A Planetary defense grid is an automated weapons system used to defend planets using unmanned defense platforms.
They are usually equipped with very powerful munitions such as missiles and high-energy weapons to destroy attacking warships.
Earth's Defense GridEdit
Earth's planetary defense grid is comprised mostly of Aegis orbital defence platforms. During the Liberation of Earth, President Morgan Clark vengefully turned the planetary defense platforms against the Earth with a Scorched Earth attempt when it was obvious he had lost. Sheridan's forces managed to destroy the platforms before they could fire.
By 2267, Earth had rebuilt its defense grid and it came into action once again in the attempt to stop the few remaining Drakh ships as they poisoned Earth with a biogenetic plague developed by their former masters, the Shadows. 
Centauri Prime's Defense GridEdit
In late 2262, Centauri Prime's planetary defense grid was shut down just as a large fleet led by the Narn and the Drazi approached the planet. Then-Regent Milo Virini was influenced to do so by his Drakh Keeper. 
|Phased Plasma Guns|
|Auricon PPG Pistol Westlake & Grummon PPG Pistol Tho'val PPG pistol Kalat PPG Pistol Sha'ann PPG Pistol Tromo PPG Pistol Auricon PPG Rifle Auricon PPG Sniper Rifle Auricon PPG Assault Rifle Tromo PPG Rifle Centauri PPG Rifle|
|Denn'bok Shock stick Coutari K'tok Barrken Minbari glove-knife Drazi Blades Graal Electro-whip Slaver's glove|
|Drakh plague Techno-mage nano-virus Telepath Morph Gas Assassination device|
|Weapons of Mass Destruction:|
|Thermonuclear device Mass driver Vorlon planetkiller Death Cloud|
|Energy mine Perimeter mine Blockade mine Planetary defense grid Slugthrower Thermal Grenade Hand-held Grenade Launcher|