Reflect Orbital: Sunlight after dark using a constellation of spatial reflectors
44 comments
·February 9, 2025GistNoesis
It boils down to building big surface area mirror cheap enough. Once you prove there is business demand, and you have your cheap Mylar satellites working, you scale your system up with better technology.
Of course they don't reveal their neat trick now because from a strategic point of view it would be bad, because other people would copy them, and probably outpace them.
Once it's only a physics problem, it becomes quite easy. Here are two potential solutions to the physics problem : Liquid mirrors, and plasma mirrors. The easiest being the liquid mirrors so let's explain this one. In fact it's so easy, it's child play.
Have your kids ever played with soap bubble : It's the same thing but in space. You make a big ring (roughly of the same area of the spot you are trying to make on the ground) (thin circular wire that you fold so that it will unfold itself like these tents) and you flow liquid metal (like mercury) on top to form a thin layer, hold by surface tension (and eventually electric field to have finer control of the shape or the surface).
The mirror will be a few atoms thick, a design that must be fabricated in space directly. It's just that we are not used to thinking with low force zero gravity environment. You don't use motors to move your mirror, you use fields spawned from precisely positioned points (and you have to compensate for solar winds).
Of course there are still technological problems due to the harsh conditions of space, but it's not something unheard of : https://engr.ncsu.edu/news/2024/03/06/reflecting-the-future-...
hakonjdjohnsen
> You make a big ring (roughly of the same area of the spot you are trying to make on the ground)
Unfortunately, this is not how the size of the spot on the ground is decided. Sunlight, even if reflected by a perfectly shaped mirror, spreads by approx 1 meter every hundred meters. At the "edge of space" at 100km, your spot already has a 1km diameter, in reality with a higher orbit and imperfect mirror & tracking it will be much larger. The size of your (ideal) mirror decides the brightness of the spot, not the size of the spot.
Liquid mirrors in space seem like a cool concept though!
GistNoesis
The area comment was more relative about the power received : To be able to have the power on the ground you need to reflect it from space (pointing the obvious that with 100sqm of surface area, you can't collect more power than surface area * power density). You also don't want to overheat everything (otherwise you need sun towers instead of solar panels), so a ball park of around 1:1 is a good starting point.
To focus light, the ideal shape is a parabola, and it's a shape that occur naturally when you spin liquid in gravity. (Their are process to build big telescopes which only point up). Of course you don't have gravity anymore, but you can pull on your surface with fields, or you can have concentric rings that you align more or less along the axis to deform the surface. We don't need perfect focus just a rough spot.
sxp
YT video going into the math and physics involved: https://www.youtube.com/watch?v=lkjyeI0ykGM
TL;DW: not practical in it's current design.
danielvf
I did a bunch of my own math on this a while back related to this.
1. On of the big tradeoffs is the sun sync orbit altitude chosen. The higher up you are, the slower you have to tilt to track, the longer time possible on a given customer, and bigger range of possible customers you have as the sat goes around. But, as you are higher, the size of sunlight you send gets bigger and bigger. A 5km by 5km circle is going to waste a lot of energy on not-solar panels all but the largest solar installations. If you double the light radius, you quarter the intensity.
2. Most of the earth is water. Of that land left, most of the land is quite uninhabited. This means that most of your time orbiting is going to be over areas with no paying customers.
3. I think the EEVBLog video overestimates the cost per sat, but I still didn't get the economics to work out to something profitable.
RossBencina
Reflect's website banner announces $6.5 million seed round led by Sequoia.
A few comments here claim to have run the numbers. With negative results. How do seed rounds with name-brand VC work? Please tell me an independent party would have been paid to do due diligence on the feasibility of the approach. Or is this perhaps an investment in the team with an openness to pivot.
bagels
For 6.5M round? Very unlikely it was more than financial models and pitch decks.
moralestapia
The pivot will likely be space ads ... ugh.
cebert
I’m curious to know the effects of beaming additional solar energy to Earth on climate change. I can’t imagine it’d be good.
goku12
Unlikely to have any effect on the scale they describe. The first part of the power balance of our planet is the solar radiation that is intercepted by the surface of Earth. The theoretical maximum additional power added to it by these sats is going to be equivalent to the solar radiation intercepted by their mirrors. Guess how much bigger the surface of Earth is compared to those mirrors.
One important thing to note is that the climate change is not caused by the heat we released into the atmosphere. It's due to the change in the power equilibrium of the Earth caused by the greenhouse gases we released.
tired_and_awake
If this is a legitimate concern perhaps they can launch a second set of satellites to block peak sunlight.
tonymillion
Or just put mirrors on the ground to reflect the sunlight back out /s
Dylan16807
Honestly, I don't think you need the /s.
The satellites are dumb and would have a negligible effect. But if you want to offset the heat just to be on the right side, some mirrors or simply white surfaces on the ground could do the job.
hermitcrab
Sounds like a James Bond villain's plot. They just need to be able to focus the beam enough to start fires.
Nux
Any customers unable to pay can still join a free trial, but will be shown ads.
ryandvm
I am so tired of seeing ideas that are indiscernible from satire. This is like something that they would have come up with on HBO's Silicon Valley.
Who do I complain to when a nearby golf course orders some nightshine and now my sky looks like I'm under a fucking police helicopter?
margalabargala
This has in fact already been done, by the Soviets.
jldugger
I've seen this proposed two decades ago, but basically under a dual use proposal: orbital solar concentrator and death laser.
disqard
I had the same thought as you -- glad to see I'm not the only one.
ungreased0675
I prefer it to be dark at night. I’d make every streetlight 60% less bright if I could. Sorry, but I hate this idea.
goda90
You might find yourself at home with this group: https://darksky.org/who-we-are/advocates/
danielvf
I don't think they are aiming to be lighting things up at night, just twilight. It's a day extender.
croes
The explicitly mention Solar Energy at Night.
johnea
+1
perihelions
I think this could be life-changing for cities at high latitudes. You wouldn't even need that much: simple twilight-levels of illumination would a long way towards helping people's psychology and quality-of-life in winter.
A key thing that would make this easier than it'd naively seem, is that human perception of ambient light levels (like many kinds of human sense) is sort-of logarithmic. Twilight is just 10^{-5} – 10^{-4} the illumination level of sunlight,
https://www.engineeringtoolbox.com/light-level-rooms-d_708.h...
(That is, to my naive first take: a 100 x 100-meter collector in orbit intercepts enough sunlight to bring a 10km x 10km city to bright twilit level).
InDubioProRubio
Wont somebody think of the vodka industry?
banga
It's astounding to me that such ignorance is even acknowledged.
The reason we get a lot of light from the sun is not that the sun is particularily "bright" (high radiance) compared to other stars, it is because the the sun has an absolutely huge apparent size in the sky compared to all the other bright objects we can see.
Let's say you go to one of the illuminated areas that paid for reflectorbital-light and look up. What would you see? You would see a tiny bright spot flying past, with an angular size of about 10^-10 steradians [1].
This tiny spot has the same "brightness" (radiance) as the sun, because a mirror preserves radiance. However the mirror looks about 10 000 times smaller than the sun from your perspective (the sun has an angular size of about 10^-5 steradians). This means that the satellite would only give you 0.01% of the light compared to the real sun.
If you could somehow take 10k satellites and use them to illuminate the same spot, you could technically get it to resemble real sunlight. But imagine what this would look like: These satellite would need to be many enough / huge enough to cover a very significant portion of our sky, on the order of the apparent size our actual sun. They would be spread out in a sun-synchronous orbit, so they would be visible at dusk with this size, from all points on the earth. Would we really want that?
The founder has been thinking about using mirrors to collimate the sunlight to get around this problem, but it won't work. The collimator design he showed in a 2022 article [2] would decrease the focal spot from a 5km diameter to some smaller diameter as intended, but it would do so by throwing away light, not by increasing the brightness in this smaller spot. This is given by conservation of ètendue, one of the fundamental laws of nonimaging optics (where I do research).
[1] They are planning a 100sqm mirror at 600km altitude, which gives a solid angle of (100 m^2)/(600e3 m)^2
[2] https://www.vice.com/en/article/this-man-is-trying-to-put-mi...