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Solar Power Satellites

  1. Dec 14, 2005 #1
    I’ve been wondering for a while now whether there were any projects on the drawing board for Solar Power Satellites, (SPS) and today I came across a Japanese experiment set to launch on January 18, called the Furoshiki experiment. Furoshiki is a Japanese word for a cloth used to wrap up small possession. The experiment will test whether large structures can be constructed in space by having 3 satellites holding the corners of a Furoshiki 20m on each side, and having small robots crawl along and align themselves in order to transmit a signal.

    ESA News Release can be found here:
    http://www.esa.int/esaCP/SEMHVXVLWFE_index_0.html

    Along with some videos here:
    http://www.esa.int/gsp/ACT/power/solar_power_satellites_furoshiki.htm

    And a pdf here:
    http://www.esa.int/gsp/ACT/doc/Furoshiki%20IAF04%20Paper%20KayaMankinsSummerer.pdf

    Would anybody know how much solar power could be generated from a SPS? What size would be needed to have any impact at all on our energy needs?
     
  2. jcsd
  3. Dec 14, 2005 #2

    DaveC426913

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    I always thought the problem was how to get the power from "up there" to "down here".
     
  4. Dec 14, 2005 #3

    Danger

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    The amount of energy generated will depend upon the specific type of SPS. There are several different possibilities. Unless photovoltaic cells become even more efficient than they are now, I suspect that concentrated sunlight focused on a thermal generator will be the practical way to go.
     
  5. Dec 14, 2005 #4
    What problems are you thinking of specifically? My guess would be to first put a satellite into a geosynchronous orbit which would allow it to be stationary over head, and forgive my ignorance, but beam the energy down to a ground station.

    Ok, found a little something which describes the process.

    http://www.freemars.org/history/sps.html
     
  6. Dec 14, 2005 #5

    Danger

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    While it's theoretically an ideal approach, there are still stumbling blocks regarding beamed power. For one thing, microwaves aren't great at penetrating water. Heavy clouds or rain can interrupt delivery. There's also the necessary size of the receiving array, which is rather sizeable. (It's been suggested that it be elevated with farmland underneath, so that might be a minor problem.) There are probably concerns as well about the effect of a beam upon aircraft systems that happen to get into the path.
    One of the biggest obstacles, unfortunately, is political. You know how stupid the general public is when it comes to science. I wouldn't doubt that at least 80% of US citizens would be terrified by the concept of microwaves coming from space and vote out anybody who endorsed it.
     
    Last edited: Dec 14, 2005
  7. Dec 14, 2005 #6
    From the site I linked above, they say the power would be beamed in microwaves at a frequency of 2.45 GHZ which can apparently pass through heavy clouds.

    A conventional power plant supplies 1 billion watts, while the SPS they propose would generate 5 billion watts. 10 x 13 kilometers in size is quite sizable, but considering the returns, a project of this size should easily make their money back pretty quickly.

    And yet they also say that even at the peak of the beam, the intensity of the microwaves are practically nil. As far as aircraft, I’m not too sure whether it would interfere with instruments, but then just restrict the airspace.

    The public are stupid, but unlike things which they have good reason to fear, this is not one of them, and could easily be educated about the misconception.
     
  8. Dec 14, 2005 #7

    russ_watters

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    Well, the mean solar flux at our distance from the sun is 1369 w/m^2. Let's say you could make a parabolic dish and focus solar energy on the earth and convert it to electricity at 40% efficiency. You'd need 1.8 square km to generate as much energy as a typical nuclear reactor or medium sized conventional plant of 1000 megawatts.
    Well, mylar has a mass of 1.3 g/cc. At .1mm thick, that 10x13km collector would have a mass of 160,000 kg and cost roughly $3.7 billion just to launch...

    Someone please check my numbers....
     
    Last edited: Dec 14, 2005
  9. Dec 14, 2005 #8

    Danger

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    I was unaware of that. Good counterpoint.

    I wasn't concerned about the cost, actually; it's a matter of where the hell do you put the thing.

    I'm not surea about it either, but I suspect that it would interfere with computerized control systems as well as instruments. There's a lot of restricted airspace already, and it's getting worse all of the time. An ocean-based receiver would alleviate the problem.

    Just don't try to build it in Kansas.

    Russ, I know that you're referring to the solar collector there, and have no idea how to check your numbers. The hugeness that I was referring to is the receiving antenna.
     
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