Massive Solar Mirror To Bring Light at Night

[SiliconWizard]

http://en.businesstimes.cn/articles/104124/20181018/chinese-city-chengdu-orbit-massive-solar-mirror-bring-light-night.htm

Have we humans gone completely mad?
Night light pollution is increasingly problematic and now they are coming up with horrors like this?

What do you guys think?

[Bud]

I think Elon Musk is pulling his hair out how come he could miss such a great idea.

[f4eru]

Nice idea, but not really feasible.
A huge mirror is a debris catcher and debris source, and will basically render it's own orbit useless really fast.

[Kleinstein]

How bad the debis problem is depends on the orbit. To make the mirror work it would likely need an orbit close to the Geo-statinary and thus quite far out. 

Still not a good idea. The problem is more with too much heat from the sun, so it would more about a shade for the day.

[Gyro]

Not satisfied with global warming, they want to experience local warming too.   

[fourtytwo42]

Sounds like fake news on a slow news day to me, how can the launch and vehicle costs of this project possibly compete with the costs of a few thousand street lamps for its likely orbital life!! Hmm perhaps the city would like to hire me as a financial analyst I could save them mega bucks for a few percent 

[SiliconWizard]

Sounds like fake news on a slow news day to me, how can the launch and vehicle costs of this project possibly compete with the costs of a few thousand street lamps for its likely orbital life!! Hmm perhaps the city would like to hire me as a financial analyst I could save them mega bucks for a few percent 

Unfortunately, it doesn't look like it is:
https://www.thesun.co.uk/news/7523696/china-launch-artificial-moon-chengdu-sichuan/
https://www.bbc.com/news/world-asia-china-45910479

but I wish it were.

Do you think those absurdely stupid solar roads make any more sense financially? And many of the so-called green power projects?

It's not just absurd but obviously potentially detrimental on a lot of levels.
Maybe someone here living in China can confirm the project and explain this to us.

[f4eru]

To make the mirror work it would likely need an orbit close to the Geo-statinary and thus quite far out. 

Not sure.
Losing a lot of brightness when going far away, but gaining sun time and regularity.

Why not use a 12 hour orbit instead of a geo ? 2 passes/night are better than one !


Or even a highly elliptical pseude geo orbit like the Sirius sats...



Another approach if the target is to use a constellation, would make sense only for use in multiple cities.

[CatalinaWOW]

Solar thrust on a mirror (sail) the size they are proposing would be about 200 newtons.    They will have fun keeping it on station.

[DougSpindler]

Didn’t a city in Italy mount a larg mirror on a mountain?  Worked for them.

[Bud]

With the right curvature on the mirror you can probably can burn places down 

[DougSpindler]

Already happening in the UK and Germany with there big tall glass office building melting cars parked on the street. 

[StillTrying]

It's all right saying they're going to put a very large mirror in orbit, but haven't they noticed that the Sun goes in at night.

[Kleinstein]

Didn’t a city in Italy mount a larg mirror on a mountain?  Worked for them.

Not sure it this was Italy of Austria, but they did this to get some sum in winter. It's a village in a rather deep valley so that normally they don't see the sun for quite some part of the year.  The mirror on a mountain gives them some sun in winter too.

[DougSpindler]

Didn’t a city in Italy mount a larg mirror on a mountain?  Worked for them.

Not sure it this was Italy of Austria, but they did this to get some sum in winter. It's a village in a rather deep valley so that normally they don't see the sun for quite some part of the year.  The mirror on a mountain gives them some sun in winter too.

Just looked, it was Italy....  But then are not the only ones.  A Norwegian village did the same and I’m sure there are many others including in Austria.

[boB]

It's just another stooopid idea for gullible people...

[ahbushnell]

It's all right saying they're going to put a very large mirror in orbit, but haven't they noticed that the Sun goes in at night.

Probably in high geostationary orbit where the sun shines. 

[JackJones]

"This "fake moon," which is really a sophisticated "solar mirror," will be placed in a geosynchronous orbit so that it will hover only over Chengdu."

You can only have a geosynchronous orbit above the equator, considering Chengdu is over 3000 km above the equator, I'm not sure how they are going to do it.

The article does say the Russians did something like this and the wikipedia article says: "The mirror deployed successfully, and, when illuminated, produced a 5 km wide bright spot, which traversed Europe from southern France to western Russia at a speed of 8 km/s."

Another article I read stated that they are going to send three artificial moons to orbit. I don't know if they are all meant for Chengdu or separate ones.

I reckon there's something fishy about this.

[cdev]

If they were to put a slightly concave mirror up there it would be a very powerful weapon. 

Imagine if they lost control of it - say a meteor hit it, and it went spinning and every few days (hours?) it would focus a ray of intense light that swept across the earth. Even if it crossed the entire planet in a few seconds it still would incinerate whole cities in an instant.

A flat mirror would double the sunlight in one place, approximately its own size, a convex mirror would diffuse the light. But by turning night into day it would screw up both plant growth and peoples circadian rhythm, causing health problems because peoples bodies would get confused as to whether it was day or night.

[CatalinaWOW]

If they were to put a slightly concave mirror up there it would be a very powerful weapon. 

Imagine if they lost control of it - say a meteor hit it, and it went spinning and every few days (hours?) it would focus a ray of intense light that swept across the earth. Even if it crossed the entire planet in a few seconds it still would incinerate whole cities in an instant.

A flat mirror would double the sunlight in one place, approximately its own size, a convex mirror would diffuse the light. But by turning night into day it would screw up both plant growth and peoples circadian rhythm, causing health problems because peoples bodies would get confused as to whether it was day or night.

This is a technical forum.  So numbers rather than emotion.  Calculate how large a mirror would be required to incinerate a city if its focus was transiting the earth in a few seconds.  Then comment on your own comment.  The numbers don't have to be perfect, for this task even getting within a couple of orders of magnitude is good enough.

[cdev]

"Huge" of course. Really huge.

Much larger than the area it was focusing the light on. Presumably the mirror would have to be held open by something, given its size it would have to be very thin and likely its edges would be weighed and the force would be provided by spin, the spin would hold it open with its inertia.

It would also perhaps have the effect of a solar sail. Would the solar wind - like a conventional sail, displace the center more? - creating a concave mirror shape- I don't know, the calculation requires knowledge of the force and the relative elasticity of the silvery material and its mass, but having read extensively about the feasibility of creating parabola by various means in space, it sounds much more feasible than many other methods.

Its been a while since I went looking for that kind of info but indeed, it is possible to make parabola by methods similar to that on a much smaller scale. Physical forces often create beautiful, mathematically perfect shapes in microgravity.

I am not a celestial mechanics type guy, not even close so I don't know if the force of the suns light and charged particles would make it concave or not, but it seems at least slightly plausible, more plausible than it remaining totally flat or being convex in relationship to the Earth while a solar wind was blowing on it from its 'front'. It is a mirror, right? or is it white?

Wouldn't it be a disaster if they put it up there painted white but the paint started to flake off, (Lots of UV light up there, right!?) making it progressively more mirror like?

If the beam of light did in fact sweep across the earth, that would be terrible. But I suppose the force being exerted on it by the sun would eventually propel it far enough from the Earth to no longer be a threat. And perhaps eventually out into interstellar space. If it remained oriented in the proper plane to catch the suns rays at its center.

Hopefully we are not that stupid a planet to do something like that to ourselves.

However, it would make a good "B" movie plot.

[digsys]

<applies for solar skyways patent> ... suckers !! :-)

[cdev]

All of China is on one time zone. When they really should have at least three.

[CatalinaWOW]

"Huge" of course. Really huge.

Much larger than the area it was focusing the light on. Presumably the mirror would have to be held open by something, given its size it would have to be very thin and likely its edges would be weighed and the force would be provided by spin, the spin would hold it open with its inertia.

It would also perhaps have the effect of a solar sail. Would the solar wind - like a conventional sail, displace the center more? - creating a concave mirror shape- I don't know, the calculation requires knowledge of the force and the relative elasticity of the silvery material and its mass, but having read extensively about the feasibility of creating parabola by various means in space, it sounds much more feasible than many other methods.

Its been a while since I went looking for that kind of info but indeed, it is possible to make parabola by methods similar to that on a much smaller scale. Physical forces often create beautiful, mathematically perfect shapes in microgravity.

I am not a celestial mechanics type guy, not even close so I don't know if the force of the suns light and charged particles would make it concave or not, but it seems at least slightly plausible, more plausible than it remaining totally flat or being convex in relationship to the Earth while a solar wind was blowing on it from its 'front'. It is a mirror, right? or is it white?

Wouldn't it be a disaster if they put it up there painted white but the paint started to flake off, (Lots of UV light up there, right!?) making it progressively more mirror like?

If the beam of light did in fact sweep across the earth, that would be terrible. But I suppose the force being exerted on it by the sun would eventually propel it far enough from the Earth to no longer be a threat. And perhaps eventually out into interstellar space. If it remained oriented in the proper plane to catch the suns rays at its center.

Hopefully we are not that stupid a planet to do something like that to ourselves.

However, it would make a good "B" movie plot.

I am going to prod you a little further.  My estimate, based on childhood ant burning experiments is that the diameter of the mirror would have to about 100 times larger than the diameter of the city you were burning. (There are relatively easy ways to get better estimates.  Solar power density is well known.  Reflectances and transmission can be estimated accurately.  Heat density to start fires is also obtainable, or you could do some backyard experiments.)

Small cities are 10 miles in diameter.  Large cities are 100 miles or more in diameter.  So your mirror would be 1000 to 10,000 miles in diameter.  Now google mylar film and figure the mass of such a disk.  Compare it to the launch capacity of Musk's BFR .  It should give you some idea how long we have before we have to worry about stupidity.  If that time is short enough to worry you, throw in a somewhat heavier rim for spin forming, some mass for a deployment mechanism, think about the time constant of something that scale (for the initial waves and ripples to die out) and it should buy you enough time to let the grandkids worry  about it.

In which case the most prudent thing for you to do is not to worry about this, but to worry about your kid's education so that their kids are well enough educated to not do this, or if they don't control everyone, to toss a load of gravel up to rip the thing to shreds before it stabilizes.

[DougSpindler]

Or we could pursue the technology which would provide endless power, next gen nuclear.  With next gen nuclear There is no long lived radioactive waste, a Chernobyl size accident would be habitable in 25 years and we have a universe of fuel.   Unlike, solar or wind nuclear power provides electricity day and night.  And we don’t have to do any silly engineering like a mirror in space or transmit gig-watts of electricity thousands of miles and over land and through the oceans,