Analyzing the building of a giant ‘umbrella’ floating in space to reduce global warming and slow down climate change. Yes, it’s just as audacious as it sounds.

We are filling the thin atmosphere keeping us alive with more greenhouse gases every day.
Credit: ISS, Earth Science and Remote Sensing Unit, NASA JSC

The climate problem is still growing

Climate change caused by the emission of greenhouse gases is posing an existential threat for human life on Earth and we need to stop it from progressing and reaching a tipping point. Lowering our emissions and transitioning our energy infrastructure is essential but, at the same time, a long and arduous process. In the meantime, we keep emitting more CO2 and other greenhouse gases making the situation worse every day.

Experts around the globe are working on technologies that could help us reverse the damage we’ve already caused to our climate by filtering the greenhouse gases back out of the atmosphere and storing them underground or even using them to make products. Unfortunately, this technology still requires more research, investment as well as time to become mature and sizeable enough to make a tangible difference in the short term. I’m not even going to start mentioning the ungodly amounts of energy required to break the CO2 bonds we have created. Since time is of the essence, and scaling the solutions above will take a while, we need all the ideas we can get to reduce or slow the warming and gain us more time to transition our energy infrastructure.

I am convinced that we will find a way out of this mess and emerge with a greater understanding of how Earth’s geophysical systems are interacting and in turn influence our delicate climate, weather, and the conditions for life to form and thrive. This knowledge will not only help us solve challenges here on Earth, but also enable us to venture further out into the universe. To get there, we will need all the bold ideas and – seemingly crazy – solutions we can get.

Disclaimer
Geoengineering, the deliberate large-scale manipulation of an environmental process that affects the earth's climate, is not a replacement for making drastic changes to our energy infrastructure and critics have rightfully attacked similar ideas in the past. For more information on this topic please check out the post Why people disagree about geoengineering by Oliver Morton. My motivation for writing this article is simple: If we have to take emergency measures to mitigate climate change, we do it in a way where we don’t accidentally disrupt other conditions vital to our survival in the process.

Geoengineering more reflective clouds? An emergency solution with serious drawbacks

One way to keep the temperature on earth stable despite our greenhouse gas output is to reflect some of the sunlight back into space before it can warm up the Earth. Researchers have for years proposed a solution for rapidly cooling the planet inspired by volcanic activity. Similar to a natural volcanic outbreak scientists have proposed that we fly planes that spray sulfur into the stratosphere to create a thicker and more reflective cloud cover. While the effectiveness of this process has been established through natural observation and could be executed relatively quickly, there are also some significant drawbacks to this idea. The biggest issues that stand out to me are the resulting acid rain which impacts fresh water, animals and plants, a white haze in the sky as well as the ongoing costs of having to ‘re-spray’ the particles over and over since the necessary concentration has a half life of only a few weeks to months.

An alternative solution: Sunjammer

Instead of chemically modifying our atmosphere and clouds to reflect more light, I propose the building of a giant shield in space to partially occlude the rays of the sun and prevent them from reaching Earth.

Sunjammer modules on the way to their destination. Artist’s rendering by Aleksandar Papez

An analysis by Bala Govindasamy and Ken Caldeira states that if we manage to block roughly 1.8% of the sunlight reaching Earth, we can cool the average temperature back to pre-industrial levels. Similar to the idea of the american Astronomer Roger Angel, the Sunjammer shield would be composed of millions of smaller satellite modules. Instead of static disks like Roger Angel proposed, Sunjammer modules, similar to a Solar Sail, would unfold and expand once in space, saving space and cost at launch. And, instead of floating around randomly, these modules would be designed to autonomously link up to form a massive, sun-blocking wall once they reach their final position. While Sunjammer would certainly be more capital and labor intensive than the comparatively cheap chemical geoengineering, it stands to reason that not having to deal with any of the previously mentioned associated health and ecosystem concerns is invaluable.

While ‘blocking the sun’ might initially sound like an idea a ‘Bond villain’ would come up with, the potential benefits for humanity, especially compared to chemical geoengineering, do warrant a closer look. To ensure that we weigh the societal tradeoffs correctly, it makes sense to delve deeper and analyze the feasability and costs associated with the implementation of this idea.

Why now?

While similar ideas have been rejected as impossible and unworkable, the main criticism can mostly be boiled down to cost and ‘unproven’ technology. In the last decade though, a lot has changed in the space launch market with the entry of SpaceX and their reusable rocket booster technology. The rapid decrease in launch costs changes the calculations for this and similar ideas drastically and has lead to a subsequent massive increase in investment in the space industry. The real game changer might be the upcoming SpaceX Starship rocket which is designed to lift 100t to Low Earth Orbit, is fully reusable and supposed to be able to launch three times in a single day, bringing costs down by another order of magnitude.

Technology, Cost And Feasability

To keep costs under control, the scale of production and a modular design are crucial. That means all pieces of the Sunjammer should be identical and designed to arrange themselves into one large structure at their destination. We already have the technology today for building large foldable structures that can grow their surface area many multiples once they reach space. Well-known examples already using similar technology are Solar Sails like Solar Cruiser made from Mylar and the James Webb Space Telescope with its Kapton shield.

Sails based on this existing technology, attached to small and lightweight CubeSats, and our new re-usable rocket technology could allow us to build this structure for a surprisingly small capital effort. A similar idea in 2006 projected roughly $5 trillion as feasible for all necessary development, manufacturing, deployment and ongoing operations. If a lifetime of 50 years is achieved that would bring costs to ~$100b per year, or roughly 0.2% of world GDP (Numbers from 2006).

With our newest satellite technology and upcoming rockets like SpaceX's Starship, Pavel Konecny has estimated in 2018 that it would cost only $130b over 20 years, or roughly $6.5b per year, to build out a solution similar to Sunjammer. As the projected costs of climate change continue to rise and the price for a sunshield continues to fall, it makes sense to seriously consider this emergency solution to gain us the time we need for a smooth energy transition.

Placement and Transport

The ideal spot to place Sunjammer would be at the Lagrange point 1 (L1), a special spot between the earth and sun that sits in a gravity equilibrium and moves in tandem to always be situated between the two. Since station keeping around L1 already uses very little energy it is possible to stay there with just the passive propulsion principle of Solar Sails. Using this technology means we don’t need to launch any fuel for the satellites’ station-keeping and they can slowly move themselves to L1 from Low Earth Orbit (LEO), increasing space and weight efficiency and decreasing launch costs. Since the occlusion would be of purely mechanical origin, it can also easily be ‘turned off’ at any time by sending a signal to the satellites to adjust their sails and slowly drift out of their fixed position.

The benefit of controlling positioning of modules within the larger structure

Because of the Polar Amplification effect the warming is more pronounced in Arctic areas. This leads to sea ice melting and rising sea levels, which are threatening to displace 187M people by 2100. For perspective: Currently roughly 247M people live outside of their country of birth and migration of this magnitude is almost certain to lead to political instability and violence.

Compared to chemical geoengineering, which is subject to atmospheric winds, the mechanical nature of Sunjammer would allow us to vary the amount of shading precisely for different latitudes of Earth with different module arrangements. These arrangements could also be modified over time depending on the development of the situation on Earth.

Things we still need to figure out

Crucial for this idea to work will obviously be the price tag and time requirements to deliver it ‘in time’. We already have some of the crucial technological puzzle pieces in place but others are still missing or still need to be improved. Nonetheless, I want to try to provide some perspective on the size of the challenge, provide some starting points to solicit help and inspire others to make the necessary investments to make this solution feasible.

Can we manufacture something on this scale?

Scientists say that blocking roughly 1.8% of the Sunlight that reaches Earth would be enough to cool the earth’s average temperature back to pre industrial levels (roughly 1.1° Celsius or 1.9° F).

To cover an area of this size we would need roughly:
22.5 Million Sunjammers modules, ~1km² each when unfolded, or
45 Million Sunjammers modules, ~0.5km² each when unfolded, or
90 Million Sunjammers modules, ~0.25km² each when unfolded

The biggest Solar Sail currently under construction, Solar Cruiser, to be launched in 2025, has a surface area of approximately 1653m² or just 0.001653km² and weighs ~90kg. In the year 2021 humans built roughly 233M iPhones and 79.1M motor vehicles but launched only 1743 SmallSats. So, while the manufacturing scale seems feasible from an engineering and resource standpoint alone, the ramp-up would still have to be massive. Scaling towards producing 90M SmallSats yearly, compared to our currently low production levels, would require us to double production for the next 10 years in a row.

How many sails should we make and what size should they be?

There is a sweet-spot to be found between the size, and amount of Sunjammer modules we should make. Important for finding that spot are the maximum sail size we can feasibly create, optimal economy of scale manufacturing and avoiding supply bottle necks for chips, sensors or solar panels used in the core units. If we make them too small, we might not have enough supplies for the comparatively more complex core modules, and if we make them too big we might not reach the right economies of scale, leading to higher costs overall. Currently technology constrains the size of Solar Sails to roughly 0.001 km2 but innovations on the boom construction and sail materials will allow as to build bigger and lighter sails in the near future.

Do we have the capability to launch this mass in time?

The efficiency of launch logistics is influenced both by the weight and size of the payload. For the size of individual Solar Sails we are talking about here, the mylar sail and the necessary booms needed to stiffen it would make up the bulk of the launch weight. In 2002 we achieved a weight of just 2g/m2 with an extra thin Mylar film. Together with the booms the weight reached 4.5g/m2 which would lead to a minimum launch weight of 101.25M tons for the entire Sunjammer structure, core modules not included. Since then scientists have already reduced the weight of booms by 75%, proposed carbon fibre sails that could eliminate the need for booms altogether and our current ambitions are to reach 1km2 sized sails with a total weight of 1g/m2. If we realize these ambitions, the launch-weight would be reduced to roughly 22.5M tons.

With the dramatically improved launch technology of SpaceX’s Starship we’re supposed to be able to launch 100t+ to LEO three times a day, or 109’500t per year across 1095 launches. Even with this very ambitious launch schedule it would take us 205 years to launch the entire sail structure with a single Starship. Luckily, current SpaceX ambitions are targeting the building of 1 additional Starship a month by end of 2022 and a total of 1000 Starships by 2050. These material advances, combined with 50 Starships operational and at full capacity, would enable us to launch the entire constellation in roughly 4 years.

A visual comparison between Solar Cruiser and two of the proposed Sunjammer module sizes. The tiny black dot next to Solar Cruiser is a human to scale.

A brief summary

Climate change caused by greenhouse gases is already having big impacts around the world that are only predicted to get worse, from sea-level rises to changing weather patterns leading to droughts and famines. We know that in the long term there is no alternative but to transition our energy generation, storage, and distribution networks to eliminate our greenhouse gas emissions.

To preserve our current standard of living during this transition, the move to a zero carbon world will need to happen gradually. While this is probably a good call for social cohesion, it also brings us dangerously close to critical climate tipping points. Because of this, different geoengineering ideas are being discussed to gain us more time and allow for a smooth transition in a world of hightened CO2 levels.

The Sunjammer emergency geoengineering project, which involves sun blocking satellites in space, replicates most of the benefits of the chemical geoengineering solutions that alter our atmosphere but avoids most of their downsides like acid rain, hazy skies or ozone depletion. The main downsides remaining for a space based solution are the necessary technological advancements and time to implementation. The implementation costs of a Sunjammer like solution will continue to come down further with our renewed investment in space technologies, the resulting rapid technological progress and price pressures. If key technologies to create Solar Sails that weight just 1g/m2 can be advanced until 2030, that should coincide with humanity having gained the capabilities to launch the entire structure in just a few years for a manageable budget.

If this article has made you think, or even hopeful for our exciting future, please share it with your network and help spread the idea! There is no time for desperation.

Thank you!
Written by Aleksandar Papez

Thank you to Mania Psaltidi, Stijn Van Willigen, Lukas Reichart, Susanne Sigrist and Mo Gawdat for your encouragement and feedback as I was writing this article.

The name Sunjammer is inspired by a Solar Sail project that got cancelled in 2014 and a short story of the same name by Arthur C. Clarke.

Sunjammer: Blocking the Sun could save Earth

The climate problem is still growing

An alternative solution: Sunjammer

Things we still need to figure out

A brief summary