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Thread: Solar Sails

  1. #1 Solar Sails 
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    http://en.wikipedia.org/wiki/Solar_sail

    I am baffled...how do they plan on conserving the laws of thermodynamics by reflecting light off of the sail in order to impose kinetic energy unto the craft? Am I missing something?


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  3. #2  
    Forum Bachelors Degree Waveman28's Avatar
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    When the light reflects off the sail, it transfers some of its energy to the craft. The light reflected back has less energy than before it strikes the sail. So in doing this, the solar sail craft gains momentum.


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  4. #3  
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    But....I was not aware that partial absorption per photon could occur, which would result in a wavelength increase of the photon. And if that is not the case, then REFLECTION is not the point, but ABSORPTION.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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    Forum Bachelors Degree Waveman28's Avatar
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    Regardless of reflection or absorption, the reflected light MUST lose energy. Otherwise conservation of energy would be violated, as you initially feared.
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  6. #5  
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    Wait...do you mean loose energy in terms of individual photon wavelength, or in terms of total quantity of photons being reflected as opposed to absorbed?

    This is weirding me out...I always thought that solar sails used cosmic radiation (alpha radiation namely) for propulsion....however, if they use light, AND IT ACTUALLY WORKS.....this completely changes my view of quantum mechanics.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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  7. #6  
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    I am a prominent supporter of light being a wave, not a particle (or both for that matter). So when the light is reflected off the sail, it will lose intensity and the sail will gain kinetic energy.
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  8. #7  
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    Quote Originally Posted by Cold Fusion
    Wait...do you mean loose energy in terms of individual photon wavelength, or in terms of total quantity of photons being reflected as opposed to absorbed?

    This is weirding me out...I always thought that solar sails used cosmic radiation (alpha radiation namely) for propulsion....however, if they use light, AND IT ACTUALLY WORKS.....this completely changes my view of quantum mechanics.
    By shift of photon wavelength. In other words, if you point a light at a light sail and then measure the frequency of that light when it returns to you, it will have a lower frequency.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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  9. #8  
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    Hmm.....I will need to read into this more and then get back to you guys.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

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    Use your computing strength for science!
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  10. #9  
    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by Waveman28
    I am a prominent supporter of light being a wave, not a particle (or both for that matter).
    Out of interest, how do you explain the photoelectric effect?
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  11. #10  
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    Ok...did some thinking. It appears to me, that because the emission of light coming off of the solar sail and hence the reflection of the incident photons, must be red shifted due to the wave nature of matter....because the light is red shifted, energy must be given up. Due to that, energy is 'artificially' transmitted as kinetic energy into the solar sail. Hilarious.....
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
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  12. #11  
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    Post promoting personal theory removed.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  13. #12 re-emission 
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    Does not photon reflection equal absorption and re-emission?
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  14. #13  
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    Yes...but apparently the solar sail process partially saps energy from the photons, rather inadvertently. I find it fascinating.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
    Reply With Quote  
     

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