>> Uncle Al wrote: >>>>> Sylvia Else wrote: >>>>>> Uncle Al wrote: >>>>>> >>>>>>> 80% bullshit business plan number for RF >>>>>>> conversion >>>>>> At 80%, the remaining 20%, or 80MW, is heat that has to be got rid >>>>>> of, >>>>>> by radiation alone. >>>>>> >>>>>> Sylvia. >>>>> >>>>> Given 0% carbon footprint, 80 MW continuous ground heating cannot add >>>>> to Global Warming. Besides, it is add over a broad area. It's not >>>>> like lighting a candle or grilling a steak - both of which are >>>>> Enviro-whiner atrocities. >>>>> >>>> >>>> I wasn't talking about on the ground. If the space side conversion >>>> of generated power to microwaves is only 80% efficient, then there's >>>> 20% loss in heat. That heat has to be got rid of, or the system will >>>> melt. Given that it's in a vacuum, the heat has to be got rid of >>>> entirely by radiation. >>> >>> For physics reasons (in order to get a small enough beam spread) the >>> transmitter will need to be 0.5-1 km across, regardless of power; and >>> there is no real reason why it should not be made from heat-tolerant >>> materials, excepting maybe some of the electronics. >> >> Typically, the transmitting antenna would be a mesh to minimise the >> mass - the holes merely have to be small compared with the transmitted >> wavelength. But a mesh doesn't have a large surface area, which would >> be required to radiate away the heat. > > Most designs don't use a mesh, but rather a matrix of transmitting > elements in a solid plane. The individual elements are closely spaced, > and even if a grid was used it would be fairly full. Think of a phased > array antenna rather than a loose grid of wires > >>> >>> Even for my proposed 100 GW systems, cooling the transmitter isn't a >>> big problem. No external cooling systems are needed, just sunshades. >>> Indeed if it can operate at a few hundred C even sunshades are not >>> required. >> >> What's the blackbody radiation per square metre at a few hundred Celsius? > > 7348 w/m^2 at 600 K or 327 C. > > A 3 km^2 area transmitter at 327C would radiate over 20GW, enough for a > 100 GW transmitter at 20% efficiency. Duh, 20% loss, not 20% efficiency. Sorry. For a 400 MW system, as opposed to a 100 GW system, even with a wire grid, the cooling requirements are ... piffling. You'd want to take them into account, but that's about all. Oh, on antenna sizes - the larger the antenna in orbit the tighter the beam, and thus the smaller the required ground antenna, and the required exclusion zone. For a 100 GW system I'd use a considerably larger space antenna than the 1.4 km diameter antenna implied above so that the irradiation at the edge of the terrestrial antenna's exclusion zone was *much* less than eg the exposure caused by carrying a mobile phone or using a microwave oven. Safety first, precautionary principle (you don't want to get sued), and so on. -- Peter Fairbrother
From: Pat Flannery on 15 Dec 2009 02:21 Peter Fairbrother wrote: > I was just pointing out that the aircraft, even a composite one, > wouldn't melt or anything like that! I was more worried about the microwaves going right through the composite parts of the aircraft and hitting the people and electronics inside of it. As someone pointed out earlier, a all-metal aircraft works like a Faraday Cage and shields its interior from the microwaves...although I'd expect some pretty impressive electrical displays off of the static discharge wicks at the wing and tail tips as the plane itself will act like a rectenna for the microwaves, and that electrical energy has to go somewhere. It's best just to have aircraft just steer clear of the beam. Pat
From: Pat Flannery on 15 Dec 2009 02:34
Peter Fairbrother wrote: > > Most designs don't use a mesh, but rather a matrix of transmitting > elements in a solid plane. The individual elements are closely spaced, > and even if a grid was used it would be fairly full. Think of a phased > array antenna rather than a loose grid of wires Something like a huge version of this: http://www.bharat-rakshak.com/NAVY/Images/MR-775.jpg Unlike a big parabolic dish, you can steer the microwave beam from a flat array electronically without having to physically move the antenna. Pat |