NonCredibleDefense

My scientific research of squinting at the poster says a spy satellite is probably about as long as a pickup truck which is probably about 20 feet long.

xkcd says space is 100 km away and I'm sure there's nothing else I need to understand about that.

At 100 km away, the change of angle that will move your beam by 20 feet (enough to make the difference between hitting or not, if the thing and the flat mirror are both about 20 feet long I guess) is (20 feet / 100 km / pi) radians or 0.0000194 radians, meaning you raised or lowered one edge of the mirror by 0.004 inches or around the width of pretty-thick hair. I would be a little surprised if the mirrors even stayed within that tolerance just from flexing around in the wind for as big as they are.

On the other hand, you wouldn't have to hit the spy satellite with every mirror; you could probably heat it up significantly just by hitting it with a bunch of the beams as they were swinging wildly around and mostly missing it. And if it was specifically a spy satellite, you could probably fry its optics with not really a lot of mirrors for not a long time actually managing to hit it.

On the other other hand the thing would be flying along at around 8 km/s, so you'd have to get your mirrors positioned accurately enough, and then start moving them at a relatively insane speed while still keeping their absolute positioning dead accurate when their motors and overall construction clearly weren't designed for either of those tasks at the required level of precision.

TL;DR Let's try it

Also there's this

It should work. Trust me. I have a theoretical degree in physics.

The suns angular diameter is about 0.01 radian, so at a distance of 100km, the suns reflection will spread out to a disc about 1km across.

392MW over a disc that size is 500w/m2, which is weaker than direct sunlight.

Uh… losses from transmitting through the atmosphere a second time?

Damn. I wonder what its operational range would be.

You might even need adaptive mirrors to deal with atmospheric distortion. Also, they would have to move relatively quickly and very precisely (read: an impossible combination) to track satellites in low orbit. Plus, you could only hit satellites that crossed overhead at a relatively high angle.

But yeah, one solar tower plant did a stunt where they reflected an image made of sunlight at the ISS and an astronaut took a picture. They didn't melt.

thats what they want you to think

Someone's been drinking their government supplied fluoride tainted tap water, you're thinking like one of them. Don't believe The Man's lies!

… for now!

The power density square law is for an emitting light source that emits in all directions. Since the incoming light is basically parallel that doesn't really apply. If you were able to accurately track a satellite (a feat I'm sure is pretty hard) you would definitely vaporize it pretty quickly I'm talking under a minute since space is a good insulator.

There is a cool easy-to-show fact that you can never make something hotter than the light source my focusing its light.
Since otherwise you could take heat and divide it into a hotter and colder region, decreasing entropy without using energy.

Not just stat helio-stat

I disagree, you need to melt it, because space is more interesting when its full of lances of molten metal whipping about at orbital speeds

Well all things (human) in space have special paint in order to modify their blackbody radiation and maintain a trade off between disipation heat by EM radiation and keeping a temperature that allows semiconductors to work.

The point is that satellites do disipate heat. Convection disipation is the worst disipation of heat. The best disipation of energy (heat) is by radiation. Thats why the thermal blankets look shinny weird, just like the satellites. You would need a realiable source of heat in order to overcome the satellite disipation and saturate the satellite.