California-based startup Reflect Orbital aims to build a swarm of 4,000 giant mirrors in low Earth orbit to “sell sunlight” to customers at night. Experts warn that the mirrors could mess with telescopes, blind stargazers and impact the environment.
Reflect Orbital, which was founded in 2021, has recently taken the first step in a scheme to sell sunlight at night by bouncing solar rays off giant “reflectors” that can redirect the vital resource almost anywhere on our planet. By doing this, the company aims to extend daylight hours in specific locations, thus allowing paying customers to generate solar power, grow crops and replace urban lighting.
But experts say it is a wildly impractical plan that should never get off the ground. What’s more, the resulting light pollution could devastate ground-based astronomy, distract aircraft pilots and even blind stargazers.
I’d like to see that comment if you could link it!
I mean just on the surface of it, this is completely preposterous.
The first thing that comes to mind is you can only cover so much area. 4000 satellites would cover the dog park near me. In the scope of an undertaking like this, it’s a trivial amount of energy they could possibly gather?
That’s the main hurdle.
Re-finding this was a pain in the ass because I didn’t save it. https://lemmy.world/post/19485246/12219336
Editing to add some more meandering. Now this is even longer than the first one.
In addition to surface area limitations, there’s also a pretty obvious line of sight problem in that if your satellite is positioned such that its shiny side is facing the sun, by definition it must be facing the same direction as the Earth’s currently lighted side. The further past the dusk line onto the dark side of the Earth you’re trying to hit the further you have to rotate your mirror until ultimately the surface of it is perpendicular to the incoming sunlight. This is the angle of incidence, in optical terms, and it reduces the effective reflection not only off of the mirror proportionally to the increase in angle (in a roughly geometric manner, I believe) but also where that reflected beam of light hits the ground at its oblique angle. In real terms, it will be impossible to hit any target more than a few degrees past the dusk line with any meaningful amount of energy. Insofar as this harebrained scheme could possibly hit the ground with any amount of energy at all.
The diagram (which is surely not to scale) on these idiots’ website seems to depict a mirror in orbit around the Earth that’s about the size of Massachusetts, which is orbiting at a height that’d put it somewhere in the vicinity of the Van Allen belt, which is also a bad idea (no radio communication for you!) and would result in an orbital period of around 2.5 hours. If so, that means your mirror is whizzing over the surface at something like 14,000 MPH, and you would have some kind of line of sight to it from the ground for maybe 25% of its orbit. So even with the best will in the world and absolutely mathematically perfect rotation control it’ll only be able to remain on a surface target for about 37 minutes at most, most of which would be while it’s uselessly passing through the Earth’s shadow and is reflecting no sunlight at all, and for the remaining handful of minutes with its effective output tapering off to uselessness as it sets over the opposite horizon.
“I’ll just position my mirrors in a geostationary orbit,” says Mr. Clever. “Then I’ll have line of sight to a big chunk of the surface and my satellite won’t move relative to it.”
Well, the further you park your mirrors from the surface, the harder they are to aim. You can’t have it both ways. A geostationary orbit is about 22,000 miles from the surface, a distance from which even the tiniest error in alignment will result in you hitting the wrong target. You can use some middle school trig to calculate this for yourself: At a distance of 22,000 miles, an alignment error of just 0.01 degrees will result in the centerline of your beam missing the target by four miles, which in terrestrial terms is what we refer to as kind of a lot. Maintaining an alignment precision that high especially taking into account gravitational perturbation by the moon, etc., is a rather tall order. To maintain targeting precision within 223 feet, which is probably already unacceptable, you need a constant alignment precision of 0.0001 degrees, and you need to hold it there 100% of the time.
I don’t care how big your rocket is, that’s not happening.
All of this also assumes perfectly flat and 100% reflective surfaces on the mirrors, which never degrades or gets scuffed up or punctured by space debris. Which is also impossible.
To recap:
TL;DR: The whole thing won’t work.
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.
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.
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.
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.
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 the Hubble 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.
Thanks for the write up!
I’m curious how strong an effect atmospheric scattering would have, even after all that
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.
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.
Oh, yeah. Or, 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 before it can hit the mirror satellite, how much attenuation you get from that. Tons, I’m sure.