I am not well versed but my impression is it’s essentially a bunch of tin foil and the main impediment are geopolitical reasons and cost to orbit, which SpaceX has been and continues to improve.
Okay, so having gone down this path I can tell you it is impossible. To reduce the output of the sun by 2% at L1 would require 20 MM tons of metal. In order to launch that much tonnage we would have needed to start launching mass 500 years ago. And that assumes no loss of material over time, which would mean even more launches.
> A more recent design has been proposed by Olivia Borgue and Andreas M. Hein in 2022, proposing a distributed sunshade with a mass on the order of 100,000 tons, composed of ultra-thin polymeric films and SiO2 nanotubes.[7] The author estimated that launching such mass would require 399 yearly launches of a vehicle such as SpaceX Starship for 10 years.[7]
100000 tons is 907184749 kgs and the max capacity of a starliner is 150000kgs. So to launch 100000 tons it would require 6048 launches or one launch a day for 16.5 years.
That would mean we'd have all the mass launched by 2040, if we started today. Nope, not feasible.
That's honestly not all that unfeasible if SpaceX gets Starship reuse down. Assuming we get launch costs down to a few million, it won't even be that expensive relative to the size of the problem. And launches can be parallelized pretty well - just build more launch pads.
The cool thing about reusable rockets is that even for a project like this you're not going to be rocket construction limited. If every rocket can launch 20 times (and that's pessimistic!) you only need to build 300 of them. And say you have ten launch pads, you only need to launch once a week per, to grind through the problem in a decade.
And that's all of course assuming SpaceX don't manage to scale the platform up further, improve cargo capacity etc.
It's a civilizational project, sure, but it wouldn't even be as expensive as the Apollo program.
Thank you for adding some numbers regarding the feasibility of launching the required materials into space. Do you have any thoughts/numbers about how "mining/construction" in-situ in space might affect those outcomes? E.g. Might we soon be able to "recycle" old in-orbit objects (trash/old_sats) into a slowly growing space mirror? Or several smaller ones over (richer/more_affected) areas?
So not really. Space mining is a very attractive idea but just not really feasible at the moment. I wrote a paper on attempting to capture the asteroid 433 Eros (a very attractive asteroid due to it's composition of rare metals [Data from the Near Earth Asteroid Rendezvous spacecraft collected on Eros in December 1998 suggests that it could contain 20 billion tonnes of aluminum and similar amounts of metals that are rare on Earth, such as gold and platinum.]) and found that in order to knock it into an orbit around the moon we'd need something on the order of 1 THOUSAND or 10 THOUSAND (I could be off by even another magnitude, the numbers are fuzzy after all this time) tsar bomba grade weapons to effectively knock it out of the current orbit and back into one around the moon. Why the moon? Because throwing a planet killer sized object at the Earth just didn't seem reasonable.
I situ mining might make this more feasible, but that has all of its own complications. None of which I would feel confident in saying are feasible.
