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For example, I did read about an exploding asteroid at Lagrange Point 1 to block some of the Sun's light. Just two degrees change in Earth's overall temperature can trigger an Ice Ages.

There was a development relevant to this question: "Scientists led by Yoram Rozen, a physics professor and the director of the Asher Space Research Institute at Technion-Israel Institute of Technology, say they are ready to build a prototype shade to show that the idea will work. Prototype shade of 100 square feet at the cost of $ \$10-\$20$ million." nytimes.com

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    $\begingroup$ Downvoting for two reasons: I think an appropriate answer to this question would require an in-depth study (though maybe one already exists that could just be quoted from, who knows), and mentioning a Lagrange point doesn't make the question about Lagrange points so the tag is inappropriate. Tags should indicate what the question is about. $\endgroup$
    – Erin Anne
    Commented Apr 11, 2023 at 0:52
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    $\begingroup$ @uhoh - personally, I would think of semi-translucent inflatables, but my googling did not bring any proposed projects of that kind. $\endgroup$ Commented Apr 11, 2023 at 4:22
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    $\begingroup$ @TheMatrixEquation-balance did not take long to find the relevant wikipedia page with en.wikipedia.org/wiki/Space_sunshade#One_Fresnel_lens. Your questions would have a less drama if you took the time you spent finding pictures that are unrelated and looked up the relevant wikipedia pages and followed the source links. Both to read and to include in your question to show what you already know. Translucent shields are probably not mentioned since in general for the same mass lifted to orbit a fully mirrored structure will block more light. $\endgroup$ Commented Apr 11, 2023 at 8:53
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    $\begingroup$ @TheMatrixEquation-balance funny, it's like we're on a Question and Answer site, not a brainstorming site $\endgroup$
    – Erin Anne
    Commented Apr 11, 2023 at 17:06
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    $\begingroup$ @TheMatrixEquation-balance It's like you are against the most obvious solution to global warming, which is to stop injecting so many greenhouse gases into the atmosphere. There are many very good reasons to avoid geoengineering solutions, particularly so with regard to wackadoodle ideas that will take decades to implement, that have a low chance of working, that cost a lot of money, and that deprive humanity of a key resource in space such as the Sun-Earth L1 area. $\endgroup$ Commented Apr 11, 2023 at 20:35

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Finding price tags for solar shades is tricky, there are two Wikipedia pages on the topic, with various price tags from billions to trillions depending on assumptions, starting with how much heat reduction you feel is 'correct'.

Relevant is that L1 is actually hard to get to and unstable. Any transfer from earth or elsewhere in space will need to use non trivial amounts of thrust to take station there, and some means to keep station against gravity perturbation and the solar wind.

If using reflective sails it is possible to do both by solar sailing taking position slightly away from L1 and using reflected thrust to counter the gravity. This means just blowing up an asteroid passing by pointless since the debris will keep going, and even if pushed into position is problematic since the lighter (and most useful for shade) debris will tend to get blow away while the heavier will hang around endangering any future attempts. Though if you dump enough of that dust and debris into the upper atmosphere you might get a cooling effect.

This paper includes a useful graph

Graph of masses for various sunshields in millions of tons

Showing mass of sunshield in millions of tonnes for various proposals to achieve 1.5% reduction in received sunlight.

This 'millions of tons' mass is the second issue, since it is not just to LEO but to out near earth escape velocity, so sensible costings are even harder. An assumed element of many shade schemes is building and launching from the moon, which can give nicely low 'cost of shade' but involves building a substantial moonbase and rail launch system first.

If launching from earth on Hydrocarbon burning rockets at this scale the 'cost' of the released carbon needs to be factored into final sunshield performance.

The linked paper uses some very ambitious assumptions including gun launch to come up with 0.2% of earth's total wealth per year spread across 50 years.

All of this makes 'cost of a sunshade' pretty broad, from 'what moonbase does with mining waste' to 'more money than exists in the global economy'.

Update based on tweaking of question in terms of lowering cost using an asteroid: The utility of the shade depends mostly on the cross sectional area, with a dust cloud from an exploded asteroid being a mass inefficient sphere - in most cases if you can get an asteroid parked at L1, processing the mass into something approximating a flat sheet will justify the effort of getting the sheet making machine out there.


Link to paper discussing size and position of a solar shade based on discussion in comments. Includes possibility of using slightly sub optimal orbital placement to tweak cooling distribution for possibly more effective total result (or make it into a weapon).

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