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The big mirror effect

Or why big mirrors are not a good idea...
  (+4, -5)
(+4, -5)
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Jim has noticed that it gets cold every once in a while and figures that this could be fixed with a big mirror in geo-stationary orbit. Said reflective surface will deflect stray nuclear energy whistling past the earth onto the earths surface. As far is Jim is concerned thats about all that needs to be said --- but...

Jim being a realistic soul realises that people that notice him basking in the relative warmth of that little extra nuclear radiation will be jealous. So purely for the social good he figures he could make the mirror really big or move it closer to the nearest source of redundant radiant nuclear waste.

As the deflector moves closer to the sun the angle of deflection will decrease so a mirror will become redundant at some point. A more or less doughnut shapped crystaline deflector at the lagrangian point springs to mind...

Now Jim is not a weathy man so it might be cheaper to whack a mirror up and wait for the social unrest...

madness, Jan 21 2009

Venus 2.0 Venus 2.0
A part of Vernon's terraforming Venus idea describes exactly this, Lagrange points and all. [zen_tom, Jan 21 2009]

[link]






       [+] never thought of using a LaGrange point, cool... would need occasional tweaking of course since we're on an ellipse.
FlyingToaster, Jan 21 2009
  

       Sorry, but I don't really see any difference between this and Vernon's earlier space-mirror based incarnation (Lagrange points and all) so [edit]-[not mfd] redundant.   

       On a side note, in a climate (ho ho) where it's widely thought to be getting rather too warm already, adding more heat is probably not the ideal solution.
zen_tom, Jan 21 2009
  

       [zen_tom] To be honest vernon placed a mirror in orbit and a solar blocker at the lagrange point. As far as I can see he did not mention doughnuts at all...   

       With regards to global warming, controlling the amount of sunlight hitting the earths surface is a different problem to controlling the amount of radiant energy the leaves the earths surface...
madness, Jan 21 2009
  

       [zen_tom], I tend to agree with [madness] on this. Not to mention, from the main description here, it looks to me that the thing he finally puts at the Lagrange point should be called a "lens", however oddly shaped, and not be called a mirror.
Vernon, Jan 21 2009
  

       Well Vernon, I can't argue with that - mfd rescinded.
zen_tom, Jan 21 2009
  

       When you say "langrangian point", [madness], I'm assuming you mean Earth/Sun L1 (there are four others), and not any of the five Earth/moon Langrangian points. (They're interesting, also...)   

       First off, all L1 (and 2 and 3) points are inherently unstable: they need propulsion for anything there to stay put - not counting photonic pressure. (L4s and 5s are stable.)   

       The cool thing is that there is an orbit which orbits all L1s - a Lissajous orbit - which IS stable, and also fits in with your reflecting doughnut (torus) idea. (A Lissajous orbit is on a plane at right angles to both orbiting bodies in the "three-body" problem: in this case Earth, Sun, mirror.)   

       If the centerline of the large, truncated, reflecting cone (as you posited) were exactly on the Lissajous orbit, it would be stable. (To counteract collapse from it's own mass, it should be spinning...) But the incident/reflective angle, I suspect (and as you mentioned), would still be near 180 degrees; a waste of effort.   

       [Vernon]'s mention of an (giant, spinning) lens at L1 (Earth/Sun) might be a better idea if your main aim is just to divert more sunlight to Earth.   

       Also, your initial premise - a reflecting mirror at geo-stationary orbit - might not be optimum for lighting Earth. It would need constant thrust to change attitude relative to the Sun and Earth. (If you only wanted to light the back/dark side of Earth, had a two-sided mirror, and the mirror only revolved once on it's axis every two days - it still would not exactly track the same spot on Earth without powered adjustment - but pretty close! Credit: Galileo Galilei.)   

       Probably, a better idea would be the *baked* polar-orbiting Solar Power Satellite (SPS) idea. No need to turn it: it always faces the sun. No need to filter high-energy UV rays (that's like throwing away $$$). Energy could be intermittently beamed down to Earth as microwaves to rectennas and converted to electricity at ~90% effeciency. It could light anywhere, not just one spot...   

       [+] For sincerity of vision and making me think...
Wily Peyote, Jan 21 2009
  

       I was hoping this would be an affectation reminiscent of Mary Poppins involving a big mirror.
bungston, Jan 21 2009
  

       Hmmm, cool, its been so long since a saw the word sincerity I had to look it up on google...   

       To be honest I have not done the math but understood that L1 was stable for masses sufficiently small compared to the sun and the earth. And as I understand it there is a little bit of kit already there casting a tiny shadow on the earth and sending back details on how hot it is...   

       Anyway... taking your comments on board, a suspect that the stability of a Lissajous orbit will be a function of mass and velocity so --- a rotating fixed angle deflector of suitable mass and velocity would divert extra sunlight toward the earth and not require orbital correction.   

       However, if as you say, lights angle of incidence at the Lissajous orbit is already 180 degrees the amount of light deflected will be negliable compared to that collected by the surface area of the earth already exposed to the sun. As will be the light collected by a polar orbiting satellite --- so both a waste of effort...   

       To increase the effectiveness of a solar deflector it needs to be close enough to the sun that it collects relatively more energy (per square whatever) compared to the surface of the earth.   

       I am not sure if it will be more "effective" to defuse the energy across the planet or concentrate it at one point...
madness, Jan 22 2009
  

       Obviously any orbiting reflector will act as a solar sail and be pushed out of orbit; by the same token, the solar sail effect could hypothetically be controlled and used to correct for drift.
spidermother, Jan 27 2009
  

       //to defuse the energy //
sp. "diffuse"?
coprocephalous, Jan 27 2009
  

       [Spidermother] really... your saying that (at close orbit) the suns light/radiation outweighs the suns gravity. (Thats not the case by the way.)   

       Yip it should be diffuse --- but I figure concentrating the solar energy is the way to go. The solar collector should be a massive laser crystal in close orbit that concentrates solar energy and beams it back to earth...   

       Anyone care to calculate how big it needs to be to collect the same amount of energy currently hitting the earths surface...?
madness, Jan 28 2009
  
      
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