One of my discarded project ideas was exactly this, but on a smaller scale. A steerable mirror on a mount with a camera for targeting. The idea was to place one

One of my discarded project ideas was exactly this, but on a smaller scale. A steerable mirror on a mount with a camera for targeting. The idea was to place one on the ground outside a north facing window. The device would then busy itself reflecting the sun up into the room making a nice sunny patch on the ceiling to light the room. They could also be used to deliver extra light to windows with plants in them to grow plants which require more light than is available or to modulate the daily light to fake a different season. Sitting in 2020 the technology is near trivial. The problem is that some knucklehead would point a bunch of them at the same window and set curtains and pigeons on fire. (You’d do this because you had a large room with few windows, so dispersed mirrors would give you multiple dispersed lighting spots in the room… and incinerated pigeons.) I was unable to make the leap to what happens if you are a deliberate and well reasoned knucklehead! In a controlled situation a megawatt of light might be just the thing. Addendum: The mass field of mirrors introduces a lot more work. Some of the immediately interesting problems: • you need a “everyone stop shining at the target” mode for emergency stop, but the mirrors need to move away from the target in such a way that they don’t create convergences elsewhere. Obviously sweeping your portal to hell down the tower would be a bad idea. So you have a collection of autonomous, free thinking mirrors, but when commanded to stop hitting the target they need to not make the same decisions. • your camera probably needs to be able to stare into the heart of a thousand suns (literally). But it also needs to see in ordinary daylight. Maybe a pinhole filter that moves over the lens would be appropriate. • with 999 mirrors shining on the target, you will not be able to see your own contribution to aim. There probably needs to be a “hey! Everyone else look away for a second” command for unit to aim and calibrate itself. See complexities from the first bullet and not incinerating things you like. So yeah, they could have started with my garden heliostats, but then it would be a crack the knuckles, bring in the eggheads, and get to work operation to solve all the hard problems.