Added 1 new A* page:The BBC had an article a few weeks back about a Chinese company's announcement of a scheme to illuminate a city by reflecting sunlight from a geosynchronous satellite down to the ground, saying it should be possible to cover "an area of of between 10km and 80km" with reflected sunlight "eight times" as bright as moonlight.
It's being proposed as a cost-saving device, cheaper than the cost of lighting a city with street lights.
While a space mirror could do that, the article points out technical hurdles: it would have to have a very stable orbit over its target, and very steady, precise targeting to prevent the light beam from wandering across the Earth's surface.
And even an on-target beam might cause problems, say for wildlife (or even just for light-sensitive human sleepers without heavy curtains on their bedroom windows : P), because it would be shining that brighter-than-moonlight illumination everywhere in the target zone, not just on streets.
Russia actually ran a test of such a space mirror in 1993: their Znamya 2 satellite's 65-foot reflective solar sail trailed a 2.5-mile-wide beam across Europe for a few hours one evening (the spotlight moved over the ground at 8 km/s).
The test was considered a positive result for the concept, but a 1999 follow-up satellite with a 20% larger mirror accidentally caught its fragile foil on an antenna of its Progress spacecraft as it deployed, and the mission had to be scrapped. Russia had an even larger mirror satellite in production, but cancelled it after that second test failed—and that has been it for the space mirror concept up to this point.
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