• dual_sport_dork 🐧🗡️@lemmy.worldEnglish
    35·
    18 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.

      • hobovision@mander.xyzEnglish
        5·
        17 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?

          • davad@lemmy.worldEnglish
            3·
            17 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
          • exasperation@lemmy.dbzer0.comEnglish
            2·
            16 days 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)?

  • marcos@lemmy.worldEnglish
    26·
    18 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.