So he wants a geostationary satellite. In that case aiming is as simple as pointing the barrel in the right direction, you have a lot fewer calculations to make.

Hmm, this thread is enticing me to make a whole constellation of attack satellites that will cover every square inch of the world at all times. It would take about 70 birds to do it from LEO. 3 to do it from Geo (if you exclude the poles, significantly more if you want to cover the poles).