Giant, remotely alterable mirror in space

[woolyhead 15]

What about the idea of building a gigantic mirror in space to reflect unwanted sunlight into deep space and reduce global warming or shine it where it's needed, eg for better crop growing? I haven't heard anyone's idea about the practicality or cost or usefulness of this. Any comments, anyone?

[Ghozer 112]

It would take years to build (would have to be shipped up piece by piece like the ISS was) and would cost a fortune, it would need to be the largest man made structure to date to be effective!

 

The radius of the earth is approx 3958.75587 miles - it would need to be AT LEAST 1/2 this size (so approx 2000 miles) to be effective, to the point of being able to reflect the sunlight to specific places on the earth..

[woolyhead 15]

It would take years to build (would have to be shipped up piece by piece like the ISS was) and would cost a fortune, it would need to be the largest man made structure to date to be effective!

 

The radius of the earth is approx 3958.75587 miles - it would need to be AT LEAST 1/2 this size (so approx 2000 miles) to be effective, to the point of being able to reflect the sunlight to specific places on the earth..

 

Yes, I realise that it would be big and expensive and slow to build but aren't the earth's people worth it? Because the data about the global warming question gives such a marginal answer do you really think the mirror would have to be so big? Wouldn't a smaller one do? What minimum temperature reduction would be needed to call the project a success, do you think? We get sunlight for 24 hours a day and we seem to need about 2 degrees C less, or so I've heard, so how much less sunlight would do the job? What heats the earth now? Is it mainly radioactivity from deep down inside or sunlight? If sunlight then a 2 deg C reduction should be possible on a pro rata basis, shouldn't it? Half the earth's diameter means a quarter the area so a quarter of the sunlight falls, so the temperature may fall too far. If the average surface temperature is 30 degC, ie 303 deg absolute, a reduction of 2 deg is only 0.66 %. Isn't that the way to work it out? Or should I allow for the constant due to radioactive heating? In that case the area of the mirror would need to be slightly bigger to achieve 2 dec less heating, but not a lot. One observation is that the sun is so big that ANY mirror would seem small compared to the apparant size of the sun's disc. Sunlight pressure on the mirror is another factor. Where would we park to mirror, in earth orbit, geostationary or moving?

Edited October 7, 2013 by woolyhead

[Dardandec 32]

It would be impossible to build, would cost a fortune to make (Probably not enough money on earth) type money, would have to be engineered without a single measurement or anything slightly out. Also what if it went wrong and sent us into a man made ice age?

[Ghostrider 11]

Already been done...but James Bond blew it up

[Alky 10]

Was also done in Highlander II I think.....

[woolyhead 15]

It would be impossible to build, would cost a fortune to make (Probably not enough money on earth) type money, would have to be engineered without a single measurement or anything slightly out. Also what if it went wrong and sent us into a man made ice age?

 

Get James Bond to blow it up?

 

---------- Post added 08-10-2013 at 17:48 ----------

 

Was also done in Highlander II I think.....

 

So why not do it for real?

 

---------- Post added 08-10-2013 at 18:16 ----------

 

It would be impossible to build, would cost a fortune to make (Probably not enough money on earth) type money, would have to be engineered without a single measurement or anything slightly out. Also what if it went wrong and sent us into a man made ice age?

 

Better than a man made heat death, anyway? About accuracy, the idea is to make it remotely alterable so small mirror-pointing errors can be adjusted out. How much would it cost? More than Mir (or however you spell it)? Why impossible to build? Man built Mir so why not a mirror? I imagine using a flattish mirror, not one with a tight curvature specification like a telescope mirror has. A simple aluminium framework and it all assembles from identical pieces. To keep it in place despite sunlight pressure could we place it slightly sunward of the L1 point where the pull from the sun balances the pull from the earth? Small ion rockets could perhaps make up for tiny errors in position, powered by sunlight. The whole thing controlled by computers (in lead boxes to block out dangerous solar radiation if necessary? Not sure about this. Does cosmic radiation penetrate say 20 mm of lead?). Why might it go catastrophically wrong? What failure mode? My rough calculation suggests that a mirror diameter of 2000 miles is unecessarily big. It comes down to which temperature we would be trying to reduce by 2 deg C. 30 deg C is 303 deg absolute and most of this would be needed for keeping us alive. A reduction of 2 deg C represents 200/303 %, which wouln't need such a big mirror, maybe 140 miles diameter?

Edited October 11, 2013 by woolyhead

[speleo1 10]

what about shining it down on great britain,we could do with it

[Obelix 11]

It would take years to build (would have to be shipped up piece by piece like the ISS was) and would cost a fortune, it would need to be the largest man made structure to date to be effective!

 

The radius of the earth is approx 3958.75587 miles - it would need to be AT LEAST 1/2 this size (so approx 2000 miles) to be effective, to the point of being able to reflect the sunlight to specific places on the earth..

 

It would need to be much larger than that - if you want to to cover the daylight side of the earth then you have to put it on the inner LaGrange point for it to remain over the dayside. If you want it in a geosynchronous position they you need a whole string of them round the equator and you might just as well say stuff it and build a full on space elevator...

 

Alos if you reflect the light away that'll have a big impact on food production - photosynthesis needs light and if you turn that off..

[dosxuk 10]

Firstly, a reduction of 2°C from 303°K is 301°K.

 

Secondly, this is madness. Yes, we built Mir, a few tens of metres long, yes we the IIS, just over a hundred metres long. You're talking about building something hundreds of thousands of metres across.

 

Finally, when we have a solar eclipse, how much does effect does it have on the planet?

[woolyhead 15]

what about shining it down on great britain,we could do with it

 

Good idea!

 

---------- Post added 08-10-2013 at 19:30 ----------

 

It would need to be much larger than that - if you want to to cover the daylight side of the earth then you have to put it on the inner LaGrange point for it to remain over the dayside. If you want it in a geosynchronous position they you need a whole string of them round the equator and you might just as well say stuff it and build a full on space elevator...

 

Alos if you reflect the light away that'll have a big impact on food production - photosynthesis needs light and if you turn that off..

 

I'm not talking about putting the entire dayside surface of the earth in darkness for very long. A 2 deg C temp reduction would be produces by a small percent reduction in the average sun light falling (all over?) the surface. Or that surface could be the desert areas, maybe. It need not be for all the day. Carbon dioxide levels are going up so that would help food production.

 

---------- Post added 08-10-2013 at 20:06 ----------

 

Firstly, a reduction of 2°C from 303°K is 301°K.

 

Secondly, this is madness. Yes, we built Mir, a few tens of metres long, yes we the IIS, just over a hundred metres long. You're talking about building something hundreds of thousands of metres across.

 

Finally, when we have a solar eclipse, how much does effect does it have on the planet?

 

What's the difference in principle between building over 100 metres and say 140 miles? It just takes longer and costs more. Yes, as you say, 303K - 2C = 301K What's your point? I assumed a surface average of 30C as being what we've got now and went for a 2C reduction target. If my 30C is wrong, no matter. Just use the correct figure instead. My point remains the same. If the 303 comes from -273 plus the result of heating that we have always had ie taking us to 30C, it gives us, say 303K (30C). To reduce this by 2C we have to reduce the sun's heating in the proportion that does so. I assumed that sun heat is proportional to temperature over the temp range in question. So since 2C is 200/303 % required reduction, then the sun heat falling on us needs to be reduced in the same proportion. That's how I arrived at the 140 miles diameter mirror at a distance of 172 miles. Looking back, I see that these figures were in error. The relative L1 point is at 1.5 million miles so the mirror would have to be in earth orbit instead of at the L1 point. That would automatically share the shading effect ocross the earth's surface. But it will also increase the amount of shading needed per pass so the mirror would have to increase, say to 202 miles. depending on the geometry involved. OK it may have to go up to 300 miles but so what. With the right design, access gangways can be designed to lie between the mirror segments and the whole structure can be modular. Just go on adding more panels.

Where did I go wrong? How do you mean what about solar eclipse? Are you saying that it doesn't reduce our temperature therefore the mirror will be ineffective? I don't know the answer, do you? But the solar eclipse moves across the earth and where it hits, it must reduce the temp slightly, surely.

Edited October 11, 2013 by woolyhead

[Guest]

What next? Are you going suggest a giant toupee to cover up the holes in the ozone layer?