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Comment by MR4D | Hacker News Reader

I wonder how that would look from a feasibility perspective...

Let's see - Earth's radius is 6,378 km.

Area exposed to the sun therefore would be 6,378 * 6,378 * 3.14 = 127,731,695 [1]

If you wanted to block just 1% of the light, that would take a shade of 1 million square kilometers, which would be equivalent to a shade that is 1,130 km on a side.

Seems like it would be tough to do given all the dust and rocks floating around the sun. Also, you're only covering 1%, which is much less than cloud cover.

I'd assume you'd aim to block at the equator since that would have the most direct impact on the intensity of the sun over the course of a year.

[1] - I'm calculating the projection as a flat surface here, so the numbers aren't exact but close enough.

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Interesting. That area would be roughly one million Sunjammers[1]. One Sunjammer is 1200 m^2 and wights 32 kg. To lift all this would be 32 million kg or 32000 tons. One Starship launch is designed for 250 metric tons when expendable so it would take 128 launches. Add in some fudge factor for orbital burns and I figure 150 launches would do it. Doesn't seem insurmountable.

Edit: Seems I misread the Starship capacity. This is probably only to LEO. Its hard to estimate but going by the geostationary payload, it would be one third of that, so triple the amount of flights. At a cadence of 2 launches per week it would take 4.5 years to launch all of it. ( 450 launches / 2 launches per week / 50 weeks a year)

1. https://en.wikipedia.org/wiki/Sunjammer_(spacecraft)

If you are clever with cabling through your shade and launch in the right orbit you can use the Earths magnetic field to keep the things oriented properly. Astronomers would hate you though.

I'd guess it would be far more efficient to launch more of these into regular orbit than trying to assemble them out in L1 and keep them from drifting off, even though you would need to launch at least twice as many for the same amount of coverage.

1 million square kilometers is 1 trillion square meters, or 833 million Sunjammers. It would take 3748 years to launch them at 2 Starship launches per week.

Does it have to be a sheet of material? If all we want to do is shade the earth, we could launch a few million KGs of glitter into low earth orbit or to the Sun-Earth L1.

They would attract each other and clump into a loose ball.

Probably only over thousands or millions of years?

>Seems like it would be tough to do given all the dust and rocks

I wonder if there's a solution that uses the dust and rocks. Maybe you nudge some near-Earth asteroid near L1 and then blow it up or something.

To provide full Sun shade, the shield should be at L1. and it should have the same angular size from Earth as the angular size of the Sun

> and it should have the same angular size from Earth as the angular size of the Sun.

Technically you need a bit more than that, for its umbra to block out the entire photosphere over the entire Earth:

https://en.wikipedia.org/wiki/Tangent_lines_to_circles#Outer...

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