A Real Icarus

[Johnny Pneumatic]

The creation of this thread is motivated by the Icarus thread at BAB. On said thread I was made aware that the mirror would have to be about 10km in diameter instead of a few hundred feet like you see in that awful Die Another Day Bond film to do what it does in said film. So this is not the point of this thread. I want to know what if we had the technology to create a 10,000km mirror and place it in solar orbit in the same orbital path as the Earth, just a few million km ahead of us. This mirror could be flat for reflecting light upon one side of the Earth for a perpetual day. Or the nanotech smart matter on the non-reflective side could warp the entire flat mirror into a parabola of a desired dip level or whatever the word is; it can vary where the focal point is. Great for melting cities down, maybe; could the focal length even work out from that far away?
Anyway I think it would be really cool if my Thebannese had several of these kind of mirrors orbiting Thebann thus making it an even better plant growing world than its already Cretaceous -like climate. People who know much more than I please come to my aid.

[Dilb]

Well, if we assume that the mirror is mostly 2mm thick glass with a thin/negligible coating of metal, that would be 4.08*10^14 kg of glass. Moving that much from earths surface to a geosynchronous orbit, assuming $10000 per kg, as I think that's what the shuttle costs, would make for $408000 trillion dollars, an utterly rediculous amount.

Looking at energy, moving that much from the earths surface would take 1.4*10^20 Joules of energy. Assuming this occurs constantly over 10 years, that represents 443 gigawatts. The USA electical net summer generating capacity is 905 gigawatts, so if we assume a constant conversion of electrical energy to gravitational potential, it would take a almost 5 years of using all of the USA's electricity to move that into space. I'm not sure what a more realistic conversion factor is, but I'd think it's well below 1%, so essentially it would take a metric boatload of power. An entire planet, with nuclear energy and a fanatical dedication to it could do it as a monumental undertaking over several hundred years, maybe faster if space elevators are possible and really really good, or if some technology makes it much much simpler to get things into space (mass drivers, maybe).

However, no way is any politician going to launch such a project so that farmers can work more. If they can build a mirror like that, I'd say they're far beyond considering ecology as anything other than a hobby.

Of course, it might be much easier to get it from a moon or asteroids, what with the much smaller gravitational well, so most of the above probably wouldn't matter anyway.

As for a parabolic death ray, it seems to me it would be way easier to do it, since you would make smaller angles from far away. At the edge, you'd be 5 km away from the centre, but 35 km away from the surface of the earth, so you'd only need to get an 8 degree curve. I'd consider it one of your smallest problems, at 5 km I'm pretty sure most materials could elasticly bend to that without much force. I think it would be more of a spherical curve though, since the sun's rays should be pretty much parallel by the time you get out to a planet.

As always, I could be entirely wrong about the above, but I did actually learn stuff like this in physics.

[espritch]

I don't know much about the practicality of building such a thing, but I have played with the idea that some kind of big reflectors could be set up in orbit around Mars to increase the amount of sun light hitting it's surface in order to warm it up as part of a terraforming scheme.

[geni]

I've run across some mentions of soviet experments in this area and there was a definte failed experiment in 1999 (the Znamya space mirror). There are also some mentions of the nazis thinking about using space mirrors a weapons. As a weapon it wouldn't be much use since it would be a pain to aim it and a simple lasser with some solar pannels and big big capactors would work much better

[Johnny Pneumatic]

Originally posted by Dilb
Well, if we assume that the mirror is mostly 2mm thick glass with a thin/negligible coating of metal, that would be 4.08*10^14 kg of glass. Moving that much from earths surface to a geosynchronous orbit, assuming $10000 per kg, as I think that's what the shuttle costs, would make for $408000 trillion dollars, an utterly rediculous amount.

Looking at energy, moving that much from the earths surface would take 1.4*10^20 Joules of energy. Assuming this occurs constantly over 10 years, that represents 443 gigawatts. The USA electical net summer generating capacity is 905 gigawatts, so if we assume a constant conversion of electrical energy to gravitational potential, it would take a almost 5 years of using all of the USA's electricity to move that into space. I'm not sure what a more realistic conversion factor is, but I'd think it's well below 1%, so essentially it would take a metric boatload of power. An entire planet, with nuclear energy and a fanatical dedication to it could do it as a monumental undertaking over several hundred years, maybe faster if space elevators are possible and really really good, or if some technology makes it much much simpler to get things into space (mass drivers, maybe).

However, no way is any politician going to launch such a project so that farmers can work more. If they can build a mirror like that, I'd say they're far beyond considering ecology as anything other than a hobby.

Of course, it might be much easier to get it from a moon or asteroids, what with the much smaller gravitational well, so most of the above probably wouldn't matter anyway.

As for a parabolic death ray, it seems to me it would be way easier to do it, since you would make smaller angles from far away. At the edge, you'd be 5 km away from the centre, but 35 km away from the surface of the earth, so you'd only need to get an 8 degree curve. I'd consider it one of your smallest problems, at 5 km I'm pretty sure most materials could elasticly bend to that without much force. I think it would be more of a spherical curve though, since the sun's rays should be pretty much parallel by the time you get out to a planet.

As always, I could be entirely wrong about the above, but I did actually learn stuff like this in physics.

You are right if it was a glass mirror. However this is a strawman. Not even a fool would use glass. Mylar. You know that stuff metalic balloons are made of? Actually to be more precise, a future version of mylar like NASA is working on that will only weigh a gram to few grams per square meter.

[Dilb]

Originally posted by SkepticJ
You are right if it was a glass mirror. However this is a strawman. Not even a fool would use glass. Mylar. You know that stuff metalic balloons are made of? Actually to be more precise, a future version of mylar like NASA is working on that will only weigh a gram to few grams per square meter.

True, strawman sounds so harsh though. I was actually just thinking that gold could be used, what with it's amazing malleability.

Assuming 1 gram per square metre, that lowers my numbers by about 5000 times, which still represents a lot of energy. I do wish I had a better estimate of how efficiently you could fling stuff into space, or how well you could get stuff from moons, as this could be trivial compared to problems involved in the construction.
edit-nevermind, first edit was wrong-/edit

Then there are issues like protecting this from anything that happens to come near earth, I'd think it would take one very large beating everytime the planet experiences meteor showers.
These aside, I think it would be possible, I just don't think growing stuff would be an issue for people with the technology to create something so monumental, not to mention the incredible disruption of the ecosystems on a planet. Maybe as a way to edge a planet like mars just above freezing, but for an earthlike planet is seems kinda pointless. And then all the eco-terrorists who don't want a giant death ray pointed at them, it's going to be a hard sell.

[Johnny Pneumatic]

The materials for the mirrror a supposed to come from metal ores in asteroids from their system's asteroid belt. Much lower gravity and ores in huge amounts. Their civilisation is centuries ahead of us in space faring. They don't have eco terrorists either. They haven't made a mess of their planet like we have because they're not as stupid, nearsighted and money grubbing as we. I thought of meteors too. I guess the mirror would be so advanced it can heal tears. My big problem is what keeps it from blowing out of orbit from the solar wind including CMEs?

[Dilb]

Originally posted by SkepticJ
The materials for the mirrror a supposed to come from metal ores in asteroids from their system's asteroid belt. Much lower gravity and ores in huge amounts. Their civilisation is centuries ahead of us in space faring. They don't have eco terrorists either. They haven't made a mess of their planet like we have because they're not as stupid, nearsighted and money grubbing as we. I thought of meteors too. I guess the mirror would be so advanced it can heal tears. My big problem is what keeps it from blowing out of orbit from the solar wind including CMEs?

I really can't begin the calculations, but plopping it at a Lagrange point would let it settle into a larger orbit when it's disturbed, and then a propulsion system ought to be able to slowely re-allign it. Or just make it heavy enough that solar wind isn't an issue. That would also help keep the mirror from tearing anytime anything comes near it. Google "thin foils" for an idea of how delicate things are at that size, the company making foils around that density (or even lower, actually) dosn't make them larger than 20x20 cms, and cautions against any moving air at all.

But I still don't quite get why they want to heat a planet up on purpose, which would make a mess of things at first. Earth can barely handle a few degrees without a mass extinction or two, what makes it such a great idea for this planet?