An island nation has a lot of coastal territory and has become gravely concerned about the threat of global warming. They've decided to fix this by launching reflective satellites into orbit -- similar to China's man-made moon plan, but instead of reflecting sunlight to Earth at night, they're reflecting sunlight away from Earth during the day.

Is this viable?

I assume it's not actually viable since real-life geoengineering efforts seem to be mostly interested in adding reflective material to the atmosphere. But what's the problem?

Does it take an unreasonable number of satellites? Are the satellites too expensive even when bulk-manufactured? Are the satellites too expensive to launch into orbit? Do the satellites get damaged too quickly by orbital debris? Is there some sort of weird thing where the satellites act as solar sails and the pressure pushes them out of orbit? Or is it just that the satellites fly over countries that would prefer not to suffer eclipse conditions most of the time?

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    $\begingroup$ Can you limit the number of questions? $\endgroup$
    – L.Dutch
    Commented Dec 12, 2018 at 19:30
  • $\begingroup$ @L.Dutch I really did mean "direly concerned" in my question. The word "direly" is an adjective meaning "gravely", "dreadfully", or "terribly". It seems the word caused some confusion, so I've now edited it to "gravely". $\endgroup$
    – Dan B
    Commented Dec 12, 2018 at 19:50
  • $\begingroup$ Sorry, I wrongly took it as a typo $\endgroup$
    – L.Dutch
    Commented Dec 12, 2018 at 20:14
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    $\begingroup$ A country which took it upon itself to decrease the amount of sunlight falling on Russia may soon find iself the recipient of many Russian-made explodey objects falling from the sky. Remember that for a very large Eurasian country which possesses a lot of permanently frozen land, global warming may not necessarily be a danger to be avoided, but potentially something to be welcomed. $\endgroup$
    – AlexP
    Commented Dec 12, 2018 at 20:31
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    $\begingroup$ @Amarth: They gas which Russia sells to their clients and the kind of gas which may leak out of the permafrost are different. Russia is not extracting natural gas by thawing vast amounts of permafrost. $\endgroup$
    – AlexP
    Commented Dec 12, 2018 at 21:00

5 Answers 5


Could we do this?

Yes, we could. It's been proposed before in a number of forms. Most calculations agree that this sunshade would need to reduce solar insolation by anywhere from 2-10%. If we take an optimistic figure - the lower bound of 2% - then we could achieve this by putting a shade 4.5 million square kilometers in area at the Sun-Earth Lagrange point, $L_1$. Alternatively, we could send 16 trillion tiny satellites there, or put a 1 million square kilometer lens at $L_1$.

What are the problems?

This might be technically feasible. However, there are some barriers to it.

  • Given current launch costs, these plans would require perhaps hundreds of billions of dollars.
  • $L_1$ isn't stable; we'd need to continuously adjust the orbit of every object we place there. This costs money, too.
  • You'd probably have to get the agreement of most countries before undertaking a project that would affect literally the entire planet.

Physics says that yes, this can work. But it would require orbital readjustment, a large amount of money, and international agreements.

Other notes

As jamesqf noted, this plan would not reverse effects of global warming like ocean acidification. These are directly related to the concentration of greenhouse gases such as carbon dioxide and methane, and we would need to reduce levels of those if we wanted to avoid certain catastrophic effects.

Additionally, it wouldn't be great to put the satellite(s) in orbit; they have to go to $L_1$. Why? Satellites spend half of their time on the daytime side of Earth and half of their time on the nighttime side of Earth. This means they would only be blocking sunlight for half of their orbits. Putting them at $L_1$ is much more effective.

As a final thing to keep in mind: Placing these objects at $L_1$ won't cause an eclipse or any similar effect. The umbra will not reach Earth. Instead, the satellites will simply decrease the overall amount of sunlight we get, rather than completely blocking any particular area.

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    $\begingroup$ It would work as far as the warming is concerned. However, it does nothing to address other problems, such as ocean acidification, that are associated with large increases in atmospheric CO2. $\endgroup$
    – jamesqf
    Commented Dec 12, 2018 at 19:44
  • $\begingroup$ I had wondered if launching to Earth orbit would be cheaper than launching to the L1 point, but it sounds like this is not so. $\endgroup$
    – Dan B
    Commented Dec 12, 2018 at 21:07
  • $\begingroup$ Don't want to be this guy, but just like killing all mosquitoes, this kind of answer to a problem can have unknown consequences maybe far worse than the problem itself. $\endgroup$
    – bob dylan
    Commented Dec 12, 2018 at 23:59
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    $\begingroup$ Minor, pedantic note: "effects of global warming like ocean acidification" is incorrect. Global warming and ocean acidification are both effects, and greenhouse gases are the cause. $\endgroup$
    – MJ713
    Commented Dec 13, 2018 at 0:32
  • $\begingroup$ Yeah, no. Broadly speaking we can say that killing off/altering processes that take greenhouse gases out of the atmosphere...increases greenhouse gases in the atmosphere, self-reinforcing. The answer doesn't bring up the cost to the atmosphere of building & launching such masses =) Being as people won't agree to be nice to the world we clearly need a Hunger Games. $\endgroup$
    – Giu Piete
    Commented Dec 13, 2018 at 2:13

Just to throw some numbers out, the space shuttle could deliver a 65,000 pound payload into space. To do this, it used 2.8 million pounds of fuel.


  • NASA Space Shuttle FAQ: 1,607,185 pounds of fuel in the External Tank and internal.
  • Cool Cosmos: 1.1 million pounds in each rocket booster (two); 65,000 pound payload.

Space X's Falcon 9 produces an estimated 250 thousand kilograms of carbon dioxide per launch and has a payload of 13,000 kg. Using the energy content of kerosene, that's about four billion BTUs per launch.

So 13 Mg of reflectives would have to more than counteract four billion BTUs plus the greenhouse effects of 250 Mg of carbon dioxide. Plus of course the amortized carbon cost from building and operating the Falcon 9 (e.g. moving it from its landing area to its launch pad).

One proposal would use 16 Tg of reflectives. That's more than a million Falcon 9 launches.

This would be much more feasible if the reflectives were built in space and moved into position by solar sail.

Some will point out that we could instead burn hydrogen. Of course, that produces water vapor, another greenhouse gas. It's less of a greenhouse gas than carbon dioxide, but hydrogen is also less energy dense than kerosene.

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    $\begingroup$ +1, yay numbers! Doing some more math on this,it seems there are 1M kilograms in a kiloton. So one million Falcon 9 launches would be 250K kilotons. World emissions in 2015 were 36M kilotons, so one million Falcon 9 launches would be a bit less than 1% of world yearly carbon emissions... $\endgroup$
    – Dan B
    Commented Dec 13, 2018 at 4:07
  • $\begingroup$ You're on the right track, but the argument that water vapor is a greenhouse gas ... doesn't hold water. There's already plenty of water on Earth, and adding more water vapor to the air will only mean there is a bit more rain due sometime soon. $\endgroup$ Commented Jul 10, 2021 at 3:45

Just use glitter!!

There are some real world proposals to use a cloud of glitter as a mirror


In the proposed Orbiting Rainbows system, the small cloud of glitter-like grains would be trapped and manipulated with multiple laser beams. The trapping happens because of pressure from the laser light -- specifically, the momentum of photons translates into two forces: one that pushes particles away, and another that pushes the particles toward the axis of the light beam. The pressure of the laser light coming from different directions shapes the cloud and pushes the small grains to align in the same direction. In a space telescope, the tenuous cloud would be formed by millions of grains, each possibly as small as fractions of a millimeter in diameter

It only stands to reason if you can use it to capture images, you can also use it to reflect unwanted sunlight. Then it's just a matter of scale.

Another big advantage is, think if it gets hit with orbital debris or meteorites. So what it punches a hole in a cloud of glitter. Adjust the lasers a bit, no hole.

A Bonus Idea

As a bonus idea, it would be worth while to convert the sunlight into electricity. In this example it would take more advanced "glitter" but the biggest stumbling block would be transmitting the power, not actually generating it.

But this way, not only are you "shading" the planet and reducing the temperature, your also supplying a large amount of (essentially free) solar electricity. Which would also be beneficial to any climate change scenario as it would cut down on the use of power generation on the planet (fossil fuels, nuclear waste etc..)



As others have pointed out, it's theoretically, if not technically possible or feasible to shade the earth, but we are faced with the fact that most of our tech and accessible resources are inside of a large enough gravity well, that will likely continue to pull-in more material (~40Kt) per year than we will ever be able to launch, with current launch systems. But we can bootstrap the process:

You would only have to launch automated mining and manufacturing equipment to begin the process of building a self sustaining space economy that lives off of the material available in tiny gravity wells (asteroids/comets/Moon), and uses abundant solar energy to power it all. And most of what does get launched from earth, would have to be inserted into LEO by electromagnetic means (rail/coil guns. Elevators are presently off the menu).

We could probably build practical guns with current tech, that could place bulk materials into orbit, but they would subject their payloads to such extreme accelerations, that most assembled equipment and no human could survive. The bulk of the parts and raw materials could be launched that way, for assembly in orbit. But, since nothing below escape velocity can avoid falling back to earth, you'd have to have some space tugs out there, to intercept the payloads and move them into stable orbits.

The first hurdle would be to construct the guns, which would be nearly vertical structures built at high altitudes, and rising 20km or more. The longer the gun, the lower the mass of atmosphere, that the projectile must decelerate through, to be reachable by the tugs. Such a structure would have to be flexible and dynamically stabilized by a variety of means, including thrusters, which would also be needed for aiming.

While that's happening you need to get out to some carbon and ice bodies where you can make fuel. We can launch the first tugs and some fuel into orbit using rockets, but acquiring fuel off-world, would be the highest initial priority, to keep the tugs running. The tugs wont be able to use solar power for propulsion, because they will be entering the upper layers of the atmosphere, where solar panels would produce too much drag, and they are going to need a lot of thrust, so that means chemical propulsion. It's possible that a hydrocarbon based fuel could be a good choice, at least initially, as it might produce enough smog to temporarily cool the planet (TBD), but there's plenty of hydrogen and oxygen out there that can be produced using solar power, and those two elements would likely be the least environmentally damaging in the long run.

Next you launch a minimal number of assembly stations via rockets. These will be used to build more robotic stations as supplies arrive from the guns. They can use solar power and ion thrusters for maneuvering and stabilization.

When you get your orbital production levels high enough, you can start using some of it to build miners and transports. With those, you can get out to the metallic and rocky bodies to start mining the rest of what you need. At some point you will rely entirely on off-world resources and disassemble or mothball most of the earth-bound launch systems.


An alternative would be to use rockets to provision the surface of the moon with robotic miners and assembly systems. If you can produce Teflon and/or carbon fiber on the moon, then you can build space elevators there, greatly reducing the need for rocket fuel. Guns also work there, for launching large masses into space. Lacking an atmosphere, and having far less gravity, you can use guns to safely launch humans into space from the surface of the moon.

The moon is ideal, but to get there with enough equipment to bootstrap the process at a high enough rate to build your shield in time to prevent total collapse of the earth ecosystems, you'd still need to build some guns on earth, to deliver the initial equipment.


The current limit of human built vertical structures, is <1Km. The tallest buildings, use dynamic stabilization for human comfort and to prevent destructive oscillations, driven by the winds. The structures needed for rail or coil guns, would not in any way be built for human comfort, so their total mass/km would be a great deal lower than our current tallest buildings. I don't think it would be too much of a stretch to push the limit to ~2Km with current construction technologies. That's an order of magnitude lower than you'd need for a practical system, so we'd have to invest more in materials research and divert a larger fraction of our hydrocarbon production into making Teflon, graphene's, carbon fibers and other advanced materials.

It is likely that in the short run, you'd have to deploy some vertical thrust to keep the gun from collapsing. This could be provided by electrically driven fans. Rather than model the gun as a vertical spike, it would be more like a stiff rope or conduit, that could possible be leaned over/curved to some extreme angles (10 degrees maybe?) for aiming purposes. Some modeling of the atmospheric effects of operating such a structure for up to several decades, would be very important. Such a system would have it's own, local, small redundant nuclear power plants, in addition to being connected to the power grid, to ensure the structure doesn't collapse unintentionally.


The key economic benefit of using guns, even when they must be permanently supported by some thrusters, is in the avoidance of the rocket equation. You don't have to lift any fuel, to provide lift a second later. And electrically driven propulsion all around, is more environmentally safe. They are the only way we can bootstrap any kind of major push beyond our gravity well, without destroying the ozone.


Elevators to earth orbit, currently require the use of unobtanium. Graphene and carbon nanotubes have been ruled out, because they don't have the required tensile strength and those were the previous front runners.


**Satellite Design **

If you wanted to use satellites to decrease climate change, then you would either need lots of very large, reflective, and heat absorbent satellites. Another way that you could use satellites is by having them use some kind of filter or collection device within the atmosphere that would gather up pollutants like carbon dioxide for the satellite to then retrieve and find some way to dispose of.


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