There are some interesting applications where a radiative surface that is shielded from radiation coming back the other way can emit radiation to cool itself by a few degrees below ambient temperatures. There’s one paper from a few years ago that describes being able to cool to 5°C below ambient temperature even in direct sunlight with some exotic materials.
Interesting stuff.
It’s a stupid idea, but it also won’t make a difference. Mirrors aren’t going to increase the total amount of radiation hitting the Earth, in an amount that can actually make any difference.
The surface area of the Earth is 510,000,000 square kilometers. How much surface area of mirrors can they even fit in a sun synchronous orbit at the edge of dusk or dawn, where the satellite is catching sunlight but not casting a shadow over a part of Earth? Even if they put up a million satellites with mirrors that are 324 square meters that’s only 324 million square meters, or 324 square kilometers. In other words, their most optimistic projection involves increasing sunlight by about 0.00006%.
It’s a disaster for astronomy, and for ecological balance for any affected wildlife, but won’t actually heat up the Earth.