Comment on Controversial startup's plan to 'sell sunlight' using giant mirrors in space would be 'catastrophic' and 'horrifying,' astronomers warn

• 5too@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

  Thanks for the write up!

  I’m curious how strong an effect atmospheric scattering would have, even after all that!

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  • dual_sport_dork@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    The same a what the sun already has to deal with, really. If your reflection and focus were somehow 100% perfect (impossible, but maybe you could get close) then attenuation from the atmosphere would be the same as what happens to ordinary sunlight over the same surface area, since that also has to pass through the same amount of atmosphere.

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    • 5too@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      Right, but in the daytime, the portion of sunlight that is scattered on the way through the atmosphere to a given spot is partially made up for by sunlight that was scattered to that spot away from other areas, which wouldn’t happen under this scheme.

      I’m curious how much scattering occurs - I have no idea how to find or model that.

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      • dual_sport_dork@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

        Oh, yeah. If you’re very close to the horizon and reflecting light that’s already plowed through most of the atmosphere at a very shallow angle. Tons, I’m sure.

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• toddestan@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

  If I had to build such a system, instead of a few satellites with really big mirrors I’d instead have a massive number of small satellites with smaller mirrors. Obviously then any area I’d want to light up, I’d have to hit with a number of the satellites - probably dozens at least or even hundreds of them for decent sized area. That would at least alleviate a few of the problems - aiming would be easier. As satellites move out of range new satellites would be moving in range. Long shadows from the angle of satellite near the edge of their range wouldn’t be as much of a problem as I’d be hitting any spot from a variety of angles. That the satellites would be useless for about 75% of their orbit I could make up for by launching even more satellites.

  Of course, it would still be hugely impractical and there would still be major limitations. I’m still not sure how you could manage the aiming - the satellites would have to be continuously adjusting their aim to track their target. Reaction wheels can only do so much and using thrusters you’d burn through propellant like crazy. Launching the required array of satellites would be outrageously expensive and you’d need thousands of them. Eventually something would go wrong - you’d have a collision or one would break up and you’d Kessler yourself right out of business.

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• Womble@piefed.world ⁨3⁩ ⁨weeks⁩ ago

  Your point about poinitng (ha!) is incorrect, its pretty trivial to maintain pointing at the target. Hubble achived 7mas pointing accuracy over extended periods (thats ~0.000002degrees) with technology more than 30 years out of date. That gives you ~1.2m accuracy from geostationary orbit, which seems fine.

  The real point is getting a mirror which is large enough and perfect enough into orbit is completely infeasible. As you rightly say, the maximum potential power it can provide is equal to solar insolation time its area.

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  • cynar@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    The aiming is still a problem. The Hubble is relatively small. Even then, it can’t track fast enough to image the moon, let alone the earth’s surface.

    Any useful reflector would be measured in Km^2 . Aiming that, with the same precision as Hubble would be a tall order. Added to that, the mirror would have to be light enough to launch. You’re basically trying to aim a sheet of tinfoil, as large as a stadium (minimum), with active tracking.

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    • dual_sport_dork@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      The Hubble is also in a rather low Earth orbit (340-ish miles), which enables it to use magnetic brakes which allow it to ditch the excess energy from its reaction wheels into the Earth’s magnetic field so it can stop pivoting when it aims. The further away you get from the planet the less effective that becomes. The bigger your object is, the bigger your reaction mass needs to be.

      And the Hubble doesn’t inherently roast or blind innocent bystanders as it swings its point of aim across all of the intervening space between its targets. Maintaining a steady shine on one particular point on the surface is one thing, but these idiots seem to be implying that they will sell sunlight-as-a-service via some kind of subscription model to multiple customers, so they would presumably be changing targets all the time.

      The amount of time it takes for it to get on a target is broadly irrelevant, only that it can keep itself there once it eventually achieves targeting. This would not be so with the hypothetical solar reflectors, regardless of what altitude they were flown at.

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• Alcoholicorn@mander.xyz ⁨3⁩ ⁨weeks⁩ ago

  What about Lagrange points? If the JWST can focus on a target millions of LY away, surely a few giant mirrors could focus on a reasonably small section of earth.

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  • dual_sport_dork@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    Even if they could, the L1 point would be directly centered between the Sun and Earth on the already illuminated side of the planet, which is obviously not helpful. The L2 point would be on the other side of the Earth, on its dark side, and completely within its shadow so also not helpful.

    From the L4/L5 points you would not only be rather far away but also only able to hit areas pretty close to the dusk line anyhow.

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