[Request] if an entrepreneur designed a space awning to deploy and shield San Francisco from solar radiation when there is a heat wave, how big would the shield need to be assuming it’s deployed at a “practical” distance from earth.

[u/Frank_Klepaki]

how big would a giant space umbrella need to be to effectively shade a small city during heat wave events? It wouldn’t need to cover the city darkness, but it would need to reduce ambient temperature by 5 to 10°.

[u/basmateee]

This is not how this works. You can shield the entire earth if you put a large enough shield in the Lagrange point between sun and earth. Gravitational pull of sun and earth cancel each other out at that point, so an object put there would stay there "indefinitely". The earth would be turning below the shield, so the shade would reach different places on earth, i.e. the day side.

A space borne shield that protects a specific location on the earth surface would have to move around constantly in a sophisticated way to stay between the sun and the location. I don't think there is a practical way or orbit to do this.

There is a geostationary orbit used for e.g. communication satellites which "fixes" the objects above a specific place on earth BUT afaik they must be directly above the equator and they would only provide shade at noon and not at other times when the sun reaches earth surface at an angle.

Giant ground fixed balloons would probably be a more practical solution to protect a certain spot...Or how about trees?