The shield generator is a ship fitting of two field coils wound with superconductor and run by a control unit, built in an Assembler. It holds a field around the ship that absorbs hits before the ship's structure does. Each minute that a working ship has not been hit in the last minute, the field recharges, burning fuel from the ship's tank.
It is a medium fitting for a slot, not a hardpoint. It is fitted and removed at a station with a shipyard in the ship's system.