LIGHT SAILS:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jan 26, 2015.

  1. Russ_Watters Not a Trump supporter... Valued Senior Member

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    You don't know how to copy and paste a link or block of text? Highlight it, right click, click "copy", then right click in your post and click "paste". Otherwise, you'll have to manually copy the information and equations. I'm not going to just do it for you -- that's not how learning works.
     
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  3. nebel Registered Senior Member

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    re: size of forces on rotating solar sails: The Yarkovsky effect (giving thrust in the orbital direction of an prograde rotating body) has been measured in asteroid orbit change, and news today, that the YORP effect, (solar radiation will increase the spin of a rotating body,-- aka solar sail) ---- will increase the rotation of the spinning body to a point that centrifugal forces will spin off a debris trail, -- as read in Astronomy Today Magazine, March 23 , 2015 on asteroid p/2012F5 .
     
    Last edited: Mar 23, 2015
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  5. origin Trump is the best argument against a democracy. Valued Senior Member

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    You clearly did not understand the article or the article was incorrect. The YORP effect causes the increase rotational rate of the object due to the SUBLIMATION OF ICE. That has nothing to do with how light sails operate. Apples and oranges... Here is an arxiv article that Astronomy article was probably based on.

    http://arxiv.org/pdf/1503.05632v1.pdf

    Edit to add: Thanks for raising this point, I did not know about these fast rotational asteroids until you brought it up.
     
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  7. nebel Registered Senior Member

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    origins yes, I found that interesting too. the rotating sails Yorp effect is primarily through re-radiation of the incoming solar energy, if there is ablation, as you suggest in your "sublimation of ice" comment, so much the better, adding reactive 'substance' to the meager radiation pressure. Asteroids , or all rotating bodies can be accelerated or retarded by the sun, depending on direction of their rotation, but the rotation rate is accelerated (even so slowing from tidal forces if present. ).
     
  8. origin Trump is the best argument against a democracy. Valued Senior Member

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    You are still missing the point. It is not that hard, the forces are not radiation pressure but instead the sublimation is acting like a jet causing the motion. This is nothing, I repeat nothing like a light sail.

    Edited to add:
    I was incorrect in my first post where I attributed sublimation to the YORP effect. They are 2 seperate things. The YORP effect and the Yarkovsky effect are both respnsible for an increase in rotational speed from solar radiation. The sublimation spin up is completely separate. Sublimation does seems to have a greater effect by several magnitudes.

    Regardles the time frame for the these effects are on the order of 100,000s of years for there to be a significant change in the rotational speed. So whatever you are thinking about this applying to light sails seems far fetched.
     
    Last edited: Mar 23, 2015
  9. nebel Registered Senior Member

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    origin, others before here have argued over reflection and absorption, I am drawing on a sailing analogy, the Flettner rotor. in an solar rotating sail, it is kind of an delayed reflection, photons in, photons out after being rotated. The links in the article explains it to you, so rather than commenting on my mental state, why do you not address the subject matter at hand, Yarkovsky. YORD, centrifugal forces leading to asteroids shedding matter? thank you. nebel.
     
  10. OnlyMe Valued Senior Member

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    The problem with that idea as far as solar sails is concerned is the weight.., of the sail and mechanism involved. A solar sail produces a very small but constant thrust. The Flettner rotor does not add thrust it just allows you to alter the direction of the thrust by rotor speed and direction of rotation.... But in the case of a solar sail you gain nothing!

    A solar sail is angled to increase orbital velocity, which sends you out.., or slow orbital velocity down which sends you in! And that can be done with far less mass and additional weight than trying to build a Flettner solar sail, which in the end could do not more than just angling the conventional solar sail design, as needed.

    Unless I have missed something by not following the thread to closely!
     
  11. nebel Registered Senior Member

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    OnlyMe, I did not propose to build rotating solar sails as a means of primary propulsion, but to use the existing natural Yarkovsky effect to either slow down* or speed up a small orbiting body, or control it's rotation by the YORP effect. In the articles, links above, one theorist proposes that the bombardment by comets, asteroids was caused by such retrograde rotating bodies, that were slowed in their orbits by solar radiation heating the leading side of their orbital direction, over long periods of time. One proposal has it to artificially rotate inner asteroids to give them prograde spin to propel them back out, where they are less of a threat. should have started a separate thread on rotating light sails I guess.
     
  12. OnlyMe Valued Senior Member

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    I don't believe that a rotating solar sail along the lines of the Flettner rotor would be of any use for any purpose! It would really only amount to a different and more complex means of altering the direction of a very small force.

    If you have the ability to rendezvous with any orbiting body it would seem there are far more efficient means to alter its orbit. As pointed out if you were to just alter its rotation, any change in its orbit would occur over a time frame far to long to be of value... And that assumes it is small enough that making a change in its rotation is even practical. I just don't see it...
     
  13. OnlyMe Valued Senior Member

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    Nebel, I have not been following the thread but it seems from what I have seen just recently, you should listen a little more. It seems origin did a good job of addressing the recent issue. I only piped up because I really cannot see any value in messing with how a solar sail functions.

    But hey who knows what we will see down the road? They got a car driving itself across country.....
     
  14. nebel Registered Senior Member

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    onlyme, I agree,as I said early on, it is "mouse milk" I introduced it only as a concept, but the effects are real. and of course, they are also flying a solar powered plane around the planet. Cousteau had a rotating sail,-- wind-powered. and asteroids are flying apart because of spin-up by solar power, asymmetrical albedo.
     

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