The excavator is a heavy mining ship: a destroyer-size ship that mines at twice a harvester's rate.
A Shipyard builds it from drill heads, a thruster and a frame, all made at an Assembler.
It is too large for an Outpost's dock, which takes ships up to a frigate. It unloads and is repaired at a cruiser-size station such as a Port or a Forward HQ, and it can also unload into the hull or another ship.