20 replies to this topic

[Domdron]

There's a new company Reflect Orbital which wants to put mirrors in space and allow anyone to use them to direct sunlight down to a user-chosen location at night in a 5km radius. 

 

Someone in a Whatsapp group I'm in did the maths and figured out that it doesn't work out physically, the amount of light would be quite minimal. It would be good if it could be confirmed though, anyone here with the skills and willingness to independently calculate it (we only have the info from the website to go by, and this video, though I'm not sure how accurate the info in the video is)?

 

Still, the fact that someone seems to be actually working on such is alarming.

[Zonnesteek]

Did their website go live on April 1st perhaps?

 

This would need an enormous amount of mirror surface in order to reflect meaningful amounts of sunlight onto the Earth's dark side.

[Astrojensen]

It doesn't work. If the mirror is in low earth orbit, it will pass over any given area very quickly, so there will be very little time to actually illuminate any given area. Think about how fast the ISS moves through the sky. You would need a huge number of reflectors, and indeed this is what their website show.  

 

If it's in a higher, possibly geostationary orbit, the mirrors will need to be so large, we do not yet have the technology to make them. If, lets say, we need to reflect the entire face of the Sun from geostationary orbit, the mirror needs to subtend an angular diameter of more than 1/2° as seen from Earth's surface. This would require a mirror some 280 km's in minimum diameter... In practice, it would need to be even larger. If they are significantly smaller, they will act as pinhole cameras and the illumination will drop dramatically. Even from low earth orbit, the mirrors would need to be more than 4.5 km's in diameter to avoid the pinhole effect.   

 

Such a mirror would be under significant pressure from the solar wind and require constant adjustments to its orbit, lest it begins to move away from Earth, and in turn the solar system. 

 

It is a super uneconomical way to illuminate an area. I consider all such ideas a scam and this is no different. The website is exceptionally unprofessionally made, if this project is to be considered even remotely feasible. Cartoonish pictures and lofty, dreamy promises. Nothing of any substance. There is absolutely nothing to back their claims. No calculations to show that they have taken well-known effects into account, such as the pinhole effect or the solar wind, or forces of inertia, as they try to adjust the angle of the reflectors, which they must do regularly. 

 

 

Clear skies!

Thomas, Denmark  

[columbidae]

Thankfully it's a lot harder to put something into orbit than it is to create a website.

 

Unfortunately, math is a lot harder than it is to create a website.

Edited by columbidae, 05 September 2024 - 02:50 AM.

[rob1986]

Almost reminds me of battletech's 2km photoelectric solar sails.

At least they at the wisdom to depict them as having an annular shape.

[Zonnesteek]

By the way, there is a part of The Netherlands called Westland that is mainly focused on glasshouse (aka greenhouse) agriculture. They have for decades increased their vegetable production by having very bright lights on during the night - as it turns out that plants can do photosynthesis 24h a day if given the light.

 

Because of the clear glass roofs, the unintended byproduct has been brightly lit night skies for as long as I can remember, even outside of the cities.

 

And back in the day, lighting huge areas with lamps may have been costly, but was still economical. Now, with LED lighting, the electricity cost of flooding large areas of agricultural land with lamp light is no longer significant.

[triplemon]

Lets do some back-of-the-envelope calculations. Put a big mirror into space, you have two extreme options and anything in between: LEO to geostationary. The later has the benefit of being able to shine on any one spot almost all night, the other is good for about as long as you can observe an ISS pass.

 

Gestationary orbit is some 36,000+ km away. Sun's aparent diameter is ~32 arcmin. A flat mirror of just a few km diameter would act more or less like a pinhole camera, i.e. get about thesame light spot onto the ground than a cuved mirror that focusses an image of the sun onto the ground. That image would be 333km in diameter, i.e. the brighness 33^2 = 1000x dimmer than direct sunlight for a 10km mirror.

 

The other extreme would be LEO, say as low as the ISS. So depending on where the light gets onto the ground relative to where the mirror passes overhead that is ballpark 500+km distance, creating, when focused, a 5km sun image. If the mirror is also this big - you get near full daylight. BUT, only for a minute or two at a time - cuz the mirror has moved on then.  You would need a LOT of mirrors around to have one at any give time near sun rise/set to illumminte any given spot on earth. Like - many, many times more than shoebox size starlinks.

 

The other nasty thing is - LEO is full of debries. You really don't want to fly a huge delicate object anywhere there.

Other options would be geostationary or high orbit multi-mirror (formation flying ?) things that create an overall device that has an effectively much shorter focal length than image distance. Never looked much into optics like that - but there are microscope objectives that do similar tricks. But their diameter isn't small compared to the working distance - thats likely no good.
 

But any of that sounds at least no more than one magnitude away from doing what their website suggests. So I'd not call it totally out of the realm of "theoretically possible". Financially - being an order of magnitude off with your cost vs what anyone would pay for such, that is more likely to be a really good show stopper thats often making the difference between a visionary and a snaps idee. Starlink has many, many million customer adressable market. Communication is a trillion dollar market. Moonlight for a few minutes "a bit" less ?

Edited by triplemon, 05 September 2024 - 11:07 AM.

[rob1986]

Almost reminds me of battletech's 2km photoelectric solar sails.

At least they at the wisdom to depict them as having an annular shape.

[Domdron]

Thanks all for the confirmation. I also believe it's a scam, though the team looks legit, these people exist. And they seem to have funding. Who knows what these Silicon Valley crazy types come with in the future? Musk is already causing enough havoc with the Starlinks.

 

So I'd suggest to keep an eye on it, and possibly start lobbying for stricter regulations about what can be put in orbit. That's what I I'll argue for in DarkSky.org anyway, where I'm a member.

[ILikeReflectorsRO956]

I'm aware others did the math so I'm not going to interfere, but if this would be actually real (which probably isn't), then 

1. wouldn't there need to be ungodly large mirrors on orbit to actually reflect a significant portion of sunlight, mirrors that would be hard to manufacture/maintain/launch into orbit?
2. wouldn't they need to be equipped with electronic GPS or other geopositioning equipment so that they can point exactly to the coordinates that are required? They would be insanely fast for any human and/or any pre-alignment to work, especially if these mirrors are meant to work for small areas. 
3. what if some people in the affected area don't actually need the light? What if someone has insomnia? Or photosensitivity? Or just wants to sleep? Or, what if someone's using certain optical instruments (ahem, telescopes) that carry a risk of blindness when not expecting the light?

 

These are the questions I ask when I saw this project (this is the first time I heard about it), but I guess even my (simple) questions are too much for them, because if they were serious, they could've optimized their web animations to work smoothly on MS Edge.

 

I hope these things are just another Silicon Valley type stunt that will get nowhere.

[csrlice12]

Let's build a mirror ring around the planet....there, that's the ticket....and we get a ring around the Earth, just like the big planets!

[rob1986]

Maybe we should require outdoor lighting tp use a limted red-orange band that can be easily filtered out...

(Not relevant, but this"project" seems a pipe dream too. About as realistic as an elevator to orbit.

[Forward Scatter]

But, but their YT video says one can easily order light using an "app". Very web 2.0!!!!

Another Juicero?

[aatt]

For such a “smart” species we are pretty dumb.

[PEterW]

The maths behind this one has been busted several times, not going to make much impact on anyone and certainly wouldn’t light up things much for very long. It is only planned to orbit around the twilight, not at night as the satellites would themselves then be in the dark too.

Peter

[jimeh]

What about clouds?

[Forward Scatter]

The next Juicero^TM? Maybe the Virgin HyperLoop^TM? How about Klinkle^TM or Potato Parcel?

 

I got it....it's the next Scorkl Another startup idea that defies physics. But it's got young beautiful Bros and Gals in their videos!

[columbidae]

I'm raising funds for the opposite idea actually. I send up a satellite that blocks the light of the moon from reaching your dark site. Please do not attempt to check my math, sending money will make it work much faster.

[Domdron]

I'm raising funds for the opposite idea actually. I send up a satellite that blocks the light of the moon from reaching your dark site. Please do not attempt to check my math, sending money will make it work much faster.

Why just the Moon and not the Sun? 

[csrlice12]

Cause without the Sun, it would be too cold to go out and you wouldn't  know where to find the moon.

[mr.otswons]

Google Rjukan mirror. A Norwegian town enclosed by mountains, that loses sunlight most of the year. An artist decided to put mirrors on the mountain to light up the city.

 

Not the same, but reminded me of this project

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