Pretty simple suggestion. A type of shield you can only place on stations or planets, and uses a crapton of power. It projects a bubble around the planet segment or station. It would block all enemy ships above a certain mass of getting in - the size depends on the how much power the shield has. You could edit permissions to let only allies, neutrals, or all get in. The more power, the larger the ships that can get in, but it would always remain between 100 and 1,000 mass. This way, shields would protect a station or a planet from being destroyed from orbit and gunning down all astronauts on the surface.