User blog comment:Rozh/Surface-to-Orbit Artillery/@comment-138261-20110321013844

There's a few main problems, so I'm going to list them to crush your dreams
 * Size: Orbital SMACs are 1 kilometer long. Building something of equal size on a ground station is going to be tremendous, and huge, and difficult to hide, and not as efficient
 * Range: A groundside gun would have a field of fire consisting of a cone, going upwards. In theory, a ODP could hit any target, within the sphere of mobility, since it can fly around in geosynchronous orbit and adjust its direction.
 * Manoeuvrability: In theory, with some sneaky movery, a ODP could maintain itself as a mobile target.
 * Gravity and the laws of physics : Sir Isaac Newton is the baddest mother fucker in space. Inside atmosphere, not so much.
 * Defence: In theory, if probably done and not fucked up for in-game fun, a ODP could be infinitely more well defended, with fighter complements, ship escort, etc. Covenant ships wouldn't be able to get into firing range.