Emperor Norton I;3979936 How effective would the mirror from space have been at it's job?
Very effective if in place with an advanced tracking device. From the moon (lunar revolution is every 29 days or so compared to the
Earth's 1, etc.) not so much. The Sun is a non point source, so it moves
outward at a .5 degree spread, and in a fire fight, the closer the better.
Most of the effective cost of a satellite is station keeping, in the case of
a constantly moving large one, more so. Most of the cost of the hard
equipment is not the mirror, but the mirror backing. Therefore the
question is very important. The cost is, both effective over how
long of a lifetime and the initial outlay. Lighting up the whole Vietnam,
even with a small amount of daylight intensity, seems prohibitive for
a few centuries.
Larger the array, harder it is to focus upon the source. I personally would
suggest a IR reflection only. While the absorption is much higher, the
VC would not at first know why we saw so much. Of course, they would
hide in as much cover as possible anyway.