Shielding against the Sun with a large sheet of aluminum foil in Earth orbit?

[Tiger Blood]

Could people make a large sheet of aluminum foil and send it to the Earth's orbit to cover let's say half of the Sun and thus ease down these hot climate-change-induced summers?

How feasible would something like this be? I know there was some talk years ago that a ring could be made around the Earth that could shield Earth from the sun but that seemed way too complicated and expensive. Why not just make some giant foil and cover parts of the Sun when needed?

 

[Rive]

Way too difficult

Solar sail

Please try to give an estimate about the necessary size of the structure, and then about the force required to keep it in place against the pressure of 'sunshine'...

... and all that is just one blocking issue. At that size things are ... just not simple anymore.

 

[Drakkith]

It would be extremely difficult. We couldn't place it in orbit, as it would constantly be moving around the Earth and not available to block the Sun most of the time. The only feasible place would be at the Earth's L1 lagrange point. But that is an unstable location, meaning that we would need thrusters to keep it in place. Not too difficult at first glance, but there are many other issues. The immense size of the sheet would make things very difficult. As Rive pointed out the sheet would act as a giant solar said, so we would constantly need to run our thrusters, wasting large amounts of fuel. A single layer of foil probably wouldn't work well, as it is very fragile and prone to tearing if anything goes wrong with one of the thrusters or if it gets hit by a stray pebble or something. You'd likely need a modular design that would drastically increase the cost and mass, which would then exponentially increase the size/number of launch vehicles.

Also, keep in mind that the sheer size of something like this is nearly unimaginable. At the L1 point, 1.5 million km away, our sheet would need to be 6500 km across to block half the Sun, 3250 km to block a quarter, etc. Just to block 10% of the Sun we would need 1300 km of sheet. That's about a third of the length of the continental United States.

 

[willem2]

. As Rive pointed out the sheet would act as a giant solar said, so we would constantly need to run our thrusters, wasting large amounts of fuel.

We could just move it inwards from L1 to compensate for the radiation pressure, as long as the radiation pressure is smaller than solar gravity, there will still be an equilibrium point.
If I can believe the wikipedia page on lightsails, we don't have any material, light enough to cancel the solar gravity with radiation pressure.
We might be able to tilt the sail for stationkeeping, altough this will be very hard for something with a 1000+ km size.
The better our weight/surface ratio, gets, the further away from the earth it has to be, and the larger it needs to be to get enough shadow.

A single layer of foil probably wouldn't work well, as it is very fragile and prone to tearing if anything goes wrong with one of the thrusters or if it gets hit by a stray pebble or something. You'd likely need a modular design that would drastically increase the cost and mass, which would then exponentially increase the size/number of launch vehicles.

Also, keep in mind that the sheer size of something like this is nearly unimaginable. At the L1 point, 1.5 million km away, our sheet would need to be 6500 km across to block half the Sun, 3250 km to block a quarter, etc. Just to block 10% of the Sun we would need 1300 km of sheet. That's about a third of the length of the continental United States.

Surface area is proportional to the square of the radius. If 6500 km across blocks half, 3250 would block only 12.5%.
Another thing is that L1 is about 1% of the earth-sun distance, and the shadow of an object at L1, will spread out about 10000km on all sides,, so a lot of the shadow won't fall on the earth.

To counteract the current global warming you might need to block about 1% of radiation, but you'll need a disk with about 2.5% of the earth's cross-section, with a diameter of about 2000 km.
If it has to be closer to the sun, because of the light pressure, it will have to be even bigger.

 

[Drakkith]

Surface area is proportional to the square of the radius. If 6500 km across blocks half, 3250 would block only 12.5%.

Ah yes, you are correct. My mistake. I shouldn't be doing physics within an hour of my bedtime.

 

[Ivan Seeking]

Could people make a large sheet of aluminum foil and send it to the Earth's orbit to cover let's say half of the Sun and thus ease down these hot climate-change-induced summers?

How feasible would something like this be? I know there was some talk years ago that a ring could be made around the Earth that could shield Earth from the sun but that seemed way too complicated and expensive. Why not just make some giant foil and cover parts of the Sun when needed?

It is effectively already in the works but not with a sheet of aluminum foil. The plan is to use one or more aerosols that remain aloft for a significant amount of time and block or reflect a significant percentage of the sunlight while aloft. Alcoa even patented a bright white aluminum oxide powder that can be put in jet fuel. The particulates are too small to affect the engines but produce a reflective haze at high altitudes, that jets will spread all around the world. One estimate was that on the average, the powder would remain aloft for about two years.

Here is one link that discusses it. They mention the two year duration as well for an aerosol..

The idea of injecting aerosols into the atmosphere first came to prominence in 2006, when Nobel Prize–winning atmospheric chemist Paul Crutzen argued that scientists should actively explore the possibility. He said it would be similar to what happens naturally following some volcanic eruptions. For example, the 1991 Mount Pinatubo eruption in the Philippines cooled the planet by 0.5°C, after spewing some 20 million tons of sulfur dioxide into the stratosphere. The gas created a sulfate aerosol cloud that reflected sunlight back to space for 2 years.

https://www.science.org/content/art...-change-its-sudden-collapse-would-doom-planet

 

[sophiecentaur]

The particulates are too small to affect the engines but produce a reflective haze at high altitudes,

Presumably 'they' have considered the H and S effect of inhaling the particulates. Although we can't guarantee that could rate highly in cost benefit decisions.

We don't need a massive decrease in the net input of solar radiation so where is the problem in 'painting' many square km of the Earth's surface white? Not impressive enough for many people and good Nimby fodder but not bad value. We could start with rooftops.

 

[Ivan Seeking]

Presumably 'they' have considered the H and S effect of inhaling the particulates. Although we can't guarantee that could rate highly in cost benefit decisions.

We don't need a massive decrease in the net input of solar radiation so where is the problem in 'painting' many square km of the Earth's surface white? Not impressive enough for many people and good Nimby fodder but not bad value. We could start with rooftops.

That is already a push along with painting roads. While this won't make a significant difference globally, it can help to moderate the heat island effect in cities. And that IS significant to the people who live there.

Globally, first you have to paint enough area to make up for the ongoing loss of arctic sea ice and glaciers, just to break even.

 

[sophiecentaur]

Globally, first you have to paint enough area to make up for the ongoing loss of arctic sea ice and glaciers, just to break even.

Of course. But the project would be very low tech and the results would be not hard to estimate. I have no figures for this but any comment you may have about my painting scheme would need to apply to any other shading scheme.

A large sunshade would not discriminate between places we need plants to grow and places that don't need any sunlight. We can't do without growing our food; in fact we need nearly full sunlight for that. I reckon that knocks the sunshade scheme on the head but I'm open to being convinced by someone???

 

[Vanadium 50]

When this section was opened, the proponents assured us that it wouldn't be the place where substandard threds end up. It would be about stories,

Where is the story?

Climate change has winners and losers. People like to pretend otherwise, but it is true. Mitigations have winners and losers. Again, people like to pretend otherwise, but it is true. A story about a giant shade might explore the issue of winners and losers. As an example, if this causes a devestating blizzard to hit some party of the world are they going to be expected to "take one for the team" or will the shade be adjusted?

 

[Algr]

if this causes a devestating blizzard to hit some party of the world are they going to be expected to "take one for the team" or will the shade be adjusted?

Well, there is your story.

 

[Vanadium 50]

That is my point,

 

[Nik_2213]

IIRC, there was a suggestion to use textured sheet(s) so they performed like diffraction gratings. Instead of reflecting light, so fully subject to light-sail pressure, the sections variously diffracted light, so were internally under tension.

 

[sophiecentaur]

Globally, first you have to paint enough area to make up for the ongoing loss of arctic sea ice and glaciers, just to break even.

Of course. But the project would be very low tech and the results would be not hard to estimate. Say you could reflect 50%. That would be 500W per m². Any of the proposed alternatives will be based on an informed decision about the required reduction in net absorbed radiation.

The problem is that it doesn't make a very good 'story'. I guess there could be a scenario where there's a underclass who live under the shaded parts. They would be like the morlocks in The Time Traveller by HG Wells.

 

[pbuk]

the results would be not hard to estimate. Say you could reflect 50%. That would be 500W per m².

It's not as simple as that though.

https://www.nasa.gov/feature/langle...gy-budget-five-questions-with-a-guy-who-knows

• You have started with 1,000 Wm^-2. I am not sure where you have got that figure from: have you counted diurnal and seasonal variations? NASA (see above) tell me the average figure across the Earth's surface is 340 Wm^-2; you could improve some on that by only painting at low latitudes but let's go with that for now.
• Again according to the NASA article, about 20% of the incoming solar radiation is reflected from the atmosphere and another 20% absorbed, so only about 186 Wm^-2 reaches the surface.
• Some of that 186 Wm^-2 is already being reflected back: an average of 22 Wm^-2, but let's ignore that for now and assume the bits you are going to paint are not contributing anything to that.
• So if your can reflect 50% then it's about 93 Wm^-2, but some of that is going to be absorbed or reflected back from the atmosphere; let's just assume 20% as for the amount of incoming radiation absorbed.
• So I estimate that 50% reflection would give more like 75 Wm^-2.

I guess there could be a scenario where there's a underclass who live under the shaded parts. They would be like the morlocks in The Time Traveller by HG Wells.

I think it's already been done but I can't remember who, when or where.

 

[Algr]

That is my point,

An author asking for help on science might not want to divulge their story if they don't need to. You don't need to know much about Star Wars to ask "Would an exploding giant space station kill the people living on the planet below?"

 

[Vanadium 50]

might not want to divulge their story

Good grief.

Storylines are a dime a dozen. "Boy meets girl, but although they like each other, a set of misunderstandings prevents them from saying so until then end of the story." How many books and movies have I just described?

"Nine people set out cross-country to rid themselves of some unwanted jewelry." There - now there are three books you don't have to read.

 

[Algr]

Storylines are a dime a dozen.

Ironic. Opposite cause, same result. If stories are a dime a dozen, why waste time on them when it is the physics that matters?

I answer these questions because I enjoy them. I like to find creative solutions to things. If they get boring, I just tune out and look elsewhere.

 

[sophiecentaur]

Storylines are a dime a dozen.

I think you may be missing out on some pretty entertaining reading, if you stick to that philosophy.

 

[pinball1970]

"Nine people set out cross-country to rid themselves of some unwanted jewelry." There - now there are three books you don't have to read.

That sounds quite interesting. Probably the best idea I have heard in a while. The bestest bestest?
No, I think that would be "Ethel the Aardvark goes Quantity surveying"
I really hope they make that into a trilogy one day.

 

[sophiecentaur]

It's not as simple as that though.

You are quite right on that one. I tried using the Stefan Boltzman law but found it too hard to apply. I was waiting for someone to point me at the right answer.

 

[PeterDonis]

to cover let's say half of the Sun

It would have to be a lot less than half. The radiative forcing that is contributing to current warming is only a fraction of a percent of the total radiation we get from the Sun.

 

[jedishrfu]

I moved the thread to aerospace engineering because its more of an engineering problem.

If it ever made it into story it would be along the lines of an Arthur C Clarke Rama story or a Larry Niven Ring World story with lots of speculative engineering included.

 

[sophiecentaur]

The radiative forcing that is contributing to current warming is only a fraction of a percent of the total radiation we get from the Sun.

This could very relevant but I can't figure out how it affects things. A very small change in mean absolute temperature is required. Why wouldn't things more or less scale, according to a fourth power temperature factor? (Stefan)

 

[PeterDonis]

This could very relevant but I can't figure out how it affects things.

It means that the fraction of the Sun's radiation that you would want to stop is much smaller than one half.

 

[Algr]

If light falls on solar panels and gets converted to electricity, does that reduce the thermal impact on the planet? Do the solar panels get less hot when the electricity is used?

Either way, ground based mirrors will be magnatudes cheaper and more effective-per-dollar than trying to build something in space. Given the cost of transmission lines, covering the Sahara with mirrors would likely be a smarter use of money than covering it with solar panels.

 

[jedishrfu]

Where to place the shield is an interesting problem:
- if using mirrors on the ground to reflect it back into space, then the air gets heated
- if using mirrors out in space, then radiation doesn't impact the Earth, and so its arguably cooler

The size of the mirrors:
- on Earth, mirror placement means they would be haphazardly placed
- in space, you could have one big structure

Keeping the mirrors in place:
- on Earth, the mirrors could be rigidly mounted and track the sun
- in space, you'd need to choose a good spot and then use attitude engines to maintain position which would be costly to maintain with fuel

In The Ring World stories of Larry Niven some physicists and engineers analyzed the mechanics of maintaining such a large structure orbiting the sun and found it unstable and in need of constant correction.

https://www.bbc.com/future/article/20150609-will-we-ever-build-ringworlds

 

[PeterDonis]

In The Ring World stories of Larry Niven some physicists and engineers analyzed the mechanics of maintaining such a large structure orbiting the sun and found it unstable and in need of constant correction.

The Ringworld stability problem is different from the problem of keeping a sun-shield of the sizes under discussion in between the Earth and the Sun. The latter problem is just ordinary orbital mechanics plus having enough fuel/thrust available for corrections. The Earth-Sun L1 position is a saddle, so some perturbations will cause a satellite to move further from L1 but some will cause it to move closer again. We already know how to keep a satellite there since SOHO lives there.

The Ringworld problem, OTOH, assumed a ring going around an entire planetary orbit--in other words, imagine a ring structure around the sun 150 million kilometers in radius. Such a structure has an unstable orbit in the sense that if the Sun moves slightly off center, the effects of its gravity will tend to move it further off center. And now it's not just a matter of orbit corrections for an ordinary spaceship, even with a solar shield tens of kilometers square attached to it; it's a matter of orbit corrections for a ring structure 150 million kilometers in radius, and having to coordinate them in real time to counteract arbitrary perturbations. That's a much more complicated problem.

 

[sophiecentaur]

in space, you could have one big structure

One big structure in space would have to be non-selective. Locally placed, selective shade would require less area for agriculture.
The question of cost seldom seems to get discussed but space based solutions are very attractive to enthusiasts. Launching such a massive project would, in itself have a significant carbon footprint - much greater than an efficient airborne spraying of paint. Paint could be used everywhere whereas mirrors (which might be more effective) would only be practicable on easier terrain.
They say that white roads are being tried but you'd need to be wearing sunglasses all the time and there would be other problems

 

[pinball1970]

One big structure in space would have to be non-selective. Locally placed, selective shade would require less area for agriculture.
The question of cost seldom seems to get discussed but space based solutions are very attractive to enthusiasts. Launching such a massive project would, in itself have a significant carbon footprint - much greater than an efficient airborne spraying of paint. Paint could be used everywhere whereas mirrors (which might be more effective) would only be practicable on easier terrain.
They say that white roads are being tried but you'd need to be wearing sunglasses all the time and there would be other problems

Pretty impressive idea for a sci fi story actually. Like a ring world protecting the planet or "Ring" for short.
The ring is constructed by the powers on the earth.
As long as all those powers are aligned in the best interests of the planet. No malicious intent.
If one bad element got power of that "ring" I suppose the consequences could be bad.
edit. Ie G8 would be involved in the funding development and implementation.

 

[bob012345]

It would have to be a lot less than half. The radiative forcing that is contributing to current warming is only a fraction of a percent of the total radiation we get from the Sun.

SpaceX is putting up so many Starlink satellites that they may contribute to global cooling.

 

[sophiecentaur]

Pretty impressive idea for a sci fi story actually.

I would imagine that an author who thought about the problem from an Engineering or Political point of view would give the idea better scrutiny than as a Fun Space Plotline. I've read so many SciFi stories that hang on a very fine scientific thread that they border onto fantasy.

If one bad element got power of that "ring"

They (and also the good guys) would need the power of a selective on/off switch to target the times and latitudes of the shielding. World food supply is a vital issue (e.g. Ukraine's grain) and the real life performance of a shield would be very relevant to that. It would, in fact, be a massive experiment.

One should always ask what dear of Arthur C Clarke would have made of such an idea. As the idea has been submitted to PF then I would have thought that some technical rigour had been asked for, whatever the story lines of the characters.

 

[DaveC426913]

The ring is constructed by the powers on the earth.
As long as all those powers are aligned in the best interests of the planet. No malicious intent.
If one bad element got power of that "ring" I suppose the consequences could be bad.

Indeed. The One Ring might rule them all and in the darkness bind them.

 

[hmmm27]

Do the solar panels get less hot when the electricity is used?

Sure, though arguably, it all ends up as heat, eventually.

There was a firm touting a product that was an evacuated tube that used a PV element (also) as a thermal collector ; sounded decent for cold climates. I'd link, but the last time I visited they had stopped advertising it.

One I haven't seen (yet) is a PV system which passes chlorophyll spectrum EMF.

 

[sophiecentaur]

One I haven't seen (yet) is a PV system which passes chlorophyll spectrum EMF.

A new glass for greenhouses, perhaps. The holy grail for food production.