LIGHT SAILS:

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

  1. nebel Registered Senior Member

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    R_W: __In the references provided above, there a plenty of links to the calculation of the forces generated by radiation acting on rotating bodies of all sizes,-- from the dust grains that reach escape velocity to the constant push on the Earth's eveningside. These effects are known, starting in the 19st century. If you can refute that, bring on the arguments, details. Whether I am fantasising or not, leave that judgement to my psychiatrist. After all, of all the "light sails" in nature, most of them are spinning, we would not be here without them. It is subtle. so: to contribute, can we have comments further elucidating the subject matter?
     
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  3. OnlyMe Valued Senior Member

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    For any of what you are talking about you have to provide some context of comparrison. In other words.., you need to present the numbers that demonstrate that the forces you are focused on are even remotely significant when comparred to the earth's inertial momentum and the gravitational interaction between the sun and earth....

    And then you need to demonstrate that you have accounted for all of the forces incidental forces, acting on the earth... and demonstrate what the NET effect might be and how that compares, inertial momentum and gravitation.

    The fact that even Newtonian mechanics does a good job of predicting orbits, without including the radiation pressures you refer to, should be enough to tell you, that even if they have any significant effect it is so small as to be difficult if not impossible to compare to the inertial momentum and gravitational effects that do describe the earth's orbit.

    You keep being asked for the numbers, because if you ever actually assembled the numbers, you would find that radiation pressure is insignificant to the larger picture.

    And no one else wants to try and put those numbers together for you. It is your claim and if you don't accept the responses you have received, it is your burden to crunch the numbers, to prove or disprove your assumptions.
     
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  5. Russ_Watters Not a Trump supporter... Valued Senior Member

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    No, neither of the posts you referenced included links. You are dodging because you are just guessing and don't want to admit it.
    Indeed they have: but you clearly haven't learned how to utilize them, otherwise you'd show us what you have done.
    No, the functioning of radiation pressure aren't at issue here. What is at issue is your claim that the impact of radiation pressure is significant to the Earth's orbit. But you haven't provided the details required to support your claim, so at this point, you haven't done anything that needs to be refuted. There is no need to refute a hand-waving fantasy.
     
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  7. nebel Registered Senior Member

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    I introduced the valid idea of rotating "solar sails" to this discussion on mainly 'downwind' foils, There is no question that the effect of this old concept varies with the surface to mass ratio, becoming less noticeable with increase volume., old stuff.
    The question is not MY credentials, at all, it is the how well does it work over the range of all sizes.
     
  8. Russ_Watters Not a Trump supporter... Valued Senior Member

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    We don't know if the idea is valid until you calculate what they will do. Guessing isn't enough.
    I never mentioned your credentials. I have no idea what they are. But yes, the issue is how well does it work for a large object like the Earth. You've claimed it does, but you haven't shown it with the required calculations. and its a bit sad -- all this time spent handwaving; you could have easily done the calculation already!
     
  9. Kittamaru Now nearly 40 pounds lighter. Staff Member

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    The motive? Simple - truth.
     
  10. CHRIS.Q Registered Senior Member

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    These are private sponsorship?
     
  11. nebel Registered Senior Member

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    There was never any question, that the effect of absorbing solar energy and re-radiating it in a different direction on a large body like a planet would be small, on a smaller body it becomes more significant. So:

    while we are at the effect of radiation on a progradetly rotating body, in a prograde orbit (counterclockwise) -- like a Trojan perhaps, - If such a body would have a gas envelope, the volume of that atmosphere would be expanded on the evening side, ( as is the case on this planet)*. The radiation pressure would therefore have greater purchase on the evening side, giving greater speed, torque in the prograde rotation. Call it a standing heat wave if you like.
    The velocity AND ROTATION are favored by doing it when irradiated. It is happening in nature.
    On this concept, this model of light sail, my part is limited to pointing it out.; if you like numbers, do them, pick a size where the effects would be most effective, or
    prove that that it does not work AT ALL. Please falsify IT, not the potential arithmetic glitches.
    *thermosphere
     
  12. nebel Registered Senior Member

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    correction please. I used the wrong term, so, rather than "retrograde", please read "same" as in "same" direction rotation and revolution, i.e. counterclockwise. setting sail slightly.
     
  13. origin Trump is the best argument against a democracy. Valued Senior Member

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    I would imagine most people would agree that would be a waste of their time. It is your claim YOU need to provide evidence it is viable and convince us otherwise. If you are not going to do the math then just continue to wave your arms until everyone tires of this and just ignores you.

    The ball is in your court.
     
  14. nebel Registered Senior Member

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    370
    On the torque from an expanded thermosphere, think ORIGIN of winds in gas giants when they were even more gigantic.
    Origin, you might be fascinated by calculating "pie" to the nth digit, fine, Ignoring is not ignorance,--I am dealing in big strokes of the brush, waving arms, not toes.
    *even the Big century storm on Jupiter is from solar radiation acting on it's thermosphere
     
    Last edited: Feb 3, 2015
  15. OnlyMe Valued Senior Member

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    Nebel, this thread is still in the Science forums. That places the burden of proof or at least credible evidence on you. You have, at least implied that radiation pressure is a significant force on planetary orbits. Since you don't seem to accept any of the counter arguments presented.., do the math yourself, or provide a credible reference, supporting that position.

    No one has denied that radiation pressure exists or that it has some impact on orbits, only that it is insignificant. If you believe otherwise, it is your responsibility to prove your case.

    As it stands, the thread seems to me to have reached a point where it should either be locked or moved to a more appropriate sub forum.
     
  16. origin Trump is the best argument against a democracy. Valued Senior Member

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    9,800
    Fine if that is all you have then I will use my big brush and say the radiative pressure is insignificant and your idea is DOA. No calculations needed.
     
  17. nebel Registered Senior Member

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    The only assertion I made on a significant effect on an earth-size body was that it would counteract an equally small effect that the incoming matter has on the leading, morning side of the orbiting body. The mentioning of the radiation's action on the rotating Earth was only meant as natural example, to a method to be only used on smaller. more efficient vehicles.
    I agree, the insistence on the minutiae would look more appropriate in other classifications, as it is really only a side issue here, after all nobody, has shown that there is NO effect.
     
    Last edited: Feb 3, 2015
  18. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes that effect may exist and as you noted is relative larger for small orbiting object, but of no importance compare to the closely related heating effect of sun light striking the "day side"

    I.e. those photon carry energy in addition to momentum. That energy increases the sun side heating and makes much stronger force via the associated out gassing. (There is name for this process but I forgt it. It is some times offered as a feasible way to steer* and small asteroid in an near earth collision course (some years later) into a safe for earth orbit. Here is a link on the actually measurable orbit changes made by out-gassing:
    http://adsabs.harvard.edu/full/1981A&A....98...45W

    * The CO2 laser (10.6 micron radiations, by memory ? A co-worker in my small APL/JHU group made one.) is quite efficient (near 10% as I recall) and might be directed on the object when not too far from earth. I forget how much loss there would be if earth based. If high, do that CO2 heating from LEO.
     
    Last edited by a moderator: Feb 3, 2015
  19. nebel Registered Senior Member

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    Billy, thank you, and of course there is the physiological side to this, as living beings get exposed to all the radiant energy during the daytime, there is agitation in the evening, cleared by morning.; two totally different feelings. Solar sailing is on a very LIGHT breeze.
    Steer an asteroid by rotating it ! like in the US patent out of St. Louis, No. 4 707 979.
     
    Last edited: Feb 3, 2015
  20. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Nebel, I'm not sure why you haven't done the calculations yet and keep dodging, but if you arent confident that you know how to do them and need someone to help walk you through them, I'd be willing to do that and I expect others would as well.
     
  21. nebel Registered Senior Member

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    Russ, of course, thank you for the offer. Please do. There must be a way to plot the effect from the minuscule on a large body acting over 4 billion years ,--to the overwhelming effect, when on a small dust/gas particle, the diverted radiation pressure overwhelms gravity. That way all readers will learn.
     
  22. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Ok, great. So you've got two different effects. Lets go with the radiation pressure pushing earth away from the sun first, and compare that with the gravitational force pulling earth toward the sun. Now, you can indeed google for how to do this problem. So please get it started and I'll help when you get stuck. You'll need an equation and some input data....
     
  23. nebel Registered Senior Member

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    Russ, believe it or not, I can not send you links, but just googling "radiation pressure" gets you the formulae, Following the "Yarkovsky effect" gets you the translational forces due to rotation. What would be great to see is a plot to see the effect ( on all bodies in the solar realm) giving values for different sizes. This is not a new domain, The data are there for the picking. Corrections are made on conventional size space craft all the time for these effects. It is not new, but it is true. believe them.
     

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