Lemdro.id

2 points

9 months ago

Will you bet me money on how signal mirrors work and how bright the flash is at a certain distance from the mirror?

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TropicalDingdong@lemmy.world

[ - ]

-1 points

9 months ago

I will take a bet from you that the energy arriving at the ISS from a laser pointer you or I could purchase off Amazon, so consumer grade, is more than the energy that would arrive at the ISS from a concave mirror that would be used at a solar generating station.

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[ - ]

3 points

9 months ago

A perfectly flat mirror, exactly like one of the ones in the OP generating station picture. Both are aimed perfectly on target, and the mirror is reflecting light from the sun on a sunny day. With those caveats I’ll bet $1,000. I’m happy with any university physicist or physics professor to be the judge, or Randall Munroe, or make a proposal of some other person if neither of those are acceptable to you. A lower amount of money is also fine if you’re not comfortable with $1,000.

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TropicalDingdong@lemmy.world

[ - ]

0 points

9 months ago

I think the mirror should be a standard one from the Ivanpah Solar power facility. Wikipedia puts them at 7 meters in area. Wikipedia also puts it at 7.4 kWh/m2/day. I think those would be acceptable parameters for you? I think this fits in with the spirit of the bet because these would be the specific parameters taken from the mirrors mentioned in the meme.

Do you have any suggestions for me on parameters to constrain my shopping on Amazon for laser parameters? I said a laser I could purchase on Amazon, so I’m ok with sticking with them as a source. I can buy some pretty damn beefy lasers off Amazon. For example, I can buy a 2000 watt laser on prime right now. Do you want constraints here?

Also, $1000 is out of my price range. I can afford to lose $100. Are you ok with that?

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[ - ]

3 points

9 months ago

Well but the actual mirrors would not work at all because of any number of reasons (among other reasons they can’t track fast enough or precisely enough to actually hit a satellite, and they’re going to have little imperfections in their flatness which will distort the reflected beam away from what the laws of optics say would happen for an idealized situation). The whole actually-shooting-down-satellites thing is clearly a joke; my point was more disagreeing with your description of how the laws work in the idealized situation.

Hmm… I am confident that optically, an idealized flat mirror will reflect a patch of sunbeam that’s more collimated than any human-produced laser at any price. I’m less sure about the actual Ivanpah mirrors but I would guess that they are flat enough to produce a beam that’s more collimated than a standard consumer laser. The thing is that that’s more or less impossible to test… we can ask a physicist about the physical laws, but my guess is that they would be as clueless as I am about how precisely flat the mirrors actually are and of course there’s a lot of wiggle room in how fancy a laser we want to say you can get.

We could ask one of those Youtubers like the ones I linked to if they want to fly a helicopter into the beam from one mirror at a great distance and do measurements of how much the beam had attenuated in practice, but that seems like a great setup to a “what could go wrong” disaster video in the making…

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TropicalDingdong@lemmy.world

[ - ]

0 points

9 months ago

So bet or not dude? Cus you seem like you are backing out.

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[ - ]

3 points

9 months ago

I will bet $1,000 (or $100) that this is wrong:

Lets assume each of the mirrors reflects 850 watts. The distance to the ISS is 408,000 meters.

The energy reflected by one mirror as received by the ISS is subject to the inverse square law (because it is incoherent).

E = (850 watts) / (4pi408000m)^2,, or about 4.06x10 ⁻¹⁰ watts/m²

A 5 milliwatt, off the shelf laser pointer with a beam divergence of 1.5 millirads would deliver approximately 4.25x10^-9 watts/m², or about 10x as much energy as the 850 watt mirror.

You can not melt a spy satellite with mirrors. You might be able to with lasers. A laser will be approximately 8.9x10⁶ times as power effecient at getting light from earth to the ISS as a mirror would be.

And this is right:

E = 850 watts / 149,597,971 km^2 * 149,597,871 km^2 = 849.998864 watts

I will also bet on the behavior of an idealized flat mirror. I won’t bet on whether you can actually shoot down satellites with the Ivanpah solar plant, because there are real-engineering issues that interfere with it aside from the physics of how mirrors and sunlight work.

If you want to try to chart a middle ground, I think it’d be better to talk about something actually testable than trying to argue about the real-world behavior of the Ivanpah mirrors. I’d be happy to bet $100 that:

Take a mirror and find the sun. Send a reflection to the wall nearest you. Then send the reflection to a wall further away. The reflection on the wall further away is larger and therefore, the energy more spread out.

… is wrong, as long as the mirror is flat. This one is easy to test so this might be a better bet.

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