User blog comment:RandomGuy96/So how do planetary defense cannons work?/@comment-5379655-20130128042915/@comment-4967682-20130128045215

The problems with that: one, if they can be such a pain to your fleet, why would you not simply shoot them from far away before putting your fleet in striking distance of the planet?

The PDCs are hurtling through space at thousands of miles per hour? What? Did you mix up words or am I missing something? Anyway, even the planet rotating should do nothing to decrease accuracy. It should be ridiculously easy to compensate for the rotation of the planet, as the VIs on the ships are designed to hit small targets from tens of thousands of kilometers away moving completely unpredictably at relativistic speeds. By contrast a planet's orbit and rotation are slow and predictable. So I don't see why you would need to go into orbit.

I'm glad you bothered to make a detailed response. I like discussing these things.