To shield the earth from greenhouse gas warming, scientists have all kinds of zany ideas. One of them involves creating a ‘solar shield’, or a giant structure that can reduce the amount of sunlight incident on the earth. The biggest hurdle to this kind of ‘solar shield’ is the amount of weight necessary to make it big enough to balance gravitational forces and prevent solar radiation pressure from blowing it away. This makes even the lightest materials prohibitively expensive. Scientists have proposed a new workaround or a ‘solar umbrella,’ which consists of two innovations: a tethered counterweight instead of just a massive shield, resulting in making the total mass more than 100 times less, and the use of a captured asteroid as the counterweight to avoid launching most of the mass from Earth.
To reduce solar radiation by 1.7%, or about the amount needed to prevent a catastrophic rise in global temperatures, the math suggests placing a tethered counterbalance toward the Sun which can reduce the weight of the shield and counterweight to approximately 3.5 million tons, or about one hundred times lighter than previous estimates for an untethered shield.
While these numbers are still only theoretical only 1% of the weight -- about 35,000 tons -- would be the shield itself, and that is the bit that needs to be launched from Earth. With newer, lighter materials, the mass of the shield can be reduced even further. The remaining 99% of the total mass would be asteroids or lunar dust used as a counterweight, though it is unclear where such a captive asteroid can be conveniently found.
