cross-posted from: https://lemmy.world/post/19446697
This right here. Never mind the dystopian Mr. Burns style subscription based sunlight control bullshit thatâs inherent to the very idea. Thatâs just to sucker in the investors who wonât know any better. Not enough people are talking about this.
I guess they could try to put the thing into some kind of geosynchronous orbit, but essentially the surface area of their mirrors will have to be equivalent to the area on the ground they plan to illuminate in order to achieve âsunlightâ levels of illumination. Thereâs no way around that. So motherfuckers are going to start spouting off about âparabolic dishesâ and âlensesâ and shit any minute now. This is a red herring. No amount of optics can overcome the fact that the amount of light you can reflect will never be more than the amount of light that hits the mirror. Period. You cannot, now or ever, defy the laws of physics.
The International Space Station is basically the biggest thing weâve ever managed to permanently put into orbit, yeah? And you can barely see it with the naked eye in the night sky, let alone measure any meaningful amount of light reflected off of it hitting any square inch of ground anywhere, with any instrument you can come up with. And itâs covered in reflective shit already â in fact, most manmade orbital objects are, in order to prevent the direct sunlight baking the fuck out of them in the vacuum of space where they canât rely on the atmosphere to carry the heat away.
At best, even if they manage to deploy a massive Mylar foldable mirror in orbit thatâs hundreds of feet across, theyâre only going to be able to light up a small patch of dirt like wussy old moonlight, and even then theyâll only be able to do it in one place. Adding more targets will by necessity divide the light output in a linear fashion even if they somehow make it work like a huge DLP mirror array.
This simply canât work.
Itâs certainly a stupid idea if your trying to illuminate at the suns level, but if you wanted an area to have permanent moonlight? Not so unreasonable.
The moon is 400,000 times dimmer, so 1km^2 of mirror, which is ridiculous, could illuminate an area the size of Germany.
New York metro area is 12,000km^2, which would only need a mirror 173m on each side.
Actually might not be a bad tourist attraction for a crazy city, permanent artificial moonlight.
Some calculations:
In a 1000km orbit, youâll need a mirror about 9km across to appear 0.5° in diameter from the ground (the same size as the Sun), and therefore light up an area with the same illumination as the Sun.
Note that you canât make due with a smaller mirror focused to a tighter area, as the brightest thing the mirror can reflect is the Sun, and so it must appear at least as large as the Sun in the sky to illuminate any point on the ground by the same amount.
With the much dimmer goal of moonlight illumination levels, the mirror shrinks to 9km / sqrt(400,000) = 14.2m in diameter, which is actually rather reasonable. However it would only illuminate an area 0.5° wide from the mirrorâs point of view, or around 9km. And because the mirror is orbiting at 7.4km/s, youâd only get a second or two of illumination.
TLDR: Moonlight mirror 14m across, could light up a 9km diameter area for a little over a second.
Edit: In the case of a permanent mirror in geostationary orbit, a 500m mirror could provide moonlight illumination to an area around 300km in diameter.
While it would be cool for it to appear the size of the moon, it is not necessary with a shaped mirror.
You can keep the same size in a higher orbit, maybe even geosynchronous, then sync the rotation of the mirror to keep it pointing in the same spot on earth.
Granted a shaped mirror that size would be much harder to put into orbit than a flat mirror.
Granted, but if moonlight level is all you want I can already illuminate my surroundings to that benchmark with the flashlight in my pocket. We donât need to park shit in space to accomplish that. And as a matter of fact, we already tried the âilluminate the entire town like the moonâ model in the past as well. It turned out that even on a terrestrial scale it wasnât actually a great idea because, you know, people in the vicinity who want to maybe turn it off⌠canât. (Except in the latter case, maybe with the aid of a rifle.)
I am positive this is just an investor scam of some kind. If anyone is actually stupid enough to launch anything towards this end, itâs a mathematical certainty that they will be murdered in the street by either an amateur astronomer or a chiropterologist. Itâll be a toss-up who gets to him first.
