The deep miner is a large mining ship: a cruiser-size ship that mines at three times a harvester's rate and has the same hold as a hauler.
A Shipyard builds it from drill heads, exotic alloy, a heavy frame and thrusters. It docks at a cruiser-size station such as a Port or a Forward HQ, or at an Anchorage, but not at an Outpost.
Trialled deep miner designs with a larger hold and a faster mining rate than the blueprint unlock the leviathan.