Giant, remotely alterable mirror in space

[Dardandec 32]

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

 

Naah, he's working on a massive umbrella system to prevent flooding

[steroc 10]

No need to worry people. They banned pearl lightbulbs, we're all safe now.

[woolyhead 15]

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

 

Very good.

 

---------- Post added 09-10-2013 at 19:40 ----------

 

Naah, he's working on a massive umbrella system to prevent flooding

 

Very good. Would you like to make a donation to the mirror in space project?

[Guest]

It's clear that you don't understand basic physics, astronomy, mathematics, economics or even reality if you think this is a sensible project.

[fake 10]

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

 

Russia has already tried it:

 

http://en.wikipedia.org/wiki/Znamya_(space_mirror)

[Cyclone 10]

It's clear that you don't understand basic physics, astronomy, mathematics, economics or even reality if you think this is a sensible project.

 

What problems exist from a physical, mathematical or astronomical view? (I fail to see how astronomy is even involved).

 

Economically it would be a massive undertaking given current technology though.

 

Here's a thought though, why put it in space? Building it on the floor would be much cheaper and nearly as effective. 300 mile radius mirror floating in the ocean on the equator... Or, multiple smaller mirrors strung out along the equator.

[steroc 10]

Here's a thought though, why put it in space? Building it on the floor would be much cheaper and nearly as effective. 300 mile radius mirror floating in the ocean on the equator... Or, multiple smaller mirrors strung out along the equator.

 

Not that I think this giant mirror is in the slightest feasible or even needed but how would putting it in the sea prevent the earths atmosphere heating up from the suns rays. If anything it would reflect what's normally absorbed by the sea back onto the atmosphere making it warmer. The suns rays would effectively be passing through the atmosphere twice.

[Cyclone 10]

We're talking about the earth, not just the atmosphere of the earth.

 

The way the atmosphere warms though is mainly through incident radiation being absorbed by the ground/sea and re-emitted at a shorter wavelength.

 

Reflect it with minimal absorption and it will simply pass back out in to space again.

 

Passing through is exactly right, they wouldn't stop and they wouldn't impart (much) energy to our system.

[steroc 10]

We're talking about the earth, not just the atmosphere of the earth.

 

The way the atmosphere warms though is mainly through incident radiation being absorbed by the ground/sea and re-emitted at a shorter wavelength.

 

Reflect it with minimal absorption and it will simply pass back out in to space again.

 

Passing through is exactly right, they wouldn't stop and they wouldn't impart (much) energy to our system.

 

See I thought the whole argument for global warning was that greenhouse gases are trapping heat in in atmosphere, allowing it in but not back out much like a greenhouse (hence the name). Explain why there is such a huge difference in temperature with altitude if the atmosphere has very little effect please.

[woolyhead 15]

It's clear that you don't understand basic physics, astronomy, mathematics, economics or even reality if you think this is a sensible project.

 

You could be right but in the early 2000s Lowell Wood of NASA suggested an 800 mile by 800 mile reflector be put at the L1 point to reduce earth's temp by 3 deg C. The cost was projected at 26 times the then US national debt. Technology has moved on since then. What I was discussing here was a much smaller mirror in orbit round the earth and much closer to it, giving the same effect. Like the L1 mirror it would interfere with emissions from early warning systems which are already at L1 and building/maintaining and putting the mirror in place would cost a packet but not as much as the L1 positioning would, being a lot smaller and easier to reach. If you don't believe about the sense in using giant mirrors, Google up "Giant mirrors in space to reduce global warming." Several eminent people have made similar suggestions. Perhaps you think they too are ignorant?

 

---------- Post added 10-10-2013 at 18:39 ----------

 

Russia has already tried it:

 

http://en.wikipedia.org/wiki/Znamya_(space_mirror)

 

I tried looking up this web page and was told "we haven't got this."

 

---------- Post added 10-10-2013 at 18:52 ----------

 

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..

 

There's something in what you say. I changed my mind about using tne L1 point because the mirror has to be so big if it's put there. But by putting it much closer to the earth than the L1 point (1.5 million miles) the angle subtended by it at the earth is bigger and a smaller mirror can be used. With a moving orbit (not geostationary) the shade would dissappear so the mirror would have to be bigger than I suggested originally. But I maintain that the reduction of 3 deg C can be obtained with a 27/7 shading of 1 % of the angle subtended by the sun. I reckon this part is just geometry. However, since the shade dissappears as the mirror goes behind the earth, putting earth between itself and the sun, a bigger mirror than my original estimate gave would be necessary, perhaps as much as three to four times, making it up to 560 miles in diameter. One of the people at NASA who has been studying this problem for 20 years thinks that a circular mirror of 800 miles by 800 miles would be just big enough (see Wikepedia in "Giant mirrors in space to reduce global warming?"). I don't understand his thinking myself. Seems far too big to me but who am I to disagree with a NASA scientist? Maybe it depends on how high its orbit is.

Edited October 11, 2013 by woolyhead

[Obelix 11]

Good idea!

 

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

 

 

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 ----------

 

 

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. 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.

 

Photosynthesis is constrained by energy, not CO2 availabilty...

 

Something that size in low earth orbit is going to be subject to massive tidal forces if it twitches just a little bit out of orbit. At 172 miles up there is a massive amount of drag as well which means it'll need constant boosting.

 

Assume something of 140 miles across is casting a shadow on an area 8000 miles across. The difference in size is the square of the diameters so 19600:64000000 that's about 1:3300. That's the total amount of energy you intercept, but it's only in the way of the sun for at most half the time in it's orbit so it's 1:6600 of the incident energy captured... that's going to be a 20th of a degree K assuming it's a linear relation.

[Cyclone 10]

See I thought the whole argument for global warning was that greenhouse gases are trapping heat in in atmosphere, allowing it in but not back out much like a greenhouse (hence the name). Explain why there is such a huge difference in temperature with altitude if the atmosphere has very little effect please.

 

You are correct about the argument re:CO2, but it acts on short wave radiation. If it acted on long wave radiation then it would stop the suns heat from entering the atmosphere in the first place.

What it actually does though is stop heat that is re radiated from the ground in the infra red from leaving.

 

It gets colder as you ascend because air pressure drops. It's nothing to do with the greenhouse affect though.

 

---------- Post added 10-10-2013 at 20:37 ----------

 

Obelix: you're obviously feeling more like doing maths tonight than me.

 

What area of mirror would we require to float/place on the equator to achieve the desired 2k drop?