Space sunshade
First proposed in 1989, another space sunshade concept involves putting a large occulting disc, or technology of equivalent purpose, between the Earth and Sun.
The individual autonomous flyers building up the cloud of sunshades are proposed not to reflect the sunlight but rather to be transparent lenses, deflecting the light slightly so it does not hit Earth.
[13] The remaining solar pressure and the fact that the L1 point is one of unstable equilibrium, easily disturbed by the wobble of the Earth due to gravitational effects from the Moon, requires the small autonomous flyers to be capable of maneuvering themselves to hold position.
[14] Such a group of sunshades would need to occupy an area of about 3.8 million square kilometers if placed at the L1 point[14] (see other lower disc size estimates below).
Roger Angel of the University of Arizona[11] presented the idea for a sunshade at the U.S. National Academy of Sciences in April 2006 and won a NASA Institute for Advanced Concepts grant for further research in July 2006.
"[14][16] Researchers from the University of Stuttgart, Institute of Space Systems described a roadmap for the development, construction and transport of an international planetary sun shield (IPSS) at the Lagrange point 1 in 2021, which would also be a photovoltaic plant.
[18] MIT scientists led by Carlo Ratti believe deflecting 1.8 percent of solar radiation can fully reverse climate change.
The full raft of inflatable bubbles would be roughly the size of Brazil and include a control system to regulate its distance from the Sun and optimise its effects.
[19] In July 2022, a pair of researchers from MIT Senseable City Lab, Olivia Borgue and Andreas M. Hein, have instead proposed integrating nanotubes made out of silicon dioxide into ultra-thin polymeric films (described as "space bubbles" in the media [20]), whose semi-transparent nature would allow them to resist the pressure of solar wind at L1 point better than any alternative with the same weight.
[6] In 2004, physicist and science fiction author Gregory Benford calculated that a concave rotating Fresnel lens 1000 kilometres across, yet only a few millimeters thick, floating in space at the L1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%.
[26] A similar approach involves placing a very large diffraction grating (thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun.
A proposal for a 3,000 ton diffraction mesh was made in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde,[27] although in 2002 these same authors argued for blocking solar radiation in the stratosphere rather than in orbit given then-current space launch technologies.
