• lazynooblet@lazysoci.alEnglish
    61·
    2 days ago

    Imagine lying in bed trying to sleep and suddenly it’s daylight because your neighbour ordered sunlight on Uber.

  • AmbitiousProcess (they/them)@piefed.socialEnglish
    931·
    2 days ago

    Tech bros will always choose the most overcomplicated option over the simplest, most effective ones.

    Why build a battery and just install some more solar panels to charge it during the day when you could have a mirror in orbit beam down a tiny fraction of the light required to generate power anywhere near regular daytime capacity, for only a small portion of the night before the satellite is out of range, in only a small area, in a manner that can only work for one single client per satellite at a time, meaning it gets less cost effective at scale?

  • dual_sport_dork 🐧🗡️@lemmy.worldEnglish
    541·
    3 days ago

    These morons are still around? Didn’t we thoroughly deal with them the last time their press release made the rounds which was, what, about a year ago?

    Don’t get too worked up about it. What they’re proposing is physically impossible for a myriad of reasons, which anybody who didn’t flunk their 10th grade science class would be able to tell you. Once they run out of investors to grift we’ll never hear from them again.

    There’s no loss here other than the waste of money, effort, and rocket fuel.

    • LostXOR@fedia.io
      31·
      3 days ago

      To get daylight illumination on even a small area from a 600km orbit you’d need about 20 km² of reflectors. Which is obviously absurd.

      • hobovision@mander.xyzEnglish
        5·
        2 days ago

        What is the physics or math behind that? Light from the sun is essentially aligned by the time it reaches earth. If the mirror is perfectly reflective, a 10 m^2 mirror should light up a patch of Earth roughly 10 m^2 times the cosine of the angle of the mirror. So unless the angle is close to 90°, most of the losses would be from poor reflectivity.

        I totally agree it’s a stupid idea. But maybe it’s even worse than I am thinking of?

        • LostXOR@fedia.io
          12·
          2 days ago

          The Sun has an angular diameter of about half a degree viewed from Earth. To light up a location as brightly as the Sun would, you need to cover a half-degree circle in the sky (viewed from that location) with mirrors that reflect the Sun directly at the location. You can’t get away with less because a mirror can’t appear brighter than what it’s reflecting; this is a fundamental property of optical systems.

          A mirror 600km away and 5km in diameter has an angular diameter of arctan(5/600) = 0.48°, close enough to half a degree. It has an area of π(5km/2)² = 19.6km² which is pretty much 20km².

          • exasperation@lemmy.dbzer0.comEnglish
            2·
            14 hours ago

            You can’t get away with less because a mirror can’t appear brighter than what it’s reflecting; this is a fundamental property of optical systems.

            I can understand that a single flat mirror cannot ever appear brighter than whatever is being reflected. But why can’t multiple mirrors pointed at one spot have a total intensity greater than that of any one of the mirrors (or a curved dish that focuses the light)?

            • LostXOR@fedia.io
              1·
              14 hours ago

              Multiple mirrors reflecting sunlight can indeed result in an irradiance greater than that of the Sun (this is how solar power towers work). But to do that, you need to cover more than a 0.5° circle of the sky with mirrors. The total irradiance can be as high as you want (up to covering the whole sky with mirrors, which would be equivalent to standing on the surface of the Sun) but the irradiance per angular area can never be higher than the Sun’s.

              You can think of it as dividing a mirror of any shape into a bunch of flat mirrors. Each mirror can only show you a reflection of part of the Sun (which is exactly as bright as that part of the Sun) but you can have as many mirrors as you want showing the same part of the Sun, multiplying the light you receive from it (up to filling the entire sky once again).

          • davad@lemmy.worldEnglish
            5·
            2 days ago

            To light up a location as brightly as the Sun would, you need to cover a half-degree circle in the sky (viewed from that location) with mirrors that reflect the Sun directly at the location.

            That’s the best, simplest example I’ve seen for why this doesn’t work. But…I wanted to look at it from the perspective of irradiance losses from the beam spreading. It’s been a long time since I did any optics, so I could be way off-base with my approach. Feel free to correct anything I screw up.

            Here are my assumptions:

            1. Near space irradiance from the sun is 1,367 W/m^2 [0]. Let’s round up and assume the mirror gets 1400 W/m^2 from the sun.
            2. We want 1000 W/m^2 on the ground to qualify as daylight [1]
            3. Collimated light
            4. No attenuation or scatter from the atmosphere, but we will assume the beam diameter spreads 0.5 degrees [2]
            5. Perfectly reflective mirror
            6. Mirror 600 km away from the earth

            Beam spreading loss is a function of distance. So however large the beam width (mirror diameter) starts, it’ll be this much bigger when it reaches the ground:

            600km * tan (0.5 degree) = 5.24km

            That means if we have a 1m diameter mirror, we get a beam 5.24km + 1m on the ground. If we have a 5km diameter mirror, we get a 10.24km beam on the ground.

            To get our target of 1000 W/m^2, we need at least 1000/1400 = 0.71 of what hits the mirror to hit our target.

            mirror/(mirror+spread) >= 0.71 mirror >= 12.83km

            [0] https://en.wikipedia.org/wiki/Sunlight#Measurement
[1] Wikipedia says that we actually get more like 1100 W/m^2 when the sun is at its zenith.
[2] https://en.wikipedia.org/wiki/Collimated_beam#Distant_sources
            • LostXOR@fedia.io
              4·
              1 day ago

              I don’t think that’s right. You’re assuming the intensity of the beam is constant over its entire area, which isn’t true. With a 5.24km flat circular mirror*, someone at the center of the beam would see the entire Sun reflected in the mirror and thus get the full solar irradiance. Someone near the edge would see only a small sliver of Sun and get much less.

              *Technically a circular mirror would require the Sun’s light to arrive perpendicular to the mirror surface and reflect directly back, which would mean the Sun is behind the Earth, but that’s beyond the scope of this hypothetical (and can be solved with a suitable ellipse).

    • Rivalarrival@lemmy.todayEnglish
      7·
      2 days ago

      They’re going to shine it on the Solar Freakin’ Roadways so they can keep producing power at night.

  • marcos@lemmy.worldEnglish
    45·
    3 days ago

    Nah, don’t get too worked out over it.

    It can’t be economically viable either, so as soon as that company stops gifting investors out of their money, it will just disappear and the mirror will fall back into Earth.