# Could we send a "curved mirror" type satellite around the sun to reflect photons to us?

• September 12th, 2014, 06:19 AM
Ximlab
Could we send a "curved mirror" type satellite around the sun to reflect photons to us?
And wouldn't that be a great economy of scale and a great source of extra power?
Especially including the possibility of 24/7 solar power, with probably much less waste in outer space.
Would it be extremely complicated? And what bottleneck is the problem? Anything other than an oldschool mirror capable of reflecting properly massive amounts of photons?

The basic maths of it are probably fairly easy. A few ratios would be needed to get a sense of how much more solar power we could get to earth from a single big panel being closer to the sun.

Let me clarify :

AFAIK, earth gets a lot more solar energy than we could use on earth (heard a ratio of 2000:1), yet earth is such a tiny point in the sphere with earth-sun radius. And many worry that solar power takes too much landspace.
Would reaching an orbital speed close to the sun require too much power? Excessive heat issue? Large size mirror (especially curved ones to focus power toward earth) too expensive?
You're welcome to play with different mirror sizes and orbital altitude (largest mirror and lowest orbital altitude possible obviously best), I'm not sure what would be realistic numbers for our levels of technology.
Think of my mirror satelitte as a tiny first step toward the Dyson Sphere (~fully covering the sun to capture all its energy output).

I'm not sure which forum to put this question in, feels like it could fit in a few places.

I'm sure there's been tons of people with the idea before me, so I guess there's some major issue or it would probably be more discussed, yet I couldn't find something similar while googling around and it's been bugging me cause it seems so efficient, so please tell me why it's no good? Or even better why it could be good ;)

Thanks
• September 12th, 2014, 07:23 AM
Robittybob1
I think it would just get blown away with the Solar Wind and radiant pressure.
• September 12th, 2014, 07:51 AM
cosmictraveler
What if terrorists got the frequency of the mirror to readjust it to burn up cities? What would happen if a plane went through it?
• September 12th, 2014, 08:09 AM
Ximlab
Robit: I suppose that's a factor, but I would also guess sun's gravity far outweighs solar wind's push, just a guess.
Besides, being so close to the sun, couldn't the satellite use a tiny amount of its solar power to readjust its angle and orbit? (Not sure if current technology allows converting photon energy into thrust exists beside solar sails)

Cosmic: Sure, that's how much truckload of power I suppose we're talking about (If big enough, i would slightly worry about overheating earth by basically adding another sun's output to the system), but let's try to first see if it seems remotely feasible then worry about terrorism.
I would guess you could redirect the mirror not directly toward earth but to a receptor satelitte in earth orbit first, converting possibly the stream to laser for exemple or focusing more precisely the stream toward an earth-based converter.
• September 12th, 2014, 08:21 AM
Ximlab
To add numbers to the discussion, I did the ratio of sun-earth distance to a 100km orbit to the sun (probably too close but it's an exemple).
It comes out to a ratio of 1,490,000, meaning roughly that a mirror 1,490,000 times smaller than earth would receive roughly the same amount of photons, if i'm not missing something.
Given a 6371km earth's radius, if i'm not mistaken, a simple mirror of 4.3m of diameter would receive as much photons as earth if it were on a 100km orbit.
On a 1000km orbit, I guess it would come to a 43m mirror.

These are obviously quite simplified maths, if i didn't even make a mistake.
• September 12th, 2014, 12:56 PM
Robittybob1
Quote:

Originally Posted by Ximlab
To add numbers to the discussion, I did the ratio of sun-earth distance to a 100km orbit to the sun (probably too close but it's an exemple).
It comes out to a ratio of 1,490,000, meaning roughly that a mirror 1,490,000 times smaller than earth would receive roughly the same amount of photons, if i'm not missing something.
Given a 6371km earth's radius, if i'm not mistaken, a simple mirror of 4.3m of diameter would receive as much photons as earth if it were on a 100km orbit.
On a 1000km orbit, I guess it would come to a 43m mirror.

These are obviously quite simplified maths, if i didn't even make a mistake.

The mirror would heat up and melt if that was the case!
• September 12th, 2014, 01:37 PM
physicist
Quote:

Originally Posted by Ximlab
Could we send a "curved mirror" type satellite around the sun to reflect photons to us? And wouldn't that be a great economy of scale and a great source of extra power?

Sure. But why? It's easier to get the light rays directly from the sun rather than reflecting them off a mirror. That's a very complex focusing process. The degree of precession required is extraordinary! Getting rays of light is exactly what we're doing already and have since the Earth was created. Why change that? What benefits would you get?

And what do you mean by
Quote:

Originally Posted by Ximlab
AFAIK, earth gets a lot more solar energy than we could use on earth (heard a ratio of 2000:1), yet earth is such a tiny point in the sphere with earth-sun radius.

? Thanks!
• September 12th, 2014, 04:47 PM
billvon
Quote:

Originally Posted by Ximlab
And wouldn't that be a great economy of scale and a great source of extra power? Especially including the possibility of 24/7 solar power, with probably much less waste in outer space.

Well, given our current problem with global warming, sending another few gigawatts of solar radiation Earthwards probably isn't such a good idea. However, for illumination purposes it might make sense; that takes far less radiation (hence less heating) and will reduce our need for lighting power. From Wikipedia:
==============
Another advanced space concept proposal is the notion of Space Reflectors which reflect sunlight on to small spots on the night side of the Earth to provide night time illumination. An early proponent of this concept was Dr. Krafft Arnold Ehricke, who wrote about systems called "Lunetta", "Soletta", "Biosoletta", "Powersoletta".

A preliminary series of experiments called Znamya ("Banner") was performed by Russia, using solar sail prototypes that had been repurposed as mirrors. Znamya-1 was a ground test. Znamya-2 was launched aboard the Progress M-15 resupply mission to the Mir space station on 27 October 1992. After undocked from Mir, the Progress deployed the reflector.This mission was successful in that the mirror deployed, although it did not illuminate the Earth. The next flight Znamya-2.5 failed. Znamya-3 never flew.
=============

Quote:

Would reaching an orbital speed close to the sun require too much power? Excessive heat issue? Large size mirror (especially curved ones to focus power toward earth) too expensive?
No need; there's still plenty of sunlight in Earth orbit.
• September 12th, 2014, 05:31 PM
Ximlab
Quote:

Originally Posted by physicist
Quote:

Originally Posted by Ximlab
Could we send a "curved mirror" type satellite around the sun to reflect photons to us? And wouldn't that be a great economy of scale and a great source of extra power?

Sure. But why? It's easier to get the light rays directly from the sun rather than reflecting them off a mirror. That's a very complex focusing process. The degree of precession required is extraordinary! Getting rays of light is exactly what we're doing already and have since the Earth was created. Why change that? What benefits would you get?

And what do you mean by
Quote:

Originally Posted by Ximlab
AFAIK, earth gets a lot more solar energy than we could use on earth (heard a ratio of 2000:1), yet earth is such a tiny point in the sphere with earth-sun radius.

? Thanks!

Right thanks, I suppose the precision involved could be a problem, if not 'the' problem, this type of math/engineering is out of my reach, even by thought, I just don't know enough. However, quite clearly we're not talking of changing anything, just having access to more 24/7-ish power, isn't that a good thing?
A sun-satellite would not take our sunlight, just add sunlight to earth by taking it from a "blank area" of space (excuse my english and math vocabulary isn't proficient enough to use correct words).

As for the second quote, it was from a TEDtalk going through renewable data and comparing potential input/m², I could be off on the 2000:1, but it was along these lines.
"could use on earth"= today's energy consumption

Edit: On second thought, the precision involved with targetting an earth satellite or a "factory on earth" when all points are moving constantly with a precision of something like millionth of a degree, does sound impossible or close enough, no need to know the much engineering I suspect. That instantly cuts down on the key potential of the idea, and turn it down to the much less sexy, "aim at earth, get a brighter day, and perhaps twice as much sun-power from your panels", much less interesting.
• September 12th, 2014, 05:35 PM
Ximlab
Quote:

Originally Posted by billvon
Quote:

Originally Posted by Ximlab
And wouldn't that be a great economy of scale and a great source of extra power? Especially including the possibility of 24/7 solar power, with probably much less waste in outer space.

Well, given our current problem with global warming, sending another few gigawatts of solar radiation Earthwards probably isn't such a good idea. However, for illumination purposes it might make sense; that takes far less radiation (hence less heating) and will reduce our need for lighting power. From Wikipedia:
==============
Another advanced space concept proposal is the notion of Space Reflectors which reflect sunlight on to small spots on the night side of the Earth to provide night time illumination. An early proponent of this concept was Dr. Krafft Arnold Ehricke, who wrote about systems called "Lunetta", "Soletta", "Biosoletta", "Powersoletta".

A preliminary series of experiments called Znamya ("Banner") was performed by Russia, using solar sail prototypes that had been repurposed as mirrors. Znamya-1 was a ground test. Znamya-2 was launched aboard the Progress M-15 resupply mission to the Mir space station on 27 October 1992. After undocked from Mir, the Progress deployed the reflector.This mission was successful in that the mirror deployed, although it did not illuminate the Earth. The next flight Znamya-2.5 failed. Znamya-3 never flew.
=============

Quote:

Would reaching an orbital speed close to the sun require too much power? Excessive heat issue? Large size mirror (especially curved ones to focus power toward earth) too expensive?
No need; there's still plenty of sunlight in Earth orbit.

I suspected posting the opening post that too much radiation/energy could be a serious issue, considering we're talking massive amounts. However, if having access to this type of energy meant you could cut out most of your "dirty energy", couldn't you still be ahead? Another problem out of my reach. I have no clue.

On night-time illumination, I haven't heard of, a little could be good but I'm not sure everyone would be happy if you sent too much light in the nightime. But a little could be useful to cut down our energy reqs and would help developping countries the most I guess.
• September 12th, 2014, 05:44 PM
Ximlab
Quote:

Originally Posted by Robittybob1
Quote:

Originally Posted by Ximlab
To add numbers to the discussion, I did the ratio of sun-earth distance to a 100km orbit to the sun (probably too close but it's an exemple).
It comes out to a ratio of 1,490,000, meaning roughly that a mirror 1,490,000 times smaller than earth would receive roughly the same amount of photons, if i'm not missing something.
Given a 6371km earth's radius, if i'm not mistaken, a simple mirror of 4.3m of diameter would receive as much photons as earth if it were on a 100km orbit.
On a 1000km orbit, I guess it would come to a 43m mirror.

These are obviously quite simplified maths, if i didn't even make a mistake.

The mirror would heat up and melt if that was the case!

Which case? They were just 2 exemples, 100km melt? 1000km melt?
Also, what temp would they be subject to? All I know is sunsurface isn't crazy hot, along the lines of 10,000K. There must be some high-melting point materials which could withstand 1 or 2,000K no? Or would the vacuum be an issue to keeping temperature reasonable?
• September 12th, 2014, 05:55 PM
Ximlab
Although I'd be happy to get more input and there were many good points brought up, just to learn more about the system, it looks like physicist kinda "killed the idea" with the topic of precision, unless someone knowledgeable in satellite aiming/positioning feels like it's doable, it's looking grim for my idea ;)
• September 12th, 2014, 06:26 PM
MagiMaster
The concept of surrounding the Sun with a swarm of solar-power-collecting satellites is called a Dyson Swarm, which is an evolution of the concept of a Dyson Sphere (Dyson sphere - Wikipedia, the free encyclopedia). People have done a lot of theoretical work on the idea because there's a lot of clean energy to be had if anyone can make it work (both technically and economically).
• September 12th, 2014, 06:27 PM
Robittybob1
Quote:

Originally Posted by Ximlab
Quote:

Originally Posted by Robittybob1
Quote:

Originally Posted by Ximlab
To add numbers to the discussion, I did the ratio of sun-earth distance to a 100km orbit to the sun (probably too close but it's an exemple).
It comes out to a ratio of 1,490,000, meaning roughly that a mirror 1,490,000 times smaller than earth would receive roughly the same amount of photons, if i'm not missing something.
Given a 6371km earth's radius, if i'm not mistaken, a simple mirror of 4.3m of diameter would receive as much photons as earth if it were on a 100km orbit.
On a 1000km orbit, I guess it would come to a 43m mirror.

These are obviously quite simplified maths, if i didn't even make a mistake.

The mirror would heat up and melt if that was the case!

Which case? They were just 2 exemples, 100km melt? 1000km melt?
Also, what temp would they be subject to? All I know is sunsurface isn't crazy hot, along the lines of 10,000K. There must be some high-melting point materials which could withstand 1 or 2,000K no? Or would the vacuum be an issue to keeping temperature reasonable?

What are the dimensions of the Sun? Even at 1000 km it would be just as hot as on the surface. It has a diameter of 1,392,684 km so you're not even 1000th of its diameter away from a surface at 10,000 K - it would melt, it would blow away, it would evaporate, it just wouldn't work. We've already got climate change so we don't need any more incoming radiation.
• September 13th, 2014, 05:39 AM
physicist
Quote:

Originally Posted by Ximlab
Although I'd be happy to get more input and there were many good points brought up, just to learn more about the system, it looks like physicist kinda "killed the idea" with the topic of precision, unless someone knowledgeable in satellite aiming/positioning feels like it's doable, it's looking grim for my idea ;)

I'm still not clear on why the mirror has to be so far away though. Why do we need it at all since the sun sends us that sun already? If we just want more then why can't we get it from this side of the sun?
• September 15th, 2014, 10:43 AM
Howard Roark
Quote:

Originally Posted by physicist
Quote:

Originally Posted by Ximlab
Although I'd be happy to get more input and there were many good points brought up, just to learn more about the system, it looks like physicist kinda "killed the idea" with the topic of precision, unless someone knowledgeable in satellite aiming/positioning feels like it's doable, it's looking grim for my idea ;)

I'm still not clear on why the mirror has to be so far away though. Why do we need it at all since the sun sends us that sun already? If we just want more then why can't we get it from this side of the sun?

It is very simple really: he is proposing an artificial moon. The moon is reflecting Sun light, so would this satellite.
• September 15th, 2014, 10:46 AM
Howard Roark
Quote:

Originally Posted by Robittybob1
Quote:

Originally Posted by Ximlab
Quote:

Originally Posted by Robittybob1
Quote:

Originally Posted by Ximlab
To add numbers to the discussion, I did the ratio of sun-earth distance to a 100km orbit to the sun (probably too close but it's an exemple).
It comes out to a ratio of 1,490,000, meaning roughly that a mirror 1,490,000 times smaller than earth would receive roughly the same amount of photons, if i'm not missing something.
Given a 6371km earth's radius, if i'm not mistaken, a simple mirror of 4.3m of diameter would receive as much photons as earth if it were on a 100km orbit.
On a 1000km orbit, I guess it would come to a 43m mirror.

These are obviously quite simplified maths, if i didn't even make a mistake.

The mirror would heat up and melt if that was the case!

Which case? They were just 2 exemples, 100km melt? 1000km melt?
Also, what temp would they be subject to? All I know is sunsurface isn't crazy hot, along the lines of 10,000K. There must be some high-melting point materials which could withstand 1 or 2,000K no? Or would the vacuum be an issue to keeping temperature reasonable?

What are the dimensions of the Sun? Even at 1000 km it would be just as hot as on the surface. It has a diameter of 1,392,684 km so you're not even 1000th of its diameter away from a surface at 10,000 K - it would melt, it would blow away, it would evaporate, it just wouldn't work. We've already got climate change so we don't need any more incoming radiation.

The mirrors for solar power farms do not "melt". Nor do they "blow up". The reason is that they are artificially cooled. A mirror in space would benefit from the fact that it is naturally cooled , since it is placed in cosmos vacuum.

Quote:

We've already got climate change so we don't need any more incoming radiation

Actually more moonlight would be quite useful.
• September 15th, 2014, 10:49 AM
billvon
Quote:

Originally Posted by Howard Roark
The mirrors for solar power frams do not "melt". Nor do they "blow up". The reason is that they are artificially cooled.

They are naturally cooled, via natural convection into the air. Since mirrors can be 99% efficient, that results in only a few hundred watts to dissipate, which can be dissipated by natural convection.
Quote:

A mirror in space would benefit from the fact that it is naturally cooled , since it is placed in cosmos vacuum.
That means it CANNOT be naturally cooled by convection. It must be cooled by radiation, which means it has to be much. much hotter to effectively radiate away the heat it absorbs.

• September 15th, 2014, 11:01 AM
Howard Roark
Quote:

Originally Posted by billvon
Quote:

Originally Posted by Howard Roark
The mirrors for solar power frams do not "melt". Nor do they "blow up". The reason is that they are artificially cooled.

They are naturally cooled, via natural convection into the air. Since mirrors can be 99% efficient, that results in only a few hundred watts to dissipate, which can be dissipated by natural convection.

Actually, they are artificially cooled, via conduction, not convection. See here.

Quote:

Quote:

A mirror in space would benefit from the fact that it is naturally cooled , since it is placed in cosmos vacuum.
That means it CANNOT be naturally cooled by convection.
Neither are the mirrors in the mirror farms, see above.

Quote:

It must be cooled by radiation, which means it has to be much. much hotter to effectively radiate away the heat it absorbs.
They would be exactly like the moon. The moon is being kept quite cool, isn't it?
• September 15th, 2014, 11:06 AM
billvon
Quote:

Originally Posted by Howard Roark
Actually, they are artificially cooled, via conduction, not convection. See here.

The mirrors themselves are naturally cooled. In the article you referenced they reflect light onto a central tube which has a heat transfer fluid flowing through it. This is where the heat is used, to be converted later into steam and then into electrical power.

Quote:

They would be exactly like the moon. The moon is being kept quite cool, isn't it?
?? The surface of the Moon is 253F on the daylight side - and is 93 million miles away from the Sun.
• September 15th, 2014, 11:10 AM
Howard Roark
Quote:

Originally Posted by billvon
Quote:

Originally Posted by Howard Roark
Actually, they are artificially cooled, via conduction, not convection. See here.

The mirrors themselves are naturally cooled. In the article you referenced they reflect light onto a central tube which has a heat transfer fluid flowing through it. This is where the heat is used, to be converted later into steam and then into electrical power.

It is the heat transfer that cools the mirrors, this is basic thermodynamics.

Quote:

Quote:

They would be exactly like the moon. The moon is being kept quite cool, isn't it?
?? The surface of the Moon is 253F on the daylight side - and is 93 million miles away from the Sun.
The satellite would be close to Earth, so it would be at the same distance (if not larger) wrt the Sun.
Last I checked 253F is not the melting temperature of steel, has anything changed in your physics?
Last I checked steel melts at 2500F, 10 times more than 250F.
• September 15th, 2014, 11:28 AM
billvon
Quote:

Originally Posted by Howard Roark
It is the heat transfer that cools the mirrors, this is basic thermodynamics.

No, the central pipe is far hotter than the mirrors ("over 400 °C" per your own link) so the central pipe is HEATING, not cooling the mirrors. Basic math will show you this. The mirrors are kept cool by the simple fact that they are in cooler air, and by the location of the central pipe, which is some distance from the mirror.

However, if you still don't believe me, go to any solar concentrator facility (like Ivanapah) and simply look at it. No cooling to the mirrors.
Quote:

The satellite would be close to Earth, so it would be at the same distance (if not larger) wrt the Sun.
Last I checked 253F is not the melting temperature of steel, has anything changed in your physics?
Last I checked steel melts at 2500F, 10 times more than 250F.
Yes, a satellite in Earth orbit will have no problems operating at a feasible temperature.
• September 15th, 2014, 11:32 AM
Howard Roark
Quote:

Originally Posted by billvon
Quote:

The satellite would be close to Earth, so it would be at the same distance (if not larger) wrt the Sun.
Last I checked 253F is not the melting temperature of steel, has anything changed in your physics?
Last I checked steel melts at 2500F, 10 times more than 250F.
Yes, a satellite in Earth orbit will have no problems operating at a feasible temperature.

Then we are done, right? No "melting" or "blown up" mirrors, correct?
• September 15th, 2014, 11:49 AM
Ximlab
Well, I'm still not clear on how heat dissipates/radiate in the vacuum of space, but the initial idea supposed a satellite in relatively close proximity to the sun, if it cannot dissipate heat, I suppose it will reach high temperature. From a quick google, it's apparently a fairly complicated question dependings on materials etc...
Neither am I clear on temperatures in sun's orbit. 1000km? 10000km? 1000000km?

If cooling can be done using the sun's converted energy, it still might be feasible since the sun's artificial satelitte would obviously be receiving tremedous amount of power.

Still, I'm learning here, it's all good.
• September 15th, 2014, 11:56 AM
billvon
Quote:

Originally Posted by Ximlab
Well, I'm still not clear on how heat dissipates/radiate in the vacuum of space, but the initial idea supposed a satellite in relatively close proximity to the sun, if it cannot dissipate heat, I suppose it will reach high temperature. From a quick google, it's apparently a fairly complicated question dependings on materials etc...
Neither am I clear on temperatures in sun's orbit. 1000km? 10000km? 1000000km?

The term "temperature" doesn't have much meaning in a vacuum. In general, the system will absorb heat from mirror inefficiencies, and that will depend on area, mirror efficiency, and insolation. Here at the Earth's orbit we get about 1400 watts per square meter, so a 99% efficient mirror would have to dissipate 14 watts per square meter.

How does it get rid of the heat? Only long term method is via blackbody radiation, where the object gets hot enough to radiate away all the heat it absorbs. As it heats up it starts to radiate away heat energy. At high temperatures this starts to become visible - think of lava glowing red, or the filament of an incandescent light bulb. With a sensitive enough camera you can even see the blackbody thermal radiation that your body gives off.

Energy radiated goes up by the fourth power of temperature, so any such object will quickly heat to the point at which it is radiating away enough heat to balance incoming heat and stay there. In Earth's orbit that is several hundred degrees F. Closer to the Sun it will depend on flux received from solar heating and emissivity of the object.
• September 15th, 2014, 12:05 PM
Ximlab
Melting point of mirror might be as high as 2000C at best from a quick search, is the jury still out on this being below the balance level of heat?

Although for this kind of endeavor, I'm sure engineer could work on a better material.
• September 15th, 2014, 12:09 PM
Howard Roark
Quote:

Originally Posted by Ximlab
Well, I'm still not clear on how heat dissipates/radiate in the vacuum of space, but the initial idea supposed a satellite in relatively close proximity to the sun, if it cannot dissipate heat, I suppose it will reach high temperature. From a quick google, it's apparently a fairly complicated question dependings on materials etc...
Neither am I clear on temperatures in sun's orbit. 1000km? 10000km? 1000000km?

If cooling can be done using the sun's converted energy, it still might be feasible since the sun's artificial satelitte would obviously be receiving tremedous amount of power.

Still, I'm learning here, it's all good.

You can't have the satellite close to the Sun, you need to have it close to the Earth. It will melt close to the Sun, it will act as a secondary moon close to the Earth. Actually, you could make it work better than the moon by arranging such that it orbits permanently in the "night" part of the Earth, thus acting as a never setting moon. This would require some complicated controls (definitely more complicated than GPS). On the other hand, you will need very large mirrors and/or multiple satellites in order to generate an appreciable effect.