> Ground based mirrors are very large, in the 10s of meters, and those mirrors are extremely heavy, like tons.

Seemingly fantastically - SpaceX is currently constructing a system designed to launch 100 tons to LEO, for as low as $35/kg [1]. Musk says this capability is what the Starlink business is to pay for. It appears lately, more realistic than it has sounded.

[1] https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-sta... ( https://news.ycombinator.com/item?id=21397285 )