Almost 10.000.000.000.000 kg of CO2 is every year released and mainly stays in the atmosphere. We increased the concentration from 300 ppm to more than 400 ppm during the last hundred year. And we will most likely double it before we move to CO2 neutral methods of energy production.

So, can we even avoid the negative consequences of the released CO2?

Despide all negative news on global warming, I see one viable option to save our civilization. But we need to change our thinking in two ways: Firstly, we need to start using tools of 21st century and secondly, we need to start looking for the solution out of Earth boundaries. The most effective way to counter the inevitable greenhouse effect is to build a sun-shade in space. If we block just 1% of the Sun’s light, we will compensate for the temperature increase of 1.5°C!

It is in our technological reach and it seems by far the cheapest option to correct our carbon outreach. With less solar irradiance, the temperatures on the Earth can be smoothly controlled. We could even effort to atmospheric greenhouse gas concentrations continue to rise for some time.

Credits to The Planetary Society

So, how we could we block the sunlight?

It seems counteraintuitive to look for the solution into Space. However, we can dispatch a large fleet of solar sail spacecrafts to the right location just between the Sun and Earth. The ideal spot is just next to the L1 Lagrange point, which will provide the right orbital stability. The swarm of space probes will need to be parked slightly closer to the Sun, so the solar wind will be offset by the Sun’s gravity. The probes will reflect the solar radiation. As the distance of L1 Lagrange point is about 1.5 million km far away, the shadow will smoothly cover the whole earth instead of creating one point of complete darkness.

Credits to NASA

The solar sail probes could maneuver themselves by just adjusting the sail orientation. So there is no fuel needed and their lifespan will be driven only by the momentum wheel lifetime, which is tens of years. To imagine, how the spacecraft will look like, we could refer to LightSail 2 project of Planetary Society. I proudly co-sponsored the project at Kickstart a few years ago and the spacecraft is now ready for lift-off.

Credits to The Planetary Society

LightSail 2 is a 3-Unit CubeSat with a weight of 5kg. The sail material is mylar with a thickness of 4.5 microns (1/5000th of an inch). It is powered by solar panels. It will form four triangular sails connected with cobalt steel booms with a total area just 32 sq. m.

Credits to Jason Davis / The Planetary Society

The total cost of the development of LightSail probe was just $6.6 million and it was privately funded. So I think that with a proper funding the space probe could be scaled-up from 5.5m x 5.5m to 100m x 100m size while keeping approximately similar weight by slightly thinner sail and by removing part such as DVDs. In addition, the project Breakthrough Starshot (aiming to send a small solar aircraft to the nearest star) did present some amazing miniature space electronics. So there might be a further area/weight improvements possible.

How many spacecrafts do we need?

So we would need to have 100 probes to cover an area of 1 sq. km. And we need to cover 1.2 million sq. km to block 1% of the Sun radiation hitting the Earth. So we will need 120 million of these probes. And we will need to get them to space. Luckily for us, we only need to get them to LEO as they can use the solar wind to slowly transfer to L1 by themselves.

And here is why we need SpaceX Reusable Rocket. With BFR able to deliver 100 tons to LEO cheaply, we could deploy up-to 20.000 probes at one lift-off, which would cover 200 km2. As the second stage (“Starship”) will provide 1000 cu. meters, it is more than required (60 cu. meters) to fit all the probes in. We can deploy hundreds of CubeSats today, so I am confident with a purposely build version of the second stage (no life support needed), we can deploy all of them safely.

Hence we will need about 6000 flights to deploy all the probes. It might seem like a very high number, but we will be launching probes over a quite long period. So if we decided to spread it over 20 years, it is about 300 flights a year. So less than 1 flight a day. And that seems to comfortably meet SpaceX ambitions.

Credits to SpaceX

So the remaining questions are can we build 6 million probes annually and what will be the cost. I don’t see the number of probes as an issue. We make more Apple Watches every year. A CubeSat cost is as low as $50.000 nowadays. With the mass production of thousands of units, we could reduce the cost at least 10x and with millions of units, the scalability really kicks. So I would not be surprised that we could get a probe for $1.000 with tens dollars to cover the cost of launch and logistics.

Hence the total project budget will be about $130 billion spread over 20 years, which is $6.5 billion annually. This is a fraction of the existing NASA budget and what we do invest today into green energy.

Please mind that I am not proposing to stay with fossil fuels. The solar shade is by far the cheapest solution to compensate for the already increased CO2 levels. I can also imagine positioning the probe fleet to focus the solar radiation into a powerful beam of 10TW. So we can accelerate other solar sail probes to explore our solar system or beyond.

Credits to Josh Spradling / The Planetary Society

The technology at our fingertips. Just spread the word. So the heritage of Carl Sagan could save our pale blue dot.

Please share and get the attention of the people like Elon Musk, Bill Nye, Charles Bolden, Johann-Dietrich Wörner or Jeff Bezos to this concept.