Ground defenses protect the surface of a world from invasion. Unlike infantry, however, they are used to destroy ships before they reach final landing approach. Ground defenses are build by each world according to their military population. The more troops on a planet, the more defenses will be build. Ground defenses are used automatically when an enemy attacks a world.
The least technologically sophisticated of all these weapons are the ground defense missiles (GDMs). Essentially guided nuclear-tipped missiles, these devices are common on all worlds above atomic level. Despite their simplicity, however, the great power inherent in a thermonuclear device is enough to destroy even the most heavily armored starship.
Unlike ion cannons and defense satellites, GDMs are expendable: once used against a target a new one must be built by the world. In addition, attacking GDMs can be destroyed by a ship's automatic defenses. GDMs attack ships at standard orbit and can be attacked by any ship in low orbit (or by fighters at ground level).
Ion cannons are ground-based, particle-beam weapons able to reach ships in low orbit. Although they are expensive and difficult to build, their strength lies in their ability to destroy transports attempting a ground assault. Ion cannons can be attacked by any ship from low orbit (or by fighters at ground level).
The most advanced defense that a world can have is an orbiting ring of defense satellites. Heavily armed and armored, defense satellites are the nemesis of every fleet commander. Unlike ion cannons, which can only reach low orbit, defense satellites can attack all targets in standard orbit and high orbit. Their powerful lasers and particle-beam weapons can quickly track and destroy approaching ships. Defense satellites can be attacked at standard orbit.
Long-range Attack Missiles can be used to defend worlds just as GDMs, but their main purpose is offensive. As their name implies, LAMs can attack targets well beyond the boundaries of a star system. They are equipped with small jumpdrives which provide these missiles with ranges of up to five sectors. When used as attack missiles LAMs can attack enemy fleets in orbit around neighboring star systems or even one in deep space. LAMs are not destroyed on approach by a ship's defenses as GDMs are.