[Lev1a]

Let's suppose the threat to such a laser weapons platform in orbit during conflict which you touch on in your last paragraph consists of 1+ missiles.

Could the targeting system of the platform not consist of some kind of movable/adjustable prism that could acquire a target not just straight down on Earth's surface but also in other directions?

Such a system (if feasible) could probably also cut down hugely on time needed for and the amount of repositioning the weapons platform has to do during operation (thinking about and writing this sentence made the image of Tony Starks basement particle accelerator appear in my head again).

Edit: the referenced scene of Iron Man 2 https://www.youtube.com/watch?v=mBgUsKd0cuI&t=2m25s