Sun shield

[ceetee]

Would it be possible in practice or in theory to put a shield between the earth and sun at the libration point? For the sake of simplicity so it attenuates the power by 1%. I was thinking of some ultra thin reflective film of mylar and aluminium.<br /><br />In case you hadn't guessed this would be an emergency fix to global warming. Something to do while the CO2 declines to a normal level. <br />

 

[vogon13]

Your asking for a shade at the libration point between the sun and earth to intercept 1% of the solar flux destined to hit earth.<br /><br />This object will be (IIRC) about a million miles closer to the sun (and therefore a million miles from earth). Your shade will need to be very large. (don't feel like doing math, but am thinking hundreds of miles across). The solar radiation pressure on this object will be enormous and it will rapidily move the shade off the libration point and you will need some means of keeping it stable.<br /><br />I might throw out an idea:<br /><br />Put the shade material in orbit around the earth. Try for a ~14 day orbit. Incline the orbit ~23 degrees to earth's equator.<br /><br />Shades can be much smaller, station keeping is easier. Lining up the orbit around earth with the apparent path the sun takes through our sky will allow the shade to be of the minimum size possible to do the job. Also, the 14 day orbit should be above most of the satellites we need to keep everything on earth working. The 14 day orbit is still close enough to earth that perturbations from other objects in solar system will be swamped by earths' proximity. Also, we can look at trying for a resonance with the moon that may reduce station keeping requirements.<br /><br />I would also suggest coating the earth facing side of the shade with a very dark substance so sunlight reflecting off the shade over the night time hemisphere of earth is minimized.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[Saiph]

Gregory benford has an office in my physics building. Haven't seen him around yet though. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[taolung]

Pick up this months issue of Popular Science. This sun shade is pictured on the cover, and they talk about it pretty much as you described.<br /><br />The online version of the article is available here:<br /><br />http://www.popsci.com/popsci/aviation/article/0,20967,1075786,00.html

 

[majornature]

impossible to to shield the Earth from the sun... effortless try, but I don't think there's enough aluminium and ultra thin mylar combined to shield the Earth. <div class="Discussion_UserSignature"> <font size="2" color="#14ea50"><strong><font size="1">We are born.  We live.  We experiment.  We rot.  We die.  and the whole process starts all over again!  Imagine That!</font><br /><br /><br /><img id="6e5c6b4c-0657-47dd-9476-1fbb47938264" style="width:176px;height:247px" src="http://sitelife.space.com/ver1.0/Content/images/store/14/4/6e5c6b4c-0657-47dd-9476-1fbb47938264.Large.jpg" alt="blog post photo" width="276" height="440" /><br /></strong></font> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>This object will be (IIRC) about a million miles closer to the sun (and therefore a million miles from earth). Your shade will need to be very large. (don't feel like doing math, but am thinking hundreds of miles across). The solar radiation pressure on this object will be enormous and it will rapidily move the shade off the libration point and you will need some means of keeping it stable. <p><hr /></p></p></blockquote><br /><br />Actually, you'll need some means of keeping it stable anyway. The L1 point is not stable. It is unstable on a period of (IIRC) 28 days. SOHO, which already orbits L1, has to perform regular thruster firings to maintain its position. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[vogon13]

Thanks for pointing that out.<br /><br />Should have emphasized light pressure on such a structure would be orders of magnitude greater than other perturbations. That L point is indeed unstable over longish periods.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>