At least a space sunshade is easy to undo - stop maintaining it and its "heliostatic orbit" (not quite - it'd be held in place by solar winds and the push would be controlled by rotating parts of the parasol) will destabilize. And also can be used to help terraforming Venus.
Either of those large scale projects is still well beyond our ability, but should be within reach in a century or so, if we manage to successfully insustrialize the Moon.
Isn't the moon a better place to build a solar powered thin film factory? Build the whole thing into a single starship, or series of starships and use an EM launcher to leave the surface.
100T launch every day for 20 years is a lotta launches.
We'd need to manufacture most of the mass on the Moon and rail launch it. It's still a lot of launches, but they could use the sails themselves for braking when arriving at L1. Would take a couple years to get there, but most of the mass could be the parasol itself.
I was thinking about this before, I was wondering if you could heat a ball of metal on a shaft and then spin the shaft so that the ball pancakes out and the rotational force pulls the sheet into an extremely flat disk. Manufacturing in low g could enable entirely different construction techniques.
