[ben_w]

> I'd guess aluminum mirrors in space would stay reflective for many decades.

How long stuff lasts is an interesting point I has not considered. More UV, micro-meteors, even the question of what light pressure does to the orbits over a few years, given the large surface area to mass ratio. I don’t know how similar or different conditions are in the ISS orbit versus any other.

That aside, I think optical mirrors are going to be the least acceptable with regard to security/defence types, as that’s the easiest to be surreptitiously modified into a death ray, just because all the elements are physically smaller. With RF you can at least make it so any modifications are ridiculously obvious, even if you still have to care about malicious combination of multiple systems.

But on the Moon? Not only will we probably only need at most a handful, the fact that the Earth-Moon distance is much larger than most orbits considered for space-based solar power means even a maliciously retargeted combination of system would be much less of a threat.