Invented by the Ghendari sometime in 2165, the Kessler Field is a form of planetary defense in which a sphere of sharp metallic objects is established in orbit.  The idea is to hinder the ability of an attacking fleet to assault a planet. Unless ships have properly aligned their orbits with the field, they are unlikely to get through in one piece or without sustaining heavy damage.  Ships purpose built for establishing a Field usually dock with satellites in graveyard orbit, shred them, carry the remains into the designated orbital altitude and release the bits.  Full construction takes a very long time and quite an amount of materials, but once complete the field will give the defender a great advantage.  It has been decribed by some as a 'Space Trench," or "Space Wall."