> relatively easy to redesign as weapons

There is a fiction I've read years ago that mentioned satellites becoming makeshift weapons by overheating exposed objects (think reactors, gas trucks, oil refineries) by acting as a solar furnace [1] via mirrors.

Not sure/don't recall how it deals with practical issues such as clouds and distance/intensity, but good enough for a story I guess.

[1]: https://en.wikipedia.org/wiki/Solar_furnace

> The temperature at the focal point may reach 3,500 °C

I thought this was interesting because it doesn’t really seem like an applicable top level claim, surely this is referring to a specific furnace, not all solar furnaces?

Then this got me thinking if there is some universal upper bound constraint to these temperatures. E.g. if I recall a telescope can’t make a source object brighter than it actually is, and this just seems like a thermal telescope, so I wonder if that principle applies here or not.

Probably easier to use a MASER

007: Die Another Day has it as a main plot point.

You can't focus sunlight at the satellite distances. And this is a fundamental problem, the focal distance varies for each wavelength so your focus point will be smeared. You need monochromatic light for that (a laser).

Edit: and also don't forget that the Sun is not a point source and has an appreciable angular size, further making it impossible to focus it with a reasonably-sized lens or mirror.