Question: Suppose humans of the late 21st century or beyond began constructing a solar shield as a solution to climate change. Suppose for some reason (open to suggestions) they choose to build the shield in geosynchronous orbit, rather than at the L1 point. Suppose the shield is opaque, and large enough that it casts a daily eclipse on the Earth's surface. Is this plausible?

If so, how much thrust would be required for the sunshield to maintain its position? Would it be possible to supply that thrust using only solar energy and electric propulsion, via an electrodynamic tether system for example, such that the shield could remain in orbit without ongoing deliveries of chemical propellant?

By my calculations, if the shield was proportional to the moon in terms of eclipse potential, but at the distance of geosynchronous orbit, it would be approximately 340 km in diameter. Without knowing much about the potential progress of materials science in the next century, I assume, even if shield was very thin, the mass of it would make it's construction practical only to a civilization with functional space elevators. But, perhaps astroid mining could also provide the necessary materials without the launch costs.

Answer: 
![enter image description here](https://i.stack.imgur.com/zy8s0.jpg)

Just put these highly reflective obsolete CD's in orbit spaced 6 inches apart, tied to fishing nets and spanned across some sort of frame. Each net could be spanned on its own frame and the distance between nets could be increased and decreased to control temperature
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> Suppose the shield is opaque, and large enough that it casts a daily eclipse on the Earth's surface. Is this plausible?
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Totally.

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> If so, how much thrust would be required for the sunshield to maintain its position?
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That depends on its mass, and how much area it exposes to solar wind.

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> Would it be possible to supply that thrust using only solar energy and electric propulsion, such that the shield could remain in orbit without ongoing deliveries of chemical propellant?
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As far as we know today, probably not. We could maybe push it with lasers, but it would be destroyed in the process.

[RF resonant cavity thrusters](https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster) could maybe do it without propellants, but they are the stuff of sci-fi for now.

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> Without knowing much about the potential progress of materials science in the next century, I assume, even if shield was very thin, the mass of it would make it's construction practical only to a civilization with functional space elevators. But, perhaps astroid mining could also provide the necessary materials without the launch costs.
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Whomever considers asteroids for this is not factoring the delta-v from here to the belt and back. Earth to geosync is in the vicinity of 18 km/s. Earth to the belt and back is double that amount. Notice that you'd be bringing back more mass than you'd have upon reaching the belt, so unless you can convert asteroids into fuel on the fly, you'll have a serious constraint.